linux-kernel - Re: [PATCH 2/3] rust: dma: convert the read/write macros to return Result

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Message-ID: <Z_WcXFJQtFTbHI6b@cassiopeiae>
Date: Tue, 8 Apr 2025 23:59:56 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Andreas Hindborg <a.hindborg@...nel.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
	Abdiel Janulgue <abdiel.janulgue@...il.com>, ojeda@...nel.org,
	Daniel Almeida <daniel.almeida@...labora.com>,
	Robin Murphy <robin.murphy@....com>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	"open list:DMA MAPPING HELPERS DEVICE DRIVER API [RUST]" <rust-for-linux@...r.kernel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	"open list:DMA MAPPING HELPERS" <iommu@...ts.linux.dev>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] rust: dma: convert the read/write macros to return
 Result

On Tue, Apr 08, 2025 at 09:54:13PM +0000, Benno Lossin wrote:
> On Tue Apr 8, 2025 at 9:46 PM CEST, Andreas Hindborg wrote:
> > "Miguel Ojeda" <miguel.ojeda.sandonis@...il.com> writes:
> >> On Tue, Apr 8, 2025 at 2:40 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
> >>>
> >>> But the `assert_eq!` would panic anyway if comparison fails, right?
> >>
> >> Previously the `?` generated by the macro would return out of the
> >> closure written by the sample, and thus it wouldn't reach the
> >> `assert_eq!`.
> >
> > Right, I see. So the question is whether we want to have the assert
> > panic here or not, of we get an Err. I vote yes.
> 
> The assert wouldn't be the source of the panic though, it would be the
> `.unwrap()`, but I think it's better to report the error. Although I
> think it would be nicer if the example could use better error handling,
> but this code is in a `drop` function, so no way to bubble up a
> result...

We could be more explicit and assert is_ok() instead and subsequently do the
assert_eq.