Simple vsock setup for QEMU

Configuration

Host Kernel: rawhide 4.13.0-0.rc6.git4.2.fc28.x86_64 (on Fedora 24)

QEMU is mainline built from sources: QEMU emulator version 2.10.50 (v2.10.0-105-g223cd0e)

Guest: clear-17460-kvm.img (which has vsock support)

Launching the VM

First install the vsock driver

modprobe vhost_vsock

Launch QEMU

export VMN=3
export IMAGE=clear-17460-kvm.img
/usr/local/bin/qemu-system-x86_64 \
    -device vhost-vsock-pci,id=vhost-vsock-pci0,guest-cid=${VMN} \
    -enable-kvm \
    -bios OVMF.fd \
    -smp sockets=1,cpus=4,cores=2 -cpu host \
    -m 1024 \
    -vga none -nographic \
    -drive file="$IMAGE",if=virtio,aio=threads,format=raw \
    -netdev user,id=mynet0,hostfwd=tcp::${VMN}0022-:22,hostfwd=tcp::${VMN}2375-:2375 \
    -device virtio-net-pci,netdev=mynet0 \
    -debugcon file:debug.log -global isa-debugcon.iobase=0x402 $@

How test the vsock connection using socat

Here the CID of the VM is set to 3 and the port set to 1024

In the VM

socat - SOCKET-LISTEN:40:0:x00x00x00x04x00x00x03x00x00x00x00x00x00x00
Note: CID = 3

On the host

sudo socat - SOCKET-CONNECT:40:0:x00x00x00x04x00x00x03x00x00x00x00x00x00x00

Minimal console over vsock using socat

VM: Without auth:

socat SOCKET-LISTEN:40:0:x00x00x00x04x00x00x03x00x00x00x00x00x00x00,reuseaddr,fork EXEC:bash,pty,stderr,setsid,sigint,sane,ctty,echo=0

With auth:

socat SOCKET-LISTEN:40:0:x00x00x00x04x00x00x03x00x00x00x00x00x00x00,reuseaddr,fork EXEC:login,pty,stderr,setsid,sigint,sane,ctty,echo=0

On the host

socat - SOCKET-CONNECT:40:0:x00x00x00x04x00x00x03x00x00x00x00x00x00x00

ssh over vsock using socat

VM:

socat SOCKET-LISTEN:40:0:x0000xFFxFFx0000x03x00000000000000,reuseaddr,fork TCP:localhost:22

VMM:

sudo socat TCP4-LISTEN:2222,reuseaddr,fork SOCKET-CONNECT:40:0:x0000xFFxFFx0000x03x00000000000000

Now you can ssh into the VM from the host on port 2222

ssh root@localhost -p 2222

Using specific ports

socat does not support vsock right now, so you will need to use the generic socket address option to interact with it http://www.dest-unreach.org/socat/doc/socat-genericsocket.html

To generate the appropriate generic socket option you can use this simple C program

#include <sys/socket.h>
#include <linux/vm_sockets.h>
#include <stdio.h>
#include <string.h>

#define GUEST_CID 3

int main(void)
{
        int i;
        char buf[16];
        struct sockaddr_vm sa = {
                            .svm_family = AF_VSOCK,
                            .svm_cid = GUEST_CID, 
                            .svm_port = 1024,
                       };

        printf("VM:\n");
        memcpy(buf, &sa, sizeof(sa));
        for(i=2;i<sizeof(sa);i++) {
                printf("x%02x", (unsigned char)buf[i]);
        }
        printf("\n");
        
        sa.svm_cid = 2;

        printf("VMM:\n");
        memcpy(buf, &sa, sizeof(sa));
        for(i=2;i<sizeof(sa);i++) {
                printf("x%02x", (unsigned char)buf[i]);
        }
        printf("\n");       
}

Testing with a go program

Testing with: https://github.com/mdlayher/vsock/tree/master/cmd/vscp

On the host you run: vscp -v -r -p 1024 cpuinfo.txt

On the guest: vscp -v -s -c 2 -p 1024 /proc/cpuinfo

And you will see the file contents show up

vraghavulu/Simple vsock setup for QEMU.md