libbpf: Add bpf_get_link_xdp_info() function to get more XDP information

Currently, libbpf only provides a function to get a single ID for the XDP
program attached to the interface. However, it can be useful to get the
full set of program IDs attached, along with the attachment mode, in one
go. Add a new getter function to support this, using an extendible
structure to carry the information. Express the old bpf_get_link_id()
function in terms of the new function.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/157333185164.88376.7520653040667637246.stgit@toke.dk

tools/lib/bpf/libbpf.h

@@ -427,8 +427,18 @@ LIBBPF_API int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
 LIBBPF_API int bpf_prog_load(const char *file, enum bpf_prog_type type,
 			     struct bpf_object **pobj, int *prog_fd);
 
+struct xdp_link_info {
+	__u32 prog_id;
+	__u32 drv_prog_id;
+	__u32 hw_prog_id;
+	__u32 skb_prog_id;
+	__u8 attach_mode;
+};
+
 LIBBPF_API int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags);
 LIBBPF_API int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags);
+LIBBPF_API int bpf_get_link_xdp_info(int ifindex, struct xdp_link_info *info,
+				     size_t info_size, __u32 flags);
 
 struct perf_buffer;
 

tools/lib/bpf/libbpf.map

@@ -193,6 +193,7 @@ LIBBPF_0.0.5 {
 
 LIBBPF_0.0.6 {
 	global:
+		bpf_get_link_xdp_info;
 		bpf_map__get_pin_path;
 		bpf_map__is_pinned;
 		bpf_map__set_pin_path;

tools/lib/bpf/netlink.c

@@ -25,7 +25,7 @@ typedef int (*__dump_nlmsg_t)(struct nlmsghdr *nlmsg, libbpf_dump_nlmsg_t,
 struct xdp_id_md {
 	int ifindex;
 	__u32 flags;
-	__u32 id;
+	struct xdp_link_info info;
 };
 
 int libbpf_netlink_open(__u32 *nl_pid)
@@ -203,26 +203,11 @@ static int __dump_link_nlmsg(struct nlmsghdr *nlh,
 	return dump_link_nlmsg(cookie, ifi, tb);
 }
 
-static unsigned char get_xdp_id_attr(unsigned char mode, __u32 flags)
+static int get_xdp_info(void *cookie, void *msg, struct nlattr **tb)
-{
-	if (mode != XDP_ATTACHED_MULTI)
-		return IFLA_XDP_PROG_ID;
-	if (flags & XDP_FLAGS_DRV_MODE)
-		return IFLA_XDP_DRV_PROG_ID;
-	if (flags & XDP_FLAGS_HW_MODE)
-		return IFLA_XDP_HW_PROG_ID;
-	if (flags & XDP_FLAGS_SKB_MODE)
-		return IFLA_XDP_SKB_PROG_ID;
-
-	return IFLA_XDP_UNSPEC;
-}
-
-static int get_xdp_id(void *cookie, void *msg, struct nlattr **tb)
 {
 	struct nlattr *xdp_tb[IFLA_XDP_MAX + 1];
 	struct xdp_id_md *xdp_id = cookie;
 	struct ifinfomsg *ifinfo = msg;
-	unsigned char mode, xdp_attr;
 	int ret;
 
 	if (xdp_id->ifindex && xdp_id->ifindex != ifinfo->ifi_index)
@@ -238,27 +223,40 @@ static int get_xdp_id(void *cookie, void *msg, struct nlattr **tb)
 	if (!xdp_tb[IFLA_XDP_ATTACHED])
 		return 0;
 
-	mode = libbpf_nla_getattr_u8(xdp_tb[IFLA_XDP_ATTACHED]);
+	xdp_id->info.attach_mode = libbpf_nla_getattr_u8(
-	if (mode == XDP_ATTACHED_NONE)
+		xdp_tb[IFLA_XDP_ATTACHED]);
+
+	if (xdp_id->info.attach_mode == XDP_ATTACHED_NONE)
 		return 0;
 
-	xdp_attr = get_xdp_id_attr(mode, xdp_id->flags);
+	if (xdp_tb[IFLA_XDP_PROG_ID])
-	if (!xdp_attr || !xdp_tb[xdp_attr])
+		xdp_id->info.prog_id = libbpf_nla_getattr_u32(
-		return 0;
+			xdp_tb[IFLA_XDP_PROG_ID]);
 
-	xdp_id->id = libbpf_nla_getattr_u32(xdp_tb[xdp_attr]);
+	if (xdp_tb[IFLA_XDP_SKB_PROG_ID])
+		xdp_id->info.skb_prog_id = libbpf_nla_getattr_u32(
+			xdp_tb[IFLA_XDP_SKB_PROG_ID]);
+
+	if (xdp_tb[IFLA_XDP_DRV_PROG_ID])
+		xdp_id->info.drv_prog_id = libbpf_nla_getattr_u32(
+			xdp_tb[IFLA_XDP_DRV_PROG_ID]);
+
+	if (xdp_tb[IFLA_XDP_HW_PROG_ID])
+		xdp_id->info.hw_prog_id = libbpf_nla_getattr_u32(
+			xdp_tb[IFLA_XDP_HW_PROG_ID]);
 
 	return 0;
 }
 
-int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags)
+int bpf_get_link_xdp_info(int ifindex, struct xdp_link_info *info,
+			  size_t info_size, __u32 flags)
 {
 	struct xdp_id_md xdp_id = {};
 	int sock, ret;
 	__u32 nl_pid;
 	__u32 mask;
 
-	if (flags & ~XDP_FLAGS_MASK)
+	if (flags & ~XDP_FLAGS_MASK || !info_size)
 		return -EINVAL;
 
 	/* Check whether the single {HW,DRV,SKB} mode is set */
@@ -274,14 +272,44 @@ int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags)
 	xdp_id.ifindex = ifindex;
 	xdp_id.flags = flags;
 
-	ret = libbpf_nl_get_link(sock, nl_pid, get_xdp_id, &xdp_id);
+	ret = libbpf_nl_get_link(sock, nl_pid, get_xdp_info, &xdp_id);
-	if (!ret)
+	if (!ret) {
-		*prog_id = xdp_id.id;
+		size_t sz = min(info_size, sizeof(xdp_id.info));
+
+		memcpy(info, &xdp_id.info, sz);
+		memset((void *) info + sz, 0, info_size - sz);
+	}
 
 	close(sock);
 	return ret;
 }
 
+static __u32 get_xdp_id(struct xdp_link_info *info, __u32 flags)
+{
+	if (info->attach_mode != XDP_ATTACHED_MULTI)
+		return info->prog_id;
+	if (flags & XDP_FLAGS_DRV_MODE)
+		return info->drv_prog_id;
+	if (flags & XDP_FLAGS_HW_MODE)
+		return info->hw_prog_id;
+	if (flags & XDP_FLAGS_SKB_MODE)
+		return info->skb_prog_id;
+
+	return 0;
+}
+
+int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags)
+{
+	struct xdp_link_info info;
+	int ret;
+
+	ret = bpf_get_link_xdp_info(ifindex, &info, sizeof(info), flags);
+	if (!ret)
+		*prog_id = get_xdp_id(&info, flags);
+
+	return ret;
+}
+
 int libbpf_nl_get_link(int sock, unsigned int nl_pid,
 		       libbpf_dump_nlmsg_t dump_link_nlmsg, void *cookie)
 {