Re: [PATCH v2] ovl: require xwhiteout feature flag on layer roots

[Alexander Larsson <alexl@redhat.com>]

On Fri, 2024-01-19 at 13:08 +0200, Amir Goldstein wrote:
> On Fri, Jan 19, 2024 at 12:14 PM Miklos Szeredi <mszeredi@redhat.com>
> wrote:
> 
> 
> Do you want me to fix/test and send this to Linus?
> 
> Alex, can we add your RVB to v2?

I ran into an issue converting composefs to use this.

Suppose we have a chroot of files containing some upper dirs and we
want to make a composefs of this. For example, say
/foo/lower/dir/whiteout is a traditional whiteout.

Previously, what happened is that I marked the whiteout file with
trusted.overlay.overlay.whiteout, and the /foo/lower/dir with
trusted.overlay.overlay.whiteouts.

Them when I mounted then entire chroot with overlayfs these xattrs
would get unescaped and I would get a $mnt/foo/lower/dir/whiteout with
a trusted.overlay.whiteout xattr, and a $mnt/foo/lower/dir with a
trusted.overlay.whiteout. When I then mounted another overlayfs with a
lowerdir of $mnt/foo/lower it would treat the whiteout as a xwhiteout.

However, now I need the lowerdir toplevel dir to also have a 
trusted.overlay.whiteouts xattr. But when I'm converting the entire
chroot I do not know which of the directories is going to be used as
the toplevel lower dir, so I don't know where to put this marker.

The only solution I see is to put it on *all* parent directories. Is
there a better approach here?

-- 
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
=-=-=
 Alexander Larsson                                            Red Hat,
Inc 
       alexl@redhat.com            alexander.larsson@gmail.com 
He's a scrappy day-dreaming inventor looking for a cure to the poison 
coursing through his veins. She's a foxy snooty stripper with someone 
else's memories. They fight crime!