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

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Message-ID: <aKhZ9jdiNS2SAZv2@google.com>
Date: Fri, 22 Aug 2025 11:52:22 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
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 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)
    }
};

Alice