[patch v3 22/23] btrfs: Factor out tree->ops->merge_bio_hook call

[jeffm@suse.com]

 In submit_extent_page, there's a visually noisy if statement that, in
 the midst of other conditions, does the tree dependency for tree->ops
 and tree->ops->merge_bio_hook before calling it, and then another
 condition afterwards. If an error is returned from merge_bio_hook,
 there's no way to catch it. It's considered a routine "1" return
 value instead of a failure.

 This patch factors out the dependency check into a new local merge_bio
 routine and BUG's on an error. The if statement is less noisy as a side-
 effect.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
---
 fs/btrfs/extent_io.c |   17 ++++++++++++++---
 fs/btrfs/inode.c     |    5 +++--
 2 files changed, 17 insertions(+), 5 deletions(-)

--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1871,6 +1871,19 @@ static int submit_one_bio(int rw, struct
 	return ret;
 }
 
+static int merge_bio(struct extent_io_tree *tree, struct page *page,
+		     unsigned long offset, size_t size, struct bio *bio,
+		     unsigned long bio_flags)
+{
+	int ret = 0;
+	if (tree->ops && tree->ops->merge_bio_hook)
+		ret = tree->ops->merge_bio_hook(page, offset, size, bio,
+						bio_flags);
+	BUG_ON(ret < 0);
+	return ret;
+
+}
+
 static int submit_extent_page(int rw, struct extent_io_tree *tree,
 			      struct page *page, sector_t sector,
 			      size_t size, unsigned long offset,
@@ -1899,9 +1912,7 @@ static int submit_extent_page(int rw, st
 				sector;
 
 		if (prev_bio_flags != bio_flags || !contig ||
-		    (tree->ops && tree->ops->merge_bio_hook &&
-		     tree->ops->merge_bio_hook(page, offset, page_size, bio,
-					       bio_flags)) ||
+		    merge_bio(tree, page, offset, page_size, bio, bio_flags) ||
 		    bio_add_page(bio, page, page_size, offset) < page_size) {
 			ret = submit_one_bio(rw, bio, mirror_num,
 					     prev_bio_flags);
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1425,10 +1425,11 @@ int btrfs_merge_bio_hook(struct page *pa
 	map_length = length;
 	ret = btrfs_map_block(map_tree, READ, logical,
 			      &map_length, NULL, 0);
-
+	/* Will always return 0 or 1 with map_multi == NULL */
+	BUG_ON(ret < 0);
 	if (map_length < length + size)
 		return 1;
-	return ret;
+	return 0;
 }
 
 /*