btrfs: rename check_async_write and let it return bool

The 'check_async_write' function is a helper used in
'btrfs_submit_metadata_bio' and it checks if asynchronous writing can be
used for metadata.

Make the function return bool and get rid of the local variable async in
btrfs_submit_metadata_bio storing the result of check_async_write's
tests.

As this is touching all function call sites, also rename it to
should_async_write as this is more in line with the naming we use.
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -917,23 +917,22 @@ static blk_status_t btree_submit_bio_start(struct inode *inode, struct bio *bio,
 	return btree_csum_one_bio(bio);
 }
 
-static int check_async_write(struct btrfs_fs_info *fs_info,
+static bool should_async_write(struct btrfs_fs_info *fs_info,
 			     struct btrfs_inode *bi)
 {
 	if (btrfs_is_zoned(fs_info))
-		return 0;
+		return false;
 	if (atomic_read(&bi->sync_writers))
-		return 0;
+		return false;
 	if (test_bit(BTRFS_FS_CSUM_IMPL_FAST, &fs_info->flags))
-		return 0;
-	return 1;
+		return false;
+	return true;
 }
 
 blk_status_t btrfs_submit_metadata_bio(struct inode *inode, struct bio *bio,
 				       int mirror_num, unsigned long bio_flags)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
-	int async = check_async_write(fs_info, BTRFS_I(inode));
 	blk_status_t ret;
 
 	if (btrfs_op(bio) != BTRFS_MAP_WRITE) {
@@ -946,7 +945,7 @@ blk_status_t btrfs_submit_metadata_bio(struct inode *inode, struct bio *bio,
 		if (ret)
 			goto out_w_error;
 		ret = btrfs_map_bio(fs_info, bio, mirror_num);
-	} else if (!async) {
+	} else if (!should_async_write(fs_info, BTRFS_I(inode))) {
 		ret = btree_csum_one_bio(bio);
 		if (ret)
 			goto out_w_error;