Linuxにおけるreboot

/*
 * Reboot system call: for obvious reasons only root may call it,
 * and even root needs to set up some magic numbers in the registers
 * so that some mistake won't make this reboot the whole machine.
 * You can also set the meaning of the ctrl-alt-del-key here.
 *
 * reboot doesn't sync: do that yourself before calling this.
 */
SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
        void __user *, arg)
{
    struct pid_namespace *pid_ns = task_active_pid_ns(current);
    char buffer[256];
    int ret = 0;

    /* We only trust the superuser with rebooting the system. */
    if (!ns_capable(pid_ns->user_ns, CAP_SYS_BOOT))
        return -EPERM;

    /* For safety, we require "magic" arguments. */
    if (magic1 != LINUX_REBOOT_MAGIC1 ||
            (magic2 != LINUX_REBOOT_MAGIC2 &&
            magic2 != LINUX_REBOOT_MAGIC2A &&
            magic2 != LINUX_REBOOT_MAGIC2B &&
            magic2 != LINUX_REBOOT_MAGIC2C))
        return -EINVAL;

    /*
     * If pid namespaces are enabled and the current task is in a child
     * pid_namespace, the command is handled by reboot_pid_ns() which will
     * call do_exit().
     */
    ret = reboot_pid_ns(pid_ns, cmd);
    if (ret)
        return ret;

    /* Instead of trying to make the power_off code look like
     * halt when pm_power_off is not set do it the easy way.
     */
    if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !kernel_can_power_off())
        cmd = LINUX_REBOOT_CMD_HALT;

    mutex_lock(&system_transition_mutex);
    switch (cmd) {
    case LINUX_REBOOT_CMD_RESTART:
        kernel_restart(NULL);
        break;

    case LINUX_REBOOT_CMD_CAD_ON:
        C_A_D = 1;
        break;

    case LINUX_REBOOT_CMD_CAD_OFF:
        C_A_D = 0;
        break;

    case LINUX_REBOOT_CMD_HALT:
        kernel_halt();
        do_exit(0);

    case LINUX_REBOOT_CMD_POWER_OFF:
        kernel_power_off();
        do_exit(0);
        break;

    case LINUX_REBOOT_CMD_RESTART2:
        ret = strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1);
        if (ret < 0) {
            ret = -EFAULT;
            break;
        }
        buffer[sizeof(buffer) - 1] = '\0';

        kernel_restart(buffer);
        break;

#ifdef CONFIG_KEXEC_CORE
    case LINUX_REBOOT_CMD_KEXEC:
        ret = kernel_kexec();
        break;
#endif

#ifdef CONFIG_HIBERNATION
    case LINUX_REBOOT_CMD_SW_SUSPEND:
        ret = hibernate();
        break;
#endif

    default:
        ret = -EINVAL;
        break;
    }
    mutex_unlock(&system_transition_mutex);
    return ret;
}

#define	LINUX_REBOOT_MAGIC2	672274793
#define	LINUX_REBOOT_MAGIC2A	85072278
#define	LINUX_REBOOT_MAGIC2B	369367448
#define	LINUX_REBOOT_MAGIC2C	537993216