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

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Date:   Mon, 18 Jan 2021 14:50:33 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        lennart@...ttering.net,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: Multiple MODALIAS= in uevent file confuses userspace

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?
>
> Kai-Heng
>
> >
> > [1] https://github.com/systemd/systemd/pull/18163
> >
> > Kai-Heng