linux-kernel - Re: Multiple MODALIAS= in uevent file confuses userspace

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Message-ID: <20210118141238.GQ968855@lahna.fi.intel.com>
Date:   Mon, 18 Jan 2021 16:12:38 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        lennart@...ttering.net,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: Multiple MODALIAS= in uevent file confuses userspace

Hi,

On Mon, Jan 18, 2021 at 02:50:33PM +0100, Rafael J. Wysocki wrote:
> CC Mika and Andy.
> 
> On Mon, Jan 18, 2021 at 8:27 AM Kai-Heng Feng
> <kai.heng.feng@...onical.com> wrote:
> >
> > On Sat, Jan 9, 2021 at 12:25 AM Kai-Heng Feng
> > <kai.heng.feng@...onical.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.