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>

1 files changed, 29 insertions, 0 deletions

diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 0d45a84468d2..260b215852a3 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -176,6 +176,35 @@ void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
 	oe->opaque = opaque;
 }
 
+bool ovl_redirect_dir(struct super_block *sb)
+{
+	struct ovl_fs *ofs = sb->s_fs_info;
+
+	return ofs->config.redirect_dir;
+}
+
+void ovl_clear_redirect_dir(struct super_block *sb)
+{
+	struct ovl_fs *ofs = sb->s_fs_info;
+
+	ofs->config.redirect_dir = false;
+}
+
+const char *ovl_dentry_get_redirect(struct dentry *dentry)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+
+	return oe->redirect;
+}
+
+void ovl_dentry_set_redirect(struct dentry *dentry, const char *redirect)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+
+	kfree(oe->redirect);
+	oe->redirect = redirect;
+}
+
 void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
 {
 	struct ovl_entry *oe = dentry->d_fsdata;