Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 18 Jan 2021 15:26:28 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Mika Westerberg <mika.westerberg@linux.intel.com>
Cc:     "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>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Subject: Re: Multiple MODALIAS= in uevent file confuses userspace
Message-ID: <YAWalPeMPt44lBgI@kroah.com>
References: <CAAd53p6aURhfFp1RFQxEPtGfzSdUfe4=N=P2rP27ULxp-D4GCg@mail.gmail.com>
 <CAAd53p45q+Jigje0FcWAERiBUGfJhR8nTYNh7SFxBpajAe4=oA@mail.gmail.com>
 <CAJZ5v0iyEq6+OemJNXQv46h0pW=LHxiR2HeFe4+us59_x6Nymg@mail.gmail.com>
 <20210118141238.GQ968855@lahna.fi.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210118141238.GQ968855@lahna.fi.intel.com>
Precedence: bulk

On Mon, Jan 18, 2021 at 04:12:38PM +0200, Mika Westerberg wrote:
> 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@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?

thanks,

greg k-h