Re: [PATCH 2/5] rust: add support for ethernet operations

[Benno Lossin <benno.lossin@proton.me>]

On 6/13/23 06:53, FUJITA Tomonori wrote:
> This improves abstractions for network device drivers to implement
> struct ethtool_ops, the majority of ethernet device drivers need to
> do.
> 
> struct ethtool_ops also needs to access to device private data like
> struct net_devicve_ops.
> 
> Currently, only get_ts_info operation is supported. The following
> patch adds the Rust version of the dummy network driver, which uses
> the operation.
> 
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
> ---
>  rust/bindings/bindings_helper.h |   1 +
>  rust/kernel/net/dev.rs          | 108 ++++++++++++++++++++++++++++++++
>  2 files changed, 109 insertions(+)
> 
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 468bf606f174..6446ff764980 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -8,6 +8,7 @@
> 
>  #include <linux/errname.h>
>  #include <linux/etherdevice.h>
> +#include <linux/ethtool.h>
>  #include <linux/netdevice.h>
>  #include <linux/slab.h>
>  #include <linux/refcount.h>
> diff --git a/rust/kernel/net/dev.rs b/rust/kernel/net/dev.rs
> index d072c81f99ce..d6012b2eea33 100644
> --- a/rust/kernel/net/dev.rs
> +++ b/rust/kernel/net/dev.rs
> @@ -141,6 +141,18 @@ pub fn register(&mut self) -> Result {
>          }
>      }
> 
> +    /// Sets `ethtool_ops` of `net_device`.
> +    pub fn set_ether_operations<U>(&mut self) -> Result
> +    where
> +        U: EtherOperations<D>,
> +    {
> +        if self.is_registered {
> +            return Err(code::EINVAL);
> +        }
> +        EtherOperationsAdapter::<U, D>::new().set_ether_ops(&mut self.dev);
> +        Ok(())
> +    }

Is it really necessary for a device to be able to have multiple different
`EtherOperations`? Couldnt you also just make `T` implement 
`EtherOperations<D>`?

> +
>      const DEVICE_OPS: bindings::net_device_ops = bindings::net_device_ops {
>          ndo_init: if <T>::HAS_INIT {
>              Some(Self::init_callback)
> @@ -342,3 +354,99 @@ fn drop(&mut self) {
>          }
>      }
>  }
> +
> +/// Builds the kernel's `struct ethtool_ops`.
> +struct EtherOperationsAdapter<D, T> {
> +    _p: PhantomData<(D, T)>,
> +}
> +
> +impl<D, T> EtherOperationsAdapter<T, D>

I think it would be a good idea to add a comment here that explains why
this is needed, i.e. why `ETHER_OPS` cannot be implemented via a constant
in `set_ether_ops`.

> +where
> +    D: DriverData,
> +    T: EtherOperations<D>,
> +{
> +    /// Creates a new instance.
> +    fn new() -> Self {
> +        EtherOperationsAdapter { _p: PhantomData }
> +    }
> +
> +    unsafe extern "C" fn get_ts_info_callback(
> +        netdev: *mut bindings::net_device,
> +        info: *mut bindings::ethtool_ts_info,
> +    ) -> core::ffi::c_int {
> +        from_result(|| {
> +            // SAFETY: The C API guarantees that `netdev` is valid while this function is running.
> +            let mut dev = unsafe { Device::from_ptr(netdev) };
> +            // SAFETY: The returned pointer was initialized by `D::Data::into_foreign` when
> +            // `Registration` object was created.
> +            // `D::Data::from_foreign` is only called by the object was released.
> +            // So we know `data` is valid while this function is running.
> +            let data = unsafe { D::Data::borrow(dev.priv_data_ptr()) };
> +            // SAFETY: The C API guarantees that `info` is valid while this function is running.
> +            let mut info = unsafe { EthtoolTsInfo::from_ptr(info) };
> +            T::get_ts_info(&mut dev, data, &mut info)?;
> +            Ok(0)
> +        })
> +    }
> +
> +    const ETHER_OPS: bindings::ethtool_ops = bindings::ethtool_ops {
> +        get_ts_info: if <T>::HAS_GET_TS_INFO {
> +            Some(Self::get_ts_info_callback)
> +        } else {
> +            None
> +        },
> +        ..unsafe { core::mem::MaybeUninit::<bindings::ethtool_ops>::zeroed().assume_init() }
> +    };
> +
> +    const fn build_ether_ops() -> &'static bindings::ethtool_ops {
> +        &Self::ETHER_OPS
> +    }

Why is this a function?

> +
> +    fn set_ether_ops(&self, dev: &mut Device) {
> +        // SAFETY: The type invariants guarantee that `dev.0` is valid.
> +        unsafe {
> +            (*dev.0).ethtool_ops = Self::build_ether_ops();
> +        }
> +    }
> +}
> +
> +/// Corresponds to the kernel's `struct ethtool_ops`.
> +#[vtable]
> +pub trait EtherOperations<D: DriverData> {
> +    /// Corresponds to `get_ts_info` in `struct ethtool_ops`.
> +    fn get_ts_info(
> +        _dev: &mut Device,
> +        _data: <D::Data as ForeignOwnable>::Borrowed<'_>,
> +        _info: &mut EthtoolTsInfo,

`&mut EthtoolTsInfo` is again a double pointer.

> +    ) -> Result {
> +        Err(Error::from_errno(bindings::EOPNOTSUPP as i32))
> +    }
> +}
> +
> +/// Corresponds to the kernel's `struct ethtool_ts_info`.
> +///
> +/// # Invariants
> +///
> +/// The pointer is valid.
> +pub struct EthtoolTsInfo(*mut bindings::ethtool_ts_info);
> +
> +impl EthtoolTsInfo {
> +    /// Creates a new `EthtoolTsInfo' instance.
> +    ///
> +    /// # Safety
> +    ///
> +    /// Callers must ensure that `ptr` must be valid.
> +    unsafe fn from_ptr(ptr: *mut bindings::ethtool_ts_info) -> Self {
> +        // INVARIANT: The safety requirements ensure the invariant.
> +        Self(ptr)
> +    }
> +}
> +
> +/// Sets up the info for software timestamping.
> +pub fn ethtool_op_get_ts_info(dev: &mut Device, info: &mut EthtoolTsInfo) -> Result {
> +    // SAFETY: The type invariants guarantee that `dev.0` and `info.0` are valid.
> +    unsafe {
> +        bindings::ethtool_op_get_ts_info(dev.0, info.0);
> +    }
> +    Ok(())
> +}

Why isn't this an associated function on `EthtoolTsInfo`?

--
Cheers,
Benno

> --
> 2.34.1
>