Support detaching xdp_link-based attachments fix #361

Signed-off-by: Mohamed Mahmoud <[email protected]>

lib/libxdp/libxdp.c

@@ -3223,6 +3223,42 @@ static int xdp_multiprog__unpin(struct xdp_multiprog *mp)
 	return err;
 }
 
+static void xdp_detach_links(uint32_t ifindex) {
+	struct bpf_link_info link_info;
+	u_int32_t link_info_len = sizeof(link_info), id;
+	int err, fd;
+
+	while (true) {
+		err = bpf_link_get_next_id(id, &id);
+		if (err) {
+			if (errno == ENOENT)
+				break;
+			pr_debug("can't get next link: %s (id %d)", strerror(errno), id);
+			break;
+		}
+
+		fd = bpf_link_get_fd_by_id(id);
+		if (fd < 0) {
+			pr_debug("can't get link by id (%u): %s", id, strerror(errno));
+			continue;
+		}
+		memset(&link_info, 0, sizeof(link_info));
+		err = bpf_obj_get_info_by_fd(fd, &link_info, &link_info_len);
+		if (err) {
+			pr_debug("can't get link info for %u: %s", id, strerror(errno));
+			continue;
+		}
+		if (link_info.type == BPF_LINK_TYPE_XDP && link_info.xdp.ifindex == ifindex) {
+			err = bpf_link_detach(fd);
+			if (err) {
+				pr_debug("can't detach link %u: %s", id, strerror(errno));
+			}
+			close(fd);
+			break;
+		}
+	}
+}
+
 static int xdp_multiprog__attach(struct xdp_multiprog *old_mp,
 				 struct xdp_multiprog *mp,
 				 enum xdp_attach_mode mode)
@@ -3253,8 +3289,15 @@ static int xdp_multiprog__attach(struct xdp_multiprog *old_mp,
 
 
 	err = xdp_attach_fd(prog_fd, old_fd, ifindex, mode);
-	if (err < 0)
+	if (err < 0) {
+		if (!mp) {
+			pr_debug("Detaching links on ifindex %d%s\n", ifindex,
+			mode == XDP_MODE_SKB? " in skb mode":"");
+			xdp_detach_links(ifindex);
+			return 0;
+		}
 		goto err;
+	}
 
 	if (mp)
 		pr_debug("Loaded %zu programs on ifindex %d%s\n",