x/sys/unix: support AF_CAN in anyToSockaddr

[skladd]

What version of Go are you using (go version)?

$ go version
go version go1.14.3 linux/amd64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GOARCH="amd64"
GOOS="linux"
CGO_ENABLED="1"

What did you do?

Calling e.g. unix.Recvmsg for a SocketCAN socket (AF_CAN)

Example program

First set up VCAN interface and generate data (via canutils):

$ sudo ip link add dev vcan0 type vcan && sudo ip link set up vcan0
$ cangen vcan0 -g 4 -I 42A -L 2 -D 1234 -v -v

package main

import (
	"fmt"
	"net"

	"golang.org/x/sys/unix"
)

const ifaceName = "vcan0"

func main() {
	var (
		err   error
		iface *net.Interface
		fd    int
	)

	if iface, err = net.InterfaceByName(ifaceName); err != nil {
		panic(err)
	}

	if fd, err = unix.Socket(unix.AF_CAN, unix.SOCK_RAW, unix.CAN_RAW); err != nil {
		panic(err)
	}

	if err = unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_TIMESTAMPNS, 1); err != nil {
		panic(err)
	}

	if err = unix.Bind(fd, &unix.SockaddrCAN{Ifindex: iface.Index}); err != nil {
		panic(err)
	}

	b := make([]byte, 256)
	oob := make([]byte, 256)
	var (
		n, oobn, recvflags int
		from unix.Sockaddr
	)

	// returns error
	n, oobn, recvflags, from, err = unix.Recvmsg(fd, b, oob, 0)

	fmt.Printf("unix.Recvmsg() b: %v, oob: %v, recvflags: %v, from: %v, err: \"%v\"\n", b[:n], oob[:oobn], recvflags, from, err)
}

What did you expect to see?

unix.Recvmsg() b: [42 4 0 0 2 0 0 0 18 52 0 0 0 0 0 0], oob: [32 0 0 0 0 0 0 0 1 0 0 0 29 0 0 0 3 150 58 95 0 0 0 0 178 148 5 0 0 0 0 0], recvflags: 4, from: &{7 0 0 {0 0 [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]}}, err: "<nil>"

What did you see instead?

Method returns error EAFNOSUPPORT "address family not supported by protocol" and from <nil>.

unix.Recvmsg() b: [42 4 0 0 2 0 0 0 18 52 0 0 0 0 0 0], oob: [32 0 0 0 0 0 0 0 1 0 0 0 29 0 0 0 65 150 58 95 0 0 0 0 174 73 9 0 0 0 0 0], recvflags: 4, from: <nil>, err: "address family not supported by protocol"

Comments

Obviously, private unix.anyToSockaddr is called by unix.Recvmsg and returns EAFNOSUPPORT as AF_CAN is not yet supported. SockaddrCAN and AF_CAN support was added via #16188 by @ianlancetaylor and @elliotmr.

Perhaps something like

	case AF_CAN:
		pp := (*RawSockaddrCAN)(unsafe.Pointer(rsa))
		sa := &SockaddrCAN{
			Ifindex: int(pp.Ifindex),
		}
		return sa, nil

in the switch statement in anyToSockaddr() would be sufficient.

[tklauser]

	case AF_CAN:
		pp := (*RawSockaddrCAN)(unsafe.Pointer(rsa))
		sa := &SockaddrCAN{
			Ifindex: int(pp.Ifindex),
		}
		return sa, nil

in the switch statement in anyToSockaddr() would be sufficient.

I think you'll also need to set sa.Addr, other than that it looks like this should be sufficient. Want to send a CL?

[skladd]

SockaddrCAN has no field Addr, but I do not know what has to be done here. In fact, I am not really interested in the returned from socket. Instead, I stumbled on the EAFNOSUPPORT error.

CLA is signed.

[tklauser]

SockaddrCAN has no field Addr, but I do not know what has to be done here.

Right. My mistake, I was looking at RawSockaddrCAN.

I think we need to fill sa.RxID and sa.TxID from pp.Addr, basically reverse what (*SockaddrCAN).sockaddr() does.

[gopherbot]

Change https://golang.org/cl/248977 mentions this issue: unix: extend AF_CAN socket support