[tor-commits] [tor/master] Try using INT_MAX, not SOMAXCONN, to set listen() backlog.

[nickm at torproject.org]

commit a2754d418dffb6188717d5e84d9bea59a2c9853b
Author: Nick Mathewson <nickm at torproject.org>
Date:   Wed Sep 11 13:30:45 2013 -0400

    Try using INT_MAX, not SOMAXCONN, to set listen() backlog.
    
    Fall back to SOMAXCONN if INT_MAX doesn't work.
    
    We'd like to do this because the actual maximum is overrideable by the
    kernel, and the value in the header file might not be right at all.
    All implementations I can find out about claim that this is supported.
    
    Fix for 9716; bugfix on every Tor.
---
 changes/bug9716     |    4 ++++
 src/or/connection.c |   23 ++++++++++++++++++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/changes/bug9716 b/changes/bug9716
new file mode 100644
index 0000000..5e39077
--- /dev/null
+++ b/changes/bug9716
@@ -0,0 +1,4 @@
+  o Bugfixes (performance):
+    - Set the listen() backlog limit to the largest actually supported
+      on the system, not to the value in a header file. Fixes bug 9716;
+      bugfix on every released Tor.
diff --git a/src/or/connection.c b/src/or/connection.c
index 6e754a0..41946e4 100644
--- a/src/or/connection.c
+++ b/src/or/connection.c
@@ -926,6 +926,27 @@ make_socket_reuseable(tor_socket_t sock)
 #endif
 }
 
+/** Max backlog to pass to listen.  We start at */
+static int listen_limit = INT_MAX;
+
+/* Listen on <b>fd</b> with appropriate backlog. Return as for listen. */
+static int
+tor_listen(tor_socket_t fd)
+{
+  int r;
+
+  if ((r = listen(fd, listen_limit)) < 0) {
+    if (listen_limit == SOMAXCONN)
+      return r;
+    if ((r = listen(fd, SOMAXCONN)) == 0) {
+      listen_limit = SOMAXCONN;
+      log_warn(LD_NET, "Setting listen backlog to INT_MAX connections "
+               "didn't work, but SOMAXCONN did. Lowering backlog limit.");
+    }
+  }
+  return r;
+}
+
 /** Bind a new non-blocking socket listening to the socket described
  * by <b>listensockaddr</b>.
  *
@@ -1009,7 +1030,7 @@ connection_listener_new(const struct sockaddr *listensockaddr,
     }
 
     if (is_tcp) {
-      if (listen(s,SOMAXCONN) < 0) {
+      if (tor_listen(s) < 0) {
         log_warn(LD_NET, "Could not listen on %s:%u: %s", address, usePort,
                  tor_socket_strerror(tor_socket_errno(s)));
         tor_close_socket(s);