[PATCH bpf-next v4 0/9] Transit between BPF TCP congestion controls.

[PATCH bpf-next v4 0/9] Transit between BPF TCP congestion controls.

[Kui-Feng Lee]

Major changes:

 - Create bpf_links in the kernel for BPF struct_ops to register and
   unregister it.

 - Enables switching between implementations of bpf-tcp-cc under a
   name instantly by replacing the backing struct_ops map of a
   bpf_link.

Previously, BPF struct_ops didn't go off, as even when the user
program creating it was terminated, none of these ever were pinned.
For instance, the TCP congestion control subsystem indirectly
maintains a reference count on the struct_ops of any registered BPF
implemented algorithm. Thus, the algorithm won't be deactivated until
someone deliberately unregisters it.  For compatibility with other BPF
programs, bpf_links have been created to work in coordination with
struct_ops maps. This ensures that the registration and unregistration
of these respective maps is carried out at the start and end of the
bpf_link.

We also faced complications when attempting to replace an existing TCP
congestion control algorithm with a new implementation on the fly. A
struct_ops map was used to register a TCP congestion control algorithm
with a unique name.  We had to either register the alternative
implementation with a new name and move over or unregister the current
one before being able to reregistration with the same name.  To fix
this problem, we can an option to migrate the registration of the
algorithm from struct_ops maps to bpf_links. By modifying the backing
map of a bpf_link, it suddenly becomes possible to replace an existing
TCP congestion control algorithm with ease.

The major differences from v3:

 - Remove bpf_struct_ops_map_free_rcu(), and use synchronize_rcu().

 - Improve the commit log of the part 1.

 - Before transitioning to the READY state, we conduct a value check
   to ensure that struct_ops can be successfully utilized and links
   created later.

The major differences from v2:

 - Simplify states

   - Remove TOBEUNREG.

   - Rename UNREG to READY.

 - Stop using the refcnt of the kvalue of a struct_ops. Explicitly
   increase and decrease the refcount of struct_ops.

 - Prepare kernel vdata during the load phase of libbpf.

The major differences from v1:

 - Added bpf_struct_ops_link to replace the previous union-based
   approach.

 - Added UNREG and TOBEUNREG to the state of bpf_struct_ops_map.

   - bpf_struct_ops_transit_state() maintains state transitions.

 - Fixed synchronization issue.

 - Prepare kernel vdata of struct_ops during the loading phase of
   bpf_object.

 - Merged previous patch 3 to patch 1.

v3: https://lore.kernel.org/all/20230303012122.852654-1-kuifeng@meta.com/
v2: https://lore.kernel.org/bpf/20230223011238.12313-1-kuifeng@meta.com/
v1: https://lore.kernel.org/bpf/20230214221718.503964-1-kuifeng@meta.com/

Kui-Feng Lee (9):
  bpf: Retire the struct_ops map kvalue->refcnt.
  bpf: Create links for BPF struct_ops maps.
  net: Update an existing TCP congestion control algorithm.
  bpf: Validate kdata of a struct_ops before transiting to READY.
  libbpf: Create a bpf_link in bpf_map__attach_struct_ops().
  bpf: Update the struct_ops of a bpf_link.
  libbpf: Update a bpf_link with another struct_ops.
  libbpf: Use .struct_ops.link section to indicate a struct_ops with a
    link.
  selftests/bpf: Test switching TCP Congestion Control algorithms.

 include/linux/bpf.h                           |  16 ++
 include/net/tcp.h                             |   3 +
 include/uapi/linux/bpf.h                      |  20 +-
 kernel/bpf/bpf_struct_ops.c                   | 218 +++++++++++++++---
 kernel/bpf/syscall.c                          |  68 ++++--
 net/bpf/bpf_dummy_struct_ops.c                |   6 +
 net/ipv4/bpf_tcp_ca.c                         |  14 +-
 net/ipv4/tcp_cong.c                           |  57 ++++-
 tools/include/uapi/linux/bpf.h                |  19 +-
 tools/lib/bpf/libbpf.c                        | 184 ++++++++++++---
 tools/lib/bpf/libbpf.h                        |   1 +
 tools/lib/bpf/libbpf.map                      |   2 +
 .../selftests/bpf/prog_tests/bpf_tcp_ca.c     |  38 +++
 .../selftests/bpf/progs/tcp_ca_update.c       |  62 +++++
 14 files changed, 616 insertions(+), 92 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/tcp_ca_update.c

-- 
2.34.1

[PATCH bpf-next v4 1/9] bpf: Retire the struct_ops map kvalue->refcnt.

[Kui-Feng Lee]

We have replaced kvalue-refcnt with synchronize_rcu() to wait for an
RCU grace period.

Maintenance of kvalue->refcnt was a complicated task, as we had to
simultaneously keep track of two reference counts: one for the
reference count of bpf_map. When the kvalue->refcnt reaches zero, we
also have to reduce the reference count on bpf_map - yet these steps
are not performed in an atomic manner and require us to be vigilant
when managing them. By eliminating kvalue->refcnt, we can make our
maintenance more straightforward as the refcount of bpf_map is now
solely managed!

To prevent the trampoline image of a struct_ops from being released
while it is still in use, we wait for an RCU grace period. The
setsockopt(TCP_CONGESTION, "...") command allows you to change your
socket's congestion control algorithm and can result in releasing the
old struct_ops implementation. Moreover, since this function is
exposed through bpf_setsockopt(), it may be accessed by BPF programs
as well. To ensure that the trampoline image belonging to struct_op
can be safely called while its method is in use, struct_ops is
safeguarded with rcu_read_lock(). Doing so prevents any destruction of
the associated images before returning from a trampoline and requires
us to wait for an RCU grace period.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
 include/linux/bpf.h         |  2 ++
 kernel/bpf/bpf_struct_ops.c | 60 ++++++++++++++++++-------------------
 kernel/bpf/syscall.c        |  2 +-
 3 files changed, 32 insertions(+), 32 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 8b5d0b4c4ada..fc47c756455e 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -78,6 +78,7 @@ struct bpf_map_ops {
 	struct bpf_map *(*map_alloc)(union bpf_attr *attr);
 	void (*map_release)(struct bpf_map *map, struct file *map_file);
 	void (*map_free)(struct bpf_map *map);
+	void (*map_free_rcu)(struct bpf_map *map);
 	int (*map_get_next_key)(struct bpf_map *map, void *key, void *next_key);
 	void (*map_release_uref)(struct bpf_map *map);
 	void *(*map_lookup_elem_sys_only)(struct bpf_map *map, void *key);
@@ -1869,6 +1870,7 @@ struct bpf_map *bpf_map_get_with_uref(u32 ufd);
 struct bpf_map *__bpf_map_get(struct fd f);
 void bpf_map_inc(struct bpf_map *map);
 void bpf_map_inc_with_uref(struct bpf_map *map);
+struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref);
 struct bpf_map * __must_check bpf_map_inc_not_zero(struct bpf_map *map);
 void bpf_map_put_with_uref(struct bpf_map *map);
 void bpf_map_put(struct bpf_map *map);
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index ece9870cab68..815b5e1cf325 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -58,6 +58,8 @@ struct bpf_struct_ops_map {
 	struct bpf_struct_ops_value kvalue;
 };
 
+static DEFINE_MUTEX(update_mutex);
+
 #define VALUE_PREFIX "bpf_struct_ops_"
 #define VALUE_PREFIX_LEN (sizeof(VALUE_PREFIX) - 1)
 
@@ -249,6 +251,7 @@ int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map, void *key,
 	struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;
 	struct bpf_struct_ops_value *uvalue, *kvalue;
 	enum bpf_struct_ops_state state;
+	s64 refcnt;
 
 	if (unlikely(*(u32 *)key != 0))
 		return -ENOENT;
@@ -267,7 +270,9 @@ int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map, void *key,
 	uvalue = value;
 	memcpy(uvalue, st_map->uvalue, map->value_size);
 	uvalue->state = state;
-	refcount_set(&uvalue->refcnt, refcount_read(&kvalue->refcnt));
+
+	refcnt = atomic64_read(&map->refcnt) - atomic64_read(&map->usercnt);
+	refcount_set(&uvalue->refcnt, max_t(s64, refcnt, 0));
 
 	return 0;
 }
@@ -491,7 +496,6 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 		*(unsigned long *)(udata + moff) = prog->aux->id;
 	}
 
-	refcount_set(&kvalue->refcnt, 1);
 	bpf_map_inc(map);
 
 	set_memory_rox((long)st_map->image, 1);
@@ -536,8 +540,7 @@ static int bpf_struct_ops_map_delete_elem(struct bpf_map *map, void *key)
 	switch (prev_state) {
 	case BPF_STRUCT_OPS_STATE_INUSE:
 		st_map->st_ops->unreg(&st_map->kvalue.data);
-		if (refcount_dec_and_test(&st_map->kvalue.refcnt))
-			bpf_map_put(map);
+		bpf_map_put(map);
 		return 0;
 	case BPF_STRUCT_OPS_STATE_TOBEFREE:
 		return -EINPROGRESS;
@@ -574,6 +577,19 @@ static void bpf_struct_ops_map_free(struct bpf_map *map)
 {
 	struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;
 
+	/* The struct_ops's function may switch to another struct_ops.
+	 *
+	 * For example, bpf_tcp_cc_x->init() may switch to
+	 * another tcp_cc_y by calling
+	 * setsockopt(TCP_CONGESTION, "tcp_cc_y").
+	 * During the switch,  bpf_struct_ops_put(tcp_cc_x) is called
+	 * and its refcount may reach 0 which then free its
+	 * trampoline image while tcp_cc_x is still running.
+	 *
+	 * Thus, a rcu grace period is needed here.
+	 */
+	synchronize_rcu();
+
 	if (st_map->links)
 		bpf_struct_ops_map_put_progs(st_map);
 	bpf_map_area_free(st_map->links);
@@ -660,41 +676,23 @@ const struct bpf_map_ops bpf_struct_ops_map_ops = {
 bool bpf_struct_ops_get(const void *kdata)
 {
 	struct bpf_struct_ops_value *kvalue;
+	struct bpf_struct_ops_map *st_map;
+	struct bpf_map *map;
 
 	kvalue = container_of(kdata, struct bpf_struct_ops_value, data);
+	st_map = container_of(kvalue, struct bpf_struct_ops_map, kvalue);
 
-	return refcount_inc_not_zero(&kvalue->refcnt);
-}
-
-static void bpf_struct_ops_put_rcu(struct rcu_head *head)
-{
-	struct bpf_struct_ops_map *st_map;
-
-	st_map = container_of(head, struct bpf_struct_ops_map, rcu);
-	bpf_map_put(&st_map->map);
+	map = __bpf_map_inc_not_zero(&st_map->map, false);
+	return !IS_ERR(map);
 }
 
 void bpf_struct_ops_put(const void *kdata)
 {
 	struct bpf_struct_ops_value *kvalue;
+	struct bpf_struct_ops_map *st_map;
 
 	kvalue = container_of(kdata, struct bpf_struct_ops_value, data);
-	if (refcount_dec_and_test(&kvalue->refcnt)) {
-		struct bpf_struct_ops_map *st_map;
-
-		st_map = container_of(kvalue, struct bpf_struct_ops_map,
-				      kvalue);
-		/* The struct_ops's function may switch to another struct_ops.
-		 *
-		 * For example, bpf_tcp_cc_x->init() may switch to
-		 * another tcp_cc_y by calling
-		 * setsockopt(TCP_CONGESTION, "tcp_cc_y").
-		 * During the switch,  bpf_struct_ops_put(tcp_cc_x) is called
-		 * and its map->refcnt may reach 0 which then free its
-		 * trampoline image while tcp_cc_x is still running.
-		 *
-		 * Thus, a rcu grace period is needed here.
-		 */
-		call_rcu(&st_map->rcu, bpf_struct_ops_put_rcu);
-	}
+	st_map = container_of(kvalue, struct bpf_struct_ops_map, kvalue);
+
+	bpf_map_put(&st_map->map);
 }
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index cda8d00f3762..6351d50e3d8b 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1276,7 +1276,7 @@ struct bpf_map *bpf_map_get_with_uref(u32 ufd)
 }
 
 /* map_idr_lock should have been held */
-static struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref)
+struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref)
 {
 	int refold;
 
-- 
2.34.1

[PATCH bpf-next v4 2/9] bpf: Create links for BPF struct_ops maps.

[Kui-Feng Lee]

BPF struct_ops maps are employed directly to register TCP Congestion
Control algorithms. Unlike other BPF programs that terminate when
their links gone. The link of a BPF struct_ops map provides a uniform
experience akin to other types of BPF programs.

bpf_links are responsible for registering their associated
struct_ops. You can only use a struct_ops that has the BPF_F_LINK flag
set to create a bpf_link, while a structs without this flag behaves in
the same manner as before and is registered upon updating its value.

The BPF_LINK_TYPE_STRUCT_OPS serves a dual purpose. Not only is it
used to craft the links for BPF struct_ops programs, but also to
create links for BPF struct_ops them-self.  Since the links of BPF
struct_ops programs are only used to create trampolines internally,
they are never seen in other contexts. Thus, they can be reused for
struct_ops themself.

To maintain a reference to the map supporting this link, we add
bpf_struct_ops_link as an additional type. The pointer of the map is
RCU and won't be necessary until later in the patchset.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
 include/linux/bpf.h            |  11 +++
 include/uapi/linux/bpf.h       |  12 +++-
 kernel/bpf/bpf_struct_ops.c    | 119 +++++++++++++++++++++++++++++++--
 kernel/bpf/syscall.c           |  23 ++++---
 tools/include/uapi/linux/bpf.h |  12 +++-
 5 files changed, 163 insertions(+), 14 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index fc47c756455e..855b27f847eb 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1481,6 +1481,7 @@ static inline void bpf_module_put(const void *data, struct module *owner)
 	else
 		module_put(owner);
 }
+int bpf_struct_ops_link_create(union bpf_attr *attr);
 
 #ifdef CONFIG_NET
 /* Define it here to avoid the use of forward declaration */
@@ -1521,6 +1522,11 @@ static inline int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map,
 {
 	return -EINVAL;
 }
+static inline int bpf_struct_ops_link_create(union bpf_attr *attr)
+{
+	return -EOPNOTSUPP;
+}
+
 #endif
 
 #if defined(CONFIG_CGROUP_BPF) && defined(CONFIG_BPF_LSM)
@@ -2307,6 +2313,11 @@ static inline void bpf_link_put(struct bpf_link *link)
 {
 }
 
+static inline int bpf_struct_ops_link_create(union bpf_attr *attr)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int bpf_obj_get_user(const char __user *pathname, int flags)
 {
 	return -EOPNOTSUPP;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 17afd2b35ee5..eb3e435c5303 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1033,6 +1033,7 @@ enum bpf_attach_type {
 	BPF_PERF_EVENT,
 	BPF_TRACE_KPROBE_MULTI,
 	BPF_LSM_CGROUP,
+	BPF_STRUCT_OPS,
 	__MAX_BPF_ATTACH_TYPE
 };
 
@@ -1266,6 +1267,9 @@ enum {
 
 /* Create a map that is suitable to be an inner map with dynamic max entries */
 	BPF_F_INNER_MAP		= (1U << 12),
+
+/* Create a map that will be registered/unregesitered by the backed bpf_link */
+	BPF_F_LINK		= (1U << 13),
 };
 
 /* Flags for BPF_PROG_QUERY. */
@@ -1507,7 +1511,10 @@ union bpf_attr {
 	} task_fd_query;
 
 	struct { /* struct used by BPF_LINK_CREATE command */
-		__u32		prog_fd;	/* eBPF program to attach */
+		union {
+			__u32		prog_fd;	/* eBPF program to attach */
+			__u32		map_fd;		/* struct_ops to attach */
+		};
 		union {
 			__u32		target_fd;	/* object to attach to */
 			__u32		target_ifindex; /* target ifindex */
@@ -6354,6 +6361,9 @@ struct bpf_link_info {
 		struct {
 			__u32 ifindex;
 		} xdp;
+		struct {
+			__u32 map_id;
+		} struct_ops;
 	};
 } __attribute__((aligned(8)));
 
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 815b5e1cf325..dcb7a408d4e9 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -16,6 +16,7 @@ enum bpf_struct_ops_state {
 	BPF_STRUCT_OPS_STATE_INIT,
 	BPF_STRUCT_OPS_STATE_INUSE,
 	BPF_STRUCT_OPS_STATE_TOBEFREE,
+	BPF_STRUCT_OPS_STATE_READY,
 };
 
 #define BPF_STRUCT_OPS_COMMON_VALUE			\
@@ -58,6 +59,11 @@ struct bpf_struct_ops_map {
 	struct bpf_struct_ops_value kvalue;
 };
 
+struct bpf_struct_ops_link {
+	struct bpf_link link;
+	struct bpf_map __rcu *map;
+};
+
 static DEFINE_MUTEX(update_mutex);
 
 #define VALUE_PREFIX "bpf_struct_ops_"
@@ -496,11 +502,19 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 		*(unsigned long *)(udata + moff) = prog->aux->id;
 	}
 
-	bpf_map_inc(map);
-
 	set_memory_rox((long)st_map->image, 1);
+	if (st_map->map.map_flags & BPF_F_LINK) {
+		/* Let bpf_link handle registration & unregistration.
+		 *
+		 * Pair with smp_load_acquire() during lookup_elem().
+		 */
+		smp_store_release(&kvalue->state, BPF_STRUCT_OPS_STATE_READY);
+		goto unlock;
+	}
+
 	err = st_ops->reg(kdata);
 	if (likely(!err)) {
+		bpf_map_inc(map);
 		/* Pair with smp_load_acquire() during lookup_elem().
 		 * It ensures the above udata updates (e.g. prog->aux->id)
 		 * can be seen once BPF_STRUCT_OPS_STATE_INUSE is set.
@@ -516,7 +530,6 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 	 */
 	set_memory_nx((long)st_map->image, 1);
 	set_memory_rw((long)st_map->image, 1);
-	bpf_map_put(map);
 
 reset_unlock:
 	bpf_struct_ops_map_put_progs(st_map);
@@ -534,6 +547,9 @@ static int bpf_struct_ops_map_delete_elem(struct bpf_map *map, void *key)
 	struct bpf_struct_ops_map *st_map;
 
 	st_map = (struct bpf_struct_ops_map *)map;
+	if (st_map->map.map_flags & BPF_F_LINK)
+		return -EOPNOTSUPP;
+
 	prev_state = cmpxchg(&st_map->kvalue.state,
 			     BPF_STRUCT_OPS_STATE_INUSE,
 			     BPF_STRUCT_OPS_STATE_TOBEFREE);
@@ -601,7 +617,7 @@ static void bpf_struct_ops_map_free(struct bpf_map *map)
 static int bpf_struct_ops_map_alloc_check(union bpf_attr *attr)
 {
 	if (attr->key_size != sizeof(unsigned int) || attr->max_entries != 1 ||
-	    attr->map_flags || !attr->btf_vmlinux_value_type_id)
+	    (attr->map_flags & ~BPF_F_LINK) || !attr->btf_vmlinux_value_type_id)
 		return -EINVAL;
 	return 0;
 }
@@ -696,3 +712,98 @@ void bpf_struct_ops_put(const void *kdata)
 
 	bpf_map_put(&st_map->map);
 }
+
+static void bpf_struct_ops_map_link_dealloc(struct bpf_link *link)
+{
+	struct bpf_struct_ops_link *st_link;
+	struct bpf_struct_ops_map *st_map;
+
+	st_link = container_of(link, struct bpf_struct_ops_link, link);
+	st_map = (struct bpf_struct_ops_map *)st_link->map;
+	st_map->st_ops->unreg(&st_map->kvalue.data);
+	bpf_map_put(st_link->map);
+	kfree(st_link);
+}
+
+static void bpf_struct_ops_map_link_show_fdinfo(const struct bpf_link *link,
+					    struct seq_file *seq)
+{
+	struct bpf_struct_ops_link *st_link;
+	struct bpf_map *map;
+
+	st_link = container_of(link, struct bpf_struct_ops_link, link);
+	rcu_read_lock();
+	map = rcu_dereference(st_link->map);
+	if (map)
+		seq_printf(seq, "map_id:\t%d\n", map->id);
+	rcu_read_unlock();
+}
+
+static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link,
+					       struct bpf_link_info *info)
+{
+	struct bpf_struct_ops_link *st_link;
+	struct bpf_map *map;
+
+	st_link = container_of(link, struct bpf_struct_ops_link, link);
+	rcu_read_lock();
+	map = rcu_dereference(st_link->map);
+	if (map)
+		info->struct_ops.map_id = map->id;
+	rcu_read_unlock();
+	return 0;
+}
+
+static const struct bpf_link_ops bpf_struct_ops_map_lops = {
+	.dealloc = bpf_struct_ops_map_link_dealloc,
+	.show_fdinfo = bpf_struct_ops_map_link_show_fdinfo,
+	.fill_link_info = bpf_struct_ops_map_link_fill_link_info,
+};
+
+int bpf_struct_ops_link_create(union bpf_attr *attr)
+{
+	struct bpf_struct_ops_link *link = NULL;
+	struct bpf_link_primer link_primer;
+	struct bpf_struct_ops_map *st_map;
+	struct bpf_map *map;
+	int err;
+
+	map = bpf_map_get(attr->link_create.map_fd);
+	if (!map)
+		return -EINVAL;
+
+	st_map = (struct bpf_struct_ops_map *)map;
+
+	if (map->map_type != BPF_MAP_TYPE_STRUCT_OPS || !(map->map_flags & BPF_F_LINK) ||
+	    /* Pair with smp_store_release() during map_update */
+	    smp_load_acquire(&st_map->kvalue.state) != BPF_STRUCT_OPS_STATE_READY) {
+		err = -EINVAL;
+		goto err_out;
+	}
+
+	link = kzalloc(sizeof(*link), GFP_USER);
+	if (!link) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+	bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_struct_ops_map_lops, NULL);
+	RCU_INIT_POINTER(link->map, map);
+
+	err = bpf_link_prime(&link->link, &link_primer);
+	if (err)
+		goto err_out;
+
+	err = st_map->st_ops->reg(st_map->kvalue.data);
+	if (err) {
+		bpf_link_cleanup(&link_primer);
+		goto err_out;
+	}
+
+	return bpf_link_settle(&link_primer);
+
+err_out:
+	bpf_map_put(map);
+	kfree(link);
+	return err;
+}
+
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6351d50e3d8b..25b044fdd82b 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2794,16 +2794,19 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp)
 	const struct bpf_prog *prog = link->prog;
 	char prog_tag[sizeof(prog->tag) * 2 + 1] = { };
 
