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Support for XATTR and ACL including several branch attributes to ignore
the copy error around XATTR and ACL.

NFS always sets MS_POSIXACL regardless its mount option 'noacl.'
When MS_POSIXACL is set, generic_permission() calls check_acl() (via
acl_permission_check()) and gets -EOPNOTSUPP because the NFS branch is
mounted as 'noacl.'
In aufs, h_permission() should not call generic_permission() in this
case.
The similar thing happens in coping-up XATTR. vfs_getxattr_alloc()
returns -EOPNOTSUPP.

See also the document in this commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

An enhancement for udba=none if possible.
The condition is same to the 'no ->d_revalidate()' patch series.
Refresh i_op in all cached inodes at the remount-time.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

An enhancement for udba=none if possible.
The condition is same to the 'no ->d_revalidate()' patch series.
In this mode, i_op->getattr() is less important, and the default VFS
handler is enough.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement dir.i_op->lookup() and ->permission().
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

As a part of looking-up, construct a virtual inode.
After branch-management (add/del branches), the inode has to be
refreshed to represent a revealed file.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

This is the hardest test to support UDBA (users' direct branch access).
It uses 'fsnotify' internally.  Detecting UDBA, decrements the
generation of the cached aufs objects.  In the next access to the file,
aufs detects the generation is obsoleted and tries refreshing it.
Eventually aufs cache will be updated to latest status.

The fsnotify is set on the cached dirs on the non-RR branches.
The RR (real readonly) branches will never be modified and it is
unnecessary to set fsnotify for them.

This commit is for the declarations mainly, and the body parts will be
in succeeding commits.

This feature is compiled only when CONFIG_AUFS_HNOTIFY is enabled.
See also the document in this commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

The internal file read/write for copy-up in kernelspace.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Actually prepare the whiteout bases on the adding writable branch.
For details, refer to previous commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

For details, see previous commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>