btrfs: Factor out tree->ops->merge_bio_hook call

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>

1 files changed, 3 insertions, 2 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index f0dfd7de0205..ad1e88d25031 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1425,10 +1425,11 @@ int btrfs_merge_bio_hook(struct page *page, unsigned long offset,
         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;
 }
 
 /*