iomap: factor out a iomap_last_written_block helper

Split out a pice of logic from iomap_file_buffered_write_punch_delalloc
that is useful for all iomap_end implementations.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

fs/iomap/buffered-io.c

@@ -1280,7 +1280,6 @@ void iomap_file_buffered_write_punch_delalloc(struct inode *inode,
 {
 	loff_t			start_byte;
 	loff_t			end_byte;
-	unsigned int		blocksize = i_blocksize(inode);
 
 	if (iomap->type != IOMAP_DELALLOC)
 		return;
@@ -1289,16 +1288,8 @@ void iomap_file_buffered_write_punch_delalloc(struct inode *inode,
 	if (!(iomap->flags & IOMAP_F_NEW))
 		return;
 
-	/*
-	 * start_byte refers to the first unused block after a short write. If
-	 * nothing was written, round offset down to point at the first block in
-	 * the range.
-	 */
-	if (unlikely(!written))
-		start_byte = round_down(pos, blocksize);
-	else
-		start_byte = round_up(pos + written, blocksize);
-	end_byte = round_up(pos + length, blocksize);
+	start_byte = iomap_last_written_block(inode, pos, written);
+	end_byte = round_up(pos + length, i_blocksize(inode));
 
 	/* Nothing to do if we've written the entire delalloc extent */
 	if (start_byte >= end_byte)

include/linux/iomap.h

@@ -256,6 +256,20 @@ static inline const struct iomap *iomap_iter_srcmap(const struct iomap_iter *i)
 	return &i->iomap;
 }
 
+/*
+ * Return the file offset for the first unchanged block after a short write.
+ *
+ * If nothing was written, round @pos down to point at the first block in
+ * the range, else round up to include the partially written block.
+ */
+static inline loff_t iomap_last_written_block(struct inode *inode, loff_t pos,
+		ssize_t written)
+{
+	if (unlikely(!written))
+		return round_down(pos, i_blocksize(inode));
+	return round_up(pos + written, i_blocksize(inode));
+}
+
 ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
 		const struct iomap_ops *ops, void *private);
 int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops);