loop

gistfile1.go

	if *loopId == 0 || *loopId > *loopMax-1 {
		log.Fatalf("invalid loop device number: %d", *loopId)
	}

	loopDevNum := int((*loopId & 0xff) | ((7 & 0xfff) << 8))
	loopDevPath := "/dev/loop" + strconv.Itoa(int(*loopId))

	// ensure requested loop device is unique and read file
	// permissions from existing loop device
	devices, err := ioutil.ReadDir("/dev")
	if err != nil {
		log.Fatal("unable to list system devices")
	}

	// ensure `loopId` is unique and read the file permissions/ownership info
	// of `-loopTemplate` for new device
	var mode, uid, gid uint32
	for _, dev := range devices {
		switch dev.Name() {
		case path.Base(loopDevPath):
			log.Fatal("requested loop device path path must be unique:", loopDevPath)
		case path.Base(*loopTemplate):
			mode = dev.Mode()
			uid = dev.Sys().(*syscall.Stat_t).Uid
			gid = dev.Sys().(*syscall.Stat_t).Gid
	}

	// create loop device
	if err := syscall.Mknod(loopDevPath, syscall.S_IFBLK|mode, loopDevNum)

	// ensure loop device does not already exist
	if _, err := os.Stat(loopDevPath); err == nil {
		log.Fatal("loop device appears to already be present:", loopDevPath)
	}