Sync systemd boot next boot with current entry.

sync-systemd-boot-next-boot-with-current.go

package main

import (
	"fmt"
	"io"
	"os"
	"runtime"
	"syscall"
	"unsafe"
)

const (
	GUID            = "4a67b082-0a4c-41cf-b6c7-440b29bb8c4f" // Put your systemd-boot GUID here
	FS_IOC_SETFLAGS = 0x40086602
)

func deleteExisted() error {
	fileName := fmt.Sprintf("/sys/firmware/efi/efivars/LoaderEntryOneShot-%s", GUID)

	file, err := os.OpenFile(fileName, os.O_RDONLY, 0)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}

		return err
	}
	defer file.Close()

	sysconn, err := file.SyscallConn()
	if err != nil {
		return err
	}

	var innerErr error
	err = sysconn.Control(func(fd uintptr) {
		flags := uint32(0)

		_, _, err := syscall.Syscall(syscall.SYS_IOCTL, fd, FS_IOC_SETFLAGS, uintptr(unsafe.Pointer(&flags)))
		if err != 0 {
			innerErr = err
		}

		runtime.KeepAlive(flags)
	})
	if err != nil {
		return err
	}
	if innerErr != nil {
		return innerErr
	}

	return os.Remove(fileName)
}

func main() {
	err := deleteExisted()
	if err != nil {
		panic(err.Error())
	}

	current, err := os.OpenFile(fmt.Sprintf("/sys/firmware/efi/efivars/LoaderEntrySelected-%s", GUID), os.O_RDONLY, 0)
	if err != nil {
		panic(err.Error())
	}
	defer current.Close()

	content, err := io.ReadAll(current)
	if err != nil {
		panic(err.Error())
	}

	content[0] = 0x07

	oneshot, err := os.OpenFile(fmt.Sprintf("/sys/firmware/efi/efivars/LoaderEntryOneShot-%s", GUID), os.O_WRONLY|os.O_CREATE, 0644)
	if err != nil {
		panic(err.Error())
	}
	n, err := oneshot.Write(content)

	println(n, "written")
}