linux-kernel - Re: [RFC 0/5] mm/bpf/perf: Store build id in file object

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Date:   Thu, 2 Feb 2023 15:47:45 +0100
From:   Jiri Olsa <olsajiri@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Hao Luo <haoluo@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        bpf <bpf@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-perf-use." <linux-perf-users@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [RFC 0/5] mm/bpf/perf: Store build id in file object

On Thu, Feb 02, 2023 at 03:15:39AM -0800, Alexei Starovoitov wrote:
> On Wed, Feb 1, 2023 at 5:57 AM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > hi,
> > we have a use cases for bpf programs to use binary file's build id.
> >
> > After some attempts to add helpers/kfuncs [1] [2] Andrii had an idea [3]
> > to store build id directly in the file object. That would solve our use
> > case and might be beneficial for other profiling/tracing use cases with
> > bpf programs.
> >
> > This RFC patchset adds new config CONFIG_FILE_BUILD_ID option, which adds
> > build id object pointer to the file object when enabled. The build id is
> > read/populated when the file is mmap-ed.
> >
> > I also added bpf and perf changes that would benefit from this.
> >
> > I'm not sure what's the policy on adding stuff to file object, so apologies
> > if that's out of line. I'm open to any feedback or suggestions if there's
> > better place or way to do this.
> 
> struct file represents all files while build_id is for executables only,
> and not all executables, but those currently running, so
> I think it's cleaner to put it into vm_area_struct.

I thought file objects would be shared to some extend and we might save
some memory keeping the build id objects there, but not sure it's really
the case now.. will check, using vma might be also easier

jirka