-	bin2hex(prog_tag, prog->tag, sizeof(prog->tag));
 	seq_printf(m,
 		   "link_type:\t%s\n"
-		   "link_id:\t%u\n"
-		   "prog_tag:\t%s\n"
-		   "prog_id:\t%u\n",
+		   "link_id:\t%u\n",
 		   bpf_link_type_strs[link->type],
-		   link->id,
-		   prog_tag,
-		   prog->aux->id);
+		   link->id);
+	if (prog) {
+		bin2hex(prog_tag, prog->tag, sizeof(prog->tag));
+		seq_printf(m,
+			   "prog_tag:\t%s\n"
+			   "prog_id:\t%u\n",
+			   prog_tag,
+			   prog->aux->id);
+	}
 	if (link->ops->show_fdinfo)
 		link->ops->show_fdinfo(link, m);
 }
@@ -4278,7 +4281,8 @@ static int bpf_link_get_info_by_fd(struct file *file,
 
 	info.type = link->type;
 	info.id = link->id;
-	info.prog_id = link->prog->aux->id;
+	if (link->prog)
+		info.prog_id = link->prog->aux->id;
 
 	if (link->ops->fill_link_info) {
 		err = link->ops->fill_link_info(link, &info);
@@ -4541,6 +4545,9 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
 	if (CHECK_ATTR(BPF_LINK_CREATE))
 		return -EINVAL;
 
+	if (attr->link_create.attach_type == BPF_STRUCT_OPS)
+		return bpf_struct_ops_link_create(attr);
+
 	prog = bpf_prog_get(attr->link_create.prog_fd);
 	if (IS_ERR(prog))
 		return PTR_ERR(prog);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 17afd2b35ee5..cd0ff39981e8 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1033,6 +1033,7 @@ enum bpf_attach_type {
 	BPF_PERF_EVENT,
 	BPF_TRACE_KPROBE_MULTI,
 	BPF_LSM_CGROUP,
+	BPF_STRUCT_OPS,
 	__MAX_BPF_ATTACH_TYPE
 };
 
@@ -1266,6 +1267,9 @@ enum {
 
 /* Create a map that is suitable to be an inner map with dynamic max entries */
 	BPF_F_INNER_MAP		= (1U << 12),
+
+/* Create a map that will be registered/unregesitered by the backed bpf_link */
+	BPF_F_LINK		= (1U << 13),
 };
 
 /* Flags for BPF_PROG_QUERY. */
@@ -1507,7 +1511,10 @@ union bpf_attr {
 	} task_fd_query;
 
 	struct { /* struct used by BPF_LINK_CREATE command */
-		__u32		prog_fd;	/* eBPF program to attach */
+		union {
+			__u32		prog_fd;	/* eBPF program to attach */
+			__u32		map_fd;		/* eBPF struct_ops to attach */
+		};
 		union {
 			__u32		target_fd;	/* object to attach to */
 			__u32		target_ifindex; /* target ifindex */
@@ -6354,6 +6361,9 @@ struct bpf_link_info {
 		struct {
 			__u32 ifindex;
 		} xdp;
+		struct {
+			__u32 map_id;
+		} struct_ops;
 	};
 } __attribute__((aligned(8)));
 
-- 
2.34.1

[PATCH bpf-next v4 3/9] net: Update an existing TCP congestion control algorithm.

[Kui-Feng Lee]

This feature lets you immediately transition to another congestion
control algorithm or implementation with the same name.  Once a name
is updated, new connections will apply this new algorithm.

The 'validate' function pointer has been added to bpf_struct_ops as
well, allowing us to validate a struct_ops without having to go
through the registration process.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
 include/linux/bpf.h            |  2 ++
 include/net/tcp.h              |  3 ++
 net/bpf/bpf_dummy_struct_ops.c |  6 ++++
 net/ipv4/bpf_tcp_ca.c          | 14 +++++++--
 net/ipv4/tcp_cong.c            | 57 +++++++++++++++++++++++++++++-----
 5 files changed, 73 insertions(+), 9 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 855b27f847eb..047d2c6aba88 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1447,6 +1447,8 @@ struct bpf_struct_ops {
 			   void *kdata, const void *udata);
 	int (*reg)(void *kdata);
 	void (*unreg)(void *kdata);
+	int (*update)(void *kdata, void *old_kdata);
+	int (*validate)(void *kdata);
 	const struct btf_type *type;
 	const struct btf_type *value_type;
 	const char *name;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index db9f828e9d1e..2abb755e6a3a 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1117,6 +1117,9 @@ struct tcp_congestion_ops {
 
 int tcp_register_congestion_control(struct tcp_congestion_ops *type);
 void tcp_unregister_congestion_control(struct tcp_congestion_ops *type);
+int tcp_update_congestion_control(struct tcp_congestion_ops *type,
+				  struct tcp_congestion_ops *old_type);
+int tcp_validate_congestion_control(struct tcp_congestion_ops *ca);
 
 void tcp_assign_congestion_control(struct sock *sk);
 void tcp_init_congestion_control(struct sock *sk);
diff --git a/net/bpf/bpf_dummy_struct_ops.c b/net/bpf/bpf_dummy_struct_ops.c
index ff4f89a2b02a..158f14e240d0 100644
--- a/net/bpf/bpf_dummy_struct_ops.c
+++ b/net/bpf/bpf_dummy_struct_ops.c
@@ -222,12 +222,18 @@ static void bpf_dummy_unreg(void *kdata)
 {
 }
 
+static int bpf_dummy_update(void *kdata, void *old_kdata)
+{
+	return -EOPNOTSUPP;
+}
+
 struct bpf_struct_ops bpf_bpf_dummy_ops = {
 	.verifier_ops = &bpf_dummy_verifier_ops,
 	.init = bpf_dummy_init,
 	.check_member = bpf_dummy_ops_check_member,
 	.init_member = bpf_dummy_init_member,
 	.reg = bpf_dummy_reg,
+	.update = bpf_dummy_update,
 	.unreg = bpf_dummy_unreg,
 	.name = "bpf_dummy_ops",
 };
diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
index 13fc0c185cd9..e8b27826283e 100644
--- a/net/ipv4/bpf_tcp_ca.c
+++ b/net/ipv4/bpf_tcp_ca.c
@@ -239,8 +239,6 @@ static int bpf_tcp_ca_init_member(const struct btf_type *t,
 		if (bpf_obj_name_cpy(tcp_ca->name, utcp_ca->name,
 				     sizeof(tcp_ca->name)) <= 0)
 			return -EINVAL;
-		if (tcp_ca_find(utcp_ca->name))
-			return -EEXIST;
 		return 1;
 	}
 
@@ -266,13 +264,25 @@ static void bpf_tcp_ca_unreg(void *kdata)
 	tcp_unregister_congestion_control(kdata);
 }
 
+static int bpf_tcp_ca_update(void *kdata, void *old_kdata)
+{
+	return tcp_update_congestion_control(kdata, old_kdata);
+}
+
+static int bpf_tcp_ca_validate(void *kdata)
+{
+	return tcp_validate_congestion_control(kdata);
+}
+
 struct bpf_struct_ops bpf_tcp_congestion_ops = {
 	.verifier_ops = &bpf_tcp_ca_verifier_ops,
 	.reg = bpf_tcp_ca_reg,
 	.unreg = bpf_tcp_ca_unreg,
+	.update = bpf_tcp_ca_update,
 	.check_member = bpf_tcp_ca_check_member,
 	.init_member = bpf_tcp_ca_init_member,
 	.init = bpf_tcp_ca_init,
+	.validate = bpf_tcp_ca_validate,
 	.name = "tcp_congestion_ops",
 };
 
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index db8b4b488c31..24829390e495 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -75,14 +75,8 @@ struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
 	return NULL;
 }
 
-/*
- * Attach new congestion control algorithm to the list
- * of available options.
- */
-int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
+int tcp_validate_congestion_control(struct tcp_congestion_ops *ca)
 {
-	int ret = 0;
-
 	/* all algorithms must implement these */
 	if (!ca->ssthresh || !ca->undo_cwnd ||
 	    !(ca->cong_avoid || ca->cong_control)) {
@@ -90,6 +84,20 @@ int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
 		return -EINVAL;
 	}
 
+	return 0;
+}
+
+/* Attach new congestion control algorithm to the list
+ * of available options.
+ */
+int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
+{
+	int ret;
+
+	ret = tcp_validate_congestion_control(ca);
+	if (ret)
+		return ret;
+
 	ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
 
 	spin_lock(&tcp_cong_list_lock);
@@ -130,6 +138,41 @@ void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
 }
 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
 
+/* Replace a registered old ca with a new one.
+ *
+ * The new ca must have the same name as the old one, that has been
+ * registered.
+ */
+int tcp_update_congestion_control(struct tcp_congestion_ops *ca, struct tcp_congestion_ops *old_ca)
+{
+	struct tcp_congestion_ops *existing;
+	int ret;
+
+	ret = tcp_validate_congestion_control(ca);
+	if (ret)
+		return ret;
+
+	ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
+
+	spin_lock(&tcp_cong_list_lock);
+	existing = tcp_ca_find_key(old_ca->key);
+	if (ca->key == TCP_CA_UNSPEC || !existing || strcmp(existing->name, ca->name)) {
+		pr_notice("%s not registered or non-unique key\n",
+			  ca->name);
+		ret = -EINVAL;
+	} else if (existing != old_ca) {
+		pr_notice("invalid old congestion control algorithm to replace\n");
+		ret = -EINVAL;
+	} else {
+		list_add_tail_rcu(&ca->list, &tcp_cong_list);
+		list_del_rcu(&existing->list);
+		pr_debug("%s updated\n", ca->name);
+	}
+	spin_unlock(&tcp_cong_list_lock);
+
+	return ret;
+}
+
 u32 tcp_ca_get_key_by_name(struct net *net, const char *name, bool *ecn_ca)
 {
 	const struct tcp_congestion_ops *ca;
-- 
2.34.1

[PATCH bpf-next v4 4/9] bpf: Validate kdata of a struct_ops before transiting to READY.

[Kui-Feng Lee]

By utilizing this check, we can avoid creating a struct_ops that
cannot be registered afterward. This way, future complications can be
avoided with ease.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
 kernel/bpf/bpf_struct_ops.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index dcb7a408d4e9..c71c8d73c7ad 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -504,6 +504,11 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
 
 	set_memory_rox((long)st_map->image, 1);
 	if (st_map->map.map_flags & BPF_F_LINK) {
+		if (st_ops->validate) {
+			err = st_ops->validate(kdata);
+			if (err)
+				goto unlock;
+		}
 		/* Let bpf_link handle registration & unregistration.
 		 *
 		 * Pair with smp_load_acquire() during lookup_elem().
-- 
2.34.1

[PATCH bpf-next v4 5/9] libbpf: Create a bpf_link in bpf_map__attach_struct_ops().

[Kui-Feng Lee]

bpf_map__attach_struct_ops() was creating a dummy bpf_link as a
placeholder, but now it is constructing an authentic one by calling
bpf_link_create() if the map has the BPF_F_LINK flag.

You can flag a struct_ops map with BPF_F_LINK by calling
bpf_map__set_map_flags().

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
 tools/lib/bpf/libbpf.c | 84 +++++++++++++++++++++++++++++++-----------
 1 file changed, 62 insertions(+), 22 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 35a698eb825d..a67efc3b3763 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -115,6 +115,7 @@ static const char * const attach_type_name[] = {
 	[BPF_SK_REUSEPORT_SELECT_OR_MIGRATE]	= "sk_reuseport_select_or_migrate",
 	[BPF_PERF_EVENT]		= "perf_event",
 	[BPF_TRACE_KPROBE_MULTI]	= "trace_kprobe_multi",
+	[BPF_STRUCT_OPS]		= "struct_ops",
 };
 
 static const char * const link_type_name[] = {
@@ -7677,6 +7678,26 @@ static int bpf_object__resolve_externs(struct bpf_object *obj,
 	return 0;
 }
 
+static void bpf_map_prepare_vdata(const struct bpf_map *map)
+{
+	struct bpf_struct_ops *st_ops;
+	__u32 i;
+
+	st_ops = map->st_ops;
+	for (i = 0; i < btf_vlen(st_ops->type); i++) {
+		struct bpf_program *prog = st_ops->progs[i];
+		void *kern_data;
+		int prog_fd;
+
+		if (!prog)
+			continue;
+
+		prog_fd = bpf_program__fd(prog);
+		kern_data = st_ops->kern_vdata + st_ops->kern_func_off[i];
+		*(unsigned long *)kern_data = prog_fd;
+	}
+}
+
 static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const char *target_btf_path)
 {
 	int err, i;
@@ -7728,6 +7749,10 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
 	btf__free(obj->btf_vmlinux);
 	obj->btf_vmlinux = NULL;
 
+	for (i = 0; i < obj->nr_maps; i++)
+		if (bpf_map__is_struct_ops(&obj->maps[i]))
+			bpf_map_prepare_vdata(&obj->maps[i]);
+
 	obj->loaded = true; /* doesn't matter if successfully or not */
 
 	if (err)
@@ -11429,22 +11454,34 @@ struct bpf_link *bpf_program__attach(const struct bpf_program *prog)
 	return link;
 }
 
+struct bpf_link_struct_ops {
+	struct bpf_link link;
+	int map_fd;
+};
+
 static int bpf_link__detach_struct_ops(struct bpf_link *link)
 {
+	struct bpf_link_struct_ops *st_link;
 	__u32 zero = 0;
 
-	if (bpf_map_delete_elem(link->fd, &zero))
-		return -errno;
+	st_link = container_of(link, struct bpf_link_struct_ops, link);
 
-	return 0;
+	if (st_link->map_fd < 0) {
+		/* Fake bpf_link */
+		if (bpf_map_delete_elem(link->fd, &zero))
+			return -errno;
+		return 0;
+	}
+
+	/* Doesn't support detaching. */
+	return -EOPNOTSUPP;
 }
 
 struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
 {
-	struct bpf_struct_ops *st_ops;
-	struct bpf_link *link;
-	__u32 i, zero = 0;
-	int err;
+	struct bpf_link_struct_ops *link;
+	__u32 zero = 0;
+	int err, fd;
 
 	if (!bpf_map__is_struct_ops(map) || map->fd == -1)
 		return libbpf_err_ptr(-EINVAL);
@@ -11453,31 +11490,34 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
 	if (!link)
 		return libbpf_err_ptr(-EINVAL);
 
-	st_ops = map->st_ops;
-	for (i = 0; i < btf_vlen(st_ops->type); i++) {
-		struct bpf_program *prog = st_ops->progs[i];
-		void *kern_data;
-		int prog_fd;
+	/* kern_vdata should be prepared during the loading phase. */
+	err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
+	if (err) {
+		err = -errno;
+		free(link);
+		return libbpf_err_ptr(err);
+	}
 
-		if (!prog)
-			continue;
 
-		prog_fd = bpf_program__fd(prog);
-		kern_data = st_ops->kern_vdata + st_ops->kern_func_off[i];
-		*(unsigned long *)kern_data = prog_fd;
+	if (!(map->def.map_flags & BPF_F_LINK)) {
+		/* Fake bpf_link */
+		link->link.fd = map->fd;
+		link->map_fd = -1;
+		link->link.detach = bpf_link__detach_struct_ops;
+		return &link->link;
 	}
 
-	err = bpf_map_update_elem(map->fd, &zero, st_ops->kern_vdata, 0);
-	if (err) {
+	fd = bpf_link_create(map->fd, -1, BPF_STRUCT_OPS, NULL);
+	if (fd < 0) {
 		err = -errno;
 		free(link);
 		return libbpf_err_ptr(err);
 	}
 
-	link->detach = bpf_link__detach_struct_ops;
-	link->fd = map->fd;
+	link->link.fd = fd;
+	link->map_fd = map->fd;
 
-	return link;
+	return &link->link;
 }
 
 typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
-- 
2.34.1

[PATCH bpf-next v4 6/9] bpf: Update the struct_ops of a bpf_link.

[Kui-Feng Lee]

By improving the BPF_LINK_UPDATE command of bpf(), it should allow you
to conveniently switch between different struct_ops on a single
bpf_link. This would enable smoother transitions from one struct_ops
to another.

