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. > > Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx> > --- > 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. Vivek > > With the "inodes index" feature, on the first time mount, an NFS file > handle of the lower layer root directory, along with the UUID of the lower > -- > 2.25.4 >
