linux-kernel - Re: [PATCH] Revert kheaders feature

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Date:   Wed, 5 Feb 2020 13:53:15 -0800
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Olof Johansson <olof@...om.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tejun Heo <tj@...nel.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        David Howells <dhowells@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-kbuild@...r.kernel.org,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert kheaders feature

On Wed, Feb 5, 2020 at 1:48 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Wed, Feb 05, 2020 at 01:35:56PM -0800, Joel Fernandes wrote:
> > On Wed, Feb 5, 2020 at 1:33 PM Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > [snip]
> > > > > like the BTF approach is significantly better and said users are
> > > > > hopefully moving forward to it quickly, and if they can't move
> > > > > forward, then they're likely also not going to move forward to newer
> > > > > kernels either?
> > > >
> > > > I think BCC runs on a lot of upstream machines. I think the migration
> > > > strategy is a matter of opinion, one way is to take it out and cause some
> > > > pain in the hope that users/tools will migrate soon (while probably carrying
> > > > the reverted patches out of tree). Another is to migrate the tools first and
> > > > then take it out (which has its own disadvantages such as introducing even
> > > > more users of it while it is still upstream).
> > >
> > > Do we "know" what tools today require this, and what needs to be done to
> > > "fix" them?  If we don't know that, then there's no way to drop this,
> > > pretty much ever :(
> >
> > Is there a real reason to drop it or a problem dropping this solves though?
>
> Olof had some reasons, but as we were drinking at the time when it came
> up last night, I can't really remember them specifically.  Hopefully he
> does :)
> But that didn't answer my question of "who is still using this"?  I was
> hoping we actually knew this given it was created for specific users.

I think I mentioned this in a previous thread of this email. Several
BCC tools are using it - see for example the criticalstat BCC tool
which includes linux/sched.h :
https://github.com/iovisor/bcc/blob/master/tools/criticalstat.py#L73
, or filetop BCC tool which uses struct dentry :
https://github.com/iovisor/bcc/blob/master/tools/filetop.py#L101

These would break without kernel headers either on the host or via
CONFIG_IKHEADERS.

thanks,

 - Joel