The struct_ops maps passing along with BPF_LINK_UPDATE should have the
BPF_F_LINK flag.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
 include/linux/bpf.h            |  1 +
 include/uapi/linux/bpf.h       |  8 ++++--
 kernel/bpf/bpf_struct_ops.c    | 46 ++++++++++++++++++++++++++++++++++
 kernel/bpf/syscall.c           | 43 ++++++++++++++++++++++++++++---
 tools/include/uapi/linux/bpf.h |  7 +++++-
 5 files changed, 98 insertions(+), 7 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 047d2c6aba88..2b5f150e370e 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1405,6 +1405,7 @@ struct bpf_link_ops {
 	void (*show_fdinfo)(const struct bpf_link *link, struct seq_file *seq);
 	int (*fill_link_info)(const struct bpf_link *link,
 			      struct bpf_link_info *info);
+	int (*update_map)(struct bpf_link *link, struct bpf_map *new_map);
 };
 
 struct bpf_tramp_link {
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index eb3e435c5303..999e199ebe06 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1555,8 +1555,12 @@ union bpf_attr {
 
 	struct { /* struct used by BPF_LINK_UPDATE command */
 		__u32		link_fd;	/* link fd */
-		/* new program fd to update link with */
-		__u32		new_prog_fd;
+		union {
+			/* new program fd to update link with */
+			__u32		new_prog_fd;
+			/* new struct_ops map fd to update link with */
+			__u32           new_map_fd;
+		};
 		__u32		flags;		/* extra flags */
 		/* expected link's program fd; is specified only if
 		 * BPF_F_REPLACE flag is set in flags */
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index c71c8d73c7ad..2b850ce11617 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -759,10 +759,56 @@ static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link,
 	return 0;
 }
 
+static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map *new_map)
+{
+	struct bpf_struct_ops_value *kvalue;
+	struct bpf_struct_ops_map *st_map, *old_st_map;
+	struct bpf_struct_ops_link *st_link;
+	struct bpf_map *old_map;
+	int err = 0;
+
+	if (new_map->map_type != BPF_MAP_TYPE_STRUCT_OPS ||
+	    !(new_map->map_flags & BPF_F_LINK))
+		return -EINVAL;
+
+	mutex_lock(&update_mutex);
+
+	st_link = container_of(link, struct bpf_struct_ops_link, link);
+
+	/* The new and old struct_ops must be the same type. */
+	st_map = container_of(new_map, struct bpf_struct_ops_map, map);
+
+	old_map = st_link->map;
+	old_st_map = container_of(old_map, struct bpf_struct_ops_map, map);
+	if (st_map->st_ops != old_st_map->st_ops ||
+	    /* Pair with smp_store_release() during map_update */
+	    smp_load_acquire(&st_map->kvalue.state) != BPF_STRUCT_OPS_STATE_READY) {
+		err = -EINVAL;
+		goto err_out;
+	}
+
+	kvalue = &st_map->kvalue;
+
+	err = st_map->st_ops->update(kvalue->data, old_st_map->kvalue.data);
+	if (err)
+		goto err_out;
+
+	bpf_map_inc(new_map);
+	rcu_assign_pointer(st_link->map, new_map);
+
+	bpf_map_put(old_map);
+
+err_out:
+	mutex_unlock(&update_mutex);
+
+	return err;
+}
+
 static const struct bpf_link_ops bpf_struct_ops_map_lops = {
 	.dealloc = bpf_struct_ops_map_link_dealloc,
 	.show_fdinfo = bpf_struct_ops_map_link_show_fdinfo,
 	.fill_link_info = bpf_struct_ops_map_link_fill_link_info,
+	.update_map = bpf_struct_ops_map_link_update,
 };
 
 int bpf_struct_ops_link_create(union bpf_attr *attr)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 25b044fdd82b..94ab1336ff41 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -4646,6 +4646,30 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
 	return ret;
 }
 
+static int link_update_map(struct bpf_link *link, union bpf_attr *attr)
+{
+	struct bpf_map *new_map;
+	int ret = 0;
+
+	new_map = bpf_map_get(attr->link_update.new_map_fd);
+	if (IS_ERR(new_map))
+		return -EINVAL;
+
+	if (new_map->map_type != BPF_MAP_TYPE_STRUCT_OPS) {
+		ret = -EINVAL;
+		goto out_put_map;
+	}
+
+	if (link->ops->update_map)
+		ret = link->ops->update_map(link, new_map);
+	else
+		ret = -EINVAL;
+
+out_put_map:
+	bpf_map_put(new_map);
+	return ret;
+}
+
 #define BPF_LINK_UPDATE_LAST_FIELD link_update.old_prog_fd
 
 static int link_update(union bpf_attr *attr)
@@ -4658,14 +4682,25 @@ static int link_update(union bpf_attr *attr)
 	if (CHECK_ATTR(BPF_LINK_UPDATE))
 		return -EINVAL;
 
-	flags = attr->link_update.flags;
-	if (flags & ~BPF_F_REPLACE)
-		return -EINVAL;
-
 	link = bpf_link_get_from_fd(attr->link_update.link_fd);
 	if (IS_ERR(link))
 		return PTR_ERR(link);
 
+	flags = attr->link_update.flags;
+
+	if (link->ops->update_map) {
+		if (flags)	/* always replace the existing one */
+			ret = -EINVAL;
+		else
+			ret = link_update_map(link, attr);
+		goto out_put_link;
+	}
+
+	if (flags & ~BPF_F_REPLACE) {
+		ret = -EINVAL;
+		goto out_put_link;
+	}
+
 	new_prog = bpf_prog_get(attr->link_update.new_prog_fd);
 	if (IS_ERR(new_prog)) {
 		ret = PTR_ERR(new_prog);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index cd0ff39981e8..259b8ab4f54e 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1556,7 +1556,12 @@ union bpf_attr {
 	struct { /* struct used by BPF_LINK_UPDATE command */
 		__u32		link_fd;	/* link fd */
 		/* new program fd to update link with */
-		__u32		new_prog_fd;
+		union {
+			/* new program fd to update link with */
+			__u32		new_prog_fd;
+			/* new struct_ops map fd to update link with */
+			__u32           new_map_fd;
+		};
 		__u32		flags;		/* extra flags */
 		/* expected link's program fd; is specified only if
 		 * BPF_F_REPLACE flag is set in flags */
-- 
2.34.1

[PATCH bpf-next v4 7/9] libbpf: Update a bpf_link with another struct_ops.

[Kui-Feng Lee]

Introduce bpf_link__update_struct_ops(), which will allow you to
effortlessly transition the struct_ops map of any given bpf_link into
an alternative.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
 tools/lib/bpf/libbpf.c   | 36 ++++++++++++++++++++++++++++++++++++
 tools/lib/bpf/libbpf.h   |  1 +
 tools/lib/bpf/libbpf.map |  2 ++
 3 files changed, 39 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a67efc3b3763..247de39d136f 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11520,6 +11520,42 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
 	return &link->link;
 }
 
+/*
+ * Swap the back struct_ops of a link with a new struct_ops map.
+ */
+int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map)
+{
+	struct bpf_link_struct_ops *st_ops_link;
+	__u32 zero = 0;
+	int err, fd;
+
+	if (!bpf_map__is_struct_ops(map) || map->fd == -1)
+		return -EINVAL;
+
+	st_ops_link = container_of(link, struct bpf_link_struct_ops, link);
+	/* Ensure the type of a link is correct */
+	if (st_ops_link->map_fd < 0)
+		return -EINVAL;
+
+	err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
+	if (err && errno != EBUSY) {
+		err = -errno;
+		free(link);
+		return err;
+	}
+
+	fd = bpf_link_update(link->fd, map->fd, NULL);
+	if (fd < 0) {
+		err = -errno;
+		free(link);
+		return err;
+	}
+
+	st_ops_link->map_fd = map->fd;
+
+	return 0;
+}
+
 typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
 							  void *private_data);
 
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 2efd80f6f7b9..5e62878d184c 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -695,6 +695,7 @@ bpf_program__attach_freplace(const struct bpf_program *prog,
 struct bpf_map;
 
 LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
+LIBBPF_API int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map);
 
 struct bpf_iter_attach_opts {
 	size_t sz; /* size of this struct for forward/backward compatibility */
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 11c36a3c1a9f..e83571b04c19 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -384,4 +384,6 @@ LIBBPF_1.1.0 {
 } LIBBPF_1.0.0;
 
 LIBBPF_1.2.0 {
+	global:
+		bpf_link__update_map;
 } LIBBPF_1.1.0;
-- 
2.34.1

[PATCH bpf-next v4 8/9] libbpf: Use .struct_ops.link section to indicate a struct_ops with a link.

[Kui-Feng Lee]

Flags a struct_ops is to back a bpf_link by putting it to the
".struct_ops.link" section.  Once it is flagged, the created
struct_ops can be used to create a bpf_link or update a bpf_link that
has been backed by another struct_ops.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
 tools/lib/bpf/libbpf.c | 64 +++++++++++++++++++++++++++++++++---------
 1 file changed, 50 insertions(+), 14 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 247de39d136f..d66acd2fdbaa 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -467,6 +467,7 @@ struct bpf_struct_ops {
 #define KCONFIG_SEC ".kconfig"
 #define KSYMS_SEC ".ksyms"
 #define STRUCT_OPS_SEC ".struct_ops"
+#define STRUCT_OPS_LINK_SEC ".struct_ops.link"
 
 enum libbpf_map_type {
 	LIBBPF_MAP_UNSPEC,
@@ -596,6 +597,7 @@ struct elf_state {
 	Elf64_Ehdr *ehdr;
 	Elf_Data *symbols;
 	Elf_Data *st_ops_data;
+	Elf_Data *st_ops_link_data;
 	size_t shstrndx; /* section index for section name strings */
 	size_t strtabidx;
 	struct elf_sec_desc *secs;
@@ -605,6 +607,7 @@ struct elf_state {
 	int text_shndx;
 	int symbols_shndx;
 	int st_ops_shndx;
+	int st_ops_link_shndx;
 };
 
 struct usdt_manager;
@@ -1119,7 +1122,7 @@ static int bpf_object__init_kern_struct_ops_maps(struct bpf_object *obj)
 	return 0;
 }
 
-static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
+static int bpf_object__init_struct_ops_maps_link(struct bpf_object *obj, bool link)
 {
 	const struct btf_type *type, *datasec;
 	const struct btf_var_secinfo *vsi;
@@ -1127,18 +1130,33 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 	const char *tname, *var_name;
 	__s32 type_id, datasec_id;
 	const struct btf *btf;
+	const char *sec_name;
 	struct bpf_map *map;
-	__u32 i;
+	__u32 i, map_flags;
+	Elf_Data *data;
+	int shndx;
 
-	if (obj->efile.st_ops_shndx == -1)
+	if (link) {
+		sec_name = STRUCT_OPS_LINK_SEC;
+		shndx = obj->efile.st_ops_link_shndx;
+		data = obj->efile.st_ops_link_data;
+		map_flags = BPF_F_LINK;
+	} else {
+		sec_name = STRUCT_OPS_SEC;
+		shndx = obj->efile.st_ops_shndx;
+		data = obj->efile.st_ops_data;
+		map_flags = 0;
+	}
+
+	if (shndx == -1)
 		return 0;
 
 	btf = obj->btf;
-	datasec_id = btf__find_by_name_kind(btf, STRUCT_OPS_SEC,
+	datasec_id = btf__find_by_name_kind(btf, sec_name,
 					    BTF_KIND_DATASEC);
 	if (datasec_id < 0) {
 		pr_warn("struct_ops init: DATASEC %s not found\n",
-			STRUCT_OPS_SEC);
+			sec_name);
 		return -EINVAL;
 	}
 
@@ -1151,7 +1169,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 		type_id = btf__resolve_type(obj->btf, vsi->type);
 		if (type_id < 0) {
 			pr_warn("struct_ops init: Cannot resolve var type_id %u in DATASEC %s\n",
-				vsi->type, STRUCT_OPS_SEC);
+				vsi->type, sec_name);
 			return -EINVAL;
 		}
 
@@ -1170,7 +1188,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 		if (IS_ERR(map))
 			return PTR_ERR(map);
 
-		map->sec_idx = obj->efile.st_ops_shndx;
+		map->sec_idx = shndx;
 		map->sec_offset = vsi->offset;
 		map->name = strdup(var_name);
 		if (!map->name)
@@ -1180,6 +1198,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 		map->def.key_size = sizeof(int);
 		map->def.value_size = type->size;
 		map->def.max_entries = 1;
+		map->def.map_flags = map_flags;
 
 		map->st_ops = calloc(1, sizeof(*map->st_ops));
 		if (!map->st_ops)
@@ -1192,14 +1211,14 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 		if (!st_ops->data || !st_ops->progs || !st_ops->kern_func_off)
 			return -ENOMEM;
 
-		if (vsi->offset + type->size > obj->efile.st_ops_data->d_size) {
+		if (vsi->offset + type->size > data->d_size) {
 			pr_warn("struct_ops init: var %s is beyond the end of DATASEC %s\n",
-				var_name, STRUCT_OPS_SEC);
+				var_name, sec_name);
 			return -EINVAL;
 		}
 
 		memcpy(st_ops->data,
-		       obj->efile.st_ops_data->d_buf + vsi->offset,
+		       data->d_buf + vsi->offset,
 		       type->size);
 		st_ops->tname = tname;
 		st_ops->type = type;
@@ -1212,6 +1231,15 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 	return 0;
 }
 
+static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
+{
+	int err;
+
+	err = bpf_object__init_struct_ops_maps_link(obj, false);
+	err = err ?: bpf_object__init_struct_ops_maps_link(obj, true);
+	return err;
+}
+
 static struct bpf_object *bpf_object__new(const char *path,
 					  const void *obj_buf,
 					  size_t obj_buf_sz,
@@ -1248,6 +1276,7 @@ static struct bpf_object *bpf_object__new(const char *path,
 	obj->efile.obj_buf_sz = obj_buf_sz;
 	obj->efile.btf_maps_shndx = -1;
 	obj->efile.st_ops_shndx = -1;
+	obj->efile.st_ops_link_shndx = -1;
 	obj->kconfig_map_idx = -1;
 
 	obj->kern_version = get_kernel_version();
@@ -1265,6 +1294,7 @@ static void bpf_object__elf_finish(struct bpf_object *obj)
 	obj->efile.elf = NULL;
 	obj->efile.symbols = NULL;
 	obj->efile.st_ops_data = NULL;
+	obj->efile.st_ops_link_data = NULL;
 
 	zfree(&obj->efile.secs);
 	obj->efile.sec_cnt = 0;
@@ -2753,12 +2783,13 @@ static bool libbpf_needs_btf(const struct bpf_object *obj)
 {
 	return obj->efile.btf_maps_shndx >= 0 ||
 	       obj->efile.st_ops_shndx >= 0 ||
+	       obj->efile.st_ops_link_shndx >= 0 ||
 	       obj->nr_extern > 0;
 }
 
 static bool kernel_needs_btf(const struct bpf_object *obj)
 {
-	return obj->efile.st_ops_shndx >= 0;
+	return obj->efile.st_ops_shndx >= 0 || obj->efile.st_ops_link_shndx >= 0;
 }
 
 static int bpf_object__init_btf(struct bpf_object *obj,
@@ -3451,6 +3482,9 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 			} else if (strcmp(name, STRUCT_OPS_SEC) == 0) {
 				obj->efile.st_ops_data = data;
 				obj->efile.st_ops_shndx = idx;
+			} else if (strcmp(name, STRUCT_OPS_LINK_SEC) == 0) {
+				obj->efile.st_ops_link_data = data;
+				obj->efile.st_ops_link_shndx = idx;
 			} else {
 				pr_info("elf: skipping unrecognized data section(%d) %s\n",
 					idx, name);
@@ -3465,6 +3499,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 			/* Only do relo for section with exec instructions */
 			if (!section_have_execinstr(obj, targ_sec_idx) &&
 			    strcmp(name, ".rel" STRUCT_OPS_SEC) &&
+			    strcmp(name, ".rel" STRUCT_OPS_LINK_SEC) &&
 			    strcmp(name, ".rel" MAPS_ELF_SEC)) {
 				pr_info("elf: skipping relo section(%d) %s for section(%d) %s\n",
 					idx, name, targ_sec_idx,
@@ -6611,7 +6646,7 @@ static int bpf_object__collect_relos(struct bpf_object *obj)
 			return -LIBBPF_ERRNO__INTERNAL;
 		}
 
-		if (idx == obj->efile.st_ops_shndx)
+		if (idx == obj->efile.st_ops_shndx || idx == obj->efile.st_ops_link_shndx)
 			err = bpf_object__collect_st_ops_relos(obj, shdr, data);
 		else if (idx == obj->efile.btf_maps_shndx)
 			err = bpf_object__collect_map_relos(obj, shdr, data);
@@ -8954,8 +8989,9 @@ static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
 		}
 
 		/* struct_ops BPF prog can be re-used between multiple
-		 * .struct_ops as long as it's the same struct_ops struct
-		 * definition and the same function pointer field
+		 * .struct_ops & .struct_ops.link as long as it's the
+		 * same struct_ops struct definition and the same
+		 * function pointer field
 		 */
 		if (prog->attach_btf_id != st_ops->type_id ||
 		    prog->expected_attach_type != member_idx) {
-- 
2.34.1

[PATCH bpf-next v4 9/9] selftests/bpf: Test switching TCP Congestion Control algorithms.

[Kui-Feng Lee]

Create a pair of sockets that utilize the congestion control algorithm
under a particular name. Then switch up this congestion control
algorithm to another implementation and check whether newly created
connections using the same cc name now run the new implementation.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
 .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 38 ++++++++++++
 .../selftests/bpf/progs/tcp_ca_update.c       | 62 +++++++++++++++++++
 2 files changed, 100 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/tcp_ca_update.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
index e980188d4124..caaa9175ee36 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
@@ -8,6 +8,7 @@
 #include "bpf_dctcp.skel.h"
 #include "bpf_cubic.skel.h"
 #include "bpf_tcp_nogpl.skel.h"
+#include "tcp_ca_update.skel.h"
 #include "bpf_dctcp_release.skel.h"
 #include "tcp_ca_write_sk_pacing.skel.h"
 #include "tcp_ca_incompl_cong_ops.skel.h"
@@ -381,6 +382,41 @@ static void test_unsupp_cong_op(void)
 	libbpf_set_print(old_print_fn);
 }
 
+static void test_update_ca(void)
+{
+	struct tcp_ca_update *skel;
+	struct bpf_link *link;
+	int saved_ca1_cnt;
+	int err;
+
+	skel = tcp_ca_update__open();
+	if (!ASSERT_OK_PTR(skel, "open"))
+		return;
+
+	err = tcp_ca_update__load(skel);
+	if (!ASSERT_OK(err, "load")) {
+		tcp_ca_update__destroy(skel);
+		return;
+	}
+
+	link = bpf_map__attach_struct_ops(skel->maps.ca_update_1);
+	ASSERT_OK_PTR(link, "attach_struct_ops");
+
+	do_test("tcp_ca_update", NULL);
+	saved_ca1_cnt = skel->bss->ca1_cnt;
+	ASSERT_GT(saved_ca1_cnt, 0, "ca1_ca1_cnt");
+
+	err = bpf_link__update_map(link, skel->maps.ca_update_2);
+	ASSERT_OK(err, "update_struct_ops");
+
+	do_test("tcp_ca_update", NULL);
+	ASSERT_EQ(skel->bss->ca1_cnt, saved_ca1_cnt, "ca2_ca1_cnt");
+	ASSERT_GT(skel->bss->ca2_cnt, 0, "ca2_ca2_cnt");
+
+	bpf_link__destroy(link);
+	tcp_ca_update__destroy(skel);
+}
+
 void test_bpf_tcp_ca(void)
 {
 	if (test__start_subtest("dctcp"))
@@ -399,4 +435,6 @@ void test_bpf_tcp_ca(void)
 		test_incompl_cong_ops();
 	if (test__start_subtest("unsupp_cong_op"))
 		test_unsupp_cong_op();
+	if (test__start_subtest("update_ca"))
+		test_update_ca();
 }
diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_update.c b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
new file mode 100644
index 000000000000..36a04be95df5
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+int ca1_cnt = 0;
+int ca2_cnt = 0;
+
+#define USEC_PER_SEC 1000000UL
+
+#define min(a, b) ((a) < (b) ? (a) : (b))
+
+static inline struct tcp_sock *tcp_sk(const struct sock *sk)
+{
+	return (struct tcp_sock *)sk;
+}
+
+SEC("struct_ops/ca_update_1_cong_control")
+void BPF_PROG(ca_update_1_cong_control, struct sock *sk,
+	      const struct rate_sample *rs)
+{
+	ca1_cnt++;
+}
+
+SEC("struct_ops/ca_update_2_cong_control")
+void BPF_PROG(ca_update_2_cong_control, struct sock *sk,
+	      const struct rate_sample *rs)
+{
+	ca2_cnt++;
+}
+
+SEC("struct_ops/ca_update_ssthresh")
+__u32 BPF_PROG(ca_update_ssthresh, struct sock *sk)
+{
+	return tcp_sk(sk)->snd_ssthresh;
+}
+
+SEC("struct_ops/ca_update_undo_cwnd")
+__u32 BPF_PROG(ca_update_undo_cwnd, struct sock *sk)
+{
+	return tcp_sk(sk)->snd_cwnd;
+}
+
+SEC(".struct_ops.link")
+struct tcp_congestion_ops ca_update_1 = {
+	.cong_control = (void *)ca_update_1_cong_control,
+	.ssthresh = (void *)ca_update_ssthresh,
+	.undo_cwnd = (void *)ca_update_undo_cwnd,
+	.name = "tcp_ca_update",
+};
+
+SEC(".struct_ops.link")
+struct tcp_congestion_ops ca_update_2 = {
+	.cong_control = (void *)ca_update_2_cong_control,
+	.ssthresh = (void *)ca_update_ssthresh,
+	.undo_cwnd = (void *)ca_update_undo_cwnd,
+	.name = "tcp_ca_update",
+};
-- 
2.34.1

Re: [PATCH bpf-next v4 2/9] bpf: Create links for BPF struct_ops maps.

