OVL_PATH_PURE_UPPER -> __OVL_PATH_UPPER | __OVL_PATH_PURE
OVL_PATH_UPPER      -> __OVL_PATH_UPPER
OVL_PATH_MERGE      -> __OVL_PATH_UPPER | __OVL_PATH_MERGE
OVL_PATH_LOWER      -> 0

Multiple R/O layers will allow __OVL_PATH_MERGE without __OVL_PATH_UPPER.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Don't make a separate pass for checking whiteouts, since we can do it while
reading the upper directory.

This will make it easier to handle multiple layers.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Check against !OVL_PATH_LOWER instead of OVL_PATH_MERGE.  For a copied up
directory the two are currently equivalent.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Pass dentry into ovl_dir_read_merged() insted of upperpath and lowerpath.
This cleans up callers and paves the way for multi-layer directory reads.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Don't open code lockless_dereference() in ovl_upperdentry_dereference().
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Allow option separator (comma) to be escaped with backslash.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Xattr operations can race with copy up.  This does not matter as long as
we consistently fiter out "trunsted.overlay.opaque" attribute on upper
directories.

Previously we checked parent against OVL_PATH_MERGE.  This is too general,
and prone to race with copy-up.  I.e. we found the parent to be on the
lower layer but ovl_dentry_real() would return the copied-up dentry,
possibly with the "opaque" attribute.

So instead use ovl_path_real() and decide to filter the attributes based on
the actual type of the dentry we'll use.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

ovl_remove_and_whiteout() needs to check if upper dentry exists or not
after having locked upper parent directory.

Previously we used a "type" value computed before locking the upper parent
directory, which is susceptible to racing with copy-up.

There's a similar check in ovl_check_empty_and_clear().  This one is not
actually racy, since copy-up doesn't change the "emptyness" property of a
directory.  Add a comment to this effect, and check the existence of upper
dentry locally to make the code cleaner.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Some distributions carry an "old" format of overlayfs while mainline has a
"new" format.

The distros will possibly want to keep the old overlayfs alongside the new
for compatibility reasons.

To make it possible to differentiate the two versions change the name of
the new one from "overlayfs" to "overlay".
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Reported-by: NSerge Hallyn <serge.hallyn@ubuntu.com>
Cc: Andy Whitcroft <apw@canonical.com>

ovl_cache_put() can be called from ovl_dir_reset() if the cache needs to be
rebuilt.  We did list_del() on the cursor, which results in an Oops on the
poisoned pointer in ovl_seek_cursor().
Reported-by: NJordi Pujol Palomer <jordipujolp@gmail.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Tested-by: NJordi Pujol Palomer <jordipujolp@gmail.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

In an overlay directory that shadows an empty lower directory, say
/mnt/a/empty102, do:

 	touch /mnt/a/empty102/x
 	unlink /mnt/a/empty102/x
 	rmdir /mnt/a/empty102

It's actually harmless, but needs another level of nesting between
I_MUTEX_CHILD and I_MUTEX_NORMAL.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Tested-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

ovl_cache_entry.name is now an array not a pointer, so it makes no sense
test for it being NULL.

Detected by coverity.

From: Miklos Szeredi <mszeredi@suse.cz>
Fixes: 68bf8611 ("overlayfs: make ovl_cache_entry->name an array instead of
+pointer")
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

make sure that
	a) all stores done by opening struct file don't leak past storing
the reference in od->upperfile
	b) the lockless side has read dependency barrier
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

same story...
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

no sense having it a pointer - all instances have it pointing to
local variable in the same stack frame
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

just use it to serialize the assignment
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Add a simple read-only counter to super_block that indicates how deep this
is in the stack of filesystems.  Previously ecryptfs was the only stackable
filesystem and it explicitly disallowed multiple layers of itself.

Overlayfs, however, can be stacked recursively and also may be stacked
on top of ecryptfs or vice versa.

