ext4_read_bh_lock
extern int ext4_read_bh_lock(struct buffer_head *bh, blk_opf_t op_flags, bool wait);
ret = ext4_read_bh_lock(bh, REQ_META | REQ_PRIO, true);
ext4_read_bh_lock(bhs[i], REQ_META | REQ_PRIO, false);
ext4_read_bh_lock(bh, 0, false);
err = ext4_read_bh_lock(bh, 0, true);
ret = ext4_read_bh_lock(bh, REQ_META | op_flags, true);