[PATCH 3/6] Btrfs: subpagesize-blocksize: Work with extents aligned to blocksize.

[Chandan Rajendra <chandan@linux.vnet.ibm.com>]

This is a small part of a bigger set of fixes needed to get
subpagesize-blocksize to function properly. This patch is required to get 2k
blocksize writes to work correctly.

Without this patch, In lock_and_cleanup_extent_if_need() two consecutive 2k
block writes that map to first and second 2k parts of a 4k page would result
in the second 2k write to *clear* out the EXTENT_DELALLOC bit of the first 2k
block. Fix this.

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
---
 fs/btrfs/file.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 006af2f..1aa8fae 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1339,18 +1339,21 @@ fail:
 static noinline int
 lock_and_cleanup_extent_if_need(struct inode *inode, struct page **pages,
 				size_t num_pages, loff_t pos,
+				size_t write_bytes,
 				u64 *lockstart, u64 *lockend,
 				struct extent_state **cached_state)
 {
+	struct btrfs_root *root = BTRFS_I(inode)->root;
 	u64 start_pos;
 	u64 last_pos;
 	int i;
 	int ret = 0;
 
-	start_pos = pos & ~((u64)PAGE_CACHE_SIZE - 1);
-	last_pos = start_pos + ((u64)num_pages << PAGE_CACHE_SHIFT) - 1;
+       start_pos = pos & ~((u64)root->sectorsize - 1);
+       last_pos = start_pos
+               + ALIGN(pos + write_bytes - start_pos, root->sectorsize) - 1;
 
-	if (start_pos < inode->i_size) {
+       if (start_pos < inode->i_size) {
 		struct btrfs_ordered_extent *ordered;
 		lock_extent_bits(&BTRFS_I(inode)->io_tree,
 				 start_pos, last_pos, 0, cached_state);
@@ -1536,8 +1539,8 @@ again:
 			break;
 
 		ret = lock_and_cleanup_extent_if_need(inode, pages, num_pages,
-						      pos, &lockstart, &lockend,
-						      &cached_state);
+						pos, write_bytes, &lockstart, &lockend,
+						&cached_state);
 		if (ret < 0) {
 			if (ret == -EAGAIN)
 				goto again;
-- 
1.8.3.1