[Andrii Nakryiko]

On Tue, Mar 7, 2023 at 3:33 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>
> BPF struct_ops maps are employed directly to register TCP Congestion
> Control algorithms. Unlike other BPF programs that terminate when
> their links gone. The link of a BPF struct_ops map provides a uniform
> experience akin to other types of BPF programs.
>
> bpf_links are responsible for registering their associated
> struct_ops. You can only use a struct_ops that has the BPF_F_LINK flag
> set to create a bpf_link, while a structs without this flag behaves in
> the same manner as before and is registered upon updating its value.
>
> The BPF_LINK_TYPE_STRUCT_OPS serves a dual purpose. Not only is it
> used to craft the links for BPF struct_ops programs, but also to
> create links for BPF struct_ops them-self.  Since the links of BPF
> struct_ops programs are only used to create trampolines internally,
> they are never seen in other contexts. Thus, they can be reused for
> struct_ops themself.
>
> To maintain a reference to the map supporting this link, we add
> bpf_struct_ops_link as an additional type. The pointer of the map is
> RCU and won't be necessary until later in the patchset.
>
> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
> ---
>  include/linux/bpf.h            |  11 +++
>  include/uapi/linux/bpf.h       |  12 +++-
>  kernel/bpf/bpf_struct_ops.c    | 119 +++++++++++++++++++++++++++++++--
>  kernel/bpf/syscall.c           |  23 ++++---
>  tools/include/uapi/linux/bpf.h |  12 +++-
>  5 files changed, 163 insertions(+), 14 deletions(-)
>

[...]

> +int bpf_struct_ops_link_create(union bpf_attr *attr)
> +{
> +       struct bpf_struct_ops_link *link = NULL;
> +       struct bpf_link_primer link_primer;
> +       struct bpf_struct_ops_map *st_map;
> +       struct bpf_map *map;
> +       int err;
> +
> +       map = bpf_map_get(attr->link_create.map_fd);
> +       if (!map)
> +               return -EINVAL;
> +
> +       st_map = (struct bpf_struct_ops_map *)map;
> +
> +       if (map->map_type != BPF_MAP_TYPE_STRUCT_OPS || !(map->map_flags & BPF_F_LINK) ||
> +           /* Pair with smp_store_release() during map_update */
> +           smp_load_acquire(&st_map->kvalue.state) != BPF_STRUCT_OPS_STATE_READY) {
> +               err = -EINVAL;
> +               goto err_out;
> +       }
> +
> +       link = kzalloc(sizeof(*link), GFP_USER);
> +       if (!link) {
> +               err = -ENOMEM;
> +               goto err_out;
> +       }
> +       bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_struct_ops_map_lops, NULL);
> +       RCU_INIT_POINTER(link->map, map);
> +
> +       err = bpf_link_prime(&link->link, &link_primer);
> +       if (err)
> +               goto err_out;
> +
> +       err = st_map->st_ops->reg(st_map->kvalue.data);
> +       if (err) {
> +               bpf_link_cleanup(&link_primer);

link = NULL to avoid kfree()-ing it, see bpf_tracing_prog_attach() for
similar approach

> +               goto err_out;
> +       }
> +
> +       return bpf_link_settle(&link_primer);
> +
> +err_out:
> +       bpf_map_put(map);
> +       kfree(link);
> +       return err;
> +}
> +

[...]

Re: [PATCH bpf-next v4 5/9] libbpf: Create a bpf_link in bpf_map__attach_struct_ops().

[Andrii Nakryiko]

On Tue, Mar 7, 2023 at 3:33 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>
> bpf_map__attach_struct_ops() was creating a dummy bpf_link as a
> placeholder, but now it is constructing an authentic one by calling
> bpf_link_create() if the map has the BPF_F_LINK flag.
>
> You can flag a struct_ops map with BPF_F_LINK by calling
> bpf_map__set_map_flags().
>
> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
> ---
>  tools/lib/bpf/libbpf.c | 84 +++++++++++++++++++++++++++++++-----------
>  1 file changed, 62 insertions(+), 22 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 35a698eb825d..a67efc3b3763 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -115,6 +115,7 @@ static const char * const attach_type_name[] = {
>         [BPF_SK_REUSEPORT_SELECT_OR_MIGRATE]    = "sk_reuseport_select_or_migrate",
>         [BPF_PERF_EVENT]                = "perf_event",
>         [BPF_TRACE_KPROBE_MULTI]        = "trace_kprobe_multi",
> +       [BPF_STRUCT_OPS]                = "struct_ops",
>  };
>
>  static const char * const link_type_name[] = {
> @@ -7677,6 +7678,26 @@ static int bpf_object__resolve_externs(struct bpf_object *obj,
>         return 0;
>  }
>
> +static void bpf_map_prepare_vdata(const struct bpf_map *map)
> +{
> +       struct bpf_struct_ops *st_ops;
> +       __u32 i;
> +
> +       st_ops = map->st_ops;
> +       for (i = 0; i < btf_vlen(st_ops->type); i++) {
> +               struct bpf_program *prog = st_ops->progs[i];
> +               void *kern_data;
> +               int prog_fd;
> +
> +               if (!prog)
> +                       continue;
> +
> +               prog_fd = bpf_program__fd(prog);
> +               kern_data = st_ops->kern_vdata + st_ops->kern_func_off[i];
> +               *(unsigned long *)kern_data = prog_fd;
> +       }
> +}
> +
>  static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const char *target_btf_path)
>  {
>         int err, i;
> @@ -7728,6 +7749,10 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
>         btf__free(obj->btf_vmlinux);
>         obj->btf_vmlinux = NULL;
>
> +       for (i = 0; i < obj->nr_maps; i++)
> +               if (bpf_map__is_struct_ops(&obj->maps[i]))
> +                       bpf_map_prepare_vdata(&obj->maps[i]);

This is similar in spirit to what bpf_object_init_prog_arrays() is
doing, let's add this as a separate step.

How about bpf_object_prepare_struct_ops()?

> +
>         obj->loaded = true; /* doesn't matter if successfully or not */
>
>         if (err)
> @@ -11429,22 +11454,34 @@ struct bpf_link *bpf_program__attach(const struct bpf_program *prog)
>         return link;
>  }
>
> +struct bpf_link_struct_ops {
> +       struct bpf_link link;
> +       int map_fd;
> +};
> +
>  static int bpf_link__detach_struct_ops(struct bpf_link *link)
>  {
> +       struct bpf_link_struct_ops *st_link;
>         __u32 zero = 0;
>
> -       if (bpf_map_delete_elem(link->fd, &zero))
> -               return -errno;
> +       st_link = container_of(link, struct bpf_link_struct_ops, link);
>
> -       return 0;
> +       if (st_link->map_fd < 0) {
> +               /* Fake bpf_link */
> +               if (bpf_map_delete_elem(link->fd, &zero))
> +                       return -errno;
> +               return 0;

just `return bpf_map_delete_elem(...)`, it will return actual error
(libbpf 1.0 simplification)

> +       }
> +
> +       /* Doesn't support detaching. */
> +       return -EOPNOTSUPP;
>  }
>
>  struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
>  {
> -       struct bpf_struct_ops *st_ops;
> -       struct bpf_link *link;
> -       __u32 i, zero = 0;
> -       int err;
> +       struct bpf_link_struct_ops *link;
> +       __u32 zero = 0;
> +       int err, fd;
>
>         if (!bpf_map__is_struct_ops(map) || map->fd == -1)
>                 return libbpf_err_ptr(-EINVAL);
> @@ -11453,31 +11490,34 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
>         if (!link)
>                 return libbpf_err_ptr(-EINVAL);
>
> -       st_ops = map->st_ops;
> -       for (i = 0; i < btf_vlen(st_ops->type); i++) {
> -               struct bpf_program *prog = st_ops->progs[i];
> -               void *kern_data;
> -               int prog_fd;
> +       /* kern_vdata should be prepared during the loading phase. */
> +       err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
> +       if (err) {
> +               err = -errno;

no need to deal with -errno, err is already the error you need

> +               free(link);
> +               return libbpf_err_ptr(err);
> +       }
>
> -               if (!prog)
> -                       continue;
>
> -               prog_fd = bpf_program__fd(prog);
> -               kern_data = st_ops->kern_vdata + st_ops->kern_func_off[i];
> -               *(unsigned long *)kern_data = prog_fd;
> +       if (!(map->def.map_flags & BPF_F_LINK)) {
> +               /* Fake bpf_link */
> +               link->link.fd = map->fd;
> +               link->map_fd = -1;
> +               link->link.detach = bpf_link__detach_struct_ops;
> +               return &link->link;
>         }
>
> -       err = bpf_map_update_elem(map->fd, &zero, st_ops->kern_vdata, 0);
> -       if (err) {
> +       fd = bpf_link_create(map->fd, -1, BPF_STRUCT_OPS, NULL);
> +       if (fd < 0) {
>                 err = -errno;

same, fd is an error, it's true for all low-level libbpf APIs

>                 free(link);
>                 return libbpf_err_ptr(err);
>         }
>
> -       link->detach = bpf_link__detach_struct_ops;
> -       link->fd = map->fd;
> +       link->link.fd = fd;
> +       link->map_fd = map->fd;
>
> -       return link;
> +       return &link->link;
>  }
>
>  typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
> --
> 2.34.1
>

Re: [PATCH bpf-next v4 6/9] bpf: Update the struct_ops of a bpf_link.

[Andrii Nakryiko]

On Tue, Mar 7, 2023 at 3:33 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>
> By improving the BPF_LINK_UPDATE command of bpf(), it should allow you
> to conveniently switch between different struct_ops on a single
> bpf_link. This would enable smoother transitions from one struct_ops
> to another.
>
> The struct_ops maps passing along with BPF_LINK_UPDATE should have the
> BPF_F_LINK flag.
>
> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
> ---
>  include/linux/bpf.h            |  1 +
>  include/uapi/linux/bpf.h       |  8 ++++--
>  kernel/bpf/bpf_struct_ops.c    | 46 ++++++++++++++++++++++++++++++++++
>  kernel/bpf/syscall.c           | 43 ++++++++++++++++++++++++++++---
>  tools/include/uapi/linux/bpf.h |  7 +++++-
>  5 files changed, 98 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 047d2c6aba88..2b5f150e370e 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1405,6 +1405,7 @@ struct bpf_link_ops {
>         void (*show_fdinfo)(const struct bpf_link *link, struct seq_file *seq);
>         int (*fill_link_info)(const struct bpf_link *link,
>                               struct bpf_link_info *info);
> +       int (*update_map)(struct bpf_link *link, struct bpf_map *new_map);
>  };
>
>  struct bpf_tramp_link {
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index eb3e435c5303..999e199ebe06 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1555,8 +1555,12 @@ union bpf_attr {
>
>         struct { /* struct used by BPF_LINK_UPDATE command */
>                 __u32           link_fd;        /* link fd */
> -               /* new program fd to update link with */
> -               __u32           new_prog_fd;
> +               union {
> +                       /* new program fd to update link with */
> +                       __u32           new_prog_fd;
> +                       /* new struct_ops map fd to update link with */
> +                       __u32           new_map_fd;
> +               };
>                 __u32           flags;          /* extra flags */
>                 /* expected link's program fd; is specified only if
>                  * BPF_F_REPLACE flag is set in flags */
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index c71c8d73c7ad..2b850ce11617 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -759,10 +759,56 @@ static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link,
>         return 0;
>  }
>
> +static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map *new_map)
> +{
> +       struct bpf_struct_ops_value *kvalue;
> +       struct bpf_struct_ops_map *st_map, *old_st_map;
> +       struct bpf_struct_ops_link *st_link;
> +       struct bpf_map *old_map;
> +       int err = 0;
> +
> +       if (new_map->map_type != BPF_MAP_TYPE_STRUCT_OPS ||
> +           !(new_map->map_flags & BPF_F_LINK))
> +               return -EINVAL;
> +
> +       mutex_lock(&update_mutex);
> +
> +       st_link = container_of(link, struct bpf_struct_ops_link, link);
> +
> +       /* The new and old struct_ops must be the same type. */
> +       st_map = container_of(new_map, struct bpf_struct_ops_map, map);
> +
> +       old_map = st_link->map;
> +       old_st_map = container_of(old_map, struct bpf_struct_ops_map, map);
> +       if (st_map->st_ops != old_st_map->st_ops ||
> +           /* Pair with smp_store_release() during map_update */
> +           smp_load_acquire(&st_map->kvalue.state) != BPF_STRUCT_OPS_STATE_READY) {
> +               err = -EINVAL;
> +               goto err_out;
> +       }
> +
> +       kvalue = &st_map->kvalue;
> +
> +       err = st_map->st_ops->update(kvalue->data, old_st_map->kvalue.data);
> +       if (err)
> +               goto err_out;
> +
> +       bpf_map_inc(new_map);
> +       rcu_assign_pointer(st_link->map, new_map);
> +
> +       bpf_map_put(old_map);
> +
> +err_out:
> +       mutex_unlock(&update_mutex);
> +
> +       return err;
> +}
> +
>  static const struct bpf_link_ops bpf_struct_ops_map_lops = {
>         .dealloc = bpf_struct_ops_map_link_dealloc,
>         .show_fdinfo = bpf_struct_ops_map_link_show_fdinfo,
>         .fill_link_info = bpf_struct_ops_map_link_fill_link_info,
> +       .update_map = bpf_struct_ops_map_link_update,
>  };
>
>  int bpf_struct_ops_link_create(union bpf_attr *attr)
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 25b044fdd82b..94ab1336ff41 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -4646,6 +4646,30 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
>         return ret;
>  }
>
> +static int link_update_map(struct bpf_link *link, union bpf_attr *attr)
> +{
> +       struct bpf_map *new_map;
> +       int ret = 0;
> +
> +       new_map = bpf_map_get(attr->link_update.new_map_fd);
> +       if (IS_ERR(new_map))
> +               return -EINVAL;
> +
> +       if (new_map->map_type != BPF_MAP_TYPE_STRUCT_OPS) {
> +               ret = -EINVAL;
> +               goto out_put_map;
> +       }
> +
> +       if (link->ops->update_map)
> +               ret = link->ops->update_map(link, new_map);
> +       else
> +               ret = -EINVAL;
> +
> +out_put_map:
> +       bpf_map_put(new_map);
> +       return ret;
> +}
> +
>  #define BPF_LINK_UPDATE_LAST_FIELD link_update.old_prog_fd
>
>  static int link_update(union bpf_attr *attr)
> @@ -4658,14 +4682,25 @@ static int link_update(union bpf_attr *attr)
>         if (CHECK_ATTR(BPF_LINK_UPDATE))
>                 return -EINVAL;
>
> -       flags = attr->link_update.flags;
> -       if (flags & ~BPF_F_REPLACE)
> -               return -EINVAL;
> -
>         link = bpf_link_get_from_fd(attr->link_update.link_fd);
>         if (IS_ERR(link))
>                 return PTR_ERR(link);
>
> +       flags = attr->link_update.flags;
> +
> +       if (link->ops->update_map) {
> +               if (flags)      /* always replace the existing one */
> +                       ret = -EINVAL;
> +               else
> +                       ret = link_update_map(link, attr);
> +               goto out_put_link;

umm... BPF_F_REPLACE for link_update is specifying "update only if
current prog fd matches what I specify", let's not ignore it for
struct_ops. This will create a deviation in behavior unnecessarily.
Please keep it consistent.


> +       }
> +
> +       if (flags & ~BPF_F_REPLACE) {
> +               ret = -EINVAL;
> +               goto out_put_link;
> +       }
> +
>         new_prog = bpf_prog_get(attr->link_update.new_prog_fd);
>         if (IS_ERR(new_prog)) {
>                 ret = PTR_ERR(new_prog);
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index cd0ff39981e8..259b8ab4f54e 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -1556,7 +1556,12 @@ union bpf_attr {
>         struct { /* struct used by BPF_LINK_UPDATE command */
>                 __u32           link_fd;        /* link fd */
>                 /* new program fd to update link with */
> -               __u32           new_prog_fd;
> +               union {
> +                       /* new program fd to update link with */
> +                       __u32           new_prog_fd;
> +                       /* new struct_ops map fd to update link with */
> +                       __u32           new_map_fd;
> +               };
>                 __u32           flags;          /* extra flags */
>                 /* expected link's program fd; is specified only if
>                  * BPF_F_REPLACE flag is set in flags */
> --
> 2.34.1
>

Re: [PATCH bpf-next v4 7/9] libbpf: Update a bpf_link with another struct_ops.

[Andrii Nakryiko]

On Tue, Mar 7, 2023 at 3:33 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>
> Introduce bpf_link__update_struct_ops(), which will allow you to

update_map, not update_struct_ops, please update

> effortlessly transition the struct_ops map of any given bpf_link into
> an alternative.

This reads confusingly, tbh. Why not say "bpf_link__update_map()
allows to atomically update underlying struct_ops implementation for
given struct_ops BPF link" or something like this? Would it be
accurate?

>
> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
> ---
>  tools/lib/bpf/libbpf.c   | 36 ++++++++++++++++++++++++++++++++++++
>  tools/lib/bpf/libbpf.h   |  1 +
>  tools/lib/bpf/libbpf.map |  2 ++
>  3 files changed, 39 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index a67efc3b3763..247de39d136f 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -11520,6 +11520,42 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
>         return &link->link;
>  }
>
> +/*
> + * Swap the back struct_ops of a link with a new struct_ops map.
> + */
> +int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map)
> +{
> +       struct bpf_link_struct_ops *st_ops_link;
> +       __u32 zero = 0;
> +       int err, fd;
> +
> +       if (!bpf_map__is_struct_ops(map) || map->fd == -1)

let's not hard-code equality like this, < 0 is better

> +               return -EINVAL;
> +
> +       st_ops_link = container_of(link, struct bpf_link_struct_ops, link);
> +       /* Ensure the type of a link is correct */
> +       if (st_ops_link->map_fd < 0)
> +               return -EINVAL;
> +
> +       err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
> +       if (err && errno != EBUSY) {

don't use errno, err is perfectly fine to rely on

> +               err = -errno;
> +               free(link);

why freeing the link?...


> +               return err;
> +       }
> +
> +       fd = bpf_link_update(link->fd, map->fd, NULL);
> +       if (fd < 0) {
> +               err = -errno;
> +               free(link);

same... please write tests that exercise both successful and
unsuccessful scenarios

> +               return err;
> +       }
> +
> +       st_ops_link->map_fd = map->fd;
> +
> +       return 0;
> +}
> +
>  typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
>                                                           void *private_data);
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 2efd80f6f7b9..5e62878d184c 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -695,6 +695,7 @@ bpf_program__attach_freplace(const struct bpf_program *prog,
>  struct bpf_map;
>
>  LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
> +LIBBPF_API int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map);
>
>  struct bpf_iter_attach_opts {
>         size_t sz; /* size of this struct for forward/backward compatibility */
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 11c36a3c1a9f..e83571b04c19 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -384,4 +384,6 @@ LIBBPF_1.1.0 {
>  } LIBBPF_1.0.0;
>
>  LIBBPF_1.2.0 {
> +       global:
> +               bpf_link__update_map;

please always rebase before posting new versions of patch set,
LIBBPF_1.2.0 is not empty anymore

>  } LIBBPF_1.1.0;
> --
> 2.34.1
>

Re: [PATCH bpf-next v4 8/9] libbpf: Use .struct_ops.link section to indicate a struct_ops with a link.

