linux-kernel - Re: [PATCH v2 2/3] rust: dma: convert the read/write macros to return Result

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Message-ID: <D931ZGPNHUA8.U3L2C72CVH46@proton.me>
Date: Thu, 10 Apr 2025 15:11:01 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Danilo Krummrich <dakr@...nel.org>, Abdiel Janulgue <abdiel.janulgue@...il.com>
Cc: a.hindborg@...nel.org, rust-for-linux@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>, 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>, Valentin Obst <kernel@...entinobst.de>, open list <linux-kernel@...r.kernel.org>, Christoph Hellwig <hch@....de>, Marek Szyprowski <m.szyprowski@...sung.com>, Robin Murphy <robin.murphy@....com>, airlied@...hat.com, "open list:DMA MAPPING HELPERS" <iommu@...ts.linux.dev>
Subject: Re: [PATCH v2 2/3] rust: dma: convert the read/write macros to return Result

On Thu Apr 10, 2025 at 1:54 PM CEST, Danilo Krummrich wrote:
> On Thu, Apr 10, 2025 at 11:58:17AM +0300, Abdiel Janulgue wrote:
>> @@ -78,13 +74,14 @@ impl Drop for DmaSampleDriver {
>>      fn drop(&mut self) {
>>          dev_info!(self.pdev.as_ref(), "Unload DMA test driver.\n");
>>  
>> -        let _ = || -> Result {
>> -            for (i, value) in TEST_VALUES.into_iter().enumerate() {
>> -                assert_eq!(kernel::dma_read!(self.ca[i].h), value.0);
>> -                assert_eq!(kernel::dma_read!(self.ca[i].b), value.1);
>> -            }
>> -            Ok(())
>> -        }();
>> +        for (i, value) in TEST_VALUES.into_iter().enumerate() {
>> +            let val0 = kernel::dma_read!(self.ca[i].h);
>> +            let val1 = kernel::dma_read!(self.ca[i].b);
>> +            assert!(val0.is_ok());
>> +            assert!(val1.is_ok());
>> +            assert_eq!(val0.unwrap(), value.0);
>> +            assert_eq!(val1.unwrap(), value.1);
>
> Maybe use if-let to avoid the unwrap?
>
> 	if let Ok(val0) = val0 {
> 	   assert_eq!(val0, value.0);
> 	}
>
> I know it's a bit pointless, since we know it must be ok, but the educational
> message of the example should be to check and not to unwrap, so maybe that's
> better.

The if-let will silently ignore any errors, so I don't think that it's
fit for example code either.

---
Cheers,
Benno