buffer: convert page_zero_new_buffers() to folio_zero_new_buffers()

Most of the callers already have a folio; convert reiserfs_write_end() to
have a folio. Removes a couple of hidden calls to compound_head().

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
Cc: Andreas Gruenbacher <[e-mail]>
Cc: Bob Peterson <[e-mail]>
Cc: Hannes Reinecke <[e-mail]>
Cc: Luis Chamberlain <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

fs/buffer.c

···
 EXPORT_SYMBOL(__block_write_full_folio);
 
 /*
- * If a page has any new buffers, zero them out here, and mark them uptodate
+ * If a folio has any new buffers, zero them out here, and mark them uptodate
  * and dirty so they'll be written out (in order to prevent uninitialised
  * block data from leaking). And clear the new bit.
  */
-void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
+void folio_zero_new_buffers(struct folio *folio, size_t from, size_t to)
 {
-	unsigned int block_start, block_end;
+	size_t block_start, block_end;
 	struct buffer_head *head, *bh;
 
-	BUG_ON(!PageLocked(page));
-	if (!page_has_buffers(page))
+	BUG_ON(!folio_test_locked(folio));
+	head = folio_buffers(folio);
+	if (!head)
 		return;
 
-	bh = head = page_buffers(page);
+	bh = head;
 	block_start = 0;
 	do {
 		block_end = block_start + bh->b_size;
 
 		if (buffer_new(bh)) {
 			if (block_end > from && block_start < to) {
-				if (!PageUptodate(page)) {
-					unsigned start, size;
+				if (!folio_test_uptodate(folio)) {
+					size_t start, xend;
 
 					start = max(from, block_start);
-					size = min(to, block_end) - start;
+					xend = min(to, block_end);
 
-					zero_user(page, start, size);
+					folio_zero_segment(folio, start, xend);
 					set_buffer_uptodate(bh);
 				}
 
···
 		bh = bh->b_this_page;
 	} while (bh != head);
 }
-EXPORT_SYMBOL(page_zero_new_buffers);
+EXPORT_SYMBOL(folio_zero_new_buffers);
 
 static void
 iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
···
 			err = -EIO;
 	}
 	if (unlikely(err))
-		page_zero_new_buffers(&folio->page, from, to);
+		folio_zero_new_buffers(folio, from, to);
 	return err;
 }
 
···
 		if (!folio_test_uptodate(folio))
 			copied = 0;
 
-		page_zero_new_buffers(&folio->page, start+copied, start+len);
+		folio_zero_new_buffers(folio, start+copied, start+len);
 	}
 	flush_dcache_folio(folio);
 

fs/ext4/inode.c

···
 			err = -EIO;
 	}
 	if (unlikely(err)) {
-		page_zero_new_buffers(&folio->page, from, to);
+		folio_zero_new_buffers(folio, from, to);
 	} else if (fscrypt_inode_uses_fs_layer_crypto(inode)) {
 		for (i = 0; i < nr_wait; i++) {
 			int err2;
···
 }
 
 /*
- * This is a private version of page_zero_new_buffers() which doesn't
+ * This is a private version of folio_zero_new_buffers() which doesn't
  * set the buffer to be dirty, since in data=journalled mode we need
  * to call ext4_dirty_journalled_data() instead.
  */

fs/reiserfs/inode.c

···
 			      loff_t pos, unsigned len, unsigned copied,
 			      struct page *page, void *fsdata)
 {
+	struct folio *folio = page_folio(page);
 	struct inode *inode = page->mapping->host;
 	int ret = 0;
 	int update_sd = 0;
···
 
 	start = pos & (PAGE_SIZE - 1);
 	if (unlikely(copied < len)) {
-		if (!PageUptodate(page))
+		if (!folio_test_uptodate(folio))
 			copied = 0;
 
-		page_zero_new_buffers(page, start + copied, start + len);
+		folio_zero_new_buffers(folio, start + copied, start + len);
 	}
-	flush_dcache_page(page);
+	flush_dcache_folio(folio);
 
 	reiserfs_commit_page(inode, page, start, start + copied);
 

include/linux/buffer_head.h

···
 int generic_write_end(struct file *, struct address_space *,
 				loff_t, unsigned, unsigned,
 				struct page *, void *);
-void page_zero_new_buffers(struct page *page, unsigned from, unsigned to);
+void folio_zero_new_buffers(struct folio *folio, size_t from, size_t to);
 void clean_page_buffers(struct page *page);
 int cont_write_begin(struct file *, struct address_space *, loff_t,
 			unsigned, struct page **, void **,