[Andrii Nakryiko]

On Tue, Mar 7, 2023 at 3:33 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>
> Flags a struct_ops is to back a bpf_link by putting it to the
> ".struct_ops.link" section.  Once it is flagged, the created
> struct_ops can be used to create a bpf_link or update a bpf_link that
> has been backed by another struct_ops.
>
> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
> ---
>  tools/lib/bpf/libbpf.c | 64 +++++++++++++++++++++++++++++++++---------
>  1 file changed, 50 insertions(+), 14 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 247de39d136f..d66acd2fdbaa 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -467,6 +467,7 @@ struct bpf_struct_ops {
>  #define KCONFIG_SEC ".kconfig"
>  #define KSYMS_SEC ".ksyms"
>  #define STRUCT_OPS_SEC ".struct_ops"
> +#define STRUCT_OPS_LINK_SEC ".struct_ops.link"
>
>  enum libbpf_map_type {
>         LIBBPF_MAP_UNSPEC,
> @@ -596,6 +597,7 @@ struct elf_state {
>         Elf64_Ehdr *ehdr;
>         Elf_Data *symbols;
>         Elf_Data *st_ops_data;
> +       Elf_Data *st_ops_link_data;
>         size_t shstrndx; /* section index for section name strings */
>         size_t strtabidx;
>         struct elf_sec_desc *secs;
> @@ -605,6 +607,7 @@ struct elf_state {
>         int text_shndx;
>         int symbols_shndx;
>         int st_ops_shndx;
> +       int st_ops_link_shndx;
>  };
>
>  struct usdt_manager;
> @@ -1119,7 +1122,7 @@ static int bpf_object__init_kern_struct_ops_maps(struct bpf_object *obj)
>         return 0;
>  }
>
> -static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
> +static int bpf_object__init_struct_ops_maps_link(struct bpf_object *obj, bool link)

let's shorten it and not use double underscores, as this is not a
public bpf_object API, just "init_struct_ops_maps" probably is fine

>  {
>         const struct btf_type *type, *datasec;
>         const struct btf_var_secinfo *vsi;
> @@ -1127,18 +1130,33 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>         const char *tname, *var_name;
>         __s32 type_id, datasec_id;
>         const struct btf *btf;
> +       const char *sec_name;
>         struct bpf_map *map;
> -       __u32 i;
> +       __u32 i, map_flags;
> +       Elf_Data *data;
> +       int shndx;
>
> -       if (obj->efile.st_ops_shndx == -1)
> +       if (link) {
> +               sec_name = STRUCT_OPS_LINK_SEC;
> +               shndx = obj->efile.st_ops_link_shndx;
> +               data = obj->efile.st_ops_link_data;
> +               map_flags = BPF_F_LINK;
> +       } else {
> +               sec_name = STRUCT_OPS_SEC;
> +               shndx = obj->efile.st_ops_shndx;
> +               data = obj->efile.st_ops_data;
> +               map_flags = 0;
> +       }

let's pass these as function arguments instead

> +
> +       if (shndx == -1)
>                 return 0;
>
>         btf = obj->btf;
> -       datasec_id = btf__find_by_name_kind(btf, STRUCT_OPS_SEC,
> +       datasec_id = btf__find_by_name_kind(btf, sec_name,
>                                             BTF_KIND_DATASEC);
>         if (datasec_id < 0) {
>                 pr_warn("struct_ops init: DATASEC %s not found\n",
> -                       STRUCT_OPS_SEC);
> +                       sec_name);
>                 return -EINVAL;
>         }
>
> @@ -1151,7 +1169,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>                 type_id = btf__resolve_type(obj->btf, vsi->type);
>                 if (type_id < 0) {
>                         pr_warn("struct_ops init: Cannot resolve var type_id %u in DATASEC %s\n",
> -                               vsi->type, STRUCT_OPS_SEC);
> +                               vsi->type, sec_name);
>                         return -EINVAL;
>                 }
>
> @@ -1170,7 +1188,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>                 if (IS_ERR(map))
>                         return PTR_ERR(map);
>
> -               map->sec_idx = obj->efile.st_ops_shndx;
> +               map->sec_idx = shndx;
>                 map->sec_offset = vsi->offset;
>                 map->name = strdup(var_name);
>                 if (!map->name)
> @@ -1180,6 +1198,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>                 map->def.key_size = sizeof(int);
>                 map->def.value_size = type->size;
>                 map->def.max_entries = 1;
> +               map->def.map_flags = map_flags;
>
>                 map->st_ops = calloc(1, sizeof(*map->st_ops));
>                 if (!map->st_ops)
> @@ -1192,14 +1211,14 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>                 if (!st_ops->data || !st_ops->progs || !st_ops->kern_func_off)
>                         return -ENOMEM;
>
> -               if (vsi->offset + type->size > obj->efile.st_ops_data->d_size) {
> +               if (vsi->offset + type->size > data->d_size) {
>                         pr_warn("struct_ops init: var %s is beyond the end of DATASEC %s\n",
> -                               var_name, STRUCT_OPS_SEC);
> +                               var_name, sec_name);
>                         return -EINVAL;
>                 }
>
>                 memcpy(st_ops->data,
> -                      obj->efile.st_ops_data->d_buf + vsi->offset,
> +                      data->d_buf + vsi->offset,
>                        type->size);
>                 st_ops->tname = tname;
>                 st_ops->type = type;
> @@ -1212,6 +1231,15 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>         return 0;
>  }
>
> +static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)

let's name this bpf_object_init_struct_ops, no double underscores

> +{
> +       int err;
> +
> +       err = bpf_object__init_struct_ops_maps_link(obj, false);
> +       err = err ?: bpf_object__init_struct_ops_maps_link(obj, true);
> +       return err;
> +}
> +
>  static struct bpf_object *bpf_object__new(const char *path,
>                                           const void *obj_buf,
>                                           size_t obj_buf_sz,
> @@ -1248,6 +1276,7 @@ static struct bpf_object *bpf_object__new(const char *path,
>         obj->efile.obj_buf_sz = obj_buf_sz;
>         obj->efile.btf_maps_shndx = -1;
>         obj->efile.st_ops_shndx = -1;
> +       obj->efile.st_ops_link_shndx = -1;
>         obj->kconfig_map_idx = -1;
>
>         obj->kern_version = get_kernel_version();
> @@ -1265,6 +1294,7 @@ static void bpf_object__elf_finish(struct bpf_object *obj)
>         obj->efile.elf = NULL;
>         obj->efile.symbols = NULL;
>         obj->efile.st_ops_data = NULL;
> +       obj->efile.st_ops_link_data = NULL;
>
>         zfree(&obj->efile.secs);
>         obj->efile.sec_cnt = 0;
> @@ -2753,12 +2783,13 @@ static bool libbpf_needs_btf(const struct bpf_object *obj)
>  {
>         return obj->efile.btf_maps_shndx >= 0 ||
>                obj->efile.st_ops_shndx >= 0 ||
> +              obj->efile.st_ops_link_shndx >= 0 ||
>                obj->nr_extern > 0;
>  }
>
>  static bool kernel_needs_btf(const struct bpf_object *obj)
>  {
> -       return obj->efile.st_ops_shndx >= 0;
> +       return obj->efile.st_ops_shndx >= 0 || obj->efile.st_ops_link_shndx >= 0;
>  }
>
>  static int bpf_object__init_btf(struct bpf_object *obj,
> @@ -3451,6 +3482,9 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
>                         } else if (strcmp(name, STRUCT_OPS_SEC) == 0) {
>                                 obj->efile.st_ops_data = data;
>                                 obj->efile.st_ops_shndx = idx;
> +                       } else if (strcmp(name, STRUCT_OPS_LINK_SEC) == 0) {
> +                               obj->efile.st_ops_link_data = data;
> +                               obj->efile.st_ops_link_shndx = idx;
>                         } else {
>                                 pr_info("elf: skipping unrecognized data section(%d) %s\n",
>                                         idx, name);
> @@ -3465,6 +3499,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
>                         /* Only do relo for section with exec instructions */
>                         if (!section_have_execinstr(obj, targ_sec_idx) &&
>                             strcmp(name, ".rel" STRUCT_OPS_SEC) &&
> +                           strcmp(name, ".rel" STRUCT_OPS_LINK_SEC) &&
>                             strcmp(name, ".rel" MAPS_ELF_SEC)) {
>                                 pr_info("elf: skipping relo section(%d) %s for section(%d) %s\n",
>                                         idx, name, targ_sec_idx,
> @@ -6611,7 +6646,7 @@ static int bpf_object__collect_relos(struct bpf_object *obj)
>                         return -LIBBPF_ERRNO__INTERNAL;
>                 }
>
> -               if (idx == obj->efile.st_ops_shndx)
> +               if (idx == obj->efile.st_ops_shndx || idx == obj->efile.st_ops_link_shndx)
>                         err = bpf_object__collect_st_ops_relos(obj, shdr, data);

this function calls find_struct_ops_map_by_offset() which assumes we
only have one struct_ops section. This won't work now, please double
check all this, there should be no assumption about specific section
index

>                 else if (idx == obj->efile.btf_maps_shndx)
>                         err = bpf_object__collect_map_relos(obj, shdr, data);
> @@ -8954,8 +8989,9 @@ static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
>                 }
>
>                 /* struct_ops BPF prog can be re-used between multiple
> -                * .struct_ops as long as it's the same struct_ops struct
> -                * definition and the same function pointer field
> +                * .struct_ops & .struct_ops.link as long as it's the
> +                * same struct_ops struct definition and the same
> +                * function pointer field
>                  */
>                 if (prog->attach_btf_id != st_ops->type_id ||
>                     prog->expected_attach_type != member_idx) {
> --
> 2.34.1
>

Re: [PATCH bpf-next v4 9/9] selftests/bpf: Test switching TCP Congestion Control algorithms.

[Andrii Nakryiko]

On Tue, Mar 7, 2023 at 3:34 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>
> Create a pair of sockets that utilize the congestion control algorithm
> under a particular name. Then switch up this congestion control
> algorithm to another implementation and check whether newly created
> connections using the same cc name now run the new implementation.
>
> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
> ---
>  .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 38 ++++++++++++
>  .../selftests/bpf/progs/tcp_ca_update.c       | 62 +++++++++++++++++++
>  2 files changed, 100 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/tcp_ca_update.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> index e980188d4124..caaa9175ee36 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> @@ -8,6 +8,7 @@
>  #include "bpf_dctcp.skel.h"
>  #include "bpf_cubic.skel.h"
>  #include "bpf_tcp_nogpl.skel.h"
> +#include "tcp_ca_update.skel.h"
>  #include "bpf_dctcp_release.skel.h"
>  #include "tcp_ca_write_sk_pacing.skel.h"
>  #include "tcp_ca_incompl_cong_ops.skel.h"
> @@ -381,6 +382,41 @@ static void test_unsupp_cong_op(void)
>         libbpf_set_print(old_print_fn);
>  }
>
> +static void test_update_ca(void)
> +{
> +       struct tcp_ca_update *skel;
> +       struct bpf_link *link;
> +       int saved_ca1_cnt;
> +       int err;
> +
> +       skel = tcp_ca_update__open();
> +       if (!ASSERT_OK_PTR(skel, "open"))
> +               return;
> +
> +       err = tcp_ca_update__load(skel);

tcp_ca_update__open_and_load()

> +       if (!ASSERT_OK(err, "load")) {
> +               tcp_ca_update__destroy(skel);
> +               return;
> +       }
> +
> +       link = bpf_map__attach_struct_ops(skel->maps.ca_update_1);

I think it's time to generate link holder for each struct_ops map to
the BPF skeleton, and support auto-attach of struct_ops skeleton.
Please do that as a follow up, once this patch set lands.

> +       ASSERT_OK_PTR(link, "attach_struct_ops");
> +
> +       do_test("tcp_ca_update", NULL);
> +       saved_ca1_cnt = skel->bss->ca1_cnt;
> +       ASSERT_GT(saved_ca1_cnt, 0, "ca1_ca1_cnt");
> +
> +       err = bpf_link__update_map(link, skel->maps.ca_update_2);
> +       ASSERT_OK(err, "update_struct_ops");
> +
> +       do_test("tcp_ca_update", NULL);
> +       ASSERT_EQ(skel->bss->ca1_cnt, saved_ca1_cnt, "ca2_ca1_cnt");
> +       ASSERT_GT(skel->bss->ca2_cnt, 0, "ca2_ca2_cnt");

how do we know that struct_ops programs were triggered? what
guarantees that? if nothing, we are just adding another flaky
networking test

> +
> +       bpf_link__destroy(link);
> +       tcp_ca_update__destroy(skel);
> +}
> +
>  void test_bpf_tcp_ca(void)
>  {
>         if (test__start_subtest("dctcp"))
> @@ -399,4 +435,6 @@ void test_bpf_tcp_ca(void)
>                 test_incompl_cong_ops();
>         if (test__start_subtest("unsupp_cong_op"))
>                 test_unsupp_cong_op();
> +       if (test__start_subtest("update_ca"))
> +               test_update_ca();
>  }
> diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_update.c b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
> new file mode 100644
> index 000000000000..36a04be95df5
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
> @@ -0,0 +1,62 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include "vmlinux.h"
> +
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +int ca1_cnt = 0;
> +int ca2_cnt = 0;
> +
> +#define USEC_PER_SEC 1000000UL
> +
> +#define min(a, b) ((a) < (b) ? (a) : (b))
> +
> +static inline struct tcp_sock *tcp_sk(const struct sock *sk)
> +{
> +       return (struct tcp_sock *)sk;
> +}
> +
> +SEC("struct_ops/ca_update_1_cong_control")
> +void BPF_PROG(ca_update_1_cong_control, struct sock *sk,
> +             const struct rate_sample *rs)
> +{
> +       ca1_cnt++;
> +}
> +
> +SEC("struct_ops/ca_update_2_cong_control")
> +void BPF_PROG(ca_update_2_cong_control, struct sock *sk,
> +             const struct rate_sample *rs)
> +{
> +       ca2_cnt++;
> +}
> +
> +SEC("struct_ops/ca_update_ssthresh")
> +__u32 BPF_PROG(ca_update_ssthresh, struct sock *sk)
> +{
> +       return tcp_sk(sk)->snd_ssthresh;
> +}
> +
> +SEC("struct_ops/ca_update_undo_cwnd")
> +__u32 BPF_PROG(ca_update_undo_cwnd, struct sock *sk)
> +{
> +       return tcp_sk(sk)->snd_cwnd;
> +}
> +
> +SEC(".struct_ops.link")
> +struct tcp_congestion_ops ca_update_1 = {
> +       .cong_control = (void *)ca_update_1_cong_control,
> +       .ssthresh = (void *)ca_update_ssthresh,
> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
> +       .name = "tcp_ca_update",
> +};
> +
> +SEC(".struct_ops.link")
> +struct tcp_congestion_ops ca_update_2 = {
> +       .cong_control = (void *)ca_update_2_cong_control,
> +       .ssthresh = (void *)ca_update_ssthresh,
> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
> +       .name = "tcp_ca_update",
> +};

please add a test where you combine both .struct_ops and
.struct_ops.link, it's an obvious potentially problematic combination

as I mentioned in previous patches, let's also have a negative test
where bpf_link__update_map() fails

> --
> 2.34.1
>

Re: [PATCH bpf-next v4 2/9] bpf: Create links for BPF struct_ops maps.

[Kui-Feng Lee]

On 3/7/23 16:37, Andrii Nakryiko wrote:
> On Tue, Mar 7, 2023 at 3:33 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>>
>> BPF struct_ops maps are employed directly to register TCP Congestion
>> Control algorithms. Unlike other BPF programs that terminate when
>> their links gone. The link of a BPF struct_ops map provides a uniform
>> experience akin to other types of BPF programs.
>>
>> bpf_links are responsible for registering their associated
>> struct_ops. You can only use a struct_ops that has the BPF_F_LINK flag
>> set to create a bpf_link, while a structs without this flag behaves in
>> the same manner as before and is registered upon updating its value.
>>
>> The BPF_LINK_TYPE_STRUCT_OPS serves a dual purpose. Not only is it
>> used to craft the links for BPF struct_ops programs, but also to
>> create links for BPF struct_ops them-self.  Since the links of BPF
>> struct_ops programs are only used to create trampolines internally,
>> they are never seen in other contexts. Thus, they can be reused for
>> struct_ops themself.
>>
>> To maintain a reference to the map supporting this link, we add
>> bpf_struct_ops_link as an additional type. The pointer of the map is
>> RCU and won't be necessary until later in the patchset.
>>
>> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
>> ---
>>   include/linux/bpf.h            |  11 +++
>>   include/uapi/linux/bpf.h       |  12 +++-
>>   kernel/bpf/bpf_struct_ops.c    | 119 +++++++++++++++++++++++++++++++--
>>   kernel/bpf/syscall.c           |  23 ++++---
>>   tools/include/uapi/linux/bpf.h |  12 +++-
>>   5 files changed, 163 insertions(+), 14 deletions(-)
>>
> 
> [...]
> 
>> +int bpf_struct_ops_link_create(union bpf_attr *attr)
>> +{
>> +       struct bpf_struct_ops_link *link = NULL;
>> +       struct bpf_link_primer link_primer;
>> +       struct bpf_struct_ops_map *st_map;
>> +       struct bpf_map *map;
>> +       int err;
>> +
>> +       map = bpf_map_get(attr->link_create.map_fd);
>> +       if (!map)
>> +               return -EINVAL;
>> +
>> +       st_map = (struct bpf_struct_ops_map *)map;
>> +
>> +       if (map->map_type != BPF_MAP_TYPE_STRUCT_OPS || !(map->map_flags & BPF_F_LINK) ||
>> +           /* Pair with smp_store_release() during map_update */
>> +           smp_load_acquire(&st_map->kvalue.state) != BPF_STRUCT_OPS_STATE_READY) {
>> +               err = -EINVAL;
>> +               goto err_out;
>> +       }
>> +
>> +       link = kzalloc(sizeof(*link), GFP_USER);
>> +       if (!link) {
>> +               err = -ENOMEM;
>> +               goto err_out;
>> +       }
>> +       bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_struct_ops_map_lops, NULL);
>> +       RCU_INIT_POINTER(link->map, map);
>> +
>> +       err = bpf_link_prime(&link->link, &link_primer);
>> +       if (err)
>> +               goto err_out;
>> +
>> +       err = st_map->st_ops->reg(st_map->kvalue.data);
>> +       if (err) {
>> +               bpf_link_cleanup(&link_primer);
> 
> link = NULL to avoid kfree()-ing it, see bpf_tracing_prog_attach() for
> similar approach
> 

Got it! Thank you!

>> +               goto err_out;
>> +       }
>> +
>> +       return bpf_link_settle(&link_primer);
>> +
>> +err_out:
>> +       bpf_map_put(map);
>> +       kfree(link);
>> +       return err;
>> +}
>> +
> 
> [...]

Re: [PATCH bpf-next v4 7/9] libbpf: Update a bpf_link with another struct_ops.

[Kui-Feng Lee]

On 3/7/23 16:53, Andrii Nakryiko wrote:
> On Tue, Mar 7, 2023 at 3:33 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>>
>> Introduce bpf_link__update_struct_ops(), which will allow you to
> 
> update_map, not update_struct_ops, please update
> 
>> effortlessly transition the struct_ops map of any given bpf_link into
>> an alternative.
> 
> This reads confusingly, tbh. Why not say "bpf_link__update_map()
> allows to atomically update underlying struct_ops implementation for
> given struct_ops BPF link" or something like this? Would it be
> accurate?
> 

Right, it should be better.

