linux-kernel - Re: [PATCH v2 0/2] Adds support to capture module's SCM version

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Message-ID: <X8p8ZK1sXQ2E7hSA@google.com>
Date:   Fri, 4 Dec 2020 10:13:56 -0800
From:   Will McVicker <willmcvicker@...gle.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jessica Yu <jeyu@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Saravana Kannan <saravanak@...gle.com>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH v2 0/2] Adds support to capture module's SCM version

On Fri, Dec 04, 2020 at 07:51:59AM +0000, Christoph Hellwig wrote:
> I think your decription still shows absolutely no benefit for the
> kernel, so I'not sure why anyone would want to waste time on this.
Hi Christoph,

Did you get a chance to read my earlier responses regarding the uses for
in-tree modules?

The biggest benefit for the upstream community is being about to get the SCM
version for *any* module (including in-tree modules) in the initramfs via the
sysfs node. Currently there is no way to do that and there is no guarantee that
those modules in the initramfs were compiled with the running kernel. In fact,
running,

  modinfo -F vermagic MODULENAME

will return an invalid vermagic string if the same module with different
vermagic strings exists in the initramfs and on disk because modinfo only looks
at the module on disk (not in memory).

The second most useful benefit goes hand-in-hand with MODVERSIONS. The purpose
of MODVERSIONS is to create a stable interface that allows one to update the
kernel and kernel modules (including in-tree modules) independently. So when
developers do update their kernels independently (think for security bug
fixes), the `scmversion` attribute guarantees developers that they can still
identify the modules' or kernel's SCM version.

I hope that helps. If not, then please let me know why these reasons "show
absolutely no benefit for the kernel?"

Thanks,
Will