[XFS] Write at EOF may not update filesize correctly.

The recent fix for preventing NULL files from being left around does not
update the file size corectly in all cases. The missing case is a write
extending the file that does not need to allocate a block.

In that case we used a read mapping of the extent which forced the use of
the read I/O completion handler instead of the write I/O completion
handle. Hence the file size was not updated on I/O completion.

SGI-PV: 965068
SGI-Modid: xfs-linux-melb:xfs-kern:28657a
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Nathan Scott <nscott@aconex.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>

fs/xfs/linux-2.6/xfs_aops.c

@@ -701,7 +701,7 @@ xfs_is_delayed_page(
 			else if (buffer_delay(bh))
 				acceptable = (type == IOMAP_DELAY);
 			else if (buffer_dirty(bh) && buffer_mapped(bh))
-				acceptable = (type == 0);
+				acceptable = (type == IOMAP_NEW);
 			else
 				break;
 		} while ((bh = bh->b_this_page) != head);
@@ -810,7 +810,7 @@ xfs_convert_page(
 			page_dirty--;
 			count++;
 		} else {
-			type = 0;
+			type = IOMAP_NEW;
 			if (buffer_mapped(bh) && all_bh && startio) {
 				lock_buffer(bh);
 				xfs_add_to_ioend(inode, bh, offset,
@@ -968,8 +968,8 @@ xfs_page_state_convert(
 
 	bh = head = page_buffers(page);
 	offset = page_offset(page);
-	flags = -1;
-	type = IOMAP_READ;
+	flags = BMAPI_READ;
+	type = IOMAP_NEW;
 
 	/* TODO: cleanup count and page_dirty */
 
@@ -1055,7 +1055,7 @@ xfs_page_state_convert(
 			 * That means it must already have extents allocated
 			 * underneath it. Map the extent by reading it.
 			 */
-			if (!iomap_valid || type != IOMAP_READ) {
+			if (!iomap_valid || flags != BMAPI_READ) {
 				flags = BMAPI_READ;
 				size = xfs_probe_cluster(inode, page, bh,
 								head, 1);
@@ -1066,7 +1066,15 @@ xfs_page_state_convert(
 				iomap_valid = xfs_iomap_valid(&iomap, offset);
 			}
 
-			type = IOMAP_READ;
+			/*
+			 * We set the type to IOMAP_NEW in case we are doing a
+			 * small write at EOF that is extending the file but
+			 * without needing an allocation. We need to update the
+			 * file size on I/O completion in this case so it is
+			 * the same case as having just allocated a new extent
+			 * that we are writing into for the first time.
+			 */
+			type = IOMAP_NEW;
 			if (!test_and_set_bit(BH_Lock, &bh->b_state)) {
 				ASSERT(buffer_mapped(bh));
 				if (iomap_valid)