fs: remove the NULL get_block case in mpage_writepages

No one calls mpage_writepages with a NULL get_block paramter, so remove
support for that case.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

fs/mpage.c

@@ -638,8 +638,6 @@ static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
  * @mapping: address space structure to write
  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
  * @get_block: the filesystem's block mapper function.
- *             If this is NULL then use a_ops->writepage.  Otherwise, go
- *             direct-to-BIO.
  *
  * This is a library function, which implements the writepages()
  * address_space_operation.
@@ -656,24 +654,16 @@ int
 mpage_writepages(struct address_space *mapping,
 		struct writeback_control *wbc, get_block_t get_block)
 {
+	struct mpage_data mpd = {
+		.get_block	= get_block,
+	};
 	struct blk_plug plug;
 	int ret;
 
 	blk_start_plug(&plug);
-
-	if (!get_block)
-		ret = generic_writepages(mapping, wbc);
-	else {
-		struct mpage_data mpd = {
-			.bio = NULL,
-			.last_block_in_bio = 0,
-			.get_block = get_block,
-		};
-
-		ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
-		if (mpd.bio)
-			mpage_bio_submit(mpd.bio);
-	}
+	ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
+	if (mpd.bio)
+		mpage_bio_submit(mpd.bio);
 	blk_finish_plug(&plug);
 	return ret;
 }