ceph: preserve I_COMPLETE across rename

d_move puts the renamed dentry at the end of d_subdirs, screwing with our
cached dentry directory offsets.  We were just clearing I_COMPLETE to avoid
any possibility of trouble.  However, assigning the renamed dentry an
offset at the end of the directory (to match it's new d_subdirs position)
is sufficient to maintain correct behavior and hold onto I_COMPLETE.

This is especially important for workloads like rsync, which renames files
into place.  Before, we would lose I_COMPLETE and do MDS lookups for each
file.  With this patch we only talk to the MDS on create and rename.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/inode.c

@@ -1030,9 +1030,6 @@ int ceph_fill_trace(struct super_block *sb, struct ceph_mds_request *req,
 			dout("fill_trace doing d_move %p -> %p\n",
 			     req->r_old_dentry, dn);
 
-			/* d_move screws up d_subdirs order */
-			ceph_i_clear(dir, CEPH_I_COMPLETE);
-
 			d_move(req->r_old_dentry, dn);
 			dout(" src %p '%.*s' dst %p '%.*s'\n",
 			     req->r_old_dentry,
@@ -1044,12 +1041,15 @@ int ceph_fill_trace(struct super_block *sb, struct ceph_mds_request *req,
 			   rehashing bug in vfs_rename_dir */
 			ceph_invalidate_dentry_lease(dn);
 
-			/* take overwritten dentry's readdir offset */
-			dout("dn %p gets %p offset %lld (old offset %lld)\n",
-			     req->r_old_dentry, dn, ceph_dentry(dn)->offset,
+			/*
+			 * d_move() puts the renamed dentry at the end of
+			 * d_subdirs.  We need to assign it an appropriate
+			 * directory offset so we can behave when holding
+			 * I_COMPLETE.
+			 */
+			ceph_set_dentry_offset(req->r_old_dentry);
+			dout("dn %p gets new offset %lld\n", req->r_old_dentry, 
 			     ceph_dentry(req->r_old_dentry)->offset);
-			ceph_dentry(req->r_old_dentry)->offset =
-				ceph_dentry(dn)->offset;
 
 			dn = req->r_old_dentry;  /* use old_dentry */
 			in = dn->d_inode;