libkrun: vhost-user-input support by dorindabassey · Pull Request #642 · containers/libkrun

dorindabassey · 2026-04-17T10:00:06Z

Implement write_config in VhostUserDevice to support dynamic
config space (needed for virtio-input device discovery) and
Add API constants and example for vhost-user input.
depends on rust-vmm/vhost-device#955 and containers/libkrunfw#120

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>

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>

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. Co-authored-by: Matej Hrica <mhrica@redhat.com> Signed-off-by: Dorinda Bassey <dbassey@redhat.com>

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>

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>

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>

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

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>

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>

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>

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>

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>

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>

bilelmoussaoui

various comments

bilelmoussaoui · 2026-04-20T15:33:15Z

                )
            }
+            RegisterVhostUserDevice(ref err) => {
+                let mut err_msg = format!("{err}");


Given that mmio::Error likely implements Display, you could use to_string() here instead of going through format! no?

bilelmoussaoui · 2026-04-20T15:34:28Z

-            let kernel_region = unsafe {
-                MmapRegion::build_raw(kernel_host_addr as *mut u8, kernel_size, 0, 0)
-                    .map_err(StartMicrovmError::InvalidKernelBundle)?
+            #[cfg(all(feature = "vhost-user", target_os = "linux"))]


I guess you could have put this cfg above a scope defined with {} so you don't need to repeat it multiple times?

bilelmoussaoui · 2026-04-20T15:34:40Z

    }

+    // For vhost-user devices, we need file-backed memory so the backend can mmap it
+    #[cfg(all(feature = "vhost-user", target_os = "linux"))]


bilelmoussaoui · 2026-04-20T15:34:52Z

+                .iter()
+                .map(|(addr, size)| {
+                    debug!(
+                        "  Creating memfd for region: addr=0x{:x}, size=0x{:x}",


Suggested change

" Creating memfd for region: addr=0x{:x}, size=0x{:x}",

"Creating memfd for region: addr=0x{:x}, size=0x{:x}",

bilelmoussaoui · 2026-04-20T15:35:16Z

+                    // File descriptor ownership is transferred to File::from_raw_fd below.
+                    let memfd = unsafe {
+                        let fd = libc::memfd_create(
+                            b"guest_mem\0".as_ptr() as *const libc::c_char,


You can use c"" nowadays no?

bilelmoussaoui · 2026-04-20T15:35:40Z

+                            libc::close(fd);
+                            return Err(io::Error::last_os_error());
+                        }
+                        debug!("  Created memfd with fd={}", fd);


Suggested change

debug!(" Created memfd with fd={}", fd);

debug!("Created memfd with fd={}", fd);

bilelmoussaoui · 2026-04-20T15:37:04Z

+    ///
+    /// A new VhostUserDevice or an error if connection fails.
+    pub fn new(
+        socket_path: &str,


an actual Path maybe?

bilelmoussaoui · 2026-04-20T15:37:27Z

+            })
+            .collect();
+
+        Ok(VhostUserDevice {


Suggested change

Ok(VhostUserDevice {

Ok(Self {

Dorinda Bassey and others added 13 commits April 8, 2026 15:22

libkrun: Add vhost-user sound device constants and support

9e0456d

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

dorindabassey requested review from MatiasVara, jakecorrenti, mtjhrc, slp and tylerfanelli as code owners April 17, 2026 10:00

dorindabassey added the 2.0 label Apr 17, 2026

bilelmoussaoui reviewed Apr 20, 2026

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libkrun: vhost-user-input support#642

libkrun: vhost-user-input support#642
dorindabassey wants to merge 13 commits intocontainers:mainfrom
dorindabassey:vhost-user-input

dorindabassey commented Apr 17, 2026 •

edited

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	" Creating memfd for region: addr=0x{:x}, size=0x{:x}",
	"Creating memfd for region: addr=0x{:x}, size=0x{:x}",

	debug!(" Created memfd with fd={}", fd);
	debug!("Created memfd with fd={}", fd);

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dorindabassey commented Apr 17, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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dorindabassey commented Apr 17, 2026 •

edited

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