[PATCH 0/4] Support nested overlayfs mounts

[Alexander Larsson <alexl@redhat.com>]

There are cases where you want to use an overlayfs mount as a lowerdir for
another overlayfs mount. For example, if the system rootfs is on overlayfs due
to composefs, or to make it volatile (via tmps), then you cannot currently store
a lowerdir on the rootfs, becasue the inner overlayfs will eat all the whiteouts
and overlay xattrs. This means you can't e.g. store on the rootfs a prepared
container image for use using overlayfs.

This patch series adds support for nesting of overlayfs mounts by escaping the
problematic features on and unescaping them when exposing to the overlayfs user.

This series is also available here:
  https://github.com/alexlarsson/linux/tree/ovl-nesting

And xfstest to test it is available here:
  https://github.com/alexlarsson/xfstests/tree/overlayfs-nesting

Alexander Larsson (4):
  ovl: Add OVL_XATTR_TRUSTED/USER_PREFIX_LEN macros
  ovl: Support escaped overlay.* xattrs
  ovl: Support creation of whiteout files on overlayfs
  ovl: Add documentation on nesting of overlayfs mounts

 Documentation/filesystems/overlayfs.rst | 22 ++++++++++
 fs/overlayfs/dir.c                      | 14 ++++---
 fs/overlayfs/inode.c                    | 31 +++++++++++++--
 fs/overlayfs/namei.c                    | 14 ++++---
 fs/overlayfs/overlayfs.h                | 22 ++++++++++
 fs/overlayfs/readdir.c                  |  7 +++-
 fs/overlayfs/super.c                    | 53 +++++++++++++++++++++++--
 fs/overlayfs/util.c                     | 20 ++++++++++
 8 files changed, 164 insertions(+), 19 deletions(-)

-- 
2.41.0