[RFC][PATCH 00/13] overlayfs stable inodes

[Amir Goldstein <amir73il@gmail.com>]

Overlayfs inodes are considered unstable in several aspects,
because on a copy up event:
1. st_ino can change
2. st_dev can change
3. hardlinks are broken
4. NFS handle would become stale
5. content of read-only file descriptor would become stale

This patch set 'stabilizes' overlayfs inodes w.r.t. st_ino/st_dev
and takes some big steps in the direction of stabilizing hardlinks
and NFS handles.

The full work is available at [1] and includes also an untested
WIP for NFS export support.

This work relies heavily on inode and dentry cache - so long as
the overlayfs dcache is fully populated, hardlinks should never be
broken and NFS handles should never become stale on copy up.

The missing piece of the puzzle is a persistent mapping from
lower entries to upper entries, so that overlay entries could be
reconstructed from their stable (lower) unique identifier.

But the work has merit even without the missing piece, because it
stabilizes st_ino/st_dev and prevents breaking hardlinks in many
use cases.

[1] https://github.com/amir73il/linux/commits/ovl-nfs-export

Amir Goldstein (13):
  ovl: check if all layers are on the same fs
  ovl: redirect dir by file handle on copy up
  ovl: lookup redirect by file handle
  ovl: store file handle of stable inode
  ovl: lookup stable inode by file handle
  ovl: move inode helpers to inode.c
  ovl: create helpers for initializing hashed inode
  ovl: allow hashing non upper inodes
  ovl: inherit overlay inode ino/generation from real inode
  ovl: hash overlay inodes by stable inode
  ovl: fix du --one-file-system on overlay mount
  ovl: constant ino across copy up
  ovl: try to hardlink upper on copy up of lower hardlinks

 fs/overlayfs/Kconfig     |  16 ++++
 fs/overlayfs/copy_up.c   | 130 ++++++++++++++++++++++++++-
 fs/overlayfs/dir.c       |   2 +-
 fs/overlayfs/inode.c     | 106 ++++++++++++++++++++--
 fs/overlayfs/namei.c     | 226 ++++++++++++++++++++++++++++++++++++++++++-----
 fs/overlayfs/overlayfs.h |  40 +++++++--
 fs/overlayfs/ovl_entry.h |   4 +-
 fs/overlayfs/readdir.c   |  85 ++++++++++++++++--
 fs/overlayfs/super.c     |  37 +++++++-
 fs/overlayfs/util.c      |  51 +++++++----
 10 files changed, 633 insertions(+), 64 deletions(-)

-- 
2.7.4