>>
>> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
>> ---
>>   tools/lib/bpf/libbpf.c   | 36 ++++++++++++++++++++++++++++++++++++
>>   tools/lib/bpf/libbpf.h   |  1 +
>>   tools/lib/bpf/libbpf.map |  2 ++
>>   3 files changed, 39 insertions(+)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index a67efc3b3763..247de39d136f 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -11520,6 +11520,42 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
>>          return &link->link;
>>   }
>>
>> +/*
>> + * Swap the back struct_ops of a link with a new struct_ops map.
>> + */
>> +int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map)
>> +{
>> +       struct bpf_link_struct_ops *st_ops_link;
>> +       __u32 zero = 0;
>> +       int err, fd;
>> +
>> +       if (!bpf_map__is_struct_ops(map) || map->fd == -1)
> 
> let's not hard-code equality like this, < 0 is better

Ok!

> 
>> +               return -EINVAL;
>> +
>> +       st_ops_link = container_of(link, struct bpf_link_struct_ops, link);
>> +       /* Ensure the type of a link is correct */
>> +       if (st_ops_link->map_fd < 0)
>> +               return -EINVAL;
>> +
>> +       err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
>> +       if (err && errno != EBUSY) {
> 
> don't use errno, err is perfectly fine to rely on

Ok!

> 
>> +               err = -errno;
>> +               free(link);
> 
> why freeing the link?...

Urg! It is a mistake.

> 
> 
>> +               return err;
>> +       }
>> +
>> +       fd = bpf_link_update(link->fd, map->fd, NULL);
>> +       if (fd < 0) {
>> +               err = -errno;
>> +               free(link);
> 
> same... please write tests that exercise both successful and
> unsuccessful scenarios

Got it!

> 
>> +               return err;
>> +       }
>> +
>> +       st_ops_link->map_fd = map->fd;
>> +
>> +       return 0;
>> +}
>> +
>>   typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
>>                                                            void *private_data);
>>
>> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
>> index 2efd80f6f7b9..5e62878d184c 100644
>> --- a/tools/lib/bpf/libbpf.h
>> +++ b/tools/lib/bpf/libbpf.h
>> @@ -695,6 +695,7 @@ bpf_program__attach_freplace(const struct bpf_program *prog,
>>   struct bpf_map;
>>
>>   LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
>> +LIBBPF_API int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map);
>>
>>   struct bpf_iter_attach_opts {
>>          size_t sz; /* size of this struct for forward/backward compatibility */
>> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
>> index 11c36a3c1a9f..e83571b04c19 100644
>> --- a/tools/lib/bpf/libbpf.map
>> +++ b/tools/lib/bpf/libbpf.map
>> @@ -384,4 +384,6 @@ LIBBPF_1.1.0 {
>>   } LIBBPF_1.0.0;
>>
>>   LIBBPF_1.2.0 {
>> +       global:
>> +               bpf_link__update_map;
> 
> please always rebase before posting new versions of patch set,
> LIBBPF_1.2.0 is not empty anymore
> 
>>   } LIBBPF_1.1.0;
>> --
>> 2.34.1
>>

Re: [PATCH bpf-next v4 5/9] libbpf: Create a bpf_link in bpf_map__attach_struct_ops().

[Kui-Feng Lee]

On 3/7/23 16:46, Andrii Nakryiko wrote:
> On Tue, Mar 7, 2023 at 3:33 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>>
>> bpf_map__attach_struct_ops() was creating a dummy bpf_link as a
>> placeholder, but now it is constructing an authentic one by calling
>> bpf_link_create() if the map has the BPF_F_LINK flag.
>>
>> You can flag a struct_ops map with BPF_F_LINK by calling
>> bpf_map__set_map_flags().
>>
>> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
>> ---
>>   tools/lib/bpf/libbpf.c | 84 +++++++++++++++++++++++++++++++-----------
>>   1 file changed, 62 insertions(+), 22 deletions(-)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 35a698eb825d..a67efc3b3763 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -115,6 +115,7 @@ static const char * const attach_type_name[] = {
>>          [BPF_SK_REUSEPORT_SELECT_OR_MIGRATE]    = "sk_reuseport_select_or_migrate",
>>          [BPF_PERF_EVENT]                = "perf_event",
>>          [BPF_TRACE_KPROBE_MULTI]        = "trace_kprobe_multi",
>> +       [BPF_STRUCT_OPS]                = "struct_ops",
>>   };
>>
>>   static const char * const link_type_name[] = {
>> @@ -7677,6 +7678,26 @@ static int bpf_object__resolve_externs(struct bpf_object *obj,
>>          return 0;
>>   }
>>
>> +static void bpf_map_prepare_vdata(const struct bpf_map *map)
>> +{
>> +       struct bpf_struct_ops *st_ops;
>> +       __u32 i;
>> +
>> +       st_ops = map->st_ops;
>> +       for (i = 0; i < btf_vlen(st_ops->type); i++) {
>> +               struct bpf_program *prog = st_ops->progs[i];
>> +               void *kern_data;
>> +               int prog_fd;
>> +
>> +               if (!prog)
>> +                       continue;
>> +
>> +               prog_fd = bpf_program__fd(prog);
>> +               kern_data = st_ops->kern_vdata + st_ops->kern_func_off[i];
>> +               *(unsigned long *)kern_data = prog_fd;
>> +       }
>> +}
>> +
>>   static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const char *target_btf_path)
>>   {
>>          int err, i;
>> @@ -7728,6 +7749,10 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
>>          btf__free(obj->btf_vmlinux);
>>          obj->btf_vmlinux = NULL;
>>
>> +       for (i = 0; i < obj->nr_maps; i++)
>> +               if (bpf_map__is_struct_ops(&obj->maps[i]))
>> +                       bpf_map_prepare_vdata(&obj->maps[i]);
> 
> This is similar in spirit to what bpf_object_init_prog_arrays() is
> doing, let's add this as a separate step.
> 
> How about bpf_object_prepare_struct_ops()?

Good!

> 
>> +
>>          obj->loaded = true; /* doesn't matter if successfully or not */
>>
>>          if (err)
>> @@ -11429,22 +11454,34 @@ struct bpf_link *bpf_program__attach(const struct bpf_program *prog)
>>          return link;
>>   }
>>
>> +struct bpf_link_struct_ops {
>> +       struct bpf_link link;
>> +       int map_fd;
>> +};
>> +
>>   static int bpf_link__detach_struct_ops(struct bpf_link *link)
>>   {
>> +       struct bpf_link_struct_ops *st_link;
>>          __u32 zero = 0;
>>
>> -       if (bpf_map_delete_elem(link->fd, &zero))
>> -               return -errno;
>> +       st_link = container_of(link, struct bpf_link_struct_ops, link);
>>
>> -       return 0;
>> +       if (st_link->map_fd < 0) {
>> +               /* Fake bpf_link */
>> +               if (bpf_map_delete_elem(link->fd, &zero))
>> +                       return -errno;
>> +               return 0;
> 
> just `return bpf_map_delete_elem(...)`, it will return actual error
> (libbpf 1.0 simplification)

Got it!

> 
>> +       }
>> +
>> +       /* Doesn't support detaching. */
>> +       return -EOPNOTSUPP;
>>   }
>>
>>   struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
>>   {
>> -       struct bpf_struct_ops *st_ops;
>> -       struct bpf_link *link;
>> -       __u32 i, zero = 0;
>> -       int err;
>> +       struct bpf_link_struct_ops *link;
>> +       __u32 zero = 0;
>> +       int err, fd;
>>
>>          if (!bpf_map__is_struct_ops(map) || map->fd == -1)
>>                  return libbpf_err_ptr(-EINVAL);
>> @@ -11453,31 +11490,34 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
>>          if (!link)
>>                  return libbpf_err_ptr(-EINVAL);
>>
>> -       st_ops = map->st_ops;
>> -       for (i = 0; i < btf_vlen(st_ops->type); i++) {
>> -               struct bpf_program *prog = st_ops->progs[i];
>> -               void *kern_data;
>> -               int prog_fd;
>> +       /* kern_vdata should be prepared during the loading phase. */
>> +       err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
>> +       if (err) {
>> +               err = -errno;
> 
> no need to deal with -errno, err is already the error you need

ok!

> 
>> +               free(link);
>> +               return libbpf_err_ptr(err);
>> +       }
>>
>> -               if (!prog)
>> -                       continue;
>>
>> -               prog_fd = bpf_program__fd(prog);
>> -               kern_data = st_ops->kern_vdata + st_ops->kern_func_off[i];
>> -               *(unsigned long *)kern_data = prog_fd;
>> +       if (!(map->def.map_flags & BPF_F_LINK)) {
>> +               /* Fake bpf_link */
>> +               link->link.fd = map->fd;
>> +               link->map_fd = -1;
>> +               link->link.detach = bpf_link__detach_struct_ops;
>> +               return &link->link;
>>          }
>>
>> -       err = bpf_map_update_elem(map->fd, &zero, st_ops->kern_vdata, 0);
>> -       if (err) {
>> +       fd = bpf_link_create(map->fd, -1, BPF_STRUCT_OPS, NULL);
>> +       if (fd < 0) {
>>                  err = -errno;
> 
> same, fd is an error, it's true for all low-level libbpf APIs

Good to know!


> 
>>                  free(link);
>>                  return libbpf_err_ptr(err);
>>          }
>>
>> -       link->detach = bpf_link__detach_struct_ops;
>> -       link->fd = map->fd;
>> +       link->link.fd = fd;
>> +       link->map_fd = map->fd;
>>
>> -       return link;
>> +       return &link->link;
>>   }
>>
>>   typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
>> --
>> 2.34.1
>>

Re: [PATCH bpf-next v4 8/9] libbpf: Use .struct_ops.link section to indicate a struct_ops with a link.

[Kui-Feng Lee]

On 3/7/23 17:07, Andrii Nakryiko wrote:
> On Tue, Mar 7, 2023 at 3:33 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>>
>> Flags a struct_ops is to back a bpf_link by putting it to the
>> ".struct_ops.link" section.  Once it is flagged, the created
>> struct_ops can be used to create a bpf_link or update a bpf_link that
>> has been backed by another struct_ops.
>>
>> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
>> ---
>>   tools/lib/bpf/libbpf.c | 64 +++++++++++++++++++++++++++++++++---------
>>   1 file changed, 50 insertions(+), 14 deletions(-)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 247de39d136f..d66acd2fdbaa 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -467,6 +467,7 @@ struct bpf_struct_ops {
>>   #define KCONFIG_SEC ".kconfig"
>>   #define KSYMS_SEC ".ksyms"
>>   #define STRUCT_OPS_SEC ".struct_ops"
>> +#define STRUCT_OPS_LINK_SEC ".struct_ops.link"
>>
>>   enum libbpf_map_type {
>>          LIBBPF_MAP_UNSPEC,
>> @@ -596,6 +597,7 @@ struct elf_state {
>>          Elf64_Ehdr *ehdr;
>>          Elf_Data *symbols;
>>          Elf_Data *st_ops_data;
>> +       Elf_Data *st_ops_link_data;
>>          size_t shstrndx; /* section index for section name strings */
>>          size_t strtabidx;
>>          struct elf_sec_desc *secs;
>> @@ -605,6 +607,7 @@ struct elf_state {
>>          int text_shndx;
>>          int symbols_shndx;
>>          int st_ops_shndx;
>> +       int st_ops_link_shndx;
>>   };
>>
>>   struct usdt_manager;
>> @@ -1119,7 +1122,7 @@ static int bpf_object__init_kern_struct_ops_maps(struct bpf_object *obj)
>>          return 0;
>>   }
>>
>> -static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>> +static int bpf_object__init_struct_ops_maps_link(struct bpf_object *obj, bool link)
> 
> let's shorten it and not use double underscores, as this is not a
> public bpf_object API, just "init_struct_ops_maps" probably is fine
> 
>>   {
>>          const struct btf_type *type, *datasec;
>>          const struct btf_var_secinfo *vsi;
>> @@ -1127,18 +1130,33 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>>          const char *tname, *var_name;
>>          __s32 type_id, datasec_id;
>>          const struct btf *btf;
>> +       const char *sec_name;
>>          struct bpf_map *map;
>> -       __u32 i;
>> +       __u32 i, map_flags;
>> +       Elf_Data *data;
>> +       int shndx;
>>
>> -       if (obj->efile.st_ops_shndx == -1)
>> +       if (link) {
>> +               sec_name = STRUCT_OPS_LINK_SEC;
>> +               shndx = obj->efile.st_ops_link_shndx;
>> +               data = obj->efile.st_ops_link_data;
>> +               map_flags = BPF_F_LINK;
>> +       } else {
>> +               sec_name = STRUCT_OPS_SEC;
>> +               shndx = obj->efile.st_ops_shndx;
>> +               data = obj->efile.st_ops_data;
>> +               map_flags = 0;
>> +       }
> 
> let's pass these as function arguments instead
> 
>> +
>> +       if (shndx == -1)
>>                  return 0;
>>
>>          btf = obj->btf;
>> -       datasec_id = btf__find_by_name_kind(btf, STRUCT_OPS_SEC,
>> +       datasec_id = btf__find_by_name_kind(btf, sec_name,
>>                                              BTF_KIND_DATASEC);
>>          if (datasec_id < 0) {
>>                  pr_warn("struct_ops init: DATASEC %s not found\n",
>> -                       STRUCT_OPS_SEC);
>> +                       sec_name);
>>                  return -EINVAL;
>>          }
>>
>> @@ -1151,7 +1169,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>>                  type_id = btf__resolve_type(obj->btf, vsi->type);
>>                  if (type_id < 0) {
>>                          pr_warn("struct_ops init: Cannot resolve var type_id %u in DATASEC %s\n",
>> -                               vsi->type, STRUCT_OPS_SEC);
>> +                               vsi->type, sec_name);
>>                          return -EINVAL;
>>                  }
>>
>> @@ -1170,7 +1188,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>>                  if (IS_ERR(map))
>>                          return PTR_ERR(map);
>>
>> -               map->sec_idx = obj->efile.st_ops_shndx;
>> +               map->sec_idx = shndx;
>>                  map->sec_offset = vsi->offset;
>>                  map->name = strdup(var_name);
>>                  if (!map->name)
>> @@ -1180,6 +1198,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>>                  map->def.key_size = sizeof(int);
>>                  map->def.value_size = type->size;
>>                  map->def.max_entries = 1;
>> +               map->def.map_flags = map_flags;
>>
>>                  map->st_ops = calloc(1, sizeof(*map->st_ops));
>>                  if (!map->st_ops)
>> @@ -1192,14 +1211,14 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>>                  if (!st_ops->data || !st_ops->progs || !st_ops->kern_func_off)
>>                          return -ENOMEM;
>>
>> -               if (vsi->offset + type->size > obj->efile.st_ops_data->d_size) {
>> +               if (vsi->offset + type->size > data->d_size) {
>>                          pr_warn("struct_ops init: var %s is beyond the end of DATASEC %s\n",
>> -                               var_name, STRUCT_OPS_SEC);
>> +                               var_name, sec_name);
>>                          return -EINVAL;
>>                  }
>>
>>                  memcpy(st_ops->data,
>> -                      obj->efile.st_ops_data->d_buf + vsi->offset,
>> +                      data->d_buf + vsi->offset,
>>                         type->size);
>>                  st_ops->tname = tname;
>>                  st_ops->type = type;
>> @@ -1212,6 +1231,15 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
>>          return 0;
>>   }
>>
>> +static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
> 
> let's name this bpf_object_init_struct_ops, no double underscores
> 
>> +{
>> +       int err;
>> +
>> +       err = bpf_object__init_struct_ops_maps_link(obj, false);
>> +       err = err ?: bpf_object__init_struct_ops_maps_link(obj, true);
>> +       return err;
>> +}
>> +
>>   static struct bpf_object *bpf_object__new(const char *path,
>>                                            const void *obj_buf,
>>                                            size_t obj_buf_sz,
>> @@ -1248,6 +1276,7 @@ static struct bpf_object *bpf_object__new(const char *path,
>>          obj->efile.obj_buf_sz = obj_buf_sz;
>>          obj->efile.btf_maps_shndx = -1;
>>          obj->efile.st_ops_shndx = -1;
>> +       obj->efile.st_ops_link_shndx = -1;
>>          obj->kconfig_map_idx = -1;
>>
>>          obj->kern_version = get_kernel_version();
>> @@ -1265,6 +1294,7 @@ static void bpf_object__elf_finish(struct bpf_object *obj)
>>          obj->efile.elf = NULL;
>>          obj->efile.symbols = NULL;
>>          obj->efile.st_ops_data = NULL;
>> +       obj->efile.st_ops_link_data = NULL;
>>
>>          zfree(&obj->efile.secs);
>>          obj->efile.sec_cnt = 0;
>> @@ -2753,12 +2783,13 @@ static bool libbpf_needs_btf(const struct bpf_object *obj)
>>   {
>>          return obj->efile.btf_maps_shndx >= 0 ||
>>                 obj->efile.st_ops_shndx >= 0 ||
>> +              obj->efile.st_ops_link_shndx >= 0 ||
>>                 obj->nr_extern > 0;
>>   }
>>
>>   static bool kernel_needs_btf(const struct bpf_object *obj)
>>   {
>> -       return obj->efile.st_ops_shndx >= 0;
>> +       return obj->efile.st_ops_shndx >= 0 || obj->efile.st_ops_link_shndx >= 0;
>>   }
>>
>>   static int bpf_object__init_btf(struct bpf_object *obj,
>> @@ -3451,6 +3482,9 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
>>                          } else if (strcmp(name, STRUCT_OPS_SEC) == 0) {
>>                                  obj->efile.st_ops_data = data;
>>                                  obj->efile.st_ops_shndx = idx;
>> +                       } else if (strcmp(name, STRUCT_OPS_LINK_SEC) == 0) {
>> +                               obj->efile.st_ops_link_data = data;
>> +                               obj->efile.st_ops_link_shndx = idx;
>>                          } else {
>>                                  pr_info("elf: skipping unrecognized data section(%d) %s\n",
>>                                          idx, name);
>> @@ -3465,6 +3499,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
>>                          /* Only do relo for section with exec instructions */
>>                          if (!section_have_execinstr(obj, targ_sec_idx) &&
>>                              strcmp(name, ".rel" STRUCT_OPS_SEC) &&
>> +                           strcmp(name, ".rel" STRUCT_OPS_LINK_SEC) &&
>>                              strcmp(name, ".rel" MAPS_ELF_SEC)) {
>>                                  pr_info("elf: skipping relo section(%d) %s for section(%d) %s\n",
>>                                          idx, name, targ_sec_idx,
>> @@ -6611,7 +6646,7 @@ static int bpf_object__collect_relos(struct bpf_object *obj)
>>                          return -LIBBPF_ERRNO__INTERNAL;
>>                  }
>>
>> -               if (idx == obj->efile.st_ops_shndx)
>> +               if (idx == obj->efile.st_ops_shndx || idx == obj->efile.st_ops_link_shndx)
>>                          err = bpf_object__collect_st_ops_relos(obj, shdr, data);
> 
> this function calls find_struct_ops_map_by_offset() which assumes we
> only have one struct_ops section. This won't work now, please double
> check all this, there should be no assumption about specific section
> index

Yes, I will check the section index of maps.

> 
>>                  else if (idx == obj->efile.btf_maps_shndx)
>>                          err = bpf_object__collect_map_relos(obj, shdr, data);
>> @@ -8954,8 +8989,9 @@ static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
>>                  }
>>
>>                  /* struct_ops BPF prog can be re-used between multiple
>> -                * .struct_ops as long as it's the same struct_ops struct
>> -                * definition and the same function pointer field
>> +                * .struct_ops & .struct_ops.link as long as it's the
>> +                * same struct_ops struct definition and the same
>> +                * function pointer field
>>                   */
>>                  if (prog->attach_btf_id != st_ops->type_id ||
>>                      prog->expected_attach_type != member_idx) {
>> --
>> 2.34.1
>>

Re: [PATCH bpf-next v4 9/9] selftests/bpf: Test switching TCP Congestion Control algorithms.

