From f20e80ab91d298b9e670171cdac8e25ea612eca2 Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Wed, 4 May 2016 18:06:17 +0200 Subject: [PATCH] sysdeps: increase listen() backlog of AF_UNIX sockets to SOMAXCONN Previously, the listen() backlog was set to an arbitrary 30. This means that if dbus-daemon is overloaded only 30 more connections may be queued by the kernel, before connect() fails with EAGAIN. (Note that EAGAIN != EINPROGRESS -- the latter is what is returned if a connection is queued and being processed for asynchronous sockets; EAGAIN in this case is really an error, that cannot be recovered from). Most software simply sets SOMAXCONN as backlog for AF_UNIX sockets, to allow queuing of as many connections as the kernel allows. SOMAXCONN is 128 on Linux, which is not particularly high, but at least higher than 30. This patch changes dbus-daemon to do the same. I noticed this when flooding dbus-daemon with a lot of connections, where it pretty quickly ceased to respond, much earlier than it really should. Note that the backlog has nothing to do with the number of concurrent connections allowed, it simply controls how many queued, but not accept()ed connections there may be on the listening socket. --- dbus/dbus-sysdeps-unix.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/dbus/dbus-sysdeps-unix.c b/dbus/dbus-sysdeps-unix.c index 6b9e50b..ce8cbf7 100644 --- a/dbus/dbus-sysdeps-unix.c +++ b/dbus/dbus-sysdeps-unix.c @@ -1120,7 +1120,7 @@ _dbus_listen_unix_socket (const char *path, return -1; } - if (listen (listen_fd, 30 /* backlog */) < 0) + if (listen (listen_fd, SOMAXCONN /* backlog */) < 0) { dbus_set_error (error, _dbus_error_from_errno (errno), "Failed to listen on socket \"%s\": %s", -- 2.7.4