JFS: Slightly relax allocation group reservation

Minor change that got missed in the last changeset.  If opening a
non-empty file for writing, don't assume we're allocating new space.
If the file is grown, we'll take care of it then.

fs/jfs/file.c

@@ -106,8 +106,13 @@ static int jfs_open(struct inode *inode, struct file *file)
 	 * We attempt to allow only one "active" file open per aggregate
 	 * group.  Otherwise, appending to files in parallel can cause
 	 * fragmentation within the files.
+	 *
+	 * If the file is empty, it was probably just created and going
+	 * to be written to.  If it has a size, we'll hold off until the
+	 * file is actually grown.
 	 */
-	if (S_ISREG(inode->i_mode) && file->f_mode & FMODE_WRITE) {
+	if (S_ISREG(inode->i_mode) && file->f_mode & FMODE_WRITE &&
+	    (inode->i_size == 0)) {
 		struct jfs_inode_info *ji = JFS_IP(inode);
 		if (ji->active_ag == -1) {
 			ji->active_ag = ji->agno;