To limit the kernel stack usage we must limit the depth of the
filesystem stack.  Initially the limit is set to 2.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

This is useful because of the stacking nature of overlayfs.  Users like to
find out (via /proc/mounts) which lower/upper directory were used at mount
time.

AV: even failing ovl_parse_opt() could've done some kstrdup()
AV: failure of ovl_alloc_entry() should end up with ENOMEM, not EINVAL
Signed-off-by: NErez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Add support for statfs to the overlayfs filesystem.  As the upper layer
is the target of all write operations assume that the space in that
filesystem is the space in the overlayfs.  There will be some inaccuracy as
overwriting a file will copy it up and consume space we were not expecting,
but it is better than nothing.

Use the upper layer dentry and mount from the overlayfs root inode,
passing the statfs call to that filesystem.
Signed-off-by: NAndy Whitcroft <apw@canonical.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Overlayfs allows one, usually read-write, directory tree to be
overlaid onto another, read-only directory tree.  All modifications
go to the upper, writable layer.

This type of mechanism is most often used for live CDs but there's a
wide variety of other uses.

The implementation differs from other "union filesystem"
implementations in that after a file is opened all operations go
directly to the underlying, lower or upper, filesystems.  This
simplifies the implementation and allows native performance in these
cases.

The dentry tree is duplicated from the underlying filesystems, this
enables fast cached lookups without adding special support into the
VFS.  This uses slightly more memory than union mounts, but dentries
are relatively small.

Currently inodes are duplicated as well, but it is a possible
optimization to share inodes for non-directories.

Opening non directories results in the open forwarded to the
underlying filesystem.  This makes the behavior very similar to union
mounts (with the same limitations vs. fchmod/fchown on O_RDONLY file
descriptors).

Usage:

  mount -t overlayfs overlayfs -olowerdir=/lower,upperdir=/upper/upper,workdir=/upper/work /overlay

The following cotributions have been folded into this patch:

Neil Brown <neilb@suse.de>:
 - minimal remount support
 - use correct seek function for directories
 - initialise is_real before use
 - rename ovl_fill_cache to ovl_dir_read

Felix Fietkau <nbd@openwrt.org>:
 - fix a deadlock in ovl_dir_read_merged
 - fix a deadlock in ovl_remove_whiteouts

Erez Zadok <ezk@fsl.cs.sunysb.edu>
 - fix cleanup after WARN_ON

Sedat Dilek <sedat.dilek@googlemail.com>
 - fix up permission to confirm to new API

Robin Dong <hao.bigrat@gmail.com>
 - fix possible leak in ovl_new_inode
 - create new inode in ovl_link

Andy Whitcroft <apw@canonical.com>
 - switch to __inode_permission()
 - copy up i_uid/i_gid from the underlying inode

AV:
 - ovl_copy_up_locked() - dput(ERR_PTR(...)) on two failure exits
 - ovl_clear_empty() - one failure exit forgetting to do unlock_rename(),
   lack of check for udir being the parent of upper, dropping and regaining
   the lock on udir (which would require _another_ check for parent being
   right).
 - bogus d_drop() in copyup and rename [fix from your mail]
 - copyup/remove and copyup/rename races [fix from your mail]
 - ovl_dir_fsync() leaving ERR_PTR() in ->realfile
 - ovl_entry_free() is pointless - it's just a kfree_rcu()
 - fold ovl_do_lookup() into ovl_lookup()
 - manually assigning ->d_op is wrong.  Just use ->s_d_op.
 [patches picked from Miklos]:
 * copyup/remove and copyup/rename races
 * bogus d_drop() in copyup and rename

Also thanks to the following people for testing and reporting bugs:

  Jordi Pujol <jordipujolp@gmail.com>
  Andy Whitcroft <apw@canonical.com>
  Michal Suchanek <hramrach@centrum.cz>
  Felix Fietkau <nbd@openwrt.org>
  Erez Zadok <ezk@fsl.cs.sunysb.edu>
  Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>