Implement SparkOS MVP: init system, build infrastructure, and rootfs

Co-authored-by: johndoe6345789 <224850594+johndoe6345789@users.noreply.github.com>

src/init.c

@@ -0,0 +1,99 @@
+/*
+ * SparkOS Init - Minimal init system for SparkOS
+ * This is the first process that runs after the kernel boots
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/wait.h>
+#include <sys/reboot.h>
+#include <signal.h>
+#include <errno.h>
+#include <string.h>
+
+#define INIT_PATH "/sbin/init"
+
+static void signal_handler(int sig) {
+    if (sig == SIGCHLD) {
+        // Reap zombie processes
+        while (waitpid(-1, NULL, WNOHANG) > 0);
+    }
+}
+
+static void spawn_shell() {
+    pid_t pid = fork();
+    
+    if (pid < 0) {
+        perror("fork failed");
+        return;
+    }
+    
+    if (pid == 0) {
+        // Child process - exec shell
+        char *argv[] = {"/bin/bash", "--login", NULL};
+        char *envp[] = {
+            "HOME=/root",
+            "PATH=/bin:/sbin:/usr/bin:/usr/sbin",
+            "TERM=linux",
+            "PS1=SparkOS# ",
+            NULL
+        };
+        
+        execve("/bin/bash", argv, envp);
+        
+        // If bash fails, try sh
+        char *sh_argv[] = {"/bin/sh", NULL};
+        execve("/bin/sh", sh_argv, envp);
+        
+        perror("failed to exec shell");
+        exit(1);
+    }
+    
+    // Parent process - wait for shell to exit
+    int status;
+    waitpid(pid, &status, 0);
+}
+
+int main(int argc, char *argv[]) {
+    printf("SparkOS Init System Starting...\n");
+    
+    // Make sure we're PID 1
+    if (getpid() != 1) {
+        fprintf(stderr, "init must be run as PID 1\n");
+        return 1;
+    }
+    
+    // Set up signal handlers
+    signal(SIGCHLD, signal_handler);
+    
+    // Mount essential filesystems
+    printf("Mounting essential filesystems...\n");
+    if (system("mount -t proc proc /proc 2>/dev/null") != 0) {
+        fprintf(stderr, "Warning: Failed to mount /proc\n");
+    }
+    if (system("mount -t sysfs sys /sys 2>/dev/null") != 0) {
+        fprintf(stderr, "Warning: Failed to mount /sys\n");
+    }
+    if (system("mount -t devtmpfs dev /dev 2>/dev/null") != 0) {
+        fprintf(stderr, "Warning: Failed to mount /dev\n");
+    }
+    if (system("mount -t tmpfs tmpfs /tmp 2>/dev/null") != 0) {
+        fprintf(stderr, "Warning: Failed to mount /tmp\n");
+    }
+    
+    printf("Starting shell...\n");
+    printf("Welcome to SparkOS!\n");
+    printf("===================\n\n");
+    
+    // Main loop - keep respawning shell
+    while (1) {
+        spawn_shell();
+        
+        // If shell exits, ask if user wants to reboot
+        printf("\nShell exited. Press Ctrl+Alt+Del to reboot or wait for new shell...\n");
+        sleep(2);
+    }
+    
+    return 0;
+}