Bug 581750

Description of problem:
# ls /none
ls: cannot access /none: No such file or directory

Boot up a guest with "..vhost=on,vhostfd=/none.." option, it always causes a segment fault.

Version-Release number of selected component (if applicable):
# rpm -qa |grep qemu
qemu-kvm-0.12.1.2-2.37.el6.x86_64
qemu-img-0.12.1.2-2.37.el6.x86_64
qemu-kvm-tools-0.12.1.2-2.37.el6.x86_64
gpxe-roms-qemu-0.9.7-6.2.el6.noarch
qemu-kvm-debuginfo-0.12.1.2-2.37.el6.x86_64

# uname -a
Linux localhost.localdomain.englab.nay.redhat.com 2.6.32-19.el6.x86_64 #1 SMP Tue Mar 9 17:48:46 EST 2010 x86_64 x86_64 x86_64 GNU/Linux


How reproducible:
always

Steps to Reproduce:
1. boot up a guest with "..vhost=on,vhostfd=/none.." option
  
Actual results:
segment fault occurred

Expected results:
guest can boot up

Additional info:
commandline:
# /usr/libexec/qemu-kvm -no-hpet -usbdevice tablet -rtc-td-hack -startdate now -cpu qemu64,+sse2 -drive file=/home/image/RHEL-Server-5.5-64.qcow2 -net nic,model=virtio,netdev=foo,macaddr=20:20:11:23:22:03 -netdev tap,id=foo,ifname=msttap0,vhost=on,vhostfd=/none,script=/etc/qemu-ifup,downscript=no -vnc :1 -m 2G -smp 2 -boot c -monitor stdio -uuid `uuidgen`

backtrace:

# gdb /usr/libexec/qemu-kvm
GNU gdb (GDB) Red Hat Enterprise Linux (7.1-10.el6)
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/libexec/qemu-kvm...Reading symbols from /usr/lib/debug/usr/libexec/qemu-kvm.debug...done.
done.
(gdb) r -no-hpet -usbdevice tablet -rtc-td-hack -startdate now -cpu qemu64,+sse2 -drive file=/home/image/RHEL-Server-5.5-64.qcow2 -net nic,model=virtio,netdev=foo,macaddr=20:20:11:23:22:03 -netdev tap,id=foo,ifname=msttap0,vhost=on,vhostfd=/none,script=/etc/qemu-ifup,downscript=no -vnc :1 -m 2G -smp 2 -boot c -monitor stdio -uuid `uuidgen`
Starting program: /usr/libexec/qemu-kvm -no-hpet -usbdevice tablet -rtc-td-hack -startdate now -cpu qemu64,+sse2 -drive file=/home/image/RHEL-Server-5.5-64.qcow2 -net nic,model=virtio,netdev=foo,macaddr=20:20:11:23:22:03 -netdev tap,id=foo,ifname=msttap0,vhost=on,vhostfd=/none,script=/etc/qemu-ifup,downscript=no -vnc :1 -m 2G -smp 2 -boot c -monitor stdio -uuid `uuidgen`
[Thread debugging using libthread_db enabled]
Detaching after fork from child process 20678.

Program received signal SIGSEGV, Segmentation fault.
monitor_get_fd (mon=0x0, fdname=0x115a190 "/none") at /usr/src/debug/qemu-kvm-0.12.1.2/monitor.c:2591
2591        QLIST_FOREACH(monfd, &mon->fds, next) {
Missing separate debuginfos, use: debuginfo-install alsa-lib-1.0.21-3.el6.x86_64 cairo-spice-1.8.7.1-4.el6.x86_64 celt051-0.5.1.3-0.el6.x86_64 cyrus-sasl-lib-2.1.23-4.1.el6.x86_64 dbus-libs-1.2.16-10.el6.x86_64 expat-2.0.1-8.el6.x86_64 ffmpeg-spice-libs-0.4.9-0.15.5spice.20080908.el6.x86_64 fontconfig-2.8.0-1.el6.x86_64 freetype-2.3.11-3.el6.x86_64 glibc-2.11.1-1.12.el6.x86_64 gnutls-2.8.5-2.el6.x86_64 keyutils-libs-1.2-6.1.el6.x86_64 krb5-libs-1.7-18.el6.x86_64 libICE-1.0.6-1.el6.x86_64 libSM-1.1.0-7.1.el6.x86_64 libX11-1.3-1.el6.x86_64 libXau-1.0.5-1.el6.x86_64 libXdamage-1.1.2-1.el6.x86_64 libXext-1.1-2.el6.x86_64 libXfixes-4.0.4-1.el6.x86_64 libXi-1.3-1.el6.x86_64 libXtst-1.0.99.2-3.el6.x86_64 libXxf86vm-1.1.0-1.el6.x86_64 libaio-0.3.107-9.1.el6.x86_64 libasyncns-0.8-1.1.el6.x86_64 libcom_err-1.41.10-3.el6.x86_64 libdrm-2.4.17-1.el6.x86_64 libgcc-4.4.3-15.el6.x86_64 libgcrypt-1.4.5-2.el6.x86_64 libgpg-error-1.7-2.el6.x86_64 libpng-1.2.39-1.el6.x86_64 libselinux-2.0.87-1.el6.x86_64 libsndfile-1.0.20-3.el6.x86_64 libstdc++-4.4.3-1.el6.x86_64 libtasn1-2.3-2.el6.x86_64 libuuid-2.17.1-1.el6.x86_64 libxcb-1.5-1.el6.x86_64 mesa-libGL-7.7-1.el6.x86_64 mesa-libGLU-7.7-1.el6.x86_64 nss-softokn-freebl-3.12.4-11.el6.x86_64 openssl-1.0.0-0.19.beta4.el6.x86_64 pciutils-libs-3.1.4-6.el6.x86_64 pixman-spice-0.13.3-5.el6.x86_64 pulseaudio-libs-0.9.21-8.el6.x86_64 spice-server-0.4.2-8.el6.x86_64 tcp_wrappers-libs-7.6-56.2.el6.x86_64 zlib-1.2.3-23.1.el6.x86_64
(gdb) bt
#0  monitor_get_fd (mon=0x0, fdname=0x115a190 "/none") at /usr/src/debug/qemu-kvm-0.12.1.2/monitor.c:2591
#1  0x00000000004917c1 in net_handle_fd_param (mon=0x0, param=0x115a190 "/none") at net.c:744
#2  0x0000000000494da8 in net_init_tap (opts=0x1159f50, mon=0x0, name=<value optimized out>, vlan=<value optimized out>) at net/tap.c:470
#3  0x00000000004742aa in qemu_opts_foreach (list=<value optimized out>, func=0x491be0 <net_init_netdev>, opaque=0x0,
    abort_on_failure=<value optimized out>) at qemu-option.c:817
#4  0x0000000000490f50 in net_init_clients () at net.c:1355
#5  0x000000000040d445 in main (argc=<value optimized out>, argv=<value optimized out>, envp=<value optimized out>)
    at /usr/src/debug/qemu-kvm-0.12.1.2/vl.c:6035