[bpf-next,v4] bpftool: Show map IDs along with struct_ops links.

Commit Message

Kui-Feng Lee April 21, 2023, 9:41 p.m. UTC

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 <[e-mail]>
Reviewed-by: Quentin Monnet <[e-mail]>
---
 tools/bpf/bpftool/link.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Comments

John Fastabend April 23, 2023, 2:33 p.m. UTC | #1

Kui-Feng Lee 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 <[e-mail]>
> Reviewed-by: Quentin Monnet <[e-mail]>
> ---

LGTM

Acked-by: John Fastabend <[e-mail]>

[e-mail] April 27, 2023, 1 p.m. UTC | #2

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <[e-mail]>:

On Fri, 21 Apr 2023 14:41:31 -0700 you 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.
> 
> [...]

Here is the summary with links:
  - [bpf-next,v4] bpftool: Show map IDs along with struct_ops links.
    https://git.kernel.org/bpf/bpf-next/c/74fc8801edc2

You are awesome, thank you!

Patch

diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
index d98dbc50cf4c..243b74e18e51 100644
--- a/tools/bpf/bpftool/link.c
+++ b/tools/bpf/bpftool/link.c
@@ -212,7 +212,10 @@  static int show_link_close_json(int fd, struct bpf_link_info *info)
 	case BPF_LINK_TYPE_NETFILTER:
 		netfilter_dump_json(info, json_wtr);
 		break;
-
+	case BPF_LINK_TYPE_STRUCT_OPS:
+		jsonw_uint_field(json_wtr, "map_id",
+				 info->struct_ops.map_id);
+		break;
 	default:
 		break;
 	}
@@ -245,7 +248,10 @@  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 %u  ", info->struct_ops.map_id);
+	else
+		printf("prog %u  ", info->prog_id);
 }
 
 static void show_link_attach_type_plain(__u32 attach_type)