[PATCH bpf-next v2 1/2] bpf: return target info when a tracing bpf_link is queried

["Toke Høiland-Jørgensen" <toke@redhat.com>]

There is currently no way to discover the target of a tracing program
attachment after the fact. Add this information to bpf_link_info and return
it when querying the bpf_link fd.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 include/linux/bpf_verifier.h   | 9 +++++++++
 include/uapi/linux/bpf.h       | 2 ++
 kernel/bpf/syscall.c           | 3 +++
 tools/include/uapi/linux/bpf.h | 2 ++
 4 files changed, 16 insertions(+)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 51c2ffa3d901..6023a1367853 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -487,6 +487,15 @@ static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,
 		return ((u64)btf_obj_id(btf) << 32) | 0x80000000 | btf_id;
 }
 
+/* unpack the IDs from the key as constructed above */
+static inline void bpf_trampoline_unpack_key(u64 key, u32 *obj_id, u32 *btf_id)
+{
+	if (obj_id)
+		*obj_id = key >> 32;
+	if (btf_id)
+		*btf_id = key & 0x7FFFFFFF;
+}
+
 int bpf_check_attach_target(struct bpf_verifier_log *log,
 			    const struct bpf_prog *prog,
 			    const struct bpf_prog *tgt_prog,
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 49371eba98ba..397884396671 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5379,6 +5379,8 @@ struct bpf_link_info {
 		} raw_tracepoint;
 		struct {
 			__u32 attach_type;
+			__u32 target_obj_id; /* prog_id for PROG_EXT, otherwise btf object id */
+			__u32 target_btf_id; /* BTF type id inside the object */
 		} tracing;
 		struct {
 			__u64 cgroup_id;
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6428634da57e..fd495190115e 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2551,6 +2551,9 @@ static int bpf_tracing_link_fill_link_info(const struct bpf_link *link,
 		container_of(link, struct bpf_tracing_link, link);
 
 	info->tracing.attach_type = tr_link->attach_type;
+	bpf_trampoline_unpack_key(tr_link->trampoline->key,
+				  &info->tracing.target_obj_id,
+				  &info->tracing.target_btf_id);
 
 	return 0;
 }
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 69902603012c..1a240be873d7 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5373,6 +5373,8 @@ struct bpf_link_info {
 		} raw_tracepoint;
 		struct {
 			__u32 attach_type;
+			__u32 target_obj_id; /* prog_id for PROG_EXT, otherwise btf object id */
+			__u32 target_btf_id; /* BTF type id inside the object */
 		} tracing;
 		struct {
 			__u64 cgroup_id;
-- 
2.31.1