[Kui-Feng Lee]

On 3/7/23 17:10, Andrii Nakryiko wrote:
> On Tue, Mar 7, 2023 at 3:34 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>>
>> Create a pair of sockets that utilize the congestion control algorithm
>> under a particular name. Then switch up this congestion control
>> algorithm to another implementation and check whether newly created
>> connections using the same cc name now run the new implementation.
>>
>> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
>> ---
>>   .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 38 ++++++++++++
>>   .../selftests/bpf/progs/tcp_ca_update.c       | 62 +++++++++++++++++++
>>   2 files changed, 100 insertions(+)
>>   create mode 100644 tools/testing/selftests/bpf/progs/tcp_ca_update.c
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>> index e980188d4124..caaa9175ee36 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>> @@ -8,6 +8,7 @@
>>   #include "bpf_dctcp.skel.h"
>>   #include "bpf_cubic.skel.h"
>>   #include "bpf_tcp_nogpl.skel.h"
>> +#include "tcp_ca_update.skel.h"
>>   #include "bpf_dctcp_release.skel.h"
>>   #include "tcp_ca_write_sk_pacing.skel.h"
>>   #include "tcp_ca_incompl_cong_ops.skel.h"
>> @@ -381,6 +382,41 @@ static void test_unsupp_cong_op(void)
>>          libbpf_set_print(old_print_fn);
>>   }
>>
>> +static void test_update_ca(void)
>> +{
>> +       struct tcp_ca_update *skel;
>> +       struct bpf_link *link;
>> +       int saved_ca1_cnt;
>> +       int err;
>> +
>> +       skel = tcp_ca_update__open();
>> +       if (!ASSERT_OK_PTR(skel, "open"))
>> +               return;
>> +
>> +       err = tcp_ca_update__load(skel);
> 
> tcp_ca_update__open_and_load()
> 
>> +       if (!ASSERT_OK(err, "load")) {
>> +               tcp_ca_update__destroy(skel);
>> +               return;
>> +       }
>> +
>> +       link = bpf_map__attach_struct_ops(skel->maps.ca_update_1);
> 
> I think it's time to generate link holder for each struct_ops map to
> the BPF skeleton, and support auto-attach of struct_ops skeleton.
> Please do that as a follow up, once this patch set lands.

Got it.

> 
>> +       ASSERT_OK_PTR(link, "attach_struct_ops");
>> +
>> +       do_test("tcp_ca_update", NULL);
>> +       saved_ca1_cnt = skel->bss->ca1_cnt;
>> +       ASSERT_GT(saved_ca1_cnt, 0, "ca1_ca1_cnt");
>> +
>> +       err = bpf_link__update_map(link, skel->maps.ca_update_2);
>> +       ASSERT_OK(err, "update_struct_ops");
>> +
>> +       do_test("tcp_ca_update", NULL);
>> +       ASSERT_EQ(skel->bss->ca1_cnt, saved_ca1_cnt, "ca2_ca1_cnt");
>> +       ASSERT_GT(skel->bss->ca2_cnt, 0, "ca2_ca2_cnt");
> 
> how do we know that struct_ops programs were triggered? what
> guarantees that? if nothing, we are just adding another flaky
> networking test

When an ack is received, cong_control of ca_update_1 and ca_update_2
will be called if they are activated.  By checking ca1_cnt & ca2_cnt, we
know which one is activated.  Here, we check if the ca1_cnt keeps the
same and ca2_cnt increase to make that ca_update_2 have replaced
ca_update_1.

> 
>> +
>> +       bpf_link__destroy(link);
>> +       tcp_ca_update__destroy(skel);
>> +}
>> +
>>   void test_bpf_tcp_ca(void)
>>   {
>>          if (test__start_subtest("dctcp"))
>> @@ -399,4 +435,6 @@ void test_bpf_tcp_ca(void)
>>                  test_incompl_cong_ops();
>>          if (test__start_subtest("unsupp_cong_op"))
>>                  test_unsupp_cong_op();
>> +       if (test__start_subtest("update_ca"))
>> +               test_update_ca();
>>   }
>> diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_update.c b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
>> new file mode 100644
>> index 000000000000..36a04be95df5
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
>> @@ -0,0 +1,62 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +#include "vmlinux.h"
>> +
>> +#include <bpf/bpf_helpers.h>
>> +#include <bpf/bpf_tracing.h>
>> +
>> +char _license[] SEC("license") = "GPL";
>> +
>> +int ca1_cnt = 0;
>> +int ca2_cnt = 0;
>> +
>> +#define USEC_PER_SEC 1000000UL
>> +
>> +#define min(a, b) ((a) < (b) ? (a) : (b))
>> +
>> +static inline struct tcp_sock *tcp_sk(const struct sock *sk)
>> +{
>> +       return (struct tcp_sock *)sk;
>> +}
>> +
>> +SEC("struct_ops/ca_update_1_cong_control")
>> +void BPF_PROG(ca_update_1_cong_control, struct sock *sk,
>> +             const struct rate_sample *rs)
>> +{
>> +       ca1_cnt++;
>> +}
>> +
>> +SEC("struct_ops/ca_update_2_cong_control")
>> +void BPF_PROG(ca_update_2_cong_control, struct sock *sk,
>> +             const struct rate_sample *rs)
>> +{
>> +       ca2_cnt++;
>> +}
>> +
>> +SEC("struct_ops/ca_update_ssthresh")
>> +__u32 BPF_PROG(ca_update_ssthresh, struct sock *sk)
>> +{
>> +       return tcp_sk(sk)->snd_ssthresh;
>> +}
>> +
>> +SEC("struct_ops/ca_update_undo_cwnd")
>> +__u32 BPF_PROG(ca_update_undo_cwnd, struct sock *sk)
>> +{
>> +       return tcp_sk(sk)->snd_cwnd;
>> +}
>> +
>> +SEC(".struct_ops.link")
>> +struct tcp_congestion_ops ca_update_1 = {
>> +       .cong_control = (void *)ca_update_1_cong_control,
>> +       .ssthresh = (void *)ca_update_ssthresh,
>> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
>> +       .name = "tcp_ca_update",
>> +};
>> +
>> +SEC(".struct_ops.link")
>> +struct tcp_congestion_ops ca_update_2 = {
>> +       .cong_control = (void *)ca_update_2_cong_control,
>> +       .ssthresh = (void *)ca_update_ssthresh,
>> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
>> +       .name = "tcp_ca_update",
>> +};
> 
> please add a test where you combine both .struct_ops and
> .struct_ops.link, it's an obvious potentially problematic combination
> 
> as I mentioned in previous patches, let's also have a negative test
> where bpf_link__update_map() fails

Sure

> 
>> --
>> 2.34.1
>>

Re: [PATCH bpf-next v4 6/9] bpf: Update the struct_ops of a bpf_link.

[Kui-Feng Lee]

On 3/7/23 16:49, Andrii Nakryiko wrote:
> On Tue, Mar 7, 2023 at 3:33 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>>
>> By improving the BPF_LINK_UPDATE command of bpf(), it should allow you
>> to conveniently switch between different struct_ops on a single
>> bpf_link. This would enable smoother transitions from one struct_ops
>> to another.
>>
>> The struct_ops maps passing along with BPF_LINK_UPDATE should have the
>> BPF_F_LINK flag.
>>
>> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
>> ---
>>   include/linux/bpf.h            |  1 +
>>   include/uapi/linux/bpf.h       |  8 ++++--
>>   kernel/bpf/bpf_struct_ops.c    | 46 ++++++++++++++++++++++++++++++++++
>>   kernel/bpf/syscall.c           | 43 ++++++++++++++++++++++++++++---
>>   tools/include/uapi/linux/bpf.h |  7 +++++-
>>   5 files changed, 98 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index 047d2c6aba88..2b5f150e370e 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -1405,6 +1405,7 @@ struct bpf_link_ops {
>>          void (*show_fdinfo)(const struct bpf_link *link, struct seq_file *seq);
>>          int (*fill_link_info)(const struct bpf_link *link,
>>                                struct bpf_link_info *info);
>> +       int (*update_map)(struct bpf_link *link, struct bpf_map *new_map);
>>   };
>>
>>   struct bpf_tramp_link {
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index eb3e435c5303..999e199ebe06 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -1555,8 +1555,12 @@ union bpf_attr {
>>
>>          struct { /* struct used by BPF_LINK_UPDATE command */
>>                  __u32           link_fd;        /* link fd */
>> -               /* new program fd to update link with */
>> -               __u32           new_prog_fd;
>> +               union {
>> +                       /* new program fd to update link with */
>> +                       __u32           new_prog_fd;
>> +                       /* new struct_ops map fd to update link with */
>> +                       __u32           new_map_fd;
>> +               };
>>                  __u32           flags;          /* extra flags */
>>                  /* expected link's program fd; is specified only if
>>                   * BPF_F_REPLACE flag is set in flags */
>> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
>> index c71c8d73c7ad..2b850ce11617 100644
>> --- a/kernel/bpf/bpf_struct_ops.c
>> +++ b/kernel/bpf/bpf_struct_ops.c
>> @@ -759,10 +759,56 @@ static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link,
>>          return 0;
>>   }
>>
>> +static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map *new_map)
>> +{
>> +       struct bpf_struct_ops_value *kvalue;
>> +       struct bpf_struct_ops_map *st_map, *old_st_map;
>> +       struct bpf_struct_ops_link *st_link;
>> +       struct bpf_map *old_map;
>> +       int err = 0;
>> +
>> +       if (new_map->map_type != BPF_MAP_TYPE_STRUCT_OPS ||
>> +           !(new_map->map_flags & BPF_F_LINK))
>> +               return -EINVAL;
>> +
>> +       mutex_lock(&update_mutex);
>> +
>> +       st_link = container_of(link, struct bpf_struct_ops_link, link);
>> +
>> +       /* The new and old struct_ops must be the same type. */
>> +       st_map = container_of(new_map, struct bpf_struct_ops_map, map);
>> +
>> +       old_map = st_link->map;
>> +       old_st_map = container_of(old_map, struct bpf_struct_ops_map, map);
>> +       if (st_map->st_ops != old_st_map->st_ops ||
>> +           /* Pair with smp_store_release() during map_update */
>> +           smp_load_acquire(&st_map->kvalue.state) != BPF_STRUCT_OPS_STATE_READY) {
>> +               err = -EINVAL;
>> +               goto err_out;
>> +       }
>> +
>> +       kvalue = &st_map->kvalue;
>> +
>> +       err = st_map->st_ops->update(kvalue->data, old_st_map->kvalue.data);
>> +       if (err)
>> +               goto err_out;
>> +
>> +       bpf_map_inc(new_map);
>> +       rcu_assign_pointer(st_link->map, new_map);
>> +
>> +       bpf_map_put(old_map);
>> +
>> +err_out:
>> +       mutex_unlock(&update_mutex);
>> +
>> +       return err;
>> +}
>> +
>>   static const struct bpf_link_ops bpf_struct_ops_map_lops = {
>>          .dealloc = bpf_struct_ops_map_link_dealloc,
>>          .show_fdinfo = bpf_struct_ops_map_link_show_fdinfo,
>>          .fill_link_info = bpf_struct_ops_map_link_fill_link_info,
>> +       .update_map = bpf_struct_ops_map_link_update,
>>   };
>>
>>   int bpf_struct_ops_link_create(union bpf_attr *attr)
>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>> index 25b044fdd82b..94ab1336ff41 100644
>> --- a/kernel/bpf/syscall.c
>> +++ b/kernel/bpf/syscall.c
>> @@ -4646,6 +4646,30 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
>>          return ret;
>>   }
>>
>> +static int link_update_map(struct bpf_link *link, union bpf_attr *attr)
>> +{
>> +       struct bpf_map *new_map;
>> +       int ret = 0;
>> +
>> +       new_map = bpf_map_get(attr->link_update.new_map_fd);
>> +       if (IS_ERR(new_map))
>> +               return -EINVAL;
>> +
>> +       if (new_map->map_type != BPF_MAP_TYPE_STRUCT_OPS) {
>> +               ret = -EINVAL;
>> +               goto out_put_map;
>> +       }
>> +
>> +       if (link->ops->update_map)
>> +               ret = link->ops->update_map(link, new_map);
>> +       else
>> +               ret = -EINVAL;
>> +
>> +out_put_map:
>> +       bpf_map_put(new_map);
>> +       return ret;
>> +}
>> +
>>   #define BPF_LINK_UPDATE_LAST_FIELD link_update.old_prog_fd
>>
>>   static int link_update(union bpf_attr *attr)
>> @@ -4658,14 +4682,25 @@ static int link_update(union bpf_attr *attr)
>>          if (CHECK_ATTR(BPF_LINK_UPDATE))
>>                  return -EINVAL;
>>
>> -       flags = attr->link_update.flags;
>> -       if (flags & ~BPF_F_REPLACE)
>> -               return -EINVAL;
>> -
>>          link = bpf_link_get_from_fd(attr->link_update.link_fd);
>>          if (IS_ERR(link))
>>                  return PTR_ERR(link);
>>
>> +       flags = attr->link_update.flags;
>> +
>> +       if (link->ops->update_map) {
>> +               if (flags)      /* always replace the existing one */
>> +                       ret = -EINVAL;
>> +               else
>> +                       ret = link_update_map(link, attr);
>> +               goto out_put_link;
> 
> umm... BPF_F_REPLACE for link_update is specifying "update only if
> current prog fd matches what I specify", let's not ignore it for
> struct_ops. This will create a deviation in behavior unnecessarily.
> Please keep it consistent.

Ok!

> 
> 
>> +       }
>> +
>> +       if (flags & ~BPF_F_REPLACE) {
>> +               ret = -EINVAL;
>> +               goto out_put_link;
>> +       }
>> +
>>          new_prog = bpf_prog_get(attr->link_update.new_prog_fd);
>>          if (IS_ERR(new_prog)) {
>>                  ret = PTR_ERR(new_prog);
>> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
>> index cd0ff39981e8..259b8ab4f54e 100644
>> --- a/tools/include/uapi/linux/bpf.h
>> +++ b/tools/include/uapi/linux/bpf.h
>> @@ -1556,7 +1556,12 @@ union bpf_attr {
>>          struct { /* struct used by BPF_LINK_UPDATE command */
>>                  __u32           link_fd;        /* link fd */
>>                  /* new program fd to update link with */
>> -               __u32           new_prog_fd;
>> +               union {
>> +                       /* new program fd to update link with */
>> +                       __u32           new_prog_fd;
>> +                       /* new struct_ops map fd to update link with */
>> +                       __u32           new_map_fd;
>> +               };
>>                  __u32           flags;          /* extra flags */
>>                  /* expected link's program fd; is specified only if
>>                   * BPF_F_REPLACE flag is set in flags */
>> --
>> 2.34.1
>>

Re: [PATCH bpf-next v4 9/9] selftests/bpf: Test switching TCP Congestion Control algorithms.

[Andrii Nakryiko]

On Wed, Mar 8, 2023 at 7:58 AM Kui-Feng Lee <sinquersw@gmail.com> wrote:
>
>
>
> On 3/7/23 17:10, Andrii Nakryiko wrote:
> > On Tue, Mar 7, 2023 at 3:34 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
> >>
> >> Create a pair of sockets that utilize the congestion control algorithm
> >> under a particular name. Then switch up this congestion control
> >> algorithm to another implementation and check whether newly created
> >> connections using the same cc name now run the new implementation.
> >>
> >> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
> >> ---
> >>   .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 38 ++++++++++++
> >>   .../selftests/bpf/progs/tcp_ca_update.c       | 62 +++++++++++++++++++
> >>   2 files changed, 100 insertions(+)
> >>   create mode 100644 tools/testing/selftests/bpf/progs/tcp_ca_update.c
> >>
> >> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> >> index e980188d4124..caaa9175ee36 100644
> >> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> >> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> >> @@ -8,6 +8,7 @@
> >>   #include "bpf_dctcp.skel.h"
> >>   #include "bpf_cubic.skel.h"
> >>   #include "bpf_tcp_nogpl.skel.h"
> >> +#include "tcp_ca_update.skel.h"
> >>   #include "bpf_dctcp_release.skel.h"
> >>   #include "tcp_ca_write_sk_pacing.skel.h"
> >>   #include "tcp_ca_incompl_cong_ops.skel.h"
> >> @@ -381,6 +382,41 @@ static void test_unsupp_cong_op(void)
> >>          libbpf_set_print(old_print_fn);
> >>   }
> >>
> >> +static void test_update_ca(void)
> >> +{
> >> +       struct tcp_ca_update *skel;
> >> +       struct bpf_link *link;
> >> +       int saved_ca1_cnt;
> >> +       int err;
> >> +
> >> +       skel = tcp_ca_update__open();
> >> +       if (!ASSERT_OK_PTR(skel, "open"))
> >> +               return;
> >> +
> >> +       err = tcp_ca_update__load(skel);
> >
> > tcp_ca_update__open_and_load()
> >
> >> +       if (!ASSERT_OK(err, "load")) {
> >> +               tcp_ca_update__destroy(skel);
> >> +               return;
> >> +       }
> >> +
> >> +       link = bpf_map__attach_struct_ops(skel->maps.ca_update_1);
> >
> > I think it's time to generate link holder for each struct_ops map to
> > the BPF skeleton, and support auto-attach of struct_ops skeleton.
> > Please do that as a follow up, once this patch set lands.
>
> Got it.
>
> >
> >> +       ASSERT_OK_PTR(link, "attach_struct_ops");
> >> +
> >> +       do_test("tcp_ca_update", NULL);
> >> +       saved_ca1_cnt = skel->bss->ca1_cnt;
> >> +       ASSERT_GT(saved_ca1_cnt, 0, "ca1_ca1_cnt");
> >> +
> >> +       err = bpf_link__update_map(link, skel->maps.ca_update_2);
> >> +       ASSERT_OK(err, "update_struct_ops");
> >> +
> >> +       do_test("tcp_ca_update", NULL);
> >> +       ASSERT_EQ(skel->bss->ca1_cnt, saved_ca1_cnt, "ca2_ca1_cnt");
> >> +       ASSERT_GT(skel->bss->ca2_cnt, 0, "ca2_ca2_cnt");
> >
> > how do we know that struct_ops programs were triggered? what
> > guarantees that? if nothing, we are just adding another flaky
> > networking test
>
> When an ack is received, cong_control of ca_update_1 and ca_update_2
> will be called if they are activated.  By checking ca1_cnt & ca2_cnt, we
> know which one is activated.  Here, we check if the ca1_cnt keeps the
> same and ca2_cnt increase to make that ca_update_2 have replaced
> ca_update_1.

