unix: add more illumos Lifreq helpers

This work is in support of WireGuard/wireguard-go#39

Change-Id: Id205d28935b76b49ec6b29aba0a741659c5c01d7
Reviewed-on: https://go-review.googlesource.com/c/sys/+/345610
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Tobias Klauser <[email protected]>
Trust: Cherry Mui <[email protected]>

Author: nshalman

unix/syscall_illumos.go

@@ -162,6 +162,14 @@ func (l *Lifreq) GetLifruInt() int {
 	return *(*int)(unsafe.Pointer(&l.Lifru[0]))
 }
 
+func (l *Lifreq) SetLifruUint(d uint) {
+	*(*uint)(unsafe.Pointer(&l.Lifru[0])) = d
+}
+
+func (l *Lifreq) GetLifruUint() uint {
+	return *(*uint)(unsafe.Pointer(&l.Lifru[0]))
+}
+
 func IoctlLifreq(fd int, req uint, l *Lifreq) error {
 	return ioctl(fd, req, uintptr(unsafe.Pointer(l)))
 }

unix/syscall_illumos_test.go

@@ -8,6 +8,9 @@
 package unix_test
 
 import (
+	"fmt"
+	"os/exec"
+	"strings"
 	"testing"
 
 	"golang.org/x/sys/unix"
@@ -24,3 +27,43 @@ func TestLifreqSetName(t *testing.T) {
 		t.Errorf(`Lifreq.SetName("tun0") failed: %v`, err)
 	}
 }
+
+func TestLifreqGetMTU(t *testing.T) {
+	// Find links and their MTU using CLI tooling
+	// $ dladm show-link -p -o link,mtu
+	// net0:1500
+	out, err := exec.Command("dladm", "show-link", "-p", "-o", "link,mtu").Output()
+	if err != nil {
+		t.Fatalf("unable to use dladm to find data links: %v", err)
+	}
+	lines := strings.Split(string(out), "\n")
+	tc := make(map[string]string)
+	for _, line := range lines {
+		v := strings.Split(line, ":")
+		if len(v) == 2 {
+			tc[v[0]] = v[1]
+		}
+	}
+	ip_fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, 0)
+	if err != nil {
+		t.Fatalf("could not open udp socket: %v", err)
+	}
+	// SIOCGLIFMTU is negative which confuses the compiler if used inline:
+	// Using "unix.IoctlLifreq(ip_fd, unix.SIOCGLIFMTU, &l)" results in
+	// "constant -1065850502 overflows uint"
+	reqnum := int(unix.SIOCGLIFMTU)
+	var l unix.Lifreq
+	for link, mtu := range tc {
+		err = l.SetName(link)
+		if err != nil {
+			t.Fatalf("Lifreq.SetName(%q) failed: %v", link, err)
+		}
+		if err = unix.IoctlLifreq(ip_fd, uint(reqnum), &l); err != nil {
+			t.Fatalf("unable to SIOCGLIFMTU: %v", err)
+		}
+		m := l.GetLifruUint()
+		if fmt.Sprintf("%d", m) != mtu {
+			t.Errorf("unable to read MTU correctly: expected %s, got %d", mtu, m)
+		}
+	}
+}