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

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Message-ID: <87fre4921s.fsf@kernel.org>
Date: Wed, 06 Aug 2025 12:28:47 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.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>, 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

"Alice Ryhl" <aliceryhl@...gle.com> writes:

> On Fri, Jul 11, 2025 at 01:43:11PM +0200, Andreas Hindborg 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`]
>> +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.
>> +pub const PAGE_SECTORS_SHIFT: u32 = bindings::PAGE_SECTORS_SHIFT;
>
> I was looking for the user to double-check whether u32 was the right
> choice, but I can't find it. It looks like you don't use these yet?

Only `SECTOR_SHIFT` is used in this series, the rest will be used in the
future. They are used for memory backing rnull, still out of tree [1].
Do you want me to split the patch and delay the rest of the constants? I
fully intend to upstream the user as soon as I can.

It is a #define on C side used as a shift operator on usize in Rust code
like so:

  let sector: usize = something;
  let page_offset = (sector & block::SECTOR_MASK as usize) << block::SECTOR_SHIFT;

Best regards,
Andreas Hindborg


[1] https://git.kernel.org/pub/scm/linux/kernel/git/a.hindborg/linux.git/tree/drivers/block/rnull/rnull.rs?h=rnull-v6.15#n211