init.go

// +build linux
package main

import (
	"log"
	"time"
	"syscall"
	"errors"
	"os"
	"os/exec"
)

func nuke(path string) error {
	f, err := os.Open(path)
	defer f.Close()
	if err != nil {
		return err
	}
	fi, err := f.Stat()
	if err != nil {
		return err
	}
	dev := fi.Sys().(*syscall.Stat_t).Dev
	
	if fi.IsDir() == false {
		return errors.New("not a diectory")
	}
	
	ents, err := f.Readdir(0)
	if err != nil {
		return err
	}
	for _, e := range ents {
		st := e.Sys().(*syscall.Stat_t)
	
		// skip mount points
		if st.Dev != dev {
			continue
		}
		
		if e.IsDir() {
			err = nuke(path + string(os.PathSeparator) + e.Name())
			if err != nil {
				return err
			}
		}
		os.Remove(path + string(os.PathSeparator) + e.Name())
	}
	return nil
}

var shareUrl = os.Getenv("camliroot")
var mountPoint = "/root"

func must(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

func main() {
	log.Println("init starting")
	
	must(syscall.Mount("devtmpfs", "/dev", "devtmpfs", 0, ""))
	must(syscall.Mount("procfs", "/proc", "proc", 0, ""))
	must(syscall.Mount("tmpfs", "/tmp", "tmpfs", 0, ""))
	
	log.Println("mounting camlifs")
	c := exec.Cmd{
		Path: "/bin/cammount",
		Args: []string{"cammount", mountPoint, shareUrl},
		Env: []string{"PATH=/bin"},
	}
	must(c.Start())
	time.Sleep(time.Second * 5)
	
	must(syscall.Mount("devtmpfs", "/root/dev", "devtmpfs", 0, ""))
	must(syscall.Mount("procfs", "/root/proc", "proc", 0, ""))
	must(syscall.Mount("sysfs", "/root/sys", "sysfs", 0, ""))
	must(syscall.Mount("tmpfs", "/root/run", "tmpfs", 0, ""))
	
	log.Println("switching root")
	
	// From here more or less the same idea as run-init.c
	must(os.Chdir("/root"))

	must(syscall.Mount(".", "/", "", syscall.MS_MOVE, ""))
	must(syscall.Chroot("."))
	must(os.Chdir("/"))
	
	console, err := syscall.Open("/dev/console", syscall.O_RDWR, 0777)
	if err != nil {
		log.Println(err)
	}
	syscall.Dup2(console, 0)
	syscall.Dup2(console, 1)
	syscall.Dup2(console, 2)
	syscall.Close(console)
	
	err = syscall.Exec("/sbin/init", []string{"/sbin/init"}, []string{})
	log.Println("failed to run init:", err)
}