ovl: lookup redirects

If a directory has the "trusted.overlay.redirect" xattr, it means that the
value of the xattr should be used to find the underlying directory on the
next lower layer.

The redirect may be relative or absolute.  Absolute redirects begin with a
slash.

A relative redirect means: instead of the current dentry's name use the
value of the redirect to find the directory in the next lower
layer. Relative redirects must not contain a slash.

An absolute redirect means: look up the directory relative to the root of
the overlay using the value of the redirect in the next lower layer.

Redirects work on lower layers as well.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index f6e4d3539a25..e76d9d529e64 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -19,6 +19,7 @@ enum ovl_path_type {
 
 #define OVL_XATTR_PREFIX XATTR_TRUSTED_PREFIX "overlay."
 #define OVL_XATTR_OPAQUE OVL_XATTR_PREFIX "opaque"
+#define OVL_XATTR_REDIRECT OVL_XATTR_PREFIX "redirect"
 
 #define OVL_ISUPPER_MASK 1UL