Unionfs: don't create whiteouts on rightmost branch

If we are unlinking/rmdir'ing an object on the  rightmost branch, there's no
need to  create a whiteout there: this saves on storage space and inodes.
Also, in the (degenerate) case of having only one branch, this really saves
on whiteouts.

CC: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>

diff --git a/fs/unionfs/unlink.c b/fs/unionfs/unlink.c
index f65245dcb4f94264217d4b5991a5ec3e7a506558..423ff36185588ec67dc65082bb083a270d8b7e8b 100644 (file)
--- a/fs/unionfs/unlink.c
+++ b/fs/unionfs/unlink.c
@@ -53,14 +53,23 @@ static int unionfs_unlink_whiteout(struct inode *dir, struct dentry *dentry)
        if (err && !IS_COPYUP_ERR(err))
                goto out;
 
+       /*
+        * We create whiteouts if (1) there was an error unlinking the main
+        * file; (2) there is a lower priority file with the same name
+        * (dbopaque); (3) the branch in which the file is not the last
+        * (rightmost0 branch.  The last rule is an optimization to avoid
+        * creating all those whiteouts if there's no chance they'd be
+        * masking any lower-priority branch, as well as unionfs is used
+        * with only one branch (using only one branch, while odd, is still
+        * possible).
+        */
        if (err) {
                if (dbstart(dentry) == 0)
                        goto out;
                err = create_whiteout(dentry, dbstart(dentry) - 1);
        } else if (dbopaque(dentry) != -1) {
-               /* There is a lower lower-priority file with the same name. */
                err = create_whiteout(dentry, dbopaque(dentry));
-       } else {
+       } else if (dbstart(dentry) < sbend(dentry->d_sb)) {
                err = create_whiteout(dentry, dbstart(dentry));
        }
 
@@ -167,9 +176,17 @@ int unionfs_rmdir(struct inode *dir, struct dentry *dentry)
        err = unionfs_rmdir_first(dir, dentry, namelist);
        dstart = dbstart(dentry);
        dend = dbend(dentry);
-       /* create whiteout */
+       /*
+        * We create a whiteout for the directory if there was an error to
+        * rmdir the first directory entry in the union.  Otherwise, we
+        * create a whiteout only if there is no chance that a lower
+        * priority branch might also have the same named directory.  IOW,
+        * if there is not another same-named directory at a lower priority
+        * branch, then we don't need to create a whiteout for it.
+        */
        if (!err) {
-               err = create_whiteout(dentry, dstart);
+               if (dstart < dend)
+                       err = create_whiteout(dentry, dstart);
        } else {
                int new_err;