On Sun, 10 May 2026 16:38, Manos Pitsidianakis <[email protected]> wrote:
>Hi all, this RFC series adds Rust bindings for Virtio drivers
>(frontends in virtio parlance).
>
>As a PoC, it also adds a sample virtio-rtc driver which performs
>capability discovery through the virtqueue without registering any clock.
>
>Before I send a cleaned-up non-RFC I would like some initial feedback
>(i.e. is it something the upstream wants?)
>
>This was tested with the rust-vmm vhost-device-rtc device backend that I
>wrote[^0]:
>
>[^0]: https://github.com/rust-vmm/vhost-device/tree/main/vhost-device-rtc
>
>Instructions:
>
> Run the daemon in a separate terminal:
>
> $ cargo run --bin vhost-device-rtc -- -s /tmp/rtc.sock
>
> Then run the VM:
>
> $ qemu-system-aarch64 \
> -machine type=virt,virtualization=off,acpi=on \
> -cpu host \
> -smp 8 \
> -accel kvm \
> -drive if=virtio,format=qcow2,file=./debian-13-nocloud-arm64-daily.qcow2 \
> -device virtio-net-pci,netdev=unet \
> -device virtio-scsi-pci \
> -serial mon:stdio \
> -m 8192 \
> -object memory-backend-memfd,id=mem,size=8G,share=on \
> -numa node,memdev=mem \
> -display none \
> -vga none \
> -kernel /path/to/linux/build/arch/arm64/boot/Image \
> -device
vhost-user-test-device,chardev=rtc,id=rtc,virtio-id=17,num_vqs=2,vq_size=1024 \
> -chardev socket,path=/tmp/rtc.sock,id=rtc \
> ...
>
> Example output:
> [ 1.105238] rust_virtio_rtc: Probe Rust virtio driver sample.
> [ 1.105645] rust_virtio_rtc: Found 1 vqs.
> [ 1.136050] rust_virtio_rtc: process_requestq got buf 16 bytes
> [ 1.136125] rust_virtio_rtc: Got response! Ok(RespCfg { head: ReqHead {
msg_type: Le16(0), reserved: [0, 0, 0, 0, 0, 0] }, num_clocks: Le16(3), reserved:
[0, 0, 0, 0, 0, 0] })
> [ 1.136701] rust_virtio_rtc: Got response! Ok(RespClockCap { head:
ReqHead { msg_type: Le16(0), reserved: [0, 0, 0, 0, 0, 0] }, clock_type: 3,
leap_second_smearing: 0, flags: 0, reserved: [0, 0, 0, 0, 0] })
> [ 1.136724] rust_virtio_rtc virtio0: cannot expose clock 0 (type 3,
variant 0, flags 0) to userspace
> [ 1.137259] rust_virtio_rtc: Got response! Ok(RespRead { head: ReqHead
{ msg_type: Le16(0), reserved: [0, 0, 0, 0, 0, 0] }, clock_reading:
Le64(1777890485031060388) })
> [ 1.137277] rust_virtio_rtc: #0 clock reading = 1777890485031060388
> [ 1.137749] rust_virtio_rtc: Got response! Ok(RespClockCap { head:
ReqHead { msg_type: Le16(0), reserved: [0, 0, 0, 0, 0, 0] }, clock_type: 1,
leap_second_smearing: 0, flags: 0, reserved: [0, 0, 0, 0, 0] })
> [ 1.137769] rust_virtio_rtc virtio0: cannot expose clock 1 (type 1,
variant 0, flags 0) to userspace
> [ 1.138247] rust_virtio_rtc: Got response! Ok(RespRead { head: ReqHead
{ msg_type: Le16(0), reserved: [0, 0, 0, 0, 0, 0] }, clock_reading:
Le64(1777890485032086075) })
> [ 1.138264] rust_virtio_rtc: #1 clock reading = 1777890485032086075
> [ 1.138730] rust_virtio_rtc: Got response! Ok(RespClockCap { head:
ReqHead { msg_type: Le16(0), reserved: [0, 0, 0, 0, 0, 0] }, clock_type: 2,
leap_second_smearing: 0, flags: 0, reserved: [0, 0, 0, 0, 0] })
> [ 1.138751] rust_virtio_rtc virtio0: cannot expose clock 2 (type 2,
variant 0, flags 0) to userspace
> [ 1.139253] rust_virtio_rtc: Got response! Ok(RespRead { head: ReqHead
{ msg_type: Le16(0), reserved: [0, 0, 0, 0, 0, 0] }, clock_reading:
Le64(338567896865557) })
> [ 1.139270] rust_virtio_rtc: #2 clock reading = 338567896865557
>
>Concerns - Notes - TODOs
>========================
>
>- Virtqueue lifetimes don't neatly apply to Rust as expected, so a lot
> of times we have to go through unsafe pointer dereferences (though
> which are guaranteed by Virtio subsystem to be valid, for example when
> a callback is called with the vq argument). There's a potential for
> misuse and definitely could use better thinking.
