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Add vhost-user device support (RNG, sound, vsock, CAN, console, input, rtc)#642

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Add vhost-user device support (RNG, sound, vsock, CAN, console, input, rtc)#642
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dorindabassey:vhost-user-input

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@dorindabassey dorindabassey commented Apr 17, 2026 •
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Implement vhost-user protocol support in libkrun, enabling out-of-process virtio device backends using rust-vmm/vhost-device.

Key Changes

  • Core vhost-user infrastructure: Generic VhostUserDevice wrapper, file-backed memory (memfd), config space support
  • Device support: RNG, sound, vsock, CAN, console, rtc and input devices
  • API: krun_set_vhost_user_device() with public constants for each device type
  • Examples: Integration in chroot_vm for all supported devices

All devices tested and working with corresponding vhost-device backends.

bilelmoussaoui
bilelmoussaoui reviewed Apr 20, 2026
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various comments

Comment thread src/vmm/src/builder.rs Outdated
Comment thread src/vmm/src/builder.rs
Comment thread src/vmm/src/builder.rs
Comment thread src/vmm/src/builder.rs Outdated
Comment thread src/vmm/src/builder.rs Outdated
Comment thread src/vmm/src/builder.rs Outdated
Comment thread src/devices/src/virtio/vhost_user/device.rs Outdated
Comment thread src/devices/src/virtio/vhost_user/device.rs Outdated
@dorindabassey dorindabassey force-pushed the vhost-user-input branch 2 times, most recently from 54cf7eb to 6db7dd8 Compare April 24, 2026 18:03
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dorindabassey commented Apr 24, 2026

Thanks for the reviews @bilelmoussaoui!
Since this PR builds on several other pending PRs, I'll address all the feedback here in #642 to avoid rebase churn.

@dorindabassey dorindabassey force-pushed the vhost-user-input branch 2 times, most recently from 8c8b49b to 038d252 Compare April 28, 2026 11:36
libkrun/vmm: Add vhost-user infrastructure and API
cb8b450 
Implement vhost-user support for connecting
to external virtio device backends running
in separate processes.
Add vhost-user feature flag, vhost dependency,
and krun_add_vhost_user_device() generalized
API for adding vhost-user devices.

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
@dorindabassey dorindabassey changed the title libkrun: vhost-user-input support Add vhost-user device support (RNG, sound, vsock, CAN, console, input) Apr 28, 2026
@dorindabassey dorindabassey changed the title Add vhost-user device support (RNG, sound, vsock, CAN, console, input) Add vhost-user device support (RNG, sound, vsock, CAN, console, input, rtc) Apr 29, 2026
ggoodman
ggoodman reviewed Apr 29, 2026
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Comment thread include/libkrun.h
*/
int32_t krun_add_vhost_user_device(uint32_t ctx_id,
uint32_t device_type,
const char *socket_path,
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@ggoodman ggoodman Apr 29, 2026

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Does this need to be a path at the API level? What if we already have a file descriptor?

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@mtjhrc mtjhrc Apr 29, 2026

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Fair, we should probably support that, but this is not really an issue blocking the current PR really, this is getting merged into main which is now libkrun 2.x branch. Every public API function is about to get replaced. #634

mtjhrc
mtjhrc reviewed Apr 29, 2026
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Comment thread src/utils/Cargo.toml Outdated
Dorinda Bassey and others added 11 commits April 30, 2026 15:13
vmm: Implement file-backed memory using memfd for vhost-user
6d671fe 
Add memfd-backed memory region creation to enable memory
sharing with vhost-user backends via FD passing. When
vhost-user is enabled, all guest RAM regions are created
with memfd backing instead of anonymous mmap.

This lays the groundwork for vhost-user device support
while maintaining backward compatibility such that the
VM boots normally with standard memory when vhost-user
is not configured.

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
@mtjhrc
devices/vhost: Add core VhostUserDevice implementation
0a3aca5 
Implement generic vhost-user device wrapper
with connection, feature negotiation, and
Guest physical address(GPA) to Virtual
address(VA) translation. Supports protocol
feature negotiation (CONFIG, MQ).
Backend interrupts (vring_call_event) are
monitored by the EventManager and forwarded
to the guest without spawning additional threads.

Bridge vmm-sys-util version mismatch:
vhost 0.15 requires vmm-sys-util 0.15 (for vm-memory 0.17
compatibility), while libkrun core uses 0.14 and TDX
uses 0.12. Convert EventFd types via AsRawFd/FromRawFd
when calling vhost functions to avoid type conflicts.
This allows all 3 versions coexist in the dependency tree.

Co-authored-by: Matej Hrica <mhrica@redhat.com>
Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
vmm: Implement attaching vhost-user devices
d03ccd2 
Add support for attaching vhost-user devices to the VM.
Devices are registered with the EventManager as subscribers
to integrate with the VMM's event loop for interrupt handling.

The VMM now automatically suppresses the implicit RNG
device when a vhost-user RNG is configured via
krun_add_vhost_user_device(), allowing seamless
switching between the standard virtio-rng and external
vhost-user-rng backend for better isolation and flexibility.

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
examples: Add vhost-user RNG support to chroot_vm
4a3bdf2 
Adds --vhost-user-rng command line option to
specify a vhost-user RNG backend socket path.
When provided, the VM uses the external
vhost-user RNG device instead of the built-in
virtio-rng implementation.

