btrfs_get_workspace
case BTRFS_COMPRESS_NONE: return btrfs_get_workspace(fs_info, type, level);
case BTRFS_COMPRESS_LZO: return btrfs_get_workspace(fs_info, type, level);
struct list_head *btrfs_get_workspace(struct btrfs_fs_info *fs_info, int type, int level);
struct list_head *ws = btrfs_get_workspace(fs_info, BTRFS_COMPRESS_ZLIB, level);