Btrfs: Fix variables set but not read (bugs found by gcc 4.6)

These are all the cases where a variable is set, but not
read which are really bugs.

- Couple of incorrect error handling fixed.
- One incorrect use of a allocation policy
- Some other things

Still needs more review.

Found by gcc 4.6's new warnings.

[akpm@linux-foundation.org: fix build.  Might have been bitrot]
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/dir-item.c

@@ -427,5 +427,5 @@ int btrfs_delete_one_dir_name(struct btrfs_trans_handle *trans,
 		ret = btrfs_truncate_item(trans, root, path,
 					  item_len - sub_item_len, 1);
 	}
-	return 0;
+	return ret;
 }

fs/btrfs/extent_io.c

@@ -2779,6 +2779,8 @@ int extent_prepare_write(struct extent_io_tree *tree,
 					 NULL, 1,
 					 end_bio_extent_preparewrite, 0,
 					 0, 0);
+			if (ret && !err)
+				err = ret;
 			iocount++;
 			block_start = block_start + iosize;
 		} else {

fs/btrfs/inode.c

@@ -1389,7 +1389,7 @@ int btrfs_merge_bio_hook(struct page *page, unsigned long offset,
 
 	if (map_length < length + size)
 		return 1;
-	return 0;
+	return ret;
 }
 
 /*
@@ -2709,8 +2709,8 @@ static int check_path_shared(struct btrfs_root *root,
 {
 	struct extent_buffer *eb;
 	int level;
-	int ret;
 	u64 refs = 1;
+	int uninitialized_var(ret);
 
 	for (level = 0; level < BTRFS_MAX_LEVEL; level++) {
 		if (!path->nodes[level])
@@ -2723,7 +2723,7 @@ static int check_path_shared(struct btrfs_root *root,
 		if (refs > 1)
 			return 1;
 	}
-	return 0;
+	return ret; /* XXX callers? */
 }
 
 /*

fs/btrfs/relocation.c

@@ -3094,6 +3094,8 @@ static int add_tree_block(struct reloc_control *rc,
 		BUG_ON(item_size != sizeof(struct btrfs_extent_item_v0));
 		ret = get_ref_objectid_v0(rc, path, extent_key,
 					  &ref_owner, NULL);
+		if (ret < 0)
+			return ret;
 		BUG_ON(ref_owner >= BTRFS_MAX_LEVEL);
 		level = (int)ref_owner;
 		/* FIXME: get real generation */
@@ -4218,7 +4220,7 @@ int btrfs_reloc_clone_csums(struct inode *inode, u64 file_pos, u64 len)
 		btrfs_add_ordered_sum(inode, ordered, sums);
 	}
 	btrfs_put_ordered_extent(ordered);
-	return 0;
+	return ret;
 }
 
 void btrfs_reloc_cow_block(struct btrfs_trans_handle *trans,

fs/btrfs/tree-log.c

@@ -2273,7 +2273,7 @@ int btrfs_del_dir_entries_in_log(struct btrfs_trans_handle *trans,
 	}
 	btrfs_end_log_trans(root);
 
-	return 0;
+	return err;
 }
 
 /* see comments for btrfs_del_dir_entries_in_log */