[net] Adds AddressTrackerLinux which keeps track of interface addresses using rtnetlink.

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"
+#include "net/base/network_change_notifier_linux.h"
+
+namespace net {
+namespace internal {
+
+namespace {
+
+// Retrieves address from NETLINK address message.
+bool GetAddress(const struct nlmsghdr* header, IPAddressNumber* out) {
+  const struct ifaddrmsg* msg =
+      reinterpret_cast<struct ifaddrmsg*>(NLMSG_DATA(header));
+  size_t address_length = 0;
+  switch (msg->ifa_family) {
+    case AF_INET:
+      address_length = kIPv4AddressSize;
+      break;
+    case AF_INET6:
+      address_length = kIPv6AddressSize;
+      break;
+    default:
+      // Unknown family.
+      return false;
+  }
+  unsigned char* address = NULL;
+  unsigned char* local = NULL;
+  const struct rtattr* attr = reinterpret_cast<struct rtattr*>(IFA_RTA(msg));
+  size_t length = IFA_PAYLOAD(header);
+  for (; RTA_OK(attr, length); attr = RTA_NEXT(attr, length)) {
+    switch (attr->rta_type) {
+      case IFA_ADDRESS:
+        local = reinterpret_cast<unsigned char*>(RTA_DATA(attr));

[vandebo (ex-Chrome), 2012/06/29 22:24:29]

you assign local in IFA_ADDRESS and address in IFA_LOCAL.  If this isn't a bug,
it's very confusing.

[szym, 2012/06/30 00:00:57]

Definitely a typo.

+        break;
+      case IFA_LOCAL:
+        address = reinterpret_cast<unsigned char*>(RTA_DATA(attr));
+        break;
+      default:
+        break;
+    }
+  }
+  if (local)

[vandebo (ex-Chrome), 2012/06/29 22:24:29]

A comment about what's going on here would be helpful.  It looks like
http://stackoverflow.com/questions/4678637/what-is-difference-between-ifa-loc...
?

[szym, 2012/06/30 00:00:57]

The behavior here is based on getaddrinfo in glibc (check_pf.c).

Looking at NETLINK implementation in the kernel, the problem is that IPv4
addresses have only the IFA_ADDRESS attribute, while IPv6 have the IFA_LOCAL
attribute.

I'll add a comment.

