multi-layer support for overlay filesystem

Here's the latest patchset to support multiple read-only layers for overlayfs. Diffstat is against overlayfs-current branch.

git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git overlayfs-next

I hope to have this included in 3.19.

Please review and test (I can post the full patchset if someone wants that).

Thanks,
Miklos

---
Miklos Szeredi (12):
ovl: check whiteout while reading directory
ovl: make path-type a bitmap
ovl: dont replace opaque dir
ovl: add mutli-layer infrastructure
ovl: helper to iterate layers
ovl: multi-layer readdir
ovl: multi-layer lookup
ovl: allow statfs if no upper layer
ovl: mount: change order of initialization
ovl: improve mount helpers
ovl: make upperdir optional
ovl: support multiple lower layers

---
 Documentation/filesystems/overlayfs.txt |  12 +
 fs/overlayfs/copy_up.c                  |   4 +-
 fs/overlayfs/dir.c                      |  24 +-
 fs/overlayfs/inode.c                    |   9 +-
 fs/overlayfs/overlayfs.h                |  14 +-
 fs/overlayfs/readdir.c                  | 120 +++-----
 fs/overlayfs/super.c                    | 521 ++++++++++++++++++++------------
 7 files changed, 427 insertions(+), 277 deletions(-)