>- `struct virtio_device` is not reference-counted like other implemented
> device types in rust/kernel. Maybe we need to change C API first to
> make them reference counted, assuming this doesn't break anything?
>- The sample driver obviously conflicts with the C implementation, so
> this would either need to move out of samples/ or figure out some way
> to handle this in kbuild.
>- kernel::virtio module and its types need a few rustdoc examples that I
> will add in followup series
>- Note that the registration of RTC clocks etc in the sample driver is
> not done, I'm putting it off until I receive some feedback first. The
> sample driver otherwise does send and receive data from the virtqueue
> as a PoC.
>
>PS: No LLMs used so any mistakes and goofs are solely written by me.
>
>Signed-off-by: Manos Pitsidianakis <[email protected]>
>---
>Changes in v3:
>- Removed unused methods from virtio API
>- Clean up how scattergather lists are added to virtqueues by using
> owned SGTables only, and make the API safe(r)
>- Add RAII cleanup for find_vqs return value that calls del_vqs
>- Reset device after remove callback
>- Significantly clean up sample driver as a result of the other cleanups
>- Link to v2:
https://lore.kernel.org/r/[email protected]
>
>Changes in v2:
>- Move helper ifdefs to helper file (thanks Alice)
>- Changed CONFIG checks to IS_ENABLED to allow for CONFIG_VIRTIO=m
>- Split all use imports to one item per line according to style guide
>- Fixed wait_for_completion_interruptible*() rustdocs
>- Use Jiffy type alias in wait_for_completion_interruptible_timeout()
>- Pepper and salt #[inline]s wherever appropriate as per style guide
>- Split probe() into probe() and init() to allow cleaning up if init
> fails
>- Remove unnecessary Send and Sync unsafe impls for
> kernel::virtio::Device
>- Remove unnecessary LeSize and BeSize
>- Accept Option<_> for virtqueue callback when creating a VirtqueueInfo
>- Made all vq buffer adding operations unsafe
>- Use AtomicU16 instead of Cell<u16> for sample virtio driver
>- Fix RespHead field types in sample virtio driver
>- Fix response error checking in sample virtio driver
>- Change some device contexts in method signatures
>- Link to v1:
https://lore.kernel.org/r/[email protected]
>
>---
>Manos Pitsidianakis (6):
> rust/bindings: generate virtio bindings
> rust/helpers: add virtio.c
> rust/kernel/device: return parent at same context
> rust: add virtio module
> rust: impl interruptible waits for Completion
> samples/rust: Add sample virtio-rtc driver [WIP]
>
> MAINTAINERS | 9 +
> rust/bindings/bindings_helper.h | 5 +
> rust/helpers/helpers.c | 1 +
> rust/helpers/virtio.c | 37 ++++
> rust/kernel/device.rs | 2 +-
> rust/kernel/lib.rs | 2 +
> rust/kernel/sync/completion.rs | 42 +++-
> rust/kernel/virtio.rs | 423 ++++++++++++++++++++++++++++++++++++++++
> rust/kernel/virtio/utils.rs | 57 ++++++
> rust/kernel/virtio/virtqueue.rs | 314 +++++++++++++++++++++++++++++
> samples/rust/Kconfig | 15 ++
> samples/rust/Makefile | 1 +
> samples/rust/rust_virtio_rtc.rs | 403 ++++++++++++++++++++++++++++++++++++++
> 13 files changed, 1309 insertions(+), 2 deletions(-)
>---
>base-commit: 028ef9c96e96197026887c0f092424679298aae8
>change-id: 20260504-rust-virtio-8523b01dfdc2
>
>Best regards,
>--
>Manos Pitsidianakis <[email protected]>
>
