Re: [PATCH bpf-next v2] bpftool: Show map IDs along with struct_ops links.

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On 4/20/23 16:41, Andrii Nakryiko wrote:
On Tue, Apr 18, 2023 at 5:37 PM Kui-Feng Lee <thinker.li@xxxxxxxxx> wrote:

A new link type, BPF_LINK_TYPE_STRUCT_OPS, was added to attach
struct_ops to links. (226bc6ae6405) It would be helpful for users to
know which map is associated with the link.

The assumption was that every link is associated with a BPF program, but
this does not hold true for struct_ops. It would be better to display
map_id instead of prog_id for struct_ops links. However, some tools may
rely on the old assumption and need a prog_id.  The discussion on the
mailing list suggests that tools should parse JSON format. We will maintain
the existing JSON format by adding a map_id without removing prog_id. As
for plain text format, we will remove prog_id from the header line and add
a map_id for struct_ops links.

Signed-off-by: Kui-Feng Lee <kuifeng@xxxxxxxx>
Reviewed-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>
---
  tools/bpf/bpftool/link.c | 9 ++++++++-
  1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
index f985b79cca27..8eb8520bd7b4 100644
--- a/tools/bpf/bpftool/link.c
+++ b/tools/bpf/bpftool/link.c
@@ -195,6 +195,10 @@ static int show_link_close_json(int fd, struct bpf_link_info *info)
                                  info->netns.netns_ino);
                 show_link_attach_type_json(info->netns.attach_type, json_wtr);
                 break;
+       case BPF_LINK_TYPE_STRUCT_OPS:
+               jsonw_uint_field(json_wtr, "map_id",
+                                info->struct_ops.map_id);
+               break;
         default:
                 break;
         }
@@ -227,7 +231,10 @@ static void show_link_header_plain(struct bpf_link_info *info)
         else
                 printf("type %u  ", info->type);

-       printf("prog %u  ", info->prog_id);
+       if (info->type == BPF_LINK_TYPE_STRUCT_OPS)
+               printf("map_id %u  ", info->struct_ops.map_id);
+       else
+               printf("prog %u  ", info->prog_id);

if we output "prog %u" for prog_id, shouldn't we just output "map %u"
for map_id?

"map" make sense to me.


  }

  static void show_link_attach_type_plain(__u32 attach_type)
--
2.34.1




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