unregister_sysrq_key
unregister_sysrq_key('b', __sysrq_reboot_op);
unregister_sysrq_key('v', &drm_client_sysrq_restore_op);
EXPORT_SYMBOL(unregister_sysrq_key);
int unregister_sysrq_key(u8 key, const struct sysrq_key_op *op);
unregister_sysrq_key('g', &sysrq_dbg_op);