linux-kernel - Re: [PATCH v5 1/3] Provide in-kernel headers to make extending kernel easier

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Message-ID: <CAOesGMj=BKcfa4A321y43m0qTaeQeM1M8btQmGCVM1idc9_5GA@mail.gmail.com>
Date:   Tue, 16 Apr 2019 09:47:16 -0700
From:   Olof Johansson <olof@...om.net>
To:     Karim Yaghmour <karim.yaghmour@...rsys.com>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>,
        Olof Johansson <olof@...om.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Qais Yousef <qais.yousef@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Manoj Rao <linux@...ojrajarao.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexei Starovoitov <ast@...nel.org>,
        atish patra <atishp04@...il.com>,
        Daniel Colascione <dancol@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Guenter Roeck <groeck@...omium.org>,
        Jonathan Corbet <corbet@....net>,
        Android Kernel Team <kernel-team@...roid.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        linux-trace-devel@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Shuah Khan <shuah@...nel.org>, Yonghong Song <yhs@...com>
Subject: Re: [PATCH v5 1/3] Provide in-kernel headers to make extending kernel easier

On Tue, Apr 16, 2019 at 6:32 AM Karim Yaghmour
<karim.yaghmour@...rsys.com> wrote:
>
>
> On 4/16/19 9:04 AM, Joel Fernandes wrote:
> > On Tue, Apr 16, 2019 at 02:49:39PM +0200, Greg Kroah-Hartman wrote:
> >> On Tue, Apr 16, 2019 at 08:33:06AM -0400, Steven Rostedt wrote:
> >>> On Mon, 15 Apr 2019 22:50:10 -0500
> >>> Kees Cook <keescook@...omium.org> wrote:
> >>>
> >>>> On Mon, Apr 15, 2019 at 9:41 AM Steven Rostedt <rostedt@...dmis.org> wrote:
> >>>>> I agree with this assessment. We shouldn't use config.gz as precedence
> >>>>> for this solution. config.gz should have been in debugfs to begin with,
> >>>>> but I don't believe debugfs was around when config.gz was introduced.
> >>>>> (Don't have time to look into the history of the two).
> >>>>
> >>>> I don't agree with this: /proc/config.gz is used by a lot of tools
> >>>> that do sanity-check of running systems. This isn't _debugging_...
> >>>> it's verifying correct kernel builds. It's a fancy version of checking
> >>>> /proc/version.
> >>>>
> >>>
> >>> Then we should perhaps make a new file system call tarballs ;-)
> >>>
> >>>   /sys/kernel/tarballs/
> >>>
> >>> and place everything there. That way it removes it from /proc (which is
> >>> the worse place for that) and also makes it something other than debug.
> >>> That's what I did for tracefs.
> >>
> >> As horrible as that suggestion is, it does kind of make sense :)
> >>
> >> We can't put this in debugfs as that's only for debugging and systems
> >> should never have that mounted for normal operations (users want to
> >> build ebpf programs), and /proc really should be for processes but that
> >> horse is long left the barn.
> >>
> >> But, I'm willing to consider putting this either in a system-fs-like
> >> filesystem, or just in sysfs itself, we do have /sys/kernel/ to play
> >> around in if the main objection is that we should not be cluttering up
> >> /proc with stuff like this.
> >>
> >
> > I am ok with the suggestion of /sys/kernel for the archive. That also seems
> > to fit well with the idea that the headers are kernel related and probably
> > belong here more strictly speaking, than /proc.
>
> This makes sense. And if it alleviates concerns regarding extending
> /proc ABIs then might as well switch to this.
>
> Olof, what do you think of this?

In practice we've been more lenient with changes to /sys over time, so
I think this might be a reasonable compromise.

I still think that a filesystem view is the cleanest way to do this,
but I won't push back from this going in. It does solve a real
problem, and if we want a different format later we can revisit it
then.


-Olof