Date: Fri, 14 Jul 2023 19:00:53 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: rust-for-linux@...r.kernel.org, netdev@...r.kernel.org, kuba@...nel.org, andrew@...n.ch, aliceryhl@...gle.com, miguel.ojeda.sandonis@...il.com
Subject: Re: [PATCH v2 2/5] rust: add support for ethernet operations

> 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_device_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@...il.com>
> ---
>  rust/bindings/bindings_helper.h |  1 +
>  rust/kernel/net/dev.rs          | 87 ++++++++++++++++++++++++++++++++-
>  2 files changed, 87 insertions(+), 1 deletion(-)
> 
> 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 fe20616668a9..ff00616e4fef 100644
> --- a/rust/kernel/net/dev.rs
> +++ b/rust/kernel/net/dev.rs
> @@ -142,7 +142,7 @@ pub fn register(&mut self) -> Result {
>          if self.is_registered {
>              return Err(code::EINVAL);
>          }
> -        // SAFETY: The type invariants guarantee that `self.dev.ptr` is valid.
> +        // SAFETY: The type invariants of `Device` guarantee that `self.dev.ptr` is valid.

Shouldn't this be squashed into patch 1?

>          let ret = unsafe {
>              (*self.dev.ptr).netdev_ops = &Self::DEVICE_OPS;
>              bindings::register_netdev(self.dev.ptr)
> @@ -155,6 +155,18 @@ pub fn register(&mut self) -> Result {
>          }
>      }
> 
> +    /// Sets `ethtool_ops` of `net_device`.
> +    pub fn set_ether_operations<E: EtherOperations>(&mut self) -> Result {
> +        if self.is_registered {
> +            return Err(code::EINVAL);
> +        }
> +        // SAFETY: The type invariants of `Device` guarantee that `self.dev.ptr` is valid.
> +        unsafe {
> +            (*(self.dev.ptr)).ethtool_ops = &EtherOperationsAdapter::<E>::ETHER_OPS;
> +        }
> +        Ok(())
> +    }
> +

I think it would make sense to also add

```
pub fn setup_ether_operations(&mut self) -> Result
where
    T: EtherOperations
{
    self.set_ether_operations::<T>();
}
```

Since normally you would implement `EtherOperations` for the same type
that also implement `DeviceOperations`, right?

>      const DEVICE_OPS: bindings::net_device_ops = bindings::net_device_ops {
>          ndo_init: if <T>::HAS_INIT {
>              Some(Self::init_callback)
> @@ -328,3 +340,76 @@ fn drop(&mut self) {
>          build_error!("skb must be released explicitly");
>      }
>  }
> +
> +/// Builds the kernel's `struct ethtool_ops`.
> +struct EtherOperationsAdapter<E: EtherOperations> {
> +    _p: PhantomData<E>,
> +}
> +
> +impl<E: EtherOperations> EtherOperationsAdapter<E> {
> +    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 dev = unsafe { Device::from_ptr(netdev) };
> +            // SAFETY: The C API guarantees that `info` is valid while this function is running.
> +            let info = unsafe { EthtoolTsInfo::from_ptr(info) };
> +            E::get_ts_info(dev, info)?;
> +            Ok(0)
> +        })
> +    }
> +
> +    const ETHER_OPS: bindings::ethtool_ops = bindings::ethtool_ops {
> +        get_ts_info: if <E>::HAS_GET_TS_INFO {
> +            Some(Self::get_ts_info_callback)
> +        } else {
> +            None
> +        },
> +        // SAFETY: The rest is zeroed out to initialize `struct ethtool_ops`,
> +        // set `Option<&F>` to be `None`.
> +        ..unsafe { core::mem::MaybeUninit::<bindings::ethtool_ops>::zeroed().assume_init() }
> +    };
> +}
> +
> +/// Corresponds to the kernel's `struct ethtool_ops`.
> +#[vtable]
> +pub trait EtherOperations: ForeignOwnable + Send + Sync {
> +    /// Corresponds to `get_ts_info` in `struct ethtool_ops`.
> +    fn get_ts_info(_dev: Device<Self>, _info: EthtoolTsInfo) -> Result {
> +        Err(Error::from_errno(bindings::EOPNOTSUPP as i32))

Note that you have to use `-(EOPNOTSUPP as i32)`. Maybe just add this
in `error.rs` via the `declare_err` macro.

--
Cheers,
Benno

> +    }
> +}
> +
> +/// 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<D: ForeignOwnable + Send + Sync>(
> +        dev: &Device<D>,
> +        info: &mut EthtoolTsInfo,
> +    ) -> Result {
> +        // SAFETY: The type invariants of `Device` guarantee that `dev.ptr` are valid.
> +        // The type invariants guarantee that `info.0` are valid.
> +        unsafe {
> +            bindings::ethtool_op_get_ts_info(dev.ptr, info.0);
> +        }
> +        Ok(())
> +    }
> +}
> --
> 2.34.1
> 

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