Unionfs: branch-management bug-fix to lower mnt counts

When we revalidate opened files, the files may point to a different set of
files on the lower branches: this could happen especially if we insert a new
leftmost branch which happens to have duplicate file names of already-open
files in lower-priority branches.  In this case, update the mnt counts of
the old and new branches which hold the file accordingly.  Without this fix,
the mntcnt of one branch is going to be one too high; and another will be
one too low.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>

diff --git a/fs/unionfs/commonfops.c b/fs/unionfs/commonfops.c
index 18ade2fd76bfb3e808a6c8163a2e9081bf02f0ab..46e5008fbbcb28c4dc7855d80dccf073e7e200da 100644 (file)
--- a/fs/unionfs/commonfops.c
+++ b/fs/unionfs/commonfops.c
@@ -334,6 +334,9 @@ int unionfs_file_revalidate(struct file *file, int willwrite)
         */
        if (!d_deleted(dentry) &&
            (sbgen > fgen || dbstart(dentry) != fbstart(file))) {
+               int orig_brid = /* save orig branch ID */
+                       UNIONFS_F(file)->saved_branch_ids[fbstart(file)];
+
                /* First we throw out the existing files. */
                cleanup_file(file);
 
@@ -360,10 +363,23 @@ int unionfs_file_revalidate(struct file *file, int willwrite)
                        if (err)
                                goto out;
                } else {
+                       int new_brid;
                        /* We only open the highest priority branch. */
                        err = open_highest_file(file, willwrite);
                        if (err)
                                goto out;
+                       new_brid = UNIONFS_F(file)->saved_branch_ids[fbstart(file)];
+                       if (new_brid != orig_brid) {
+                               /*
+                                * If we re-opened the file on a different
+                                * branch than the original one, then update
+                                * the mnt counts of the old and new
+                                * branches accordingly.
+                                */
+                               unionfs_mntget(dentry, bstart); /* new branch */
+                               unionfs_mntput(sb->s_root, /* orig branch */
+                                              branch_id_to_idx(sb, orig_brid));
+                       }
                }
                atomic_set(&UNIONFS_F(file)->generation,
                           atomic_read(&UNIONFS_I(dentry->d_inode)->