linux 4.14 switch boot parition

Question

It's been two years since I modified my raspberry pi 3(model B).

In linux 4.1 I usually change the value of /sys/module/bcm2709/parameters/reboot_part to switch OS I want. But now I can't find it on linux 4.14.

Guys on IRC tell me it's no longer exist：

[17:24] Guest21160: it no longer exists. You can run 'reboot $part_no' instead

After command "reboot -f 5", it still boot from partition 1.

I think reboot command may need re-built, but does anyone know where I can get the source?

Answer 1

OK, First thing is the reboot_part is no longer exist since RPI linux branch 4.8.y.

All the posts are outdated if they told you to change this attributes:

Rebooting into a new OS

Enlaces entre varios sistemas operativos

The answer for current RPI linux is simply use system call function below:

syscall(SYS_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, LINUX_REBOOT_CMD_RESTART2, reboot_part);

Most modern linux init system (upstart, systemd) will implement their reboot command included the SYS_reboot system call.

So you simply can use command "reboot 5" to reboot from partition 5.

If you use busybox or something else that might not include this system call, you can just write your own, or just get a sample code from someone's post:

how to reboot into partition with new firmware but no systemd?

Here is the sample code I copied from the post above, thanks to matthuisman:

#include <linux/reboot.h>
#include <sys/syscall.h>
#include <signal.h>
#include <stdlib.h>

int main(int argc, char *argv[])  {
    char *param = NULL;
    int cmd;

    if(argc == 2) {
        param = argv[1];
        cmd = LINUX_REBOOT_CMD_RESTART2;
    }
    else {
        cmd = LINUX_REBOOT_CMD_RESTART;
    }

    sync();
    system("/etc/init.d/rcK || /etc/init.d/rc 0");

    sync();
    syscall(SYS_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, cmd, param);

    return 0;
}