[PATCH] O_SYNC error handling fix

[Chris Mason <mason@suse.com>]

If we hit errors during generic_osync_inode(), generic_file_buffered_write 
will still return written ? written : status;  This patch ensures the -EIO 
gets back up to userland at all times.

diff -r 7e48cbfbccad mm/filemap.c
--- a/mm/filemap.c	Sat Jan 14 01:12:21 2006 +0800
+++ b/mm/filemap.c	Fri Jan 13 13:48:02 2006 -0500
@@ -2026,7 +2026,6 @@ generic_file_buffered_write(struct kiocb
 		balance_dirty_pages_ratelimited(mapping);
 		cond_resched();
 	} while (count);
-	*ppos = pos;
 
 	if (cached_page)
 		page_cache_release(cached_page);
@@ -2047,10 +2046,24 @@ generic_file_buffered_write(struct kiocb
 	 * to buffered writes (block instantiation inside i_size).  So we sync
 	 * the file data here, to try to honour O_DIRECT expectations.
 	 */
-	if (unlikely(file->f_flags & O_DIRECT) && written)
+	if (unlikely(file->f_flags & O_DIRECT) && status >= 0 && written)
 		status = filemap_write_and_wait(mapping);
 
 	pagevec_lru_add(&lru_pvec);
+
+	/*
+	 * We must let know userspace if something hasn't been written
+	 * correctly. If we got an I/O error it means we got an hardware
+	 * failure, anything can be happening to the on-disk data,
+	 * letting know userspace that a bit of data might have been
+	 * written correctly on disk is a very low priority, compared
+	 * to letting know userspace that some data has _not_ been
+	 * written at all.
+	 */
+	if (unlikely(status == -EIO))
+		return status;
+	*ppos = pos;
+
 	return written ? written : status;
 }
 EXPORT_SYMBOL(generic_file_buffered_write);