+    address = local;
+  if (!address)
+    return false;
+  out->assign(address, address + address_length);
+  return true;
+}
+
+void CloseSocket(int fd) {
+  if (HANDLE_EINTR(close(fd)) < 0)
+    PLOG(ERROR) << "Could not close NETLINK socket.";
+}
+
+}  // namespace
+
+AddressTrackerLinux::AddressTrackerLinux(const base::Closure& callback)
+    : callback_(callback), netlink_fd_(-1) {
+  DCHECK(!callback.is_null());
+}
+
+AddressTrackerLinux::~AddressTrackerLinux() {
+  if (netlink_fd_ >= 0)
+    CloseSocket(netlink_fd_);
+}
+
+void AddressTrackerLinux::Init() {
+  int sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+  if (sock < 0) {
+    PLOG(ERROR) << "Could not create NETLINK socket";
+    return;
+  }
+
+  // Request notifications.
+  struct sockaddr_nl addr = {};
+  addr.nl_family = AF_NETLINK;
+  addr.nl_pid = getpid();
+  // TODO(szym): Track RTMGRP_LINK as well for ifi_type, http://crbug.com/113993
+  addr.nl_groups = RTMGRP_IPV4_IFADDR | RTMGRP_IPV6_IFADDR | RTMGRP_NOTIFY;
+  int rv = bind(sock, reinterpret_cast<struct sockaddr*>(&addr), sizeof(addr));
+  if (rv < 0) {
+    PLOG(ERROR) << "Could not bind NETLINK socket";
+    CloseSocket(sock);
+    return;
+  }
+
+  // Watch for asynchronous messages.
+  if (SetNonBlocking(sock)) {
+    PLOG(ERROR) << "Could not make NETLINK socket non-blocking";
+    CloseSocket(sock);
+    return;
+  }
+
+  rv = MessageLoopForIO::current()->WatchFileDescriptor(
+      sock, true, MessageLoopForIO::WATCH_READ, &watcher_, this);
+  if (rv < 0) {
+    PLOG(ERROR) << "Could not watch NETLINK socket";
+    CloseSocket(sock);
+    return;
+  }
+
+  // Request dump of addresses.
+  struct sockaddr_nl peer = {};
+  peer.nl_family = AF_NETLINK;
+
+  struct {
+    struct nlmsghdr header;
+    struct rtgenmsg msg;
+  } request = {};
+
+  request.header.nlmsg_len = NLMSG_LENGTH(sizeof(request.msg));
+  request.header.nlmsg_type = RTM_GETADDR;
+  request.header.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
+  request.header.nlmsg_pid = getpid();
+  request.msg.rtgen_family = AF_UNSPEC;
+
+  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;
+}
+
+AddressTrackerLinux::AddressMap AddressTrackerLinux::GetMap() const {
+  base::AutoLock lock(lock_);
+  return map_;
+}
+
+bool AddressTrackerLinux::ReadMessages() {
+  char buf[4096];
+  bool changed = false;
+  for (;;) {
+    int rv = HANDLE_EINTR(recv(netlink_fd_, buf, sizeof(buf), 0));
+    if (rv == 0) {
+      LOG(ERROR) << "Unexpected shutdown of NETLINK socket.";
+      return false;
+    }
+    if (rv < 0) {
+      if ((errno == EAGAIN) || (errno == EWOULDBLOCK))
+        break;
+      PLOG(ERROR) << "Failed to recv from netlink socket";
+      return false;
+    }
+    changed |= HandleMessage(buf, rv);
+  };
+  return changed;
+}
+
+bool AddressTrackerLinux::HandleMessage(char* buf, size_t len) {
+  DCHECK(buf);
+  bool changed = false;
+  for (const struct nlmsghdr* header = reinterpret_cast<struct nlmsghdr*>(buf);
+       NLMSG_OK(header, len); header = NLMSG_NEXT(header, len)) {
+    switch (header->nlmsg_type) {
+      case NLMSG_DONE:
+        return changed;
+      case NLMSG_ERROR:
+        LOG(ERROR) << "Unexpected netlink error.";
+        return changed;
+      case RTM_NEWADDR: {
+        IPAddressNumber address;
+        if (GetAddress(header, &address)) {
+          base::AutoLock lock(lock_);
+          const struct ifaddrmsg* msg =
+              reinterpret_cast<struct ifaddrmsg*>(NLMSG_DATA(header));
+          // Only indicate change if the address is new or ifaddrmsg info has
+          // changed.
+          AddressMap::iterator it = map_.find(address);
+          if (it == map_.end()) {
+            map_.insert(it, std::make_pair(address, *msg));
+            changed = true;
+          } else if (memcmp(&it->second, msg, sizeof(*msg))) {

[vandebo (ex-Chrome), 2012/06/29 22:24:29]

Why do we require that the struct ifaddrmsg be identical?  A comment would be
useful.

[szym, 2012/06/30 00:00:57]

We require that something in ifaddrmsg changes before we signal
OnIPAddressChanged. The reason for this behavior is that the future consumer of
GetAddressMap (old GetMap), AddressSorter (RFC3484), will need to re-fetch the
AddressMap when ifaddrmsg changes. Currently, it only needs 2 of the ifaddrmsg
members, but I think simplicity is preferred here.

+            it->second = *msg;
+            changed = true;
+          }
+        }
+      } break;
+      case RTM_DELADDR: {
+        IPAddressNumber address;
+        if (GetAddress(header, &address)) {
+          base::AutoLock lock(lock_);
+          if (map_.erase(address))
+            changed = true;
+        }
+      } break;
+      default:
+        break;
+    }
+  }
+  return changed;
+}
+
+void AddressTrackerLinux::OnFileCanReadWithoutBlocking(int fd) {
+  if (ReadMessages())
+    callback_.Run();
+}
+
+void AddressTrackerLinux::OnFileCanWriteWithoutBlocking(int /* fd */) {}
+
+}  // namespace internal
+}  // namespace net