[PATCHv2 33/41] ext4: make ext4_block_write_begin() aware about huge pages

[Kirill A. Shutemov]

It simply matches changes to __block_write_begin_int().

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 fs/ext4/inode.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index bee21fffbfb9..1c325f62e766 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1079,9 +1079,8 @@ int do_journal_get_write_access(handle_t *handle,
 static int ext4_block_write_begin(struct page *page, 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;
+	unsigned from, to;
+	struct inode *inode = page_mapping(page)->host;
 	unsigned block_start, block_end;
 	sector_t block;
 	int err = 0;
@@ -1090,9 +1089,12 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len,
 	struct buffer_head *bh, *head, *wait[2], **wait_bh = wait;
 	bool decrypt = false;
 
+	page = compound_head(page);
+	from = pos & ~hpage_mask(page);
+	to = from + len;
 	BUG_ON(!PageLocked(page));
-	BUG_ON(from > PAGE_SIZE);
-	BUG_ON(to > PAGE_SIZE);
+	BUG_ON(from > hpage_size(page));
+	BUG_ON(to > hpage_size(page));
 	BUG_ON(from > to);
 
 	if (!page_has_buffers(page))
@@ -1127,9 +1129,15 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len,
 					mark_buffer_dirty(bh);
 					continue;
 				}
-				if (block_end > to || block_start < from)
-					zero_user_segments(page, to, block_end,
-							   block_start, from);
+				if (block_end > to || block_start < from) {
+					BUG_ON(to - from  > PAGE_SIZE);
+					zero_user_segments(page +
+							block_start / PAGE_SIZE,
+							to % PAGE_SIZE,
+							(block_start % PAGE_SIZE) + blocksize,
+							block_start % PAGE_SIZE,
+							from % PAGE_SIZE);
+				}
 				continue;
 			}
 		}
-- 
2.8.1