ext4: Convert ext4_block_write_begin() to take a folio

All the callers now have a folio, so pass that in and operate on folios.
Removes four calls to compound_head().
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20230324180129.1220691-25-willy@infradead.orgSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/inode.c

@@ -1030,12 +1030,12 @@ int do_journal_get_write_access(handle_t *handle, struct inode *inode,
 }
 
 #ifdef CONFIG_FS_ENCRYPTION
-static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len,
+static int ext4_block_write_begin(struct folio *folio, loff_t pos, unsigned len,
 				  get_block_t *get_block)
 {
 	unsigned from = pos & (PAGE_SIZE - 1);
 	unsigned to = from + len;
-	struct inode *inode = page->mapping->host;
+	struct inode *inode = folio->mapping->host;
 	unsigned block_start, block_end;
 	sector_t block;
 	int err = 0;
@@ -1045,22 +1045,24 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len,
 	int nr_wait = 0;
 	int i;
 
-	BUG_ON(!PageLocked(page));
+	BUG_ON(!folio_test_locked(folio));
 	BUG_ON(from > PAGE_SIZE);
 	BUG_ON(to > PAGE_SIZE);
 	BUG_ON(from > to);
 
-	if (!page_has_buffers(page))
-		create_empty_buffers(page, blocksize, 0);
-	head = page_buffers(page);
+	head = folio_buffers(folio);
+	if (!head) {
+		create_empty_buffers(&folio->page, blocksize, 0);
+		head = folio_buffers(folio);
+	}
 	bbits = ilog2(blocksize);
-	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
+	block = (sector_t)folio->index << (PAGE_SHIFT - bbits);
 
 	for (bh = head, block_start = 0; bh != head || !block_start;
 	    block++, block_start = block_end, bh = bh->b_this_page) {
 		block_end = block_start + blocksize;
 		if (block_end <= from || block_start >= to) {
-			if (PageUptodate(page)) {
+			if (folio_test_uptodate(folio)) {
 				set_buffer_uptodate(bh);
 			}
 			continue;
@@ -1073,19 +1075,20 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len,
 			if (err)
 				break;
 			if (buffer_new(bh)) {
-				if (PageUptodate(page)) {
+				if (folio_test_uptodate(folio)) {
 					clear_buffer_new(bh);
 					set_buffer_uptodate(bh);
 					mark_buffer_dirty(bh);
 					continue;
 				}
 				if (block_end > to || block_start < from)
-					zero_user_segments(page, to, block_end,
+					folio_zero_segments(folio, to,
+							    block_end,
 							    block_start, from);
 				continue;
 			}
 		}
-		if (PageUptodate(page)) {
+		if (folio_test_uptodate(folio)) {
 			set_buffer_uptodate(bh);
 			continue;
 		}
@@ -1105,14 +1108,13 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len,
 			err = -EIO;
 	}
 	if (unlikely(err)) {
-		page_zero_new_buffers(page, from, to);
+		page_zero_new_buffers(&folio->page, from, to);
 	} else if (fscrypt_inode_uses_fs_layer_crypto(inode)) {
 		for (i = 0; i < nr_wait; i++) {
 			int err2;
 
-			err2 = fscrypt_decrypt_pagecache_blocks(page_folio(page),
-								blocksize,
-								bh_offset(wait[i]));
+			err2 = fscrypt_decrypt_pagecache_blocks(folio,
+						blocksize, bh_offset(wait[i]));
 			if (err2) {
 				clear_buffer_uptodate(wait[i]);
 				err = err2;
@@ -1206,11 +1208,10 @@ static int ext4_write_begin(struct file *file, struct address_space *mapping,
 
 #ifdef CONFIG_FS_ENCRYPTION
 	if (ext4_should_dioread_nolock(inode))
-		ret = ext4_block_write_begin(&folio->page, pos, len,
+		ret = ext4_block_write_begin(folio, pos, len,
 					     ext4_get_block_unwritten);
 	else
-		ret = ext4_block_write_begin(&folio->page, pos, len,
-					     ext4_get_block);
+		ret = ext4_block_write_begin(folio, pos, len, ext4_get_block);
 #else
 	if (ext4_should_dioread_nolock(inode))
 		ret = __block_write_begin(&folio->page, pos, len,
@@ -2938,8 +2939,7 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
 	folio_wait_stable(folio);
 
 #ifdef CONFIG_FS_ENCRYPTION
-	ret = ext4_block_write_begin(&folio->page, pos, len,
-				     ext4_da_get_block_prep);
+	ret = ext4_block_write_begin(folio, pos, len, ext4_da_get_block_prep);
 #else
 	ret = __block_write_begin(&folio->page, pos, len, ext4_da_get_block_prep);
 #endif