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

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Date:   Mon, 18 Jan 2021 15:26:57 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        lennart@...ttering.net,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Multiple MODALIAS= in uevent file confuses userspace

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