Example usage:  ./examples/chroot_vm \
--vhost-user-rng=/tmp/vhost-rng.sock0 \
/ /bin/sh -c "head -c 32 /dev/hwrng | xxd"

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
devices/vhost: Add config space support for vhost-user devices
d72477f 
Implement read_config() for vhost-user devices using the
VHOST_USER_GET_CONFIG protocol message. This enables vhost-user
devices to expose their configuration space to the guest.

This provides a general mechanism for any vhost-user device that
needs to expose configuration to the guest (e.g., virtio-snd).

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
libkrun: Add vhost-user sound device constants and support
3b7da2c 
Add constants and device-specific configuration for virtio-snd
(vhost-user sound device).

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
examples: Add vhost-user sound device support to chroot_vm
4a6cfa0 
Add --vhost-user-snd option to chroot_vm example,
allowing VMs to use external vhost-user sound backends
for audio playback and capture.

Usage:
  ./chroot_vm --vhost-user-snd=/path/to/sound.sock ...

Note: In the guest, the ALSA default device may not work without
additional configuration. Use explicit device specification:
  aplay -D hw:0,0 /path/to/audio.wav

Or create /etc/asound.conf in the guest:
  defaults.pcm.card 0
  defaults.pcm.device 0
  pcm.!default {
      type hw
      card 0
      device 0
  }

Tested with vhost-device-sound backend using PipeWire.

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
libkrun: Add API constants and example for vhost-user vsock
7db441d 
Add public API constants for vhost-user vsock devices and example
usage in chroot_vm. The underlying support already exists via the
generic VhostUserDevice wrapper.

Example integration:
- Added --vhost-user-vsock option to chroot_vm
- Calls krun_disable_implicit_vsock() to avoid conflict with
  built-in device
- Skips TSI port mapping when vhost-user-vsock is active

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
libkrun: Add API constants and example for vhost-user CAN
3985439 
Add public API constants for vhost-user CAN devices and
example usage in chroot_vm. The underlying support already
exists via the generic VhostUserDevice wrapper.

Example integration:
- Added --vhost-user-can option to chroot_vm
- Uses 3 queues (TX, RX, control) with 64-entry queue sizes
- Follows same pattern as other vhost-user device integrations

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
libkrun: Add API constants and example for vhost-user console
f3ccd58 
Add public API constants for vhost-user console devices and example
usage in chroot_vm. The underlying support already exists via the
generic VhostUserDevice wrapper.

Console devices require 4 queues for multiport support (receiveq,
transmitq, control receiveq, control transmitq).

Example integration:
- Added --vhost-user-console option to chroot_vm
- Available as /dev/hvc1 in the guest (implicit console uses hvc0)
- Can be used with vhost-device-console for remote console access

Example workflow:
  Terminal 1: Start vhost-device-console backend
  vhost-device-console --socket-path=/tmp/console.sock \
  --socket-count=1 --tcp-port=12346 --backend=network

  Terminal 2: Connect to console (before starting VM)
    nc localhost 12346

  Terminal 3: Start VM with vhost-user console
  chroot_vm --vhost-user-console=/tmp/console.sock0 / /bin/sh
  In guest: Test with echo "hello" > /dev/hvc1

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
devices/vhost: Implement write_config for dynamic config
b8e92b8 
Implement write_config in VhostUserDevice to support
virtio devices that use dynamic configuration space,
such as virtio-input. Some virtio devices like
virtio-input use a request-response pattern for
device discovery. Without write_config support, the
backend never receives the virtio_input config values,
causing device initialization to fail.
This implementation uses VHOST_USER_SET_CONFIG to
forward writes to the backend.

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
Dorinda Bassey added 2 commits April 30, 2026 15:13
libkrun: Add API constants and example for vhost-user input
a7ef103 
Add public API constants for vhost-user input devices and example
usage in chroot_vm. The underlying support already exists via the
generic VhostUserDevice wrapper.

Console devices require 2 queues (event, status).
Example integration:
  - Added --vhost-user-console option to chroot_vm

Example usage:
On host, start vhost-device-input backend
vhost-device-input --socket-path /tmp/input.sock \
                   --event-list /dev/input/event3

In libkrun
./chroot_vm --vhost-user-input=/tmp/input.sock0 / /bin/sh

The guest will see the input device as /dev/input/event0 and
can read input events from the host device.

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
libkrun: Add API constants and example for vhost-user rtc
e2388ed 
Add public API constants for vhost-user rtc devices and example
usage in chroot_vm. The underlying support already exists via the
generic VhostUserDevice wrapper.

RTC devices require 2 queues (requestq, alarmq).
Example integration:
- Added --vhost-user-rtc option to chroot_vm

Example usage:
On host, start vhost-device-rtc backend
vhost-device-rtc --socket-path /tmp/rtc.sock

Run libkrun with RTC device
./chroot_vm --vhost-user-rtc=/tmp/rtc.sock / /bin/sh

The RTC device provides:
  - Accurate time synchronization without NTP
  - Multiple clock types (UTC, TAI, monotonic)
  - PTP clocks for precision time protocol
  - Alarm support for wake-from-suspend

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>
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