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From:   Will McVicker <willmcvicker@google.com>
Date:   Mon, 8 Feb 2021 16:41:29 -0800
Message-ID: <CABYd82bb-BiY2pQ3ghNYV3wtPeR8vJR5-nH6GH=oHB+ALFAw5w@mail.gmail.com>
Subject: Re: [PATCH v6] modules: introduce the MODULE_SCMVERSION config
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Jessica Yu <jeyu@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Christoph Hellwig <hch@infradead.org>,
        Saravana Kannan <saravanak@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        "Cc: Android Kernel" <kernel-team@android.com>
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Thanks Jessica for all the reviews. I guess we can let this die here
and I'll carry it downstream. At least it's all here for others to
see.

Thanks,
Will

On Wed, Feb 3, 2021 at 7:54 AM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Wed, Feb 03, 2021 at 04:46:16PM +0100, Jessica Yu wrote:
> > +++ Will McVicker [21/01/21 21:36 +0000]:
> > > Config MODULE_SCMVERSION introduces a new module attribute --
> > > `scmversion` -- which can be used to identify a given module's SCM
> > > version.  This is very useful for developers that update their kernel
> > > independently from their kernel modules or vice-versa since the SCM
> > > version provided by UTS_RELEASE (`uname -r`) will now differ from the
> > > module's vermagic attribute.
> > >
> > > For example, we have a CI setup that tests new kernel changes on the
> > > hikey960 and db845c devices without updating their kernel modules. When
> > > these tests fail, we need to be able to identify the exact device
> > > configuration the test was using. By including MODULE_SCMVERSION, we can
> > > identify the exact kernel and modules' SCM versions for debugging the
> > > failures.
> > >
> > > Additionally, by exposing the SCM version via the sysfs node
> > > /sys/module/MODULENAME/scmversion, one can also verify the SCM versions
> > > of the modules loaded from the initramfs. Currently, modinfo can only
> > > retrieve module attributes from the module's ko on disk and not from the
> > > actual module that is loaded in RAM.
> > >
> > > You can retrieve the SCM version in two ways,
> > >
> > > 1) By using modinfo:
> > >    > modinfo -F scmversion MODULENAME
> > > 2) By module sysfs node:
> > >    > cat /sys/module/MODULENAME/scmversion
> >
> > Hi Will,
> >
> > First off, thanks for being patient and being responsive throughout the patch
> > review process.
> >
> > Personally, I am rather neutral towards this feature. We already provide
> > CONFIG_MODULE_SRCVERSION to provide a checksum of a module's source files and I
> > think the SCMVERSION is a nicer alternative. I can see how an optional
> > scmversion field might be helpful information for distro developers in testing
> > environments and in situations where it is possible for the kernel and modules
> > to be updated/packaged separately (for instance, the kernel selftest modules
> > under lib/ are in-tree modules that are provided as a separate kernel module
> > package in SLE).
> >
> > Generally, out of principle, I do not want to merge a patch that's been NAK'd
> > repeatedly; even if I take the patch it'd likely be contested all the way up to
> > the merge window. So this boils down to whether Christoph (and maybe Greg) are
> > fine with this being a debug option that's not enabled by default.
>
> I am neutral on this, I don't care one way or the other.
>
> thanks,
>
> greg k-h