netdev - Re: [RFC PATCH bpf-next 8/8] tools/bpftool: show PIDs with FDs open against BPF map/prog/link/btf

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Date:   Mon, 15 Jun 2020 11:04:34 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>, Hao Luo <haoluo@...gle.com>,
        Song Liu <songliubraving@...com>,
        Quentin Monnet <quentin@...valent.com>
Subject: Re: [RFC PATCH bpf-next 8/8] tools/bpftool: show PIDs with FDs open against BPF map/prog/link/btf

Arnaldo Carvalho de Melo <acme@...nel.org> writes:

> Em Fri, Jun 12, 2020 at 10:57:59PM -0700, Andrii Nakryiko escreveu:
>> On Fri, Jun 12, 2020 at 8:45 PM Alexei Starovoitov
>> <alexei.starovoitov@...il.com> wrote:
>> >
>> > On Fri, Jun 12, 2020 at 03:31:50PM -0700, Andrii Nakryiko wrote:
>> > > Add bpf_iter-based way to find all the processes that hold open FDs against
>> > > BPF object (map, prog, link, btf). Add new flag (-o, for "ownership", given
>> > > -p is already taken) to trigger collection and output of these PIDs.
>> > >
>> > > Sample output for each of 4 BPF objects:
>> > >
>> > > $ sudo ./bpftool -o prog show
>> > > 1992: cgroup_skb  name egress_alt  tag 9ad187367cf2b9e8  gpl
>> > >         loaded_at 2020-06-12T14:18:10-0700  uid 0
>> > >         xlated 48B  jited 59B  memlock 4096B  map_ids 2074
>> > >         btf_id 460
>> > >         pids: 913709,913732,913733,913734
>> > > 2062: cgroup_device  tag 8c42dee26e8cd4c2  gpl
>> > >         loaded_at 2020-06-12T14:37:52-0700  uid 0
>> > >         xlated 648B  jited 409B  memlock 4096B
>> > >         pids: 1
>> > >
>> > > $ sudo ./bpftool -o map show
>> > > 2074: array  name test_cgr.bss  flags 0x400
>> > >         key 4B  value 8B  max_entries 1  memlock 8192B
>> > >         btf_id 460
>> > >         pids: 913709,913732,913733,913734
>> > >
>> > > $ sudo ./bpftool -o link show
>> > > 82: cgroup  prog 1992
>> > >         cgroup_id 0  attach_type egress
>> > >         pids: 913709,913732,913733,913734
>> > > 86: cgroup  prog 1992
>> > >         cgroup_id 0  attach_type egress
>> > >         pids: 913709,913732,913733,913734
>> >
>> > This is awesome.
>
> Indeed.
>  
>> Thanks.
>> 
>> >
>> > Why extra flag though? I think it's so useful that everyone would want to see
>
> Agreed.
>  
>> No good reason apart from "being safe by default". If turned on by
>> default, bpftool would need to probe for bpf_iter support first. I can
>> add probing and do this by default.
>
> I think this is the way to go.

+1

And also +1 on the awesomeness of this feature! :)

-Toke