[PATCH 1/2] net/af_xdp: revert use BPF link for XDP programs

[Ciara Loftus <ciara.loftus@intel.com>]

The commit ae70cc6e893b ("net/af_xdp: use BPF link for XDP programs")
caused compilation errors on kernels older than v5.8 due to absence of
the bpf_link_info struct and some definitions in the linux/bpf.h header.
Since relying on the reported kernel version is not a robust solution
and also since there doesn't appear to be a suitable definition in the bpf
header that the preprocessor could rely on to determine support for bpf
link, we will take a different approach to solving the issue that the
original patch attempted to solve. The next commit will address this.

Fixes: ae70cc6e893b ("net/af_xdp: use BPF link for XDP programs")

Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
---
 drivers/net/af_xdp/compat.h         | 124 ----------------------------
 drivers/net/af_xdp/meson.build      |   7 --
 drivers/net/af_xdp/rte_eth_af_xdp.c |  13 ++-
 3 files changed, 5 insertions(+), 139 deletions(-)

diff --git a/drivers/net/af_xdp/compat.h b/drivers/net/af_xdp/compat.h
index 1d66f5e318..3880dc7dd7 100644
--- a/drivers/net/af_xdp/compat.h
+++ b/drivers/net/af_xdp/compat.h
@@ -2,7 +2,6 @@
  * Copyright(c) 2020 Intel Corporation.
  */
 
-#include <bpf/bpf.h>
 #include <bpf/xsk.h>
 #include <linux/version.h>
 #include <poll.h>
@@ -55,126 +54,3 @@ tx_syscall_needed(struct xsk_ring_prod *q __rte_unused)
 	return 1;
 }
 #endif
-
-#ifdef RTE_LIBRTE_AF_XDP_PMD_BPF_LINK
-static int link_lookup(int ifindex, int *link_fd)
-{
-	struct bpf_link_info link_info;
-	__u32 link_len;
-	__u32 id = 0;
-	int err;
-	int fd;
-
-	while (true) {
-		err = bpf_link_get_next_id(id, &id);
-		if (err) {
-			if (errno == ENOENT) {
-				err = 0;
-				break;
-			}
-			break;
-		}
-
-		fd = bpf_link_get_fd_by_id(id);
-		if (fd < 0) {
-			if (errno == ENOENT)
-				continue;
-			err = -errno;
-			break;
-		}
-
-		link_len = sizeof(struct bpf_link_info);
-		memset(&link_info, 0, link_len);
-		err = bpf_obj_get_info_by_fd(fd, &link_info, &link_len);
-		if (err) {
-			close(fd);
-			break;
-		}
-		if (link_info.type == BPF_LINK_TYPE_XDP) {
-			if ((int)link_info.xdp.ifindex == ifindex) {
-				*link_fd = fd;
-				break;
-			}
-		}
-		close(fd);
-	}
-
-	return err;
-}
-
-static bool probe_bpf_link(void)
-{
-	DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts,
-			    .flags = XDP_FLAGS_SKB_MODE);
-	struct bpf_load_program_attr prog_attr;
-	struct bpf_insn insns[2];
-	int prog_fd, link_fd = -1;
-	int ifindex_lo = 1;
-	bool ret = false;
-	int err;
-
-	err = link_lookup(ifindex_lo, &link_fd);
-	if (err)
-		return ret;
-
-	if (link_fd >= 0)
-		return true;
-
-	/* BPF_MOV64_IMM(BPF_REG_0, XDP_PASS), */
-	insns[0].code = BPF_ALU64 | BPF_MOV | BPF_K;
-	insns[0].dst_reg = BPF_REG_0;
-	insns[0].imm = XDP_PASS;
-
-	/* BPF_EXIT_INSN() */
-	insns[1].code = BPF_JMP | BPF_EXIT;
-
-	memset(&prog_attr, 0, sizeof(prog_attr));
-	prog_attr.prog_type = BPF_PROG_TYPE_XDP;
-	prog_attr.insns = insns;
-	prog_attr.insns_cnt = RTE_DIM(insns);
-	prog_attr.license = "GPL";
-
-	prog_fd = bpf_load_program_xattr(&prog_attr, NULL, 0);
-	if (prog_fd < 0)
-		return ret;
-
-	link_fd = bpf_link_create(prog_fd, ifindex_lo, BPF_XDP, &opts);
-	close(prog_fd);
-
-	if (link_fd >= 0) {
-		ret = true;
-		close(link_fd);
-	}
-
-	return ret;
-}
-
-static int link_xdp_program(int if_index, int prog_fd, bool use_bpf_link)
-{
-	DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts);
-	int link_fd, ret = 0;
-
-	if (!use_bpf_link)
-		return bpf_set_link_xdp_fd(if_index, prog_fd,
-					   XDP_FLAGS_UPDATE_IF_NOEXIST);
-
-	opts.flags = 0;
-	link_fd = bpf_link_create(prog_fd, if_index, BPF_XDP, &opts);
-	if (link_fd < 0)
-		ret = -1;
-
-	return ret;
-}
-#else
-static bool probe_bpf_link(void)
-{
-	return false;
-}
-
-static int link_xdp_program(int if_index, int prog_fd,
-			    bool use_bpf_link __rte_unused)
-{
-	return bpf_set_link_xdp_fd(if_index, prog_fd,
-				   XDP_FLAGS_UPDATE_IF_NOEXIST);
-}
-#endif
diff --git a/drivers/net/af_xdp/meson.build b/drivers/net/af_xdp/meson.build
index 42dc6d69ac..3ed2b29784 100644
--- a/drivers/net/af_xdp/meson.build
+++ b/drivers/net/af_xdp/meson.build
@@ -16,18 +16,11 @@ endif
 
