linux-kernel - Re: [PATCH] ovl: change error message to info for empty lowerdir

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Message-ID: <CAOgh=FygeLw0jBLvPKiaBCxKkfoQXmwf=sfvyJHs4Hyy_7wDSw@mail.gmail.com>
Date: Tue, 28 May 2024 13:25:59 +0100
From: Eric Curtin <ecurtin@...hat.com>
To: Alexander Larsson <alexl@...hat.com>
Cc: Miklos Szeredi <miklos@...redi.hu>, 
	"open list:OVERLAY FILESYSTEM" <linux-unionfs@...r.kernel.org>, Wei Wang <weiwang@...hat.com>, 
	Amir Goldstein <amir73il@...il.com>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ovl: change error message to info for empty lowerdir

On Tue, 28 May 2024 at 13:23, Alexander Larsson <alexl@...hat.com> wrote:
>
>
>
> On Tue, May 28, 2024 at 1:34 PM Miklos Szeredi <miklos@...redi.hu> wrote:
>>
>> On Tue, 28 May 2024 at 12:55, Eric Curtin <ecurtin@...hat.com> wrote:
>> >
>> > On Tue, 28 May 2024 at 11:34, Miklos Szeredi <miklos@...redi.hu> wrote:
>> > >
>> > > On Tue, 28 May 2024 at 11:03, Eric Curtin <ecurtin@...hat.com> wrote:
>> > > >
>> > > > In some deployments, an empty lowerdir is not considered an error.
>> > >
>> > > I don't think this can be triggered in upstream kernel and can be
>> > > removed completely.
>> >
>> > True... Just switched to Fedora Rawhide and instead we just see this one:
>> >
>> > pr_err("cannot append lower layer");
>> >
>> > >
>> > > Or do you have a reproducer?
>> >
>> > Run one of these vms:
>> >
>> > https://github.com/osbuild/bootc-image-builder
>>
>> Apparently it is using the legacy lowerdir append mode
>> "lowerdir=:foo".  This works only on 6.5.
>>
>> In 6.6 and later the same can be achieved with "lowerdir+=foo".
>>
>> It's strange that there are not side effects other then the error message.
>
>
> The code tries to use the new mode, but then falls back on ENOSYS:
>
> https://github.com/containers/composefs/blob/main/libcomposefs/lcfs-mountc#L431
>
> So, I guess with a more recent kernel it will not print the warning.
>
> --
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>  Alexander Larsson                                Red Hat, Inc
>        alexl@...hat.com         alexander.larsson@...il.com

I realized I never posted the version of the kernel producing this
error message:

pr_err("cannot append lower layer");

So just for clarity in general, that was this one:

Linux fedora 6.9.0-64.fc41.x86_64 #1 SMP PREEMPT_DYNAMIC Mon May 13
11:58:46 UTC 2024 x86_64 GNU/Linux

Is mise le meas/Regards,

Eric Curtin