Make rawfile.MMsgHdr as nosave.

recvMMsgDispatcher.msgHdrs is not required to be saved across s/r, mark it as
nosave and make changes to re-initialize it after restore.

PiperOrigin-RevId: 673859213

pkg/rawfile/rawfile_unsafe.go

@@ -69,8 +69,6 @@ func AppendIovecFromBytes(iovs []unix.Iovec, bs []byte, max int) []unix.Iovec {
 }
 
 // MMsgHdr represents the mmsg_hdr structure required by recvmmsg() on linux.
-//
-// +stateify savable
 type MMsgHdr struct {
 	Msg unix.Msghdr
 	Len uint32

pkg/tcpip/link/fdbased/BUILD

@@ -15,6 +15,7 @@ go_library(
         "mmap_unsafe.go",
         "packet_dispatchers.go",
         "processors.go",
+        "save_restore.go",
     ],
     visibility = ["//visibility:public"],
     deps = [

pkg/tcpip/link/fdbased/packet_dispatchers.go

@@ -227,7 +227,7 @@ type recvMMsgDispatcher struct {
 	// reference an array of iovecs in the iovecs field defined above.  This
 	// array is passed as the parameter to recvmmsg call to retrieve
 	// potentially more than 1 packet per unix.
-	msgHdrs []rawfile.MMsgHdr
+	msgHdrs []rawfile.MMsgHdr `state:"nosave"`
 
 	// pkts is reused to avoid allocations.
 	pkts stack.PacketBufferList

pkg/tcpip/link/fdbased/save_restore.go

@@ -0,0 +1,26 @@
+// Copyright 2024 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fdbased
+
+import (
+	"context"
+
+	"gvisor.dev/gvisor/pkg/rawfile"
+)
+
+// afterLoad is invoked by stateify.
+func (r *recvMMsgDispatcher) afterLoad(context.Context) {
+	r.msgHdrs = make([]rawfile.MMsgHdr, MaxMsgsPerRecv)
+}