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

["Alexandre Courbot" <acourbot@nvidia.com>]

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.

[1] https://lore.kernel.org/all/DGUZ4A6W87JU.36R2KDR7YGSEX@kernel.org/