Unionfs: introduce two functions to maintain time invariants

A new function unionfs_copy_attr_times to maintain the inode time invariants
as per the Unionfs design (i.e., lower times should never be newer than our
times), as documented in Documentation/filesystems/unionfs/concepts.txt.
The second function, unionfs_copy_attr_all, is the unionfs-specific function
to copy all attributes: it uses the special Unionfs handling of hard-links
(via unionfs_get_nlinks) and it uses the special a/c/mtime handling (via
unionfs_copy_attr_times).  This second function is the special
fanout-version of fsstack_copy_attr_all, which was simplified for
linear-stack stackable file systems.

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

diff --git a/fs/unionfs/fanout.h b/fs/unionfs/fanout.h
index 366c4083ebff6eceafcbf6e6a19661ef164d78cb..4d1a620f75da8a87e1324f86ed1ad42e332ec778 100644 (file)
--- a/fs/unionfs/fanout.h
+++ b/fs/unionfs/fanout.h
@@ -261,4 +261,52 @@ static inline void verify_locked(struct dentry *d)
        BUG_ON(!mutex_is_locked(&UNIONFS_D(d)->lock));
 }
 
+/* copy a/m/ctime from the lower branch with the newest times */
+static inline void unionfs_copy_attr_times(struct inode *upper)
+{
+       int bindex;
+       struct inode *lower;
+
+       if (!upper)
+               return;
+       for (bindex=ibstart(upper); bindex <= ibend(upper); bindex++) {
+               lower = unionfs_lower_inode_idx(upper, bindex);
+               if (!lower)
+                       continue; /* not all lower dir objects may exist */
+               if (timespec_compare(&upper->i_mtime, &lower->i_mtime) < 0)
+                       upper->i_mtime = lower->i_mtime;
+               if (timespec_compare(&upper->i_ctime, &lower->i_ctime) < 0)
+                       upper->i_ctime = lower->i_ctime;
+               if (timespec_compare(&upper->i_atime, &lower->i_atime) < 0)
+                       upper->i_atime = lower->i_atime;
+               /* XXX: should we notify_change on our upper inode? */
+       }
+}
+
+/*
+ * A unionfs/fanout version of fsstack_copy_attr_all.  Uses a
+ * unionfs_get_nlinks to properly calcluate the number of links to a file.
+ * Also, copies the max() of all a/m/ctimes for all lower inodes (which is
+ * important if the lower inode is a directory type)
+ */
+static inline void unionfs_copy_attr_all(struct inode *dest,
+                                        const struct inode *src)
+{
+       dest->i_mode = src->i_mode;
+       dest->i_uid = src->i_uid;
+       dest->i_gid = src->i_gid;
+       dest->i_rdev = src->i_rdev;
+
+       unionfs_copy_attr_times(dest);
+
+       dest->i_blkbits = src->i_blkbits;
+       dest->i_flags = src->i_flags;
+
+       /*
+        * Update the nlinks AFTER updating the above fields, because the
+        * get_links callback may depend on them.
+        */
+       dest->i_nlink = unionfs_get_nlinks(dest);
+}
+
 #endif /* not _FANOUT_H */