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Date:   Mon, 18 Jan 2021 15:58:18 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     Mika Westerberg <mika.westerberg@linux.intel.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Kai-Heng Feng <kai.heng.feng@canonical.com>,
        lennart@poettering.net,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: Multiple MODALIAS= in uevent file confuses userspace
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On Mon, Jan 18, 2021 at 04:48:53PM +0200, Andy Shevchenko wrote:
> On Mon, Jan 18, 2021 at 03:26:28PM +0100, Greg Kroah-Hartman wrote:
> > On Mon, Jan 18, 2021 at 04:12:38PM +0200, Mika Westerberg wrote:
> > > On Mon, Jan 18, 2021 at 02:50:33PM +0100, Rafael J. Wysocki wrote:
> > > > On Mon, Jan 18, 2021 at 8:27 AM Kai-Heng Feng
> > > > <kai.heng.feng@canonical.com> wrote:
> > > > > On Sat, Jan 9, 2021 at 12:25 AM Kai-Heng Feng
> > > > > <kai.heng.feng@canonical.com> wrote:
> > > > > >
> > > > > > Commit 8765c5ba19490 ("ACPI / scan: Rework modalias creation when
> > > > > > "compatible" is present") creates two modaliases for certain ACPI
> > > > > > devices. However userspace (systemd-udevd in this case) assumes uevent
> > > > > > file doesn't have duplicated keys, so two "MODALIAS=" breaks the
> > > > > > assumption.
> > > > > >
> > > > > > Based on the assumption, systemd-udevd internally uses hashmap to
> > > > > > store each line of uevent file, so the second modalias always replaces
> > > > > > the first modalias.
> > > > > >
> > > > > > My attempt [1] is to add a new key, "MODALIAS1" for the second
> > > > > > modalias. This brings up the question of whether each key in uevent
> > > > > > file is unique. If it's no unique, this may break may userspace.
> > > > >
> > > > > Does anyone know if there's any user of the second modalias?
> > > > > If there's no user of the second one, can we change it to OF_MODALIAS
> > > > > or COMPAT_MODALIAS?
> > > 
> > > The only users I'm aware are udev and the busybox equivalent (udev,
> > > mdev) but I'm not sure if they use the second second modalias at all so
> > > OF_MODALIAS for the DT compatible string sounds like a good way to solve
> > > this.
> > 
> > As udev seems to "break" with this (which is where we got the original
> > report from), I don't think you need to worry about that user :)
> 
> > Does anyone use mdev anymore, and in any ACPI-supported systems?
> 
> Yes, regularly.

Ok, and how badly does it break when MODALIAS is multiple lines like
this?  Or can it handle it?

thanks,

greg k-h