[dpdk-users] Connecting VM to example/vhost Application Fails with "Failed to unlink"

[David Christensen]

Trying to connect a VM to the example/vhost switch application.  The 
dpdk-vhost command line and output as follows:

$ sudo ./build/examples/dpdk-vhost -l 120-127 -n 4 --socket-mem 
0,0,0,0,0,0,0,0,2048 --no-pci  -- -p 1 --socket-file /tmp/sock0
EAL: Detected 160 lcore(s)
EAL: Detected 2 NUMA nodes
EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
EAL: Selected IOVA mode 'VA'
EAL: No available hugepages reported in hugepages-2048kB
EAL: Probing VFIO support...
EAL: VFIO support initialized
EAL: No legacy callbacks, legacy socket not created
VHOST_PORT:
Specified port number(1) exceeds total system port number(0)
VHOST_DATA: Procesing on Core 121 started
VHOST_DATA: Procesing on Core 122 started
VHOST_DATA: Procesing on Core 126 started
VHOST_DATA: Procesing on Core 125 started
VHOST_DATA: Procesing on Core 123 started
VHOST_DATA: Procesing on Core 127 started
VHOST_CONFIG: vhost-user server: socket created, fd: 48
VHOST_DATA: Procesing on Core 124 started
VHOST_CONFIG: bind to /tmp/sock0

VM configuration in the libvirt XML as follows:

     <interface type='vhostuser'>
       <mac address='52:54:00:f8:1a:b4'/>
       <source type='unix' path='/tmp/sock0' mode='server'/>
       <model type='virtio'/>
       <driver queues='4' rx_queue_size='1024' tx_queue_size='1024'>
         <host csum='on' gso='on'/>
         <guest csum='on' tso4='on' tso6='on' ecn='on'/>
       </driver>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x01' 
function='0x0'/>
     </interface>

VM fails to start with the following error:

$ sudo virsh start --console dpdk-server-0
error: Failed to start domain dpdk-server-0
error: internal error: process exited while connecting to monitor: 
2021-03-03T22:16:20.767940Z qemu-system-ppc64: -chardev 
socket,id=charnet0,path=/tmp/sock0,server: Failed to unlink socket 
/tmp/sock0: Operation not permitted

I'm able to start the VM with OVS/DPDK (2.15.0/20.11) and testpmd from 
DPDK, but not the vhost switch application.  Any suggestions?

Dave