ovl: redirect on rename-dir
Current code returns EXDEV when a directory would need to be copied up to
move. We could copy up the directory tree in this case, but there's
another, simpler solution: point to old lower directory from moved upper
directory.
This is achieved with a "trusted.overlay.redirect" xattr storing the path
relative to the root of the overlay. After such attribute has been set,
the directory can be moved without further actions required.
This is a backward incompatible feature, old kernels won't be able to
correctly mount an overlay containing redirected directories.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt
index 7aeb8e8..fb6f307 100644
--- a/Documentation/filesystems/overlayfs.txt
+++ b/Documentation/filesystems/overlayfs.txt
@@ -130,6 +130,23 @@
Readdir on directories that are not merged is simply handled by the
underlying directory (upper or lower).
+renaming directories
+--------------------
+
+When renaming a directory that is on the lower layer or merged (i.e. the
+directory was not created on the upper layer to start with) overlayfs can
+handle it in two different ways:
+
+1) return EXDEV error: this error is returned by rename(2) when trying to
+ move a file or directory across filesystem boundaries. Hence
+ applications are usually prepared to hande this error (mv(1) for example
+ recursively copies the directory tree). This is the default behavior.
+
+2) If the "redirect_dir" feature is enabled, then the directory will be
+ copied up (but not the contents). Then the "trusted.overlay.redirect"
+ extended attribute is set to the path of the original location from the
+ root of the overlay. Finally the directory is moved to the new
+ location.
Non-directories
---------------
@@ -189,8 +206,8 @@
"break" the link. Changes will not be propagated to other names
referring to the same inode.
-Directory trees are not copied up. If rename(2) is performed on a directory
-which is on the lower layer or is merged, then -EXDEV will be returned.
+Unless "redirect_dir" feature is enabled, rename(2) on a lower or merged
+directory will fail with EXDEV.
Changes to underlying filesystems
---------------------------------