netdev - Re: [PATCH net-next v5 1/5] rust: core abstractions for network PHY drivers

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Date: Sat, 21 Oct 2023 07:25:17 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: netdev@...r.kernel.org, rust-for-linux@...r.kernel.org, andrew@...n.ch, miguel.ojeda.sandonis@...il.com, tmgross@...ch.edu, boqun.feng@...il.com, wedsonaf@...il.com, greg@...ah.com
Subject: Re: [PATCH net-next v5 1/5] rust: core abstractions for network PHY drivers

On 20.10.23 14:54, FUJITA Tomonori wrote:
> On Fri, 20 Oct 2023 09:34:46 +0900 (JST)
> FUJITA Tomonori <fujita.tomonori@...il.com> wrote:
> 
>> On Thu, 19 Oct 2023 15:20:51 +0000
>> Benno Lossin <benno.lossin@...ton.me> wrote:
>>
>>> I would like to remove the mutable static variable and simplify
>>> the macro.
>>
>> How about adding DriverVTable array to Registration?
>>
>> /// Registration structure for a PHY driver.
>> ///
>> /// # Invariants
>> ///
>> /// The `drivers` slice are currently registered to the kernel via `phy_drivers_register`.
>> pub struct Registration<const N: usize> {
>>      drivers: [DriverVTable; N],
>> }
>>
>> impl<const N: usize> Registration<{ N }> {
>>      /// Registers a PHY driver.
>>      pub fn register(
>>          module: &'static crate::ThisModule,
>>          drivers: [DriverVTable; N],
>>      ) -> Result<Self> {
>>          let mut reg = Registration { drivers };
>>          let ptr = reg.drivers.as_mut_ptr().cast::<bindings::phy_driver>();
>>          // SAFETY: The type invariants of [`DriverVTable`] ensure that all elements of the `drivers` slice
>>          // are initialized properly. So an FFI call with a valid pointer.
>>          to_result(unsafe {
>>              bindings::phy_drivers_register(ptr, reg.drivers.len().try_into()?, module.0)
>>          })?;
>>          // INVARIANT: The `drivers` slice is successfully registered to the kernel via `phy_drivers_register`.
>>          Ok(reg)
>>      }
>> }
> 
> Scratch this.
> 
> This doesn't work. Also simply putting slice of DriverVTable into
> Module strcut doesn't work.

Why does it not work? I tried it and it compiled fine for me.

> We cannot move a slice of DriverVTable. Except for static allocation,
> is there a simple way?

I do not know what you are referring to, you can certainly move an array
of `DriverVTable`s.

-- 
Cheers,
Benno