syscall: add support for FreeBSD 10

This CL tweaks syscall.InterfaceMessage to support FreeBSD 10 and
prior to 10.

See http://svnweb.freebsd.org/base?view=revision&revision=254804.

Fixes #7193.

LGTM=iant
R=golang-codereviews, rsc, minux.ma, gobot, iant
CC=golang-codereviews
https://golang.org/cl/56980043

src/pkg/syscall/route_freebsd.go

@@ -8,14 +8,20 @@ package syscall
 
 import "unsafe"
 
+// See http://www.freebsd.org/doc/en/books/porters-handbook/freebsd-versions.html.
+var freebsdVersion uint32
+
+func init() {
+	freebsdVersion, _ = SysctlUint32("kern.osreldate")
+}
+
 func (any *anyMessage) toRoutingMessage(b []byte) RoutingMessage {
 	switch any.Type {
 	case RTM_ADD, RTM_DELETE, RTM_CHANGE, RTM_GET, RTM_LOSING, RTM_REDIRECT, RTM_MISS, RTM_LOCK, RTM_RESOLVE:
 		p := (*RouteMessage)(unsafe.Pointer(any))
 		return &RouteMessage{Header: p.Header, Data: b[SizeofRtMsghdr:any.Msglen]}
 	case RTM_IFINFO:
-		p := (*InterfaceMessage)(unsafe.Pointer(any))
-		return &InterfaceMessage{Header: p.Header, Data: b[SizeofIfMsghdr:any.Msglen]}
+		return any.parseInterfaceMessage(b)
 	case RTM_IFANNOUNCE:
 		p := (*InterfaceAnnounceMessage)(unsafe.Pointer(any))
 		return &InterfaceAnnounceMessage{Header: p.Header}

src/pkg/syscall/route_freebsd_32bit.go

+// Copyright 2014 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.
+
+// +build freebsd,386 freebsd,arm
+
+package syscall
+
+import "unsafe"
+
+func (any *anyMessage) parseInterfaceMessage(b []byte) *InterfaceMessage {
+	p := (*InterfaceMessage)(unsafe.Pointer(any))
+	// FreeBSD 10 and beyond have a restructured mbuf
+	// packet header view.
+	// See http://svnweb.freebsd.org/base?view=revision&revision=254804.
+	if freebsdVersion >= 1000000 {
+		m := (*ifMsghdr)(unsafe.Pointer(any))
+		p.Header.Data.Hwassist = uint32(m.Data.Hwassist)
+		p.Header.Data.Epoch = m.Data.Epoch
+		p.Header.Data.Lastchange = m.Data.Lastchange
+		return &InterfaceMessage{Header: p.Header, Data: b[sizeofIfMsghdr:any.Msglen]}
+	}
+	return &InterfaceMessage{Header: p.Header, Data: b[SizeofIfMsghdr:any.Msglen]}
+}

src/pkg/syscall/route_freebsd_64bit.go

+// Copyright 2014 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.
+
+// +build freebsd,amd64
+
+package syscall
+
+import "unsafe"
+
+func (any *anyMessage) parseInterfaceMessage(b []byte) *InterfaceMessage {
+	p := (*InterfaceMessage)(unsafe.Pointer(any))
+	return &InterfaceMessage{Header: p.Header, Data: b[SizeofIfMsghdr:any.Msglen]}
+}