linux-kernel - Re: [PATCH 3/3] ovl: redirect on rename-dir

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Date:   Fri, 28 Oct 2016 14:59:32 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     Raphael Hertzog <hertzog@...ian.org>
Cc:     Miklos Szeredi <miklos@...redi.hu>,
        "linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>,
        Guillem Jover <guillem@...ian.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] ovl: redirect on rename-dir

On Fri, Oct 28, 2016 at 2:56 PM, Raphael Hertzog <hertzog@...ian.org> wrote:
> Hi,
>
> On Wed, 26 Oct 2016, Miklos Szeredi wrote:
>> On Tue, Oct 25, 2016 at 1:57 PM, Raphael Hertzog <hertzog@...ian.org> wrote:
>
> [ redirect feature enabled by default ]
>
>> I think it would be safe to make it the default if upperdir is empty.
>> Nonempty implies that it was created with old kernel (or it was
>> crafted by hand).   But there should be a way to explicitly turn it
>> off;  either because of the need for backward compatibility or because
>> the old format is simply easier to work with for humans.
>>
>> How about:
>>
>> - If upper is nonempty, then leave redirect feature alone except when
>> mount option "-oredirect=on" is used to force enabling it.
>> - If upper is empty, then enable redirect feature except when mount
>> option "-oredirect=off" is used to force disabling it.
>
> Looks good, but is there some stickyness of the setting? My use case is
> schroot and it always starts with an empty upperdir when I create a
> temporary/throw-away chroot but if I reboot the machine, then it's possible
> that schroot will remount the overlayfs with a non-empty upperdir
> (the temporary chroot is preserved until I explicitly end the chroot).

Yes, there is stickiness (it stores the "redirect_dir" feature in an
extended attribute on upperdir).

Thanks,
Miklos