Re: [RFC bpf-next 1/2] bpftool: Print map ID upon creation and support JSON output

[Yonghong Song]

On 10/28/25 5:57 AM, Harshit Mogalapalli wrote:

It is useful to print map ID on successful creation.

JSON case:
$ ./bpftool -j map create /sys/fs/bpf/test_map4 type hash key 4 value 8 entries 
128 name map4
{"id":12}

Generic case:
$ ./bpftool  map create /sys/fs/bpf/test_map5 type hash key 4 value 8 entries 
128 name map5
Map successfully created with ID: 15

Bpftool Issue: https://github.com/libbpf/bpftool/issues/121
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapa...@oracle.com>
---
  tools/bpf/bpftool/map.c | 24 ++++++++++++++++++++----
  1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index c9de44a45778..b6580f25361d 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -1251,6 +1251,8 @@ static int do_create(int argc, char **argv)
        LIBBPF_OPTS(bpf_map_create_opts, attr);
        enum bpf_map_type map_type = BPF_MAP_TYPE_UNSPEC;
        __u32 key_size = 0, value_size = 0, max_entries = 0;
+       struct bpf_map_info map_info = {};
+       __u32 map_info_len = sizeof(map_info);
        const char *map_name = NULL;
        const char *pinfile;
        int err = -1, fd;
@@ -1353,13 +1355,27 @@ static int do_create(int argc, char **argv)
        }

err = do_pin_fd(fd, pinfile);

-       close(fd);
-       if (err)
+       if (err) {
+               close(fd);

I think you can remove close(fd) here,

                goto exit;
+       }

- if (json_output)

-               jsonw_null(json_wtr);
+       err = bpf_obj_get_info_by_fd(fd, &map_info, &map_info_len);
+       if (err) {
+               p_err("Failed to fetch map info: %s\n", strerror(errno));
+               close(fd);

and here

+               goto exit;
+       }

+ close(fd);

and here,

+
+       if (json_output) {
+               jsonw_start_object(json_wtr);
+               jsonw_int_field(json_wtr, "id", map_info.id);
+               jsonw_end_object(json_wtr);
+       } else {
+               printf("Map successfully created with ID: %u\n", map_info.id);
+       }
  exit:

and put close(fd) here.

        if (attr.inner_map_fd > 0)
                close(attr.inner_map_fd);