linux-kernel - Re: [PATCH v2 2/5] rust: dma: add DMA addressing capabilities

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Message-Id: <B1BCB6C1-745B-4272-A0AB-8B8D1E444ECD@collabora.com>
Date: Wed, 16 Jul 2025 14:41:50 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: abdiel.janulgue@...il.com,
 robin.murphy@....com,
 a.hindborg@...nel.org,
 ojeda@...nel.org,
 alex.gaynor@...il.com,
 boqun.feng@...il.com,
 gary@...yguo.net,
 bjorn3_gh@...tonmail.com,
 lossin@...nel.org,
 aliceryhl@...gle.com,
 tmgross@...ch.edu,
 bhelgaas@...gle.com,
 kwilczynski@...nel.org,
 gregkh@...uxfoundation.org,
 rafael@...nel.org,
 rust-for-linux@...r.kernel.org,
 linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/5] rust: dma: add DMA addressing capabilities



> On 16 Jul 2025, at 14:32, Daniel Almeida <daniel.almeida@...labora.com> wrote:
> 
> Hi Danilo,
> 
>> +    #[inline]
>> +    pub const fn new(n: usize) -> Result<Self> {
>> +        Ok(Self(match n {
>> +            0 => 0,
>> +            1..=64 => u64::MAX >> (64 - n),
>> +            _ => return Err(EINVAL),
>> +        }))
>> +    }
>> +
> 
> Isn’t this equivalent to genmask_u64(0..=n) ? See [0].
> 
> You should also get a compile-time failure if n is out of bounds by default using
> genmask.
> 
> — Daniel
> 
> [0]: https://lore.kernel.org/rust-for-linux/20250714-topics-tyr-genmask2-v9-1-9e6422cbadb6@collabora.com/#r

Or genmask_u64(0..=n-1), if we disregard the previous off-by-one error

— Daniel