ifrename.go

package main

// +build freebsd,amd64

import (
        "C"
        "fmt"
        "os"
        "syscall"
        "unsafe"
)

func ioctl(fd, request uintptr, argp unsafe.Pointer) error {
        if _, _, e := syscall.Syscall6(syscall.SYS_IOCTL, fd, request, uintptr(argp), 0, 0, 0); e != 0 {
                return e
        }
        return nil
}

type ifrenameArg struct {
        name [syscall.IFNAMSIZ]byte
        data uintptr
}

func renameInterface(from, to string) error {
        s, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM, 0)
        if err != nil {
                return err
        }
        defer func() {
                syscall.Close(s)
        }()

        var ifr ifrenameArg
        copy(ifr.name[:], []byte(from))
        ifr.data = uintptr(unsafe.Pointer(C.CString(to)))

        return ioctl(uintptr(s), syscall.SIOCSIFNAME, unsafe.Pointer(&ifr))
}

func main() {
        if len(os.Args) < 3 {
                fmt.Fprintf(os.Stderr, "%s <from> <to>\n", os.Args[0])
                os.Exit(1)
        }
        if err := renameInterface(os.Args[1], os.Args[2]); err != nil {
                fmt.Fprintf(os.Stderr, "ifrename: %s\n", err)
                os.Exit(1)
        }
        os.Exit(0)
}