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]>
