samples/bpf: Check detach prog exist or not in xdp_fwd

Before detach the prog, we should check detach prog exist or not.

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20220606005425.261967-1-shaozhengchao@huawei.com

diff --git a/samples/bpf/xdp_fwd_user.c b/samples/bpf/xdp_fwd_user.c
index 1828487bae9ae3657ba18147f435906c3cda31a7..84f57f1209ce5ca9b8f5f2b52c11c99527bbff57 100644 (file)
--- a/samples/bpf/xdp_fwd_user.c
+++ b/samples/bpf/xdp_fwd_user.c
@@ -47,17 +47,60 @@ static int do_attach(int idx, int prog_fd, int map_fd, const char *name)
        return err;
 }
 
-static int do_detach(int idx, const char *name)
+static int do_detach(int ifindex, const char *ifname, const char *app_name)
 {
-       int err;
+       LIBBPF_OPTS(bpf_xdp_attach_opts, opts);
+       struct bpf_prog_info prog_info = {};
+       char prog_name[BPF_OBJ_NAME_LEN];
+       __u32 info_len, curr_prog_id;
+       int prog_fd;
+       int err = 1;
+
+       if (bpf_xdp_query_id(ifindex, xdp_flags, &curr_prog_id)) {
+               printf("ERROR: bpf_xdp_query_id failed (%s)\n",
+                      strerror(errno));
+               return err;
+       }
 
-       err = bpf_xdp_detach(idx, xdp_flags, NULL);
-       if (err < 0)
-               printf("ERROR: failed to detach program from %s\n", name);
+       if (!curr_prog_id) {
+               printf("ERROR: flags(0x%x) xdp prog is not attached to %s\n",
+                      xdp_flags, ifname);
+               return err;
+       }
 
+       info_len = sizeof(prog_info);
+       prog_fd = bpf_prog_get_fd_by_id(curr_prog_id);
+       if (prog_fd < 0) {
+               printf("ERROR: bpf_prog_get_fd_by_id failed (%s)\n",
+                      strerror(errno));
+               return prog_fd;
+       }
+
+       err = bpf_obj_get_info_by_fd(prog_fd, &prog_info, &info_len);
+       if (err) {
+               printf("ERROR: bpf_obj_get_info_by_fd failed (%s)\n",
+                      strerror(errno));
+               goto close_out;
+       }
+       snprintf(prog_name, sizeof(prog_name), "%s_prog", app_name);
+       prog_name[BPF_OBJ_NAME_LEN - 1] = '\0';
+
+       if (strcmp(prog_info.name, prog_name)) {
+               printf("ERROR: %s isn't attached to %s\n", app_name, ifname);
+               err = 1;
+               goto close_out;
+       }
+
+       opts.old_prog_fd = prog_fd;
+       err = bpf_xdp_detach(ifindex, xdp_flags, &opts);
+       if (err < 0)
+               printf("ERROR: failed to detach program from %s (%s)\n",
+                      ifname, strerror(errno));
        /* TODO: Remember to cleanup map, when adding use of shared map
         *  bpf_map_delete_elem((map_fd, &idx);
         */
+close_out:
+       close(prog_fd);
        return err;
 }
 
@@ -169,7 +212,7 @@ int main(int argc, char **argv)
                        return 1;
                }
                if (!attach) {
-                       err = do_detach(idx, argv[i]);
+                       err = do_detach(idx, argv[i], prog_name);
                        if (err)
                                ret = err;
                } else {