fs: Add helper to clean bdev aliases under a bh and use it

Add a helper function that clears buffer heads from a block device
aliasing passed bh. Use this helper function from filesystems instead of
the original unmap_underlying_metadata() to save some boiler plate code
and also have a better name for the functionalily since it is not
unmapping anything for a *long* time.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/fs/buffer.c b/fs/buffer.c
index f8beca5..912d701 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1821,8 +1821,7 @@ int __block_write_full_page(struct inode *inode, struct page *page,
 			if (buffer_new(bh)) {
 				/* blockdev mappings never come here */
 				clear_buffer_new(bh);
-				unmap_underlying_metadata(bh->b_bdev,
-							bh->b_blocknr);
+				clean_bdev_bh_alias(bh);
 			}
 		}
 		bh = bh->b_this_page;
@@ -2068,8 +2067,7 @@ int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
 			}
 
 			if (buffer_new(bh)) {
-				unmap_underlying_metadata(bh->b_bdev,
-							bh->b_blocknr);
+				clean_bdev_bh_alias(bh);
 				if (PageUptodate(page)) {
 					clear_buffer_new(bh);
 					set_buffer_uptodate(bh);
@@ -2709,7 +2707,7 @@ int nobh_write_begin(struct address_space *mapping,
 		if (!buffer_mapped(bh))
 			is_mapped_to_disk = 0;
 		if (buffer_new(bh))
-			unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
+			clean_bdev_bh_alias(bh);
 		if (PageUptodate(page)) {
 			set_buffer_uptodate(bh);
 			continue;