linux-kernel - Re: [PATCH v5 bpf-next 0/4] bpf: introduce bpf_get_task

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Date:   Wed, 1 Jul 2020 08:34:09 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH v5 bpf-next 0/4] bpf: introduce bpf_get_task_stack()

On Mon, Jun 29, 2020 at 11:28 PM Song Liu <songliubraving@...com> wrote:
>
> This set introduces a new helper bpf_get_task_stack(). The primary use case
> is to dump all /proc/*/stack to seq_file via bpf_iter__task.
>
> A few different approaches have been explored and compared:
>
>   1. A simple wrapper around stack_trace_save_tsk(), as v1 [1].
>
>      This approach introduces new syntax, which is different to existing
>      helper bpf_get_stack(). Therefore, this is not ideal.
>
>   2. Extend get_perf_callchain() to support "task" as argument.
>
>      This approach reuses most of bpf_get_stack(). However, extending
>      get_perf_callchain() requires non-trivial changes to architecture
>      specific code. Which is error prone.
>
>   3. Current (v2) approach, leverages most of existing bpf_get_stack(), and
>      uses stack_trace_save_tsk() to handle architecture specific logic.
>
> [1] https://lore.kernel.org/netdev/20200623070802.2310018-1-songliubraving@fb.com/
>
> Changes v4 => v5:
> 1. Rebase and work around git-am issue. (Alexei)
> 2. Update commit log for 4/4. (Yonghong)

Applied. Thanks
I've added /* */ tweak to BPF_FUNC_MAPPER, so we stop having
ongoing merge conflicts and preserve better 'git blame' for helpers.