relnote: Avoid redundant recvmmsg when the previous recvmmsg returned

net/tools/quic/quic_packet_reader.cc

 // Copyright 2015 The Chromium 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 "net/tools/quic/quic_packet_reader.h"
 
 #include <errno.h>
 #ifndef __APPLE__
 // This is a GNU header that is not present in /usr/include on MacOS
 #include <features.h>
 #endif
 #include <string.h>
 #include <sys/epoll.h>
 
 #include "base/logging.h"
 #include "net/base/ip_endpoint.h"
+#include "net/quic/quic_flags.h"
 #include "net/tools/quic/quic_dispatcher.h"
 #include "net/tools/quic/quic_socket_utils.h"
 
 #define MMSG_MORE 0
 
 #ifndef SO_RXQ_OVFL
 #define SO_RXQ_OVFL 40
 #endif
 
 namespace net {
@@ skipping 69 matching lines @@
                                mmsg_hdr_[i].msg_len, false);
     IPEndPoint server_address(server_ip, port);
     processor->ProcessPacket(server_address, client_address, packet);
   }
 
   if (packets_dropped != nullptr) {
     QuicSocketUtils::GetOverflowFromMsghdr(&mmsg_hdr_[0].msg_hdr,
                                            packets_dropped);
   }
 
-  return true;
+  if (FLAGS_quic_read_packets_full_recvmmsg) {
+    // We may not have read all of the packets available on the socket.
+    return packets_read == kNumPacketsPerReadMmsgCall;
+  } else {
+    return true;
+  }
 #else
   LOG(FATAL) << "Unsupported";
   return false;
 #endif
 }
 
 /* static */
 bool QuicPacketReader::ReadAndDispatchSinglePacket(
     int fd,
     int port,
@@ skipping 17 matching lines @@
   processor->ProcessPacket(server_address, client_address, packet);
 
   // The socket read was successful, so return true even if packet dispatch
   // failed.
   return true;
 }
 
 }  // namespace tools
 
 }  // namespace net