Re: [PATCH v8 1/1] rust: introduce abstractions for fwctl

["Gary Guo" <gary@garyguo.net>]

On Mon Aug 24, 2026 at 3:59 AM BST, Alexandre Courbot wrote:
> On Sat Aug 15, 2026 at 8:25 AM JST, Gary Guo wrote:
>> On Thu Aug 13, 2026 at 4:23 PM BST, Zhi Wang wrote:
>>> diff --git a/rust/kernel/fwctl.rs b/rust/kernel/fwctl.rs
>>> new file mode 100644
>>> index 000000000000..e6a8513a47d0
>>> --- /dev/null
>>> +++ b/rust/kernel/fwctl.rs
>>> @@ -0,0 +1,593 @@
>>> +// SPDX-License-Identifier: GPL-2.0-only
>>> +
>>> +//! Abstractions for the fwctl subsystem.
>>> +//!
>>> +//! C header: `include/linux/fwctl.h`
>>> +
>>> +use crate::{
>>> +    bindings,
>>> +    container_of,
>>> +    device,
>>> +    prelude::*,
>>> +    sync::aref::{
>>> +        ARef,
>>> +        AlwaysRefCounted, //
>>> +    },
>>> +    types::Opaque, //
>>> +};
>>> +use core::{
>>> +    alloc::Layout,
>>> +    cell::UnsafeCell,
>>> +    marker::PhantomData,
>>> +    ptr::NonNull,
>>> +    slice, //
>>> +};
>>> +
>>> +/// Returns a kmalloc-compatible allocation size for `T`.
>>> +const fn kmalloc_aligned_size<T>() -> usize {
>>> +    Layout::new::<T>().pad_to_align().size()
>>
>> What's this function doing?  This is just identical to `size_of::<T>()`.
>>
>> The layout from a specific type is already padded to its alignment. You only
>> need to call `pad_to_align()`, say, if you are computing a layout or increasing
>> the alignment of layout.
>
> IIRC this was meant to be a const version of `Kmalloc::aligned_layout`
> [1], which although it is equivalent carries the intent better than just
> using `size_of`. But here it would maybe be better to just make
> `Kmalloc::aligned_layout` const and call it instead.

That'd certainly be better than having a duplicate impl.

However, I do wonder if we should just codify the fact that kamlloc works for
all padded layouts (which is true for all type layouts in Rust) and so we don't
need to call that (and perhaps also just remove the method).

Best,
Gary