On Thu, Jul 9, 2020 at 5:14 PM Vivek Goyal <vgoyal@xxxxxxxxxx> 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@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. > 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.
