netdev - Re: [Patch net-next] sock_map: dump socket map id via diag

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Date:   Tue, 21 Feb 2023 10:11:12 +0100
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Cong Wang <cong.wang@...edance.com>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>
Subject: Re: [Patch net-next] sock_map: dump socket map id via diag

On Sat, Feb 11, 2023 at 12:19 PM -08, Cong Wang wrote:
> From: Cong Wang <cong.wang@...edance.com>
>
> Currently there is no way to know which sockmap a socket has been added
> to from outside, especially for that a socket can be added to multiple
> sockmap's. We could dump this via socket diag, as shown below.
>
> Sample output:
>
>   # ./iproute2/misc/ss -tnaie --sockmap
>   ESTAB  0      344329     127.0.0.1:1234     127.0.0.1:40912 ino:21098 sk:5 cgroup:/user.slice/user-0.slice/session-c1.scope <-> sockmap: 1
>
>   # bpftool map
>   1: sockmap  flags 0x0
>   	key 4B  value 4B  max_entries 2  memlock 4096B
> 	pids echo-sockmap(549)
>   4: array  name pid_iter.rodata  flags 0x480
> 	key 4B  value 4B  max_entries 1  memlock 4096B
> 	btf_id 10  frozen
> 	pids bpftool(624)
>
> In the future, we could dump other sockmap related stats too, hence I
> make it a nested attribute.
>
> Cc: John Fastabend <john.fastabend@...il.com>
> Cc: Jakub Sitnicki <jakub@...udflare.com>
> Signed-off-by: Cong Wang <cong.wang@...edance.com>
> ---

Sorry for not replying sooner. This sounds useful. Another use case I
can see here is inspecting process' sockets:

1. get a dup FD with pidfd_getfd()
2. query sock_diag by socket cookie
3. find out which maps socket is in.

I don't know if it makes sense to tie the naming to sockmap. We also
have also map type that can hold socket references -
REUSEPORT_SOCKARRAY.

We might want to add sock_diag support for REUSEPORT_SOCKARRAY in the
future as well. So a map-type-agnostic name for the new inet_diag ext
might be more future proof. Like INET_DIAG_BPF_MAP.

Also, can you please add a simple selftest? They often serve as the only
documentation for the features. Perhaps in
tools/testing/selftests/bpf/prog_tests/sockmap_basic.c.

Thanks,
Jakub