linux-kernel - Re: [PATCH v2 3/5] rust: scatterlist: Add type-state abstraction for sg

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Message-ID: <d30f085a-a031-4208-a15a-e85c7a56347f@kernel.org>
Date: Fri, 22 Aug 2025 13:54:32 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: akpm@...ux-foundation.org, ojeda@...nel.org, alex.gaynor@...il.com,
 boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
 lossin@...nel.org, a.hindborg@...nel.org, tmgross@...ch.edu,
 abdiel.janulgue@...il.com, acourbot@...dia.com, jgg@...pe.ca,
 lyude@...hat.com, robin.murphy@....com, daniel.almeida@...labora.com,
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/5] rust: scatterlist: Add type-state abstraction for
 sg_table

On 8/22/25 1:52 PM, Alice Ryhl wrote:
> On Fri, Aug 22, 2025 at 01:48:47PM +0200, Danilo Krummrich wrote:
>> On Fri Aug 22, 2025 at 1:44 PM CEST, Alice Ryhl wrote:
>>>> +impl<P> Owned<P>
>>>> +where
>>>> +    for<'a> P: page::AsPageIter<Iter<'a> = VmallocPageIter<'a>> + 'static,
>>>> +{
>>>> +    fn new(
>>>> +        dev: &Device<Bound>,
>>>> +        mut pages: P,
>>>> +        dir: dma::DataDirection,
>>>> +        flags: alloc::Flags,
>>>> +    ) -> Result<impl PinInit<Self, Error> + '_> {
>>>> +        let page_iter = pages.page_iter();
>>>> +        let size = page_iter.size();
>>>
>>> Variable naming here is confusing. There's another variable called size
>>> in an inner scope, and then afterwards in RawSGTable you use *this* size
>>> variable again.
>>
>> I can change the size in the assignment block of max_segment to max_size, or do
>> you have other suggestions?
> 
> How about just this?
> 
> let max_segment = {
>      // SAFETY: `dev.as_raw()` is a valid pointer to a `struct device`.
>      let max_segment = unsafe { bindings::dma_max_mapping_size(dev.as_raw()) };
>      if max_segment == 0 {
>          u32::MAX
>      } else {
>          u32::try_from(max_segment).unwrap_or(u32::MAX)
>      }
> };

Looks good, thanks!