From: Christoph Hellwig <hch@infradead.org>
To: Amir Goldstein <amir73il@gmail.com>
Cc: Christian Brauner <brauner@kernel.org>,
Miklos Szeredi <miklos@szeredi.hu>, Zorro Lang <zlang@kernel.org>,
linux-unionfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
fstests@vger.kernel.org
Subject: Re: [PATCH 2/2] src/vfs: skip whiteout-device fixtures on overlayfs
Date: Thu, 9 Jul 2026 22:34:41 -0700 [thread overview]
Message-ID: <alCEcbQfLY4f6Fo3@infradead.org> (raw)
In-Reply-To: <CAOQ4uxjtTd0H=DjyyxaOm56be0JOy2y4ZYV8AbVRnsdGnv4hxA@mail.gmail.com>
On Mon, Jun 15, 2026 at 08:03:02PM +0200, Amir Goldstein wrote:
> On Mon, Jun 15, 2026 at 5:33 PM Christian Brauner <brauner@kernel.org> wrote:
> >
> > The idmapped mount tests create a whiteout device,
> > mknod(S_IFCHR, makedev(0, 0)), as a fixture: a whiteout device is the
> > only character device an unprivileged caller may create, since it is
> > exempt from the CAP_MKNOD check. overlayfs reserves a 0:0 character
> > device as its on-disk whiteout marker, so ovl_mknod() returns -EPERM
> > and the fixture cannot be created, failing generic/633, generic/696 and
> > generic/697 on overlayfs.
> >
> > Add an is_overlayfs() helper and skip the whiteout-device fixtures and
> > the checks that depend on them on overlayfs. The makedev(5, 1)
> > "creation must fail" probes are unaffected and keep running. No-op on
> > every other filesystem.
>
> I have no strong objection to this patch but there was actually a request to
> support makedev(0, 0) in overlayfs for creating overlayfs on an overlayfs root,
> so perhaps it would be better to probe for makedev(0, 0) by fs owner instead
> of the is_overlayfs() check.
Where do we stand on this?
next prev parent reply other threads:[~2026-07-10 5:34 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-15 15:33 [PATCH 0/2] Support overlayfs in the idmapped mount tests Christian Brauner
2026-06-15 15:33 ` [PATCH 1/2] src/vfs: probe O_TMPFILE support on the base mount in the idmapped tests Christian Brauner
2026-06-15 17:53 ` Amir Goldstein
2026-07-10 5:34 ` Christoph Hellwig
2026-06-15 15:33 ` [PATCH 2/2] src/vfs: skip whiteout-device fixtures on overlayfs Christian Brauner
2026-06-15 18:03 ` Amir Goldstein
2026-07-10 5:34 ` Christoph Hellwig [this message]
2026-07-10 5:33 ` [PATCH 0/2] Support overlayfs in the idmapped mount tests Christoph Hellwig
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