Running libvirt using valgrind produced:
Syscall param sendmsg(msg.msg_control) points to uninitialised byte(s)
at ??? (in /lib64/libpthread-2.19.so)
by sendfd (passfd.c:86)
by virNetSocketSendFD (virnetsocket.c:1766)
by virNetServerClientDispatchWrite (virnetserverclient.c:1271)
by virNetServerClientDispatchEvent (virnetserverclient.c:1371)
by virEventPollDispatchHandles (vireventpoll.c:508)
by virEventPollRunOnce (vireventpoll.c:657)
by virEventRunDefaultImpl (virevent.c:308)
by virNetServerRun (virnetserver.c:1139)
by main (libvirtd.c:1491)
Address 0xffefff3f4 is on thread 1's stack
in frame #1, created by sendfd (passfd.c:51)
* lib/passfd.c (sendfd): Reset the msg_controllen of msghdr,
to include just the fd we've initialised, rather than including
the extra space used for alignment.