linux-ext4 - Re: [PATCH] ext4: add rename whiteout support for fast commit

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Message-ID: <CAJfpegsGpaFdLcmUsBW66qhJSfXuog=3UbsZ50O_FSw2WUGhJA@mail.gmail.com>
Date:   Fri, 19 Mar 2021 11:51:54 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     harshad shirwadkar <harshadshirwadkar@...il.com>,
        Ext4 <linux-ext4@...r.kernel.org>, Theodore Tso <tytso@....edu>,
        overlayfs <linux-unionfs@...r.kernel.org>
Subject: Re: [PATCH] ext4: add rename whiteout support for fast commit

On Fri, Mar 19, 2021 at 11:35 AM Amir Goldstein <amir73il@...il.com> wrote:

> One thing that we will probably need to do is use the RENAME_WHITEOUT
> interface as the explicit way to create the shared whiteout instead of using
> vfs_whiteout() for filesystems that support RENAME_WHITEOUT
> (we check for RENAME_WHITEOUT support anyway).
>
> The only thing that bothered me in moving from per-ovl-instance singleton
> to per-ext4-singleton is what happens if someone tries to (say) chown -R
> the upper layer or some other offline modification that was working up to
> now and seemed to make sense.

Eek.

>
> Surely, the ext4 singleton whiteout cannot allow modifications like that,
> so what do we do about this? Let those scripts fail (if they exist) and
> let their owners fix them to skip errors on whiteouts?

Might try that.  But the no-regressions rule means we'd have to change
that in case it breaks something.

Thanks,
Miklos

> Thanks,
> Amir.