Avoid poweroff on SpacemiT Com260

pow.c

// SPDX-License-Identifier: MIT
// gcc -O2 -static -s -o pow.shutdown pow.c
// sudo cp pow /usr/lib/systemd/system-shutdown/pow.shutdown
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <linux/reboot.h>
#include <sys/syscall.h>

static int write_all(int fd, const char *buf, size_t len) {
        size_t off = 0;
        while (off < len) {
                ssize_t n = write(fd, buf + off, len - off);
                if (n < 0) {
                        if (errno == EINTR) continue;
                        return -1;
                }
                off += (size_t)n;
        }
        return 0;
}

int main(int argc, char **argv) {
        const char *msg = "Power off now, or the system will reboot.\n";
        int fd;

        if (argc < 2 || strcmp(argv[1], "poweroff") != 0)
                 return 0;

        fd = open("/dev/console", O_WRONLY | O_CLOEXEC);
        if (fd < 0)
                 return 1;
        for (int i = 0; i < 20; i++) {
                if (write_all(fd, msg, strlen(msg)) != 0) break;
                fsync(fd);
                usleep(500000); // 500 ms
        }
        close(fd);

        sync();
        syscall(SYS_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
                LINUX_REBOOT_CMD_RESTART, NULL);

        return 0;
}