btrfs_check_nocow_lock
can_nocow = btrfs_check_nocow_lock(inode, start, len, nowait);
if (btrfs_check_nocow_lock(inode, page_start, &write_bytes, false) <= 0)
int btrfs_check_nocow_lock(struct btrfs_inode *inode, loff_t pos,
if (btrfs_check_nocow_lock(inode, block_start, &write_bytes, false) > 0) {