 if bpf_dep.found() and cc.has_header('bpf/xsk.h') and cc.has_header('linux/if_xdp.h')
     ext_deps += bpf_dep
-    # check for libbpf shared umem APIs
     bpf_ver_dep = dependency('libbpf', version : '>=0.2.0',
             required: false, method: 'pkg-config')
     if bpf_ver_dep.found()
         dpdk_conf.set('RTE_LIBRTE_AF_XDP_PMD_SHARED_UMEM', 1)
     endif
-    # check for libbpf bpf link support
-    bpf_link_dep = dependency('libbpf', version : '>=0.4.0',
-            required: false, method: 'pkg-config')
-    if bpf_link_dep.found()
-        dpdk_conf.set('RTE_LIBRTE_AF_XDP_PMD_BPF_LINK', 1)
-    endif
 else
     build = false
     reason = 'missing dependency, "libbpf"'
diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c b/drivers/net/af_xdp/rte_eth_af_xdp.c
index 917e0bb453..1c7689c9b4 100644
--- a/drivers/net/af_xdp/rte_eth_af_xdp.c
+++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
@@ -139,7 +139,6 @@ struct pmd_internals {
 	bool shared_umem;
 	char prog_path[PATH_MAX];
 	bool custom_prog_configured;
-	bool use_bpf_link;
 
 	struct rte_ether_addr eth_addr;
 
@@ -973,8 +972,7 @@ eth_dev_close(struct rte_eth_dev *dev)
 	 */
 	dev->data->mac_addrs = NULL;
 
-	if (!internals->use_bpf_link)
-		remove_xdp_program(internals);
+	remove_xdp_program(internals);
 
 	if (internals->shared_umem) {
 		struct internal_list *list;
@@ -1149,7 +1147,7 @@ xsk_umem_info *xdp_umem_configure(struct pmd_internals *internals,
 }
 
 static int
-load_custom_xdp_prog(const char *prog_path, int if_index, bool use_bpf_link)
+load_custom_xdp_prog(const char *prog_path, int if_index)
 {
 	int ret, prog_fd = -1;
 	struct bpf_object *obj;
@@ -1173,7 +1171,8 @@ load_custom_xdp_prog(const char *prog_path, int if_index, bool use_bpf_link)
 	}
 
 	/* Link the program with the given network device */
-	ret = link_xdp_program(if_index, prog_fd, use_bpf_link);
+	ret = bpf_set_link_xdp_fd(if_index, prog_fd,
+					XDP_FLAGS_UPDATE_IF_NOEXIST);
 	if (ret) {
 		AF_XDP_LOG(ERR, "Failed to set prog fd %d on interface\n",
 				prog_fd);
@@ -1273,8 +1272,7 @@ xsk_configure(struct pmd_internals *internals, struct pkt_rx_queue *rxq,
 	if (strnlen(internals->prog_path, PATH_MAX) &&
 				!internals->custom_prog_configured) {
 		ret = load_custom_xdp_prog(internals->prog_path,
-					   internals->if_index,
-					   internals->use_bpf_link);
+					   internals->if_index);
 		if (ret) {
 			AF_XDP_LOG(ERR, "Failed to load custom XDP program %s\n",
 					internals->prog_path);
@@ -1691,7 +1689,6 @@ init_internals(struct rte_vdev_device *dev, const char *if_name,
 	strlcpy(internals->if_name, if_name, IFNAMSIZ);
 	strlcpy(internals->prog_path, prog_path, PATH_MAX);
 	internals->custom_prog_configured = 0;
-	internals->use_bpf_link = probe_bpf_link();
 
 #ifndef ETH_AF_XDP_SHARED_UMEM
 	if (shared_umem) {
-- 
2.17.1