f2fs: support swapfile

This patch adds f2fs_bmap operation to the data address space.
This enables f2fs to support swapfile.
Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/data.c

@@ -698,6 +698,11 @@ static int f2fs_set_data_page_dirty(struct page *page)
 	return 0;
 }
 
+static sector_t f2fs_bmap(struct address_space *mapping, sector_t block)
+{
+	return generic_block_bmap(mapping, block, get_data_block_ro);
+}
+
 const struct address_space_operations f2fs_dblock_aops = {
 	.readpage	= f2fs_read_data_page,
 	.readpages	= f2fs_read_data_pages,
@@ -709,4 +714,5 @@ const struct address_space_operations f2fs_dblock_aops = {
 	.invalidatepage	= f2fs_invalidate_data_page,
 	.releasepage	= f2fs_release_data_page,
 	.direct_IO	= f2fs_direct_IO,
+	.bmap		= f2fs_bmap,
 };