internal/syscall/unix, net: improve interface_aix.go

This commit improves the interface_aix.go file, based on feedbacks about
CL 138724.

To retrieve MTU, ioctl is needed. It's implemented inside
internal/syscall/unix.

Change-Id: Ic583d26b93935a32a5f1eb5a2170b86e80a4a85e
Reviewed-on: https://go-review.googlesource.com/c/142157
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/go/build/deps_test.go

@@ -317,7 +317,7 @@ var pkgDeps = map[string][]string{
 	"net": {
 		"L0", "CGO",
 		"context", "math/rand", "os", "reflect", "sort", "syscall", "time",
-		"internal/nettrace", "internal/poll",
+		"internal/nettrace", "internal/poll", "internal/syscall/unix",
 		"internal/syscall/windows", "internal/singleflight", "internal/race",
 		"golang_org/x/net/dns/dnsmessage", "golang_org/x/net/lif", "golang_org/x/net/route",
 	},

src/internal/syscall/unix/asm_aix_ppc64.s

@@ -0,0 +1,12 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "textflag.h"
+
+//
+// System calls for aix/ppc64 are implemented in syscall/syscall_aix.go
+//
+
+TEXT ·syscall6(SB),NOSPLIT,$0
+	JMP	syscall·syscall6(SB)

src/internal/syscall/unix/ioctl_aix.go

@@ -0,0 +1,25 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package unix
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+//go:cgo_import_dynamic libc_ioctl ioctl "libc.a/shr_64.o"
+//go:linkname libc_ioctl libc_ioctl
+var libc_ioctl uintptr
+
+// Implemented in syscall/syscall_aix.go.
+func syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err syscall.Errno)
+
+func Ioctl(fd int, cmd int, args uintptr) (err error) {
+	_, _, e1 := syscall6(uintptr(unsafe.Pointer(&libc_ioctl)), 3, uintptr(fd), uintptr(cmd), uintptr(args), 0, 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}

src/net/interface_aix.go

@@ -5,12 +5,12 @@
 package net
 
 import (
-	//"os"
+	"internal/syscall/unix"
 	"syscall"
 	"unsafe"
 )
 
-type RawSockaddrDatalink struct {
+type rawSockaddrDatalink struct {
 	Len    uint8
 	Family uint8
 	Index  uint16
@@ -21,6 +21,11 @@ type RawSockaddrDatalink struct {
 	Data   [120]byte
 }
 
+type ifreq struct {
+	Name [16]uint8
+	Ifru [16]byte
+}
+
 const _KINFO_RT_IFLIST = (0x1 << 8) | 3 | (1 << 30)
 
 const _RTAX_NETMASK = 2
@@ -30,12 +35,12 @@ const _RTAX_MAX = 8
 func getIfList() ([]byte, error) {
 	needed, err := syscall.Getkerninfo(_KINFO_RT_IFLIST, 0, 0, 0)
 	if err != nil {
-		return nil, nil // XXX
+		return nil, err
 	}
 	tab := make([]byte, needed)
 	_, err = syscall.Getkerninfo(_KINFO_RT_IFLIST, uintptr(unsafe.Pointer(&tab[0])), uintptr(unsafe.Pointer(&needed)), 0)
 	if err != nil {
-		return nil, nil // XXX
+		return nil, err
 	}
 	return tab[:needed], nil
 }
@@ -57,12 +62,25 @@ func interfaceTable(ifindex int) ([]Interface, error) {
 		}
 		if ifm.Type == syscall.RTM_IFINFO {
 			if ifindex == 0 || ifindex == int(ifm.Index) {
-				sdl := (*RawSockaddrDatalink)(unsafe.Pointer(&tab[syscall.SizeofIfMsghdr]))
+				sdl := (*rawSockaddrDatalink)(unsafe.Pointer(&tab[syscall.SizeofIfMsghdr]))
 
 				ifi := &Interface{Index: int(ifm.Index), Flags: linkFlags(ifm.Flags)}
 				ifi.Name = string(sdl.Data[:sdl.Nlen])
 				ifi.HardwareAddr = sdl.Data[sdl.Nlen : sdl.Nlen+sdl.Alen]
-				/* XXX MTU? */
+
+				// Retrieve MTU
+				ifr := &ifreq{}
+				copy(ifr.Name[:], ifi.Name)
+				sock, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM, 0)
+				if err != nil {
+					return nil, err
+				}
+				err = unix.Ioctl(sock, syscall.SIOCGIFMTU, uintptr(unsafe.Pointer(ifr)))
+				if err != nil {
+					return nil, err
+				}
+				ifi.MTU = int(ifr.Ifru[0])<<24 | int(ifr.Ifru[1])<<16 | int(ifr.Ifru[2])<<8 | int(ifr.Ifru[3])
+
 				ift = append(ift, *ifi)
 				if ifindex == int(ifm.Index) {
 					break