Re: [PATCH] rust: block: mq: align init_request numa_node arg with C signature

["Gary Guo" <gary@garyguo.net>]

On Wed May 27, 2026 at 11:59 AM BST, Alice Ryhl wrote:
> On Wed, May 27, 2026 at 12:57 PM Gary Guo <gary@garyguo.net> wrote:
>>
>> On Wed May 27, 2026 at 10:18 AM BST, Andreas Hindborg wrote:
>> > Commit b040a1a4523d ("block: switch numa_node to int in
>> > blk_mq_hw_ctx and init_request") changed the type of the
>> > `numa_node` argument of `blk_mq_ops::init_request` from
>> > `unsigned int` to `int`. Update the Rust callback signature to
>> > match, so that the function item can be coerced to the C fn
>> > pointer type stored in `blk_mq_ops`.
>> >
>> > Without this change the Rust block layer fails to build:
>> >
>> >   error[E0308]: mismatched types
>> >      --> rust/kernel/block/mq/operations.rs:274:28
>> >       |
>> >   274 |         init_request: Some(Self::init_request_callback),
>> >       |                       ---- ^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> >       |                       expected fn pointer, found fn item
>> >       |
>> >       = note: expected fn pointer
>> >                 `unsafe extern "C" fn(_, _, _, i32) -> _`
>> >                     found fn item
>> >                 `unsafe extern "C" fn(_, _, _, u32) -> _ {...}`
>> >
>> > The argument is unused on the Rust side, so this is a pure
>> > type-signature change with no functional impact.
>> >
>> > Fixes: b040a1a4523d ("block: switch numa_node to int in blk_mq_hw_ctx and init_request")
>> > Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>>
>> You could also just use `i32` instead of `ffi::c_int`. But it doesn't really
>> matter for this patch.
>
> By the way, all these constants are in the prelude.

I wonder if we should actually encourage people, by removing them from prelude,
to use i32/u32 instead of c_int/c_uint, isize/usize instead of c_long/c_ulong
and similar, given all Linux ABIs have consistent mapping for them.

On a different note, perhaps it might worth adding a lint to klint to check for
path references for types available via prelude for other types.

Best,
Gary