I just don't see anything in the test ensuring that ack is
sent/received, so it seems like we are relying on some background
system activity and proper timing (unless I miss something, which is
why I'm asking), so this is fragile, as in CI environment timings and
background activity would be very different and unpredictable, causing
flakiness of the test

>
> >
> >> +
> >> +       bpf_link__destroy(link);
> >> +       tcp_ca_update__destroy(skel);
> >> +}
> >> +
> >>   void test_bpf_tcp_ca(void)
> >>   {
> >>          if (test__start_subtest("dctcp"))
> >> @@ -399,4 +435,6 @@ void test_bpf_tcp_ca(void)
> >>                  test_incompl_cong_ops();
> >>          if (test__start_subtest("unsupp_cong_op"))
> >>                  test_unsupp_cong_op();
> >> +       if (test__start_subtest("update_ca"))
> >> +               test_update_ca();
> >>   }
> >> diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_update.c b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
> >> new file mode 100644
> >> index 000000000000..36a04be95df5
> >> --- /dev/null
> >> +++ b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
> >> @@ -0,0 +1,62 @@
> >> +// SPDX-License-Identifier: GPL-2.0
> >> +
> >> +#include "vmlinux.h"
> >> +
> >> +#include <bpf/bpf_helpers.h>
> >> +#include <bpf/bpf_tracing.h>
> >> +
> >> +char _license[] SEC("license") = "GPL";
> >> +
> >> +int ca1_cnt = 0;
> >> +int ca2_cnt = 0;
> >> +
> >> +#define USEC_PER_SEC 1000000UL
> >> +
> >> +#define min(a, b) ((a) < (b) ? (a) : (b))
> >> +
> >> +static inline struct tcp_sock *tcp_sk(const struct sock *sk)
> >> +{
> >> +       return (struct tcp_sock *)sk;
> >> +}
> >> +
> >> +SEC("struct_ops/ca_update_1_cong_control")
> >> +void BPF_PROG(ca_update_1_cong_control, struct sock *sk,
> >> +             const struct rate_sample *rs)
> >> +{
> >> +       ca1_cnt++;
> >> +}
> >> +
> >> +SEC("struct_ops/ca_update_2_cong_control")
> >> +void BPF_PROG(ca_update_2_cong_control, struct sock *sk,
> >> +             const struct rate_sample *rs)
> >> +{
> >> +       ca2_cnt++;
> >> +}
> >> +
> >> +SEC("struct_ops/ca_update_ssthresh")
> >> +__u32 BPF_PROG(ca_update_ssthresh, struct sock *sk)
> >> +{
> >> +       return tcp_sk(sk)->snd_ssthresh;
> >> +}
> >> +
> >> +SEC("struct_ops/ca_update_undo_cwnd")
> >> +__u32 BPF_PROG(ca_update_undo_cwnd, struct sock *sk)
> >> +{
> >> +       return tcp_sk(sk)->snd_cwnd;
> >> +}
> >> +
> >> +SEC(".struct_ops.link")
> >> +struct tcp_congestion_ops ca_update_1 = {
> >> +       .cong_control = (void *)ca_update_1_cong_control,
> >> +       .ssthresh = (void *)ca_update_ssthresh,
> >> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
> >> +       .name = "tcp_ca_update",
> >> +};
> >> +
> >> +SEC(".struct_ops.link")
> >> +struct tcp_congestion_ops ca_update_2 = {
> >> +       .cong_control = (void *)ca_update_2_cong_control,
> >> +       .ssthresh = (void *)ca_update_ssthresh,
> >> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
> >> +       .name = "tcp_ca_update",
> >> +};
> >
> > please add a test where you combine both .struct_ops and
> > .struct_ops.link, it's an obvious potentially problematic combination
> >
> > as I mentioned in previous patches, let's also have a negative test
> > where bpf_link__update_map() fails
>
> Sure
>
> >
> >> --
> >> 2.34.1
> >>

Re: [PATCH bpf-next v4 9/9] selftests/bpf: Test switching TCP Congestion Control algorithms.

[Kui-Feng Lee]

On 3/8/23 09:18, Andrii Nakryiko wrote:
> On Wed, Mar 8, 2023 at 7:58 AM Kui-Feng Lee <sinquersw@gmail.com> wrote:
>>
>>
>>
>> On 3/7/23 17:10, Andrii Nakryiko wrote:
>>> On Tue, Mar 7, 2023 at 3:34 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>>>>
>>>> Create a pair of sockets that utilize the congestion control algorithm
>>>> under a particular name. Then switch up this congestion control
>>>> algorithm to another implementation and check whether newly created
>>>> connections using the same cc name now run the new implementation.
>>>>
>>>> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
>>>> ---
>>>>    .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 38 ++++++++++++
>>>>    .../selftests/bpf/progs/tcp_ca_update.c       | 62 +++++++++++++++++++
>>>>    2 files changed, 100 insertions(+)
>>>>    create mode 100644 tools/testing/selftests/bpf/progs/tcp_ca_update.c
>>>>
>>>> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>>>> index e980188d4124..caaa9175ee36 100644
>>>> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>>>> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>>>> @@ -8,6 +8,7 @@
>>>>    #include "bpf_dctcp.skel.h"
>>>>    #include "bpf_cubic.skel.h"
>>>>    #include "bpf_tcp_nogpl.skel.h"
>>>> +#include "tcp_ca_update.skel.h"
>>>>    #include "bpf_dctcp_release.skel.h"
>>>>    #include "tcp_ca_write_sk_pacing.skel.h"
>>>>    #include "tcp_ca_incompl_cong_ops.skel.h"
>>>> @@ -381,6 +382,41 @@ static void test_unsupp_cong_op(void)
>>>>           libbpf_set_print(old_print_fn);
>>>>    }
>>>>
>>>> +static void test_update_ca(void)
>>>> +{
>>>> +       struct tcp_ca_update *skel;
>>>> +       struct bpf_link *link;
>>>> +       int saved_ca1_cnt;
>>>> +       int err;
>>>> +
>>>> +       skel = tcp_ca_update__open();
>>>> +       if (!ASSERT_OK_PTR(skel, "open"))
>>>> +               return;
>>>> +
>>>> +       err = tcp_ca_update__load(skel);
>>>
>>> tcp_ca_update__open_and_load()
>>>
>>>> +       if (!ASSERT_OK(err, "load")) {
>>>> +               tcp_ca_update__destroy(skel);
>>>> +               return;
>>>> +       }
>>>> +
>>>> +       link = bpf_map__attach_struct_ops(skel->maps.ca_update_1);
>>>
>>> I think it's time to generate link holder for each struct_ops map to
>>> the BPF skeleton, and support auto-attach of struct_ops skeleton.
>>> Please do that as a follow up, once this patch set lands.
>>
>> Got it.
>>
>>>
>>>> +       ASSERT_OK_PTR(link, "attach_struct_ops");
>>>> +
>>>> +       do_test("tcp_ca_update", NULL);
>>>> +       saved_ca1_cnt = skel->bss->ca1_cnt;
>>>> +       ASSERT_GT(saved_ca1_cnt, 0, "ca1_ca1_cnt");
>>>> +
>>>> +       err = bpf_link__update_map(link, skel->maps.ca_update_2);
>>>> +       ASSERT_OK(err, "update_struct_ops");
>>>> +
>>>> +       do_test("tcp_ca_update", NULL);
>>>> +       ASSERT_EQ(skel->bss->ca1_cnt, saved_ca1_cnt, "ca2_ca1_cnt");
>>>> +       ASSERT_GT(skel->bss->ca2_cnt, 0, "ca2_ca2_cnt");
>>>
>>> how do we know that struct_ops programs were triggered? what
>>> guarantees that? if nothing, we are just adding another flaky
>>> networking test
>>
>> When an ack is received, cong_control of ca_update_1 and ca_update_2
>> will be called if they are activated.  By checking ca1_cnt & ca2_cnt, we
>> know which one is activated.  Here, we check if the ca1_cnt keeps the
>> same and ca2_cnt increase to make that ca_update_2 have replaced
>> ca_update_1.
> 
> I just don't see anything in the test ensuring that ack is
> sent/received, so it seems like we are relying on some background
> system activity and proper timing (unless I miss something, which is
> why I'm asking), so this is fragile, as in CI environment timings and
> background activity would be very different and unpredictable, causing
> flakiness of the test


The do_test() function creates two sockets to form a direct connection
that must receive at least one acknowledgment packet for the sockets to
progress into an ESTABLISHED state.  If they don't, that means it fails
to establish a connection.

> 
>>
>>>
>>>> +
>>>> +       bpf_link__destroy(link);
>>>> +       tcp_ca_update__destroy(skel);
>>>> +}
>>>> +
>>>>    void test_bpf_tcp_ca(void)
>>>>    {
>>>>           if (test__start_subtest("dctcp"))
>>>> @@ -399,4 +435,6 @@ void test_bpf_tcp_ca(void)
>>>>                   test_incompl_cong_ops();
>>>>           if (test__start_subtest("unsupp_cong_op"))
>>>>                   test_unsupp_cong_op();
>>>> +       if (test__start_subtest("update_ca"))
>>>> +               test_update_ca();
>>>>    }
>>>> diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_update.c b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
>>>> new file mode 100644
>>>> index 000000000000..36a04be95df5
>>>> --- /dev/null
>>>> +++ b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
>>>> @@ -0,0 +1,62 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +
>>>> +#include "vmlinux.h"
>>>> +
>>>> +#include <bpf/bpf_helpers.h>
>>>> +#include <bpf/bpf_tracing.h>
>>>> +
>>>> +char _license[] SEC("license") = "GPL";
>>>> +
>>>> +int ca1_cnt = 0;
>>>> +int ca2_cnt = 0;
>>>> +
>>>> +#define USEC_PER_SEC 1000000UL
>>>> +
>>>> +#define min(a, b) ((a) < (b) ? (a) : (b))
>>>> +
>>>> +static inline struct tcp_sock *tcp_sk(const struct sock *sk)
>>>> +{
>>>> +       return (struct tcp_sock *)sk;
>>>> +}
>>>> +
>>>> +SEC("struct_ops/ca_update_1_cong_control")
>>>> +void BPF_PROG(ca_update_1_cong_control, struct sock *sk,
>>>> +             const struct rate_sample *rs)
>>>> +{
>>>> +       ca1_cnt++;
>>>> +}
>>>> +
>>>> +SEC("struct_ops/ca_update_2_cong_control")
>>>> +void BPF_PROG(ca_update_2_cong_control, struct sock *sk,
>>>> +             const struct rate_sample *rs)
>>>> +{
>>>> +       ca2_cnt++;
>>>> +}
>>>> +
>>>> +SEC("struct_ops/ca_update_ssthresh")
>>>> +__u32 BPF_PROG(ca_update_ssthresh, struct sock *sk)
>>>> +{
>>>> +       return tcp_sk(sk)->snd_ssthresh;
>>>> +}
>>>> +
>>>> +SEC("struct_ops/ca_update_undo_cwnd")
>>>> +__u32 BPF_PROG(ca_update_undo_cwnd, struct sock *sk)
>>>> +{
>>>> +       return tcp_sk(sk)->snd_cwnd;
>>>> +}
>>>> +
>>>> +SEC(".struct_ops.link")
>>>> +struct tcp_congestion_ops ca_update_1 = {
>>>> +       .cong_control = (void *)ca_update_1_cong_control,
>>>> +       .ssthresh = (void *)ca_update_ssthresh,
>>>> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
>>>> +       .name = "tcp_ca_update",
>>>> +};
>>>> +
>>>> +SEC(".struct_ops.link")
>>>> +struct tcp_congestion_ops ca_update_2 = {
>>>> +       .cong_control = (void *)ca_update_2_cong_control,
>>>> +       .ssthresh = (void *)ca_update_ssthresh,
>>>> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
>>>> +       .name = "tcp_ca_update",
>>>> +};
>>>
>>> please add a test where you combine both .struct_ops and
>>> .struct_ops.link, it's an obvious potentially problematic combination
>>>
>>> as I mentioned in previous patches, let's also have a negative test
>>> where bpf_link__update_map() fails
>>
>> Sure
>>
>>>
>>>> --
>>>> 2.34.1
>>>>

Re: [PATCH bpf-next v4 9/9] selftests/bpf: Test switching TCP Congestion Control algorithms.

[Andrii Nakryiko]

On Wed, Mar 8, 2023 at 10:10 AM Kui-Feng Lee <sinquersw@gmail.com> wrote:
>
>
>
> On 3/8/23 09:18, Andrii Nakryiko wrote:
> > On Wed, Mar 8, 2023 at 7:58 AM Kui-Feng Lee <sinquersw@gmail.com> wrote:
> >>
> >>
> >>
> >> On 3/7/23 17:10, Andrii Nakryiko wrote:
> >>> On Tue, Mar 7, 2023 at 3:34 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
> >>>>
> >>>> Create a pair of sockets that utilize the congestion control algorithm
> >>>> under a particular name. Then switch up this congestion control
> >>>> algorithm to another implementation and check whether newly created
> >>>> connections using the same cc name now run the new implementation.
> >>>>
> >>>> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
> >>>> ---
> >>>>    .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 38 ++++++++++++
> >>>>    .../selftests/bpf/progs/tcp_ca_update.c       | 62 +++++++++++++++++++
> >>>>    2 files changed, 100 insertions(+)
> >>>>    create mode 100644 tools/testing/selftests/bpf/progs/tcp_ca_update.c
> >>>>
> >>>> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> >>>> index e980188d4124..caaa9175ee36 100644
> >>>> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> >>>> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> >>>> @@ -8,6 +8,7 @@
> >>>>    #include "bpf_dctcp.skel.h"
> >>>>    #include "bpf_cubic.skel.h"
> >>>>    #include "bpf_tcp_nogpl.skel.h"
> >>>> +#include "tcp_ca_update.skel.h"
> >>>>    #include "bpf_dctcp_release.skel.h"
> >>>>    #include "tcp_ca_write_sk_pacing.skel.h"
> >>>>    #include "tcp_ca_incompl_cong_ops.skel.h"
> >>>> @@ -381,6 +382,41 @@ static void test_unsupp_cong_op(void)
> >>>>           libbpf_set_print(old_print_fn);
> >>>>    }
> >>>>
> >>>> +static void test_update_ca(void)
> >>>> +{
> >>>> +       struct tcp_ca_update *skel;
> >>>> +       struct bpf_link *link;
> >>>> +       int saved_ca1_cnt;
> >>>> +       int err;
> >>>> +
> >>>> +       skel = tcp_ca_update__open();
> >>>> +       if (!ASSERT_OK_PTR(skel, "open"))
> >>>> +               return;
> >>>> +
> >>>> +       err = tcp_ca_update__load(skel);
> >>>
> >>> tcp_ca_update__open_and_load()
> >>>
> >>>> +       if (!ASSERT_OK(err, "load")) {
> >>>> +               tcp_ca_update__destroy(skel);
> >>>> +               return;
> >>>> +       }
> >>>> +
> >>>> +       link = bpf_map__attach_struct_ops(skel->maps.ca_update_1);
> >>>
> >>> I think it's time to generate link holder for each struct_ops map to
> >>> the BPF skeleton, and support auto-attach of struct_ops skeleton.
> >>> Please do that as a follow up, once this patch set lands.
> >>
> >> Got it.
> >>
> >>>
> >>>> +       ASSERT_OK_PTR(link, "attach_struct_ops");
> >>>> +
> >>>> +       do_test("tcp_ca_update", NULL);
> >>>> +       saved_ca1_cnt = skel->bss->ca1_cnt;
> >>>> +       ASSERT_GT(saved_ca1_cnt, 0, "ca1_ca1_cnt");
> >>>> +
> >>>> +       err = bpf_link__update_map(link, skel->maps.ca_update_2);
> >>>> +       ASSERT_OK(err, "update_struct_ops");
> >>>> +
> >>>> +       do_test("tcp_ca_update", NULL);
> >>>> +       ASSERT_EQ(skel->bss->ca1_cnt, saved_ca1_cnt, "ca2_ca1_cnt");
> >>>> +       ASSERT_GT(skel->bss->ca2_cnt, 0, "ca2_ca2_cnt");
> >>>
> >>> how do we know that struct_ops programs were triggered? what
> >>> guarantees that? if nothing, we are just adding another flaky
> >>> networking test
> >>
> >> When an ack is received, cong_control of ca_update_1 and ca_update_2
> >> will be called if they are activated.  By checking ca1_cnt & ca2_cnt, we
> >> know which one is activated.  Here, we check if the ca1_cnt keeps the
> >> same and ca2_cnt increase to make that ca_update_2 have replaced
> >> ca_update_1.
> >
> > I just don't see anything in the test ensuring that ack is
> > sent/received, so it seems like we are relying on some background
> > system activity and proper timing (unless I miss something, which is
> > why I'm asking), so this is fragile, as in CI environment timings and
> > background activity would be very different and unpredictable, causing
> > flakiness of the test
>
>
> The do_test() function creates two sockets to form a direct connection
> that must receive at least one acknowledgment packet for the sockets to
> progress into an ESTABLISHED state.  If they don't, that means it fails
> to establish a connection.

yeah, my bad, I *completely* missed `do_test("tcp_ca_update", NULL)`
(even though I went specifically looking for something like that).
It's all good here.


>
> >
> >>
> >>>
> >>>> +
> >>>> +       bpf_link__destroy(link);
> >>>> +       tcp_ca_update__destroy(skel);
> >>>> +}
> >>>> +
> >>>>    void test_bpf_tcp_ca(void)
> >>>>    {
> >>>>           if (test__start_subtest("dctcp"))
> >>>> @@ -399,4 +435,6 @@ void test_bpf_tcp_ca(void)
> >>>>                   test_incompl_cong_ops();
> >>>>           if (test__start_subtest("unsupp_cong_op"))
> >>>>                   test_unsupp_cong_op();
> >>>> +       if (test__start_subtest("update_ca"))
> >>>> +               test_update_ca();
> >>>>    }
> >>>> diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_update.c b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
> >>>> new file mode 100644
> >>>> index 000000000000..36a04be95df5
> >>>> --- /dev/null
> >>>> +++ b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
> >>>> @@ -0,0 +1,62 @@
> >>>> +// SPDX-License-Identifier: GPL-2.0
> >>>> +
> >>>> +#include "vmlinux.h"
> >>>> +
> >>>> +#include <bpf/bpf_helpers.h>
> >>>> +#include <bpf/bpf_tracing.h>
> >>>> +
> >>>> +char _license[] SEC("license") = "GPL";
> >>>> +
> >>>> +int ca1_cnt = 0;
> >>>> +int ca2_cnt = 0;
> >>>> +
> >>>> +#define USEC_PER_SEC 1000000UL
> >>>> +
> >>>> +#define min(a, b) ((a) < (b) ? (a) : (b))
> >>>> +
> >>>> +static inline struct tcp_sock *tcp_sk(const struct sock *sk)
> >>>> +{
> >>>> +       return (struct tcp_sock *)sk;
> >>>> +}
> >>>> +
> >>>> +SEC("struct_ops/ca_update_1_cong_control")
> >>>> +void BPF_PROG(ca_update_1_cong_control, struct sock *sk,
> >>>> +             const struct rate_sample *rs)
> >>>> +{
> >>>> +       ca1_cnt++;
> >>>> +}
> >>>> +
> >>>> +SEC("struct_ops/ca_update_2_cong_control")
> >>>> +void BPF_PROG(ca_update_2_cong_control, struct sock *sk,
> >>>> +             const struct rate_sample *rs)
> >>>> +{
> >>>> +       ca2_cnt++;
> >>>> +}
> >>>> +
> >>>> +SEC("struct_ops/ca_update_ssthresh")
> >>>> +__u32 BPF_PROG(ca_update_ssthresh, struct sock *sk)
> >>>> +{
> >>>> +       return tcp_sk(sk)->snd_ssthresh;
> >>>> +}
> >>>> +
> >>>> +SEC("struct_ops/ca_update_undo_cwnd")
> >>>> +__u32 BPF_PROG(ca_update_undo_cwnd, struct sock *sk)
> >>>> +{
> >>>> +       return tcp_sk(sk)->snd_cwnd;
> >>>> +}
> >>>> +
> >>>> +SEC(".struct_ops.link")
> >>>> +struct tcp_congestion_ops ca_update_1 = {
> >>>> +       .cong_control = (void *)ca_update_1_cong_control,
> >>>> +       .ssthresh = (void *)ca_update_ssthresh,
> >>>> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
> >>>> +       .name = "tcp_ca_update",
> >>>> +};
> >>>> +
> >>>> +SEC(".struct_ops.link")
> >>>> +struct tcp_congestion_ops ca_update_2 = {
> >>>> +       .cong_control = (void *)ca_update_2_cong_control,
> >>>> +       .ssthresh = (void *)ca_update_ssthresh,
> >>>> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
> >>>> +       .name = "tcp_ca_update",
> >>>> +};
> >>>
> >>> please add a test where you combine both .struct_ops and
> >>> .struct_ops.link, it's an obvious potentially problematic combination
> >>>
> >>> as I mentioned in previous patches, let's also have a negative test
> >>> where bpf_link__update_map() fails
> >>
> >> Sure
> >>
> >>>
> >>>> --
> >>>> 2.34.1
> >>>>