universalisos/guests/linux-aarch64/initramfs/init.c

/*
 * Minimal /init for UniversalisOS initramfs.
 *
 * This is the first userspace program executed by Linux after mounting
 * the rootfs. It demonstrates that the hypervisor can boot a real Linux
 * kernel to userspace via virtio-blk.
 *
 * Features:
 *   - Mounts /proc, /sys, /dev (tmpfs)
 *   - Prints system information from /proc/cpuinfo
 *   - Runs a minimal shell loop (echo + wait)
 *   - Demonstrates the full hypervisor -> Linux -> userspace path
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <sys/reboot.h>
#include <linux/reboot.h>

#define BANNER \
    "\r\n" \
    "============================================\r\n" \
    " UniversalisOS Linux Guest Boot Successful!\r\n" \
    "============================================\r\n" \
    "\r\n"

static void mount_proc(void) {
    mkdir("/proc", 0755);
    if (mount("proc", "/proc", "proc", 0, NULL) == 0) {
        printf("[init] /proc mounted\r\n");
    } else {
        printf("[init] /proc mount failed\r\n");
    }
}

static void mount_sys(void) {
    mkdir("/sys", 0755);
    if (mount("sysfs", "/sys", "sysfs", 0, NULL) == 0) {
        printf("[init] /sys mounted\r\n");
    } else {
        printf("[init] /sys mount failed\r\n");
    }
}

static void mount_dev(void) {
    mkdir("/dev", 0755);
    if (mount("tmpfs", "/dev", "tmpfs", 0, "size=64M") == 0) {
        printf("[init] /dev mounted (tmpfs)\r\n");
    } else {
        printf("[init] /dev mount failed\r\n");
    }
}

static void print_cpuinfo(void) {
    FILE *f = fopen("/proc/cpuinfo", "r");
    if (f) {
        char line[256];
        printf("[init] CPU info:\r\n");
        while (fgets(line, sizeof(line), f)) {
            if (strncmp(line, "Processor", 9) == 0 ||
                strncmp(line, "model name", 10) == 0 ||
                strncmp(line, "CPU implementer", 14) == 0 ||
                strncmp(line, "CPU variant", 10) == 0 ||
                strncmp(line, "BogoMIPS", 8) == 0) {
                printf("  %s", line);
            }
        }
        fclose(f);
    }
}

static void print_uptime(void) {
    FILE *f = fopen("/proc/uptime", "r");
    if (f) {
        double uptime;
        if (fscanf(f, "%lf", &uptime) == 1) {
            printf("[init] System uptime: %.1f seconds\r\n", uptime);
        }
        fclose(f);
    }
}

static void print_memory(void) {
    FILE *f = fopen("/proc/meminfo", "r");
    if (f) {
        char line[256];
        printf("[init] Memory info:\r\n");
        while (fgets(line, sizeof(line), f)) {
            if (strncmp(line, "MemTotal", 8) == 0 ||
                strncmp(line, "MemFree", 7) == 0 ||
                strncmp(line, "MemAvailable", 12) == 0) {
                printf("  %s", line);
            }
        }
        fclose(f);
    }
}

int main(void) {
    printf(BANNER);
    printf("[init] UniversalisOS Linux Guest Init\r\n");
    printf("[init] PID=%d\r\n", getpid());

    /* Mount essential filesystems */
    mount_dev();
    mount_proc();
    mount_sys();

    /* Create basic device nodes */
    mknod("/dev/console", 0600 | S_IFCHR, makedev(5, 1));
    mknod("/dev/null", 0666 | S_IFCHR, makedev(1, 3));
    mknod("/dev/zero", 0666 | S_IFCHR, makedev(1, 5));

    /* Print system information */
    print_cpuinfo();
    print_uptime();
    print_memory();

    /* Print mount info */
    FILE *f = fopen("/proc/mounts", "r");
    if (f) {
        char line[256];
        printf("[init] Mounts:\r\n");
        while (fgets(line, sizeof(line), f)) {
            printf("  %s", line);
        }
        fclose(f);
    }

    printf("\r\n[init] System ready. Entering idle loop.\r\n");
    printf("[init] To shutdown: echo 1 > /proc/sys/kernel/sysrq && echo o > /proc/sysrq-trigger\r\n");

    /* Idle loop — in a real system this would run a shell or service manager */
    while (1) {
        sleep(10);
        printf("[init] heartbeat\r\n");
    }

    return 0;
}