Overlayfs: Wrap accesses to ->d_inode on subordinate filesystems

Convert ->d_inode to d_backing_inode() or d_is_xxx() when it is being used to
access an inode on a subordinate filesystem of an overlay - even if that
subordinate is itself an overlay.

Accesses to an overlay's own inodes should be accessed using d_inode() and
d_really_is_positive/negative().

Signed-off-by: David Howells <dhowells@redhat.com>
5 files changed