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From: Amir Goldstein <amir73il@gmail.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
	overlayfs <linux-unionfs@vger.kernel.org>
Subject: Re: [PATCH] overlayfs, doc: Do not allow lower layer recreation with redirect_dir enabled
Date: Thu, 9 Jul 2020 17:49:05 +0300	[thread overview]
Message-ID: <CAOQ4uxj2xw8PVk40xx91JemP1JCBkvnW_ndX_wU9ScpipBWaAg@mail.gmail.com> (raw)
In-Reply-To: <20200709141439.GD150543@redhat.com>

On Thu, Jul 9, 2020 at 5:14 PM Vivek Goyal <vgoyal@redhat.com> wrote:
>
> On Thu, Jul 09, 2020 at 10:02:20AM -0400, Vivek Goyal wrote:
> > Currently we seem to support lower layer recreation and re-use with existing
> > upper until and unless "index" or "metadata only copy up" feature is
> > enabled.
> >
> > If redirect_dir feature is enabled then re-creating/modifying lower layers
> > will break things. For example.
> >
> > - mkdir lower lower/foo upper work merged
> > - touch lower/foo/foo-child
> > - mount -t overlay -o lowerdir=lower,upperdir=upper,workdir=work,redirect_dir=on none merged
> > - mv merged/foo merged/bar
> > - ls merged/bar/ (this should list foo-child)
> >
> > - umount merged
> > - mv lower/foo lower/baz
> > - mount -t overlay -o lowerdir=lower,upperdir=upper,workdir=work,redirect_dir=on none merged
> > - ls merged/bar/  (Now foo-child has disappeared)
> >
> > IOW, modifying lower layers did not crash overlay but it resulted in
> > directory contents being lost and that can be unexpected. So don't
> > support lower layer recreation/modification when redirect_dir is enabled
> > at any point of time.

I don't understand why this has to do with redirect_dir.
The same text holds also if you do not do mv merged/foo merged/bar


> >
> > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > ---
> >  Documentation/filesystems/overlayfs.rst | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst
> > index 660dbaf0b9b8..1d1a8da7fdbc 100644
> > --- a/Documentation/filesystems/overlayfs.rst
> > +++ b/Documentation/filesystems/overlayfs.rst
> > @@ -371,8 +371,8 @@ conflict with metacopy=on, and will result in an error.
> >  [*] redirect_dir=follow only conflicts with metacopy=on if upperdir=... is
> >  given.
> >
> > -Sharing and copying layers
> > ---------------------------
> > +Sharing, copying and recreating lower layers
> > +--------------------------------------------
> >
> >  Lower layers may be shared among several overlay mounts and that is indeed
> >  a very common practice.  An overlay mount may use the same lower layer
> > @@ -388,8 +388,12 @@ though it will not result in a crash or deadlock.
> >
> >  Mounting an overlay using an upper layer path, where the upper layer path
> >  was previously used by another mounted overlay in combination with a
> > -different lower layer path, is allowed, unless the "inodes index" feature
> > -or "metadata only copy up" feature is enabled.
> > +different lower layer path, is allowed, unless any of the following features
> > +is enabled at any point of time.
> > +
> > +- inode index
> > +- metadata only copy up
> > +- redirect_dir
>
> I probably should add "nfs_export" to the list as well. Though it is
> implicitly there as enabling nfs export requires to enable index. But
> saying it explicitly is even better.
>

Ok you can mention it but xino is also relevant.
I wonder if we should define "legacy mode" where no options expect for
lowerdir,upperdir,workdir,default_permissions are provided

Thanks,
Amir.

  reply	other threads:[~2020-07-09 14:49 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-09 14:02 [PATCH] overlayfs, doc: Do not allow lower layer recreation with redirect_dir enabled Vivek Goyal
2020-07-09 14:14 ` Vivek Goyal
2020-07-09 14:49   ` Amir Goldstein [this message]
2020-07-09 15:36     ` Vivek Goyal

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