[net (linux)] Don't send OnIPAddressChanged when the AddressMap is first populated.

net/base/address_tracker_linux.cc

 // Copyright (c) 2012 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/base/address_tracker_linux.h"
 
 #include <errno.h>
 
 #include "base/eintr_wrapper.h"
 #include "base/logging.h"
@@ skipping 123 matching lines @@
   rv = HANDLE_EINTR(sendto(sock, &request, request.header.nlmsg_len, 0,
                            reinterpret_cast<struct sockaddr*>(&peer),
                            sizeof(peer)));
   if (rv < 0) {
     PLOG(ERROR) << "Could not send NETLINK request";
     CloseSocket(sock);
     return;
   }
 
   netlink_fd_ = sock;
+
+  // Consume any pending messages to populate the AddressMap, but don't notify.
+  ReadMessages();

[mmenke, 2012/09/04 19:40:16]

Since this is a non-blocking socket, is there a chance that netlink hasn't
answered our first query yet?

[szym, 2012/09/04 20:10:59]

I just tested this and it seems to be working as intended.

I looked through the kernel source code. The entry point is rtnetlink_rcv_msg.
The handler for (PF_UNSPEC, RTM_GETADDR, NLM_F_DUMP) is rtnl_dump_all which
calls through all registered RTM_GETADDR dump handlers. For example:
inet_dump_ifaddr (inet)
int_dump_addr (inet6)
getaddr_dumpit (phonet)
dn_nl_dump_ifaddr (decnet)

So the kernel will create the sk_buff for the whole dump before calling through
netlink_dump_start. netlink_dump cannot fail with anything other than EINVAL,
ENOBUFS, ECONNREFUSED, or EBUSY. It will return EBUSY iff we send another
request while the previous dump is in progress.

So my conclusion is that it will not block until the initial dump is complete.

 }
 
 AddressTrackerLinux::AddressMap AddressTrackerLinux::GetAddressMap() const {
   base::AutoLock lock(lock_);
   return map_;
 }
 
 bool AddressTrackerLinux::ReadMessages() {
   char buffer[4096];
   bool changed = false;
@@ skipping 63 matching lines @@
 void AddressTrackerLinux::OnFileCanReadWithoutBlocking(int fd) {
   DCHECK_EQ(netlink_fd_, fd);
   if (ReadMessages())
     callback_.Run();
 }
 
 void AddressTrackerLinux::OnFileCanWriteWithoutBlocking(int /* fd */) {}
 
 }  // namespace internal
 }  // namespace net