vsock communication between DomU and DomD

[hayashi-90]

@yhamamachi san

Is vsock communication between DomU and DomD supported?

On v4hsbc_xen_kernel612 branch latest,
I have tried to verify vsock connectivity between DomU and DomD using socat,
but it did not work (No such device).

DomD side:

root@sparrow-hawk-domd:~# socat -v -d -d VSOCK-LISTEN:12345, STDIO
2025/05/29 19:11:03 socat[958] N VSOCK CID=2
2025/05/29 19:11:03 socat[958] N listening on AF=40 cid:4294967295 port:12345

DomU side:

root@virtio-armv8-xt:~# socat - VSOCK-CONNECT:2:12345
2025/05/29 19:11:24 socat[253] E connect(5, AF=40 cid:2 port:12345, 16): No such device

Then I found the commit that seems disabling vsock on DomU.
Finally, I reverted the change and tried it again, but it still didn’t connect (No such device =>Connection timed out).

DomD side:

root@sparrow-hawk-domd:~# socat -v -d -d VSOCK-LISTEN:12345, STDIO
2025/05/29 19:06:52 socat[896] N VSOCK CID=2
2025/05/29 19:06:52 socat[896] N listening on AF=40 cid:4294967295 port:12345

DomU side:

root@virtio-armv8-xt:~# socat - VSOCK-CONNECT:2:12345
2025/05/29 19:08:08 socat[312] E connect(5, AF=40 cid:2 port:12345, 16): Connection timed out

How can we enable vsock communication between DomU and DomD?
thank you.

[yhamamachi]

Hi @hayashi-90 -san

Sorry for the late reply.

Is vsock communication between DomU and DomD supported?

In fact, I haven't tested this feature on DomU.
I'm not familier with vsock, but I tested the command which you provided.
It seems to work in my environment.
Please check following logs:

DomU log:

root@virtio-armv8-xt:~# socat - VSOCK-CONNECT:2:12345
Hello
Sparrow-Hawk
^Croot@virtio-armv8-xt:~#

DomD log:

root@sparrow-hawk-domd:~# socat -v -d -d VSOCK-LISTEN:12345, STDIO
2026/02/05 00:27:03 socat[590] N VSOCK CID=2
2026/02/05 00:27:03 socat[590] N listening on AF=40 cid:4294967295 port:12345
2026/02/05 00:27:32 socat[590] N accepting connection from AF=40 cid:4 port:2148504794 on AF=40 cid:2 port:12345
2026/02/05 00:27:32 socat[590] N reading from and writing to stdio
2026/02/05 00:27:32 socat[590] N starting data transfer loop with FDs [6,6] and [0,1]
> 2026/02/05 00:27:35.000438501  length=6 from=0 to=5
Hello
Hello
2026/02/05 00:27:35 socat[590] N write(1, 0xaaaae90f1e30, 6) completed
> 2026/02/05 00:27:42.000540836  length=13 from=6 to=18
Sparrow-Hawk
Sparrow-Hawk
2026/02/05 00:27:42 socat[590] N write(1, 0xaaaae90f1e30, 13) completed
2026/02/05 00:31:31 socat[590] N socket 1 (fd 6) is at EOF
2026/02/05 00:31:32 socat[590] N exiting with status 0
root@sparrow-hawk-domd:~#

I used following revision and build image with ./build.sh -v -u.
61ac6fc

I think your procedure has no problem.
Could you please try again with new version?

[hayashi-90]

@yhamamachi san

I used following revision and build image with ./build.sh -v -u.
61ac6fc

It works fine.
However, when I tried building with DomA (./build.sh -v -u -a), still does not work and produces the same error as before, and the following virtio_net error:

[  114.084141] virtio_net virtio0 enp0s1: NETDEV WATCHDOG: CPU: 1: transmit queue 0 timed out 108516 ms
[  114.084273] virtio_net virtio0 enp0s1: TX timeout on queue: 0, sq: output.0, vq: 0x1, name: output.0, 108516000 usecs ago
[  119.204158] virtio_net virtio0 enp0s1: NETDEV WATCHDOG: CPU: 2: transmit queue 0 timed out 113636 ms
[  119.204258] virtio_net virtio0 enp0s1: TX timeout on queue: 0, sq: output.0, vq: 0x1, name: output.0, 113636000 usecs ago
[  124.068162] virtio_net virtio0 enp0s1: NETDEV WATCHDOG: CPU: 3: transmit queue 0 timed out 118500 ms
[  124.068260] virtio_net virtio0 enp0s1: TX timeout on queue: 0, sq: output.0, vq: 0x1, name: output.0, 118500000 usecs ago
[  129.188145] virtio_net virtio0 enp0s1: NETDEV WATCHDOG: CPU: 0: transmit queue 0 timed out 123620 ms

Could you please look into this and let me know if there's anything I should check on my side?

[yhamamachi]

Hi @hayashi-90 -san,
Thank you for your report. This issue was reproduced on my side.

It seems that DomU vhost doesn't work correctly when both DomU and DomA are enabled.
DomU vsock device is vhost-vsock-pci which is based on vhost, so vsock doesn't works on DomU.
We need to fix vhost support on DomU, but I have no idea to fix this issue as of now.