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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Message-ID: <d2220bfb-db28-251a-66ca-6f3a6377c94f@isovalent.com>
Date:   Mon, 15 Jun 2020 10:30:26 +0100
From:   Quentin Monnet <quentin@...valent.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        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>
Subject: Re: [RFC PATCH bpf-next 8/8] tools/bpftool: show PIDs with FDs open
 against BPF map/prog/link/btf

2020-06-15 11:04 UTC+0200 ~ Toke Høiland-Jørgensen <toke@...hat.com>
> 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
> 

Thanks a lot Andrii, the feature looks great indeed.

Thank you for the clean-up and refactoring in bpftool and its Makefile
as well, I am happy to confirm that test_bpftool_build.sh still passes
on my setup with your changes.

Quentin