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>

2 files changed, 17 insertions, 5 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index a4a7a18cdd3d..c342e923ea41 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2429,6 +2429,19 @@ static int submit_one_bio(int rw, struct bio *bio, int mirror_num,
         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,
@@ -2457,9 +2470,7 @@ static int submit_extent_page(int rw, struct extent_io_tree *tree,
                                 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);
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;
 }
 
 /*