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 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
