fs/buffer: simplify block_read_full_folio() with bh_offset()

When we read over all buffers in a folio we currently use the
buffer index on the folio and blocksize to get the offset. Simplify
this with bh_offset(). This simplifies the loop while making no
functional changes.

Suggested-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20250221223823.1680616-2-mcgrof@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: mcgrof

fs/buffer.c

@@ -2381,7 +2381,6 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block)
 	lblock = div_u64(limit + blocksize - 1, blocksize);
 	bh = head;
 	nr = 0;
-	i = 0;
 
 	do {
 		if (buffer_uptodate(bh))
@@ -2398,7 +2397,7 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block)
 					page_error = true;
 			}
 			if (!buffer_mapped(bh)) {
-				folio_zero_range(folio, i * blocksize,
+				folio_zero_range(folio, bh_offset(bh),
 						blocksize);
 				if (!err)
 					set_buffer_uptodate(bh);
@@ -2412,7 +2411,7 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block)
 				continue;
 		}
 		arr[nr++] = bh;
-	} while (i++, iblock++, (bh = bh->b_this_page) != head);
+	} while (iblock++, (bh = bh->b_this_page) != head);
 
 	if (fully_mapped)
 		folio_set_mappedtodisk(folio);