btrfs: Introduce extent_read_full_page_nolock()

We want this for btrfs_extent_same. Basically readpage and friends do their
own extent locking but for the purposes of dedupe, we want to have both
files locked down across a set of readpage operations (so that we can
compare data). Introduce this variant and a flag which can be set for
extent_read_full_page() to indicate that we are already locked.

Partial credit for this patch goes to Gabriel de Perthuis <g2p.code@gmail.com>
as I have included a fix from him to the original patch which avoids a
deadlock on compressed extents.

Signed-off-by: Mark Fasheh <mfasheh@suse.de>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index c450620a333f..3940a0386865 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -29,6 +29,7 @@
  */
 #define EXTENT_BIO_COMPRESSED 1
 #define EXTENT_BIO_TREE_LOG 2
+#define EXTENT_BIO_PARENT_LOCKED 4
 #define EXTENT_BIO_FLAG_SHIFT 16
 
 /* these are bit numbers for test/set bit */
@@ -199,6 +200,8 @@ int unlock_extent_cached(struct extent_io_tree *tree, u64 start, u64 end,
 int try_lock_extent(struct extent_io_tree *tree, u64 start, u64 end);
 int extent_read_full_page(struct extent_io_tree *tree, struct page *page,
                           get_extent_t *get_extent, int mirror_num);
+int extent_read_full_page_nolock(struct extent_io_tree *tree, struct page *page,
+                                 get_extent_t *get_extent, int mirror_num);
 int __init extent_io_init(void);
 void extent_io_exit(void);