linux-kernel - Re: [PATCH v3 10/16] rust: block: add block related constants

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Message-ID: <87y0rv7fu8.fsf@kernel.org>
Date: Thu, 07 Aug 2025 09:26:07 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: Boqun Feng <boqun.feng@...il.com>, Miguel Ojeda <ojeda@...nel.org>, Alex
 Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>, Björn Roy
 Baron <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, Alice
 Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, Danilo
 Krummrich <dakr@...nel.org>, Jens Axboe <axboe@...nel.dk>,
 linux-block@...r.kernel.org, rust-for-linux@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 10/16] rust: block: add block related constants

"Daniel Almeida" <daniel.almeida@...labora.com> writes:

>> On 11 Jul 2025, at 08:43, Andreas Hindborg <a.hindborg@...nel.org> wrote:
>>
>> Add a few block subsystem constants to the rust `kernel::block` name space.
>> This makes it easier to access the constants from rust code.
>>
>> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
>> ---
>> rust/kernel/block.rs | 12 ++++++++++++
>> 1 file changed, 12 insertions(+)
>>
>> diff --git a/rust/kernel/block.rs b/rust/kernel/block.rs
>> index 150f710efe5b..7461adf4d7e0 100644
>> --- a/rust/kernel/block.rs
>> +++ b/rust/kernel/block.rs
>> @@ -3,3 +3,15 @@
>> //! Types for working with the block layer.
>>
>> pub mod mq;
>> +
>> +/// Bit mask for masking out [`SECTOR_SIZE`]
>
> Missing period.

Thanks.

>
>> +pub const SECTOR_MASK: u32 = bindings::SECTOR_MASK;
>> +
>> +/// Sectors are size `1 << SECTOR_SHIFT`.
>> +pub const SECTOR_SHIFT: u32 = bindings::SECTOR_SHIFT;
>> +
>> +/// Size of a sector.
>> +pub const SECTOR_SIZE: u32 = bindings::SECTOR_SIZE;
>> +
>> +/// Power of two difference in size of a page and size of a sector.
>
> A bit hard to parse this.
>
> Maybe “The difference between the size of a page and the size of a sector,
> expressed as a power of two” ?

OK.

>
>> +pub const PAGE_SECTORS_SHIFT: u32 = bindings::PAGE_SECTORS_SHIFT;
>>
>> --
>> 2.47.2
>>
>>
>>
>
>
>  let sector: usize = something;
>  let page_offset = (sector & block::SECTOR_MASK as usize) << block::SECTOR_SHIFT;
>
>
> Wait, the parenthesis evaluate to usize, and the shift is a u32. How does this compile?

That is all good. `Shl` has a ton of impls for integers [1].

Shifting more than 64 spaces on 64 bit system makes no sense anyway.

Best regards,
Andreas Hindborg


[1] https://doc.rust-lang.org/std/ops/trait.Shl.html