Re: [PATCH 06/79] block: rust: add `Request` private data support

Alice Ryhl
2026-03-16T10:10:45Z

On Mon, Feb 16, 2026 at 12:34:53AM +0100, Andreas Hindborg wrote:
> C block device drivers can attach private data to a `struct request`. This
> data is stored next to the request structure and is part of the request
> allocation set up during driver initialization.
>
> Expose this private request data area to Rust block device drivers.
>
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>

Overall looks ok. A few nits below:

> ---
> drivers/block/rnull/rnull.rs | 5 +++++
> rust/kernel/block/mq.rs | 6 ++++++
> rust/kernel/block/mq/operations.rs | 24 +++++++++++++++++++++++-
> rust/kernel/block/mq/request.rs | 24 +++++++++++++++++++-----
> rust/kernel/block/mq/tag_set.rs | 2 +-
> 5 files changed, 54 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
> index 6a7f660d31998..065639fc4f941 100644
> --- a/drivers/block/rnull/rnull.rs
> +++ b/drivers/block/rnull/rnull.rs
> @@ -134,6 +134,11 @@ struct QueueData {
> #[vtable]
> impl Operations for NullBlkDevice {
> type QueueData = KBox<QueueData>;
> + type RequestData = ();
> +
> + fn new_request_data() -> impl PinInit<Self::RequestData> {
> + pin_init::zeroed::<Self::RequestData>()

Simpler to just return Ok(()) here.

> + }
>
> #[inline(always)]
> fn queue_rq(queue_data: &QueueData, rq: Owned<mq::Request<Self>>, _is_last: bool) -> Result {
> diff --git a/rust/kernel/block/mq.rs b/rust/kernel/block/mq.rs
> index b8ecd69abe980..a285b753ada88 100644
> --- a/rust/kernel/block/mq.rs
> +++ b/rust/kernel/block/mq.rs
> @@ -69,8 +69,14 @@
> //!
> //! #[vtable]
> //! impl Operations for MyBlkDevice {
> +//! type RequestData = ();
> //! type QueueData = ();
> //!
> +//! fn new_request_data(
> +//! ) -> impl PinInit<()> {
> +//! pin_init::zeroed::<()>()

Simpler to just return Ok(()) here.

> +//! }
> +//!
> //! fn queue_rq(_queue_data: (), rq: Owned<Request<Self>>, _is_last: bool) -> Result {
> //! rq.end_ok();
> //! Ok(())
> diff --git a/rust/kernel/block/mq/operations.rs b/rust/kernel/block/mq/operations.rs
> index 3dea79d647ff7..cd37b939bbf30 100644
> --- a/rust/kernel/block/mq/operations.rs
> +++ b/rust/kernel/block/mq/operations.rs
> @@ -13,6 +13,7 @@
> types::{ForeignOwnable, Owned},
> };
> use core::{marker::PhantomData, ptr::NonNull};
> +use pin_init::PinInit;
>
> type ForeignBorrowed<'a, T> = <T as ForeignOwnable>::Borrowed<'a>;
>
> @@ -28,10 +29,24 @@
> /// [module level documentation]: kernel::block::mq
> #[macros::vtable]
> pub trait Operations: Sized {
> + /// Data associated with a request. This data is located next to the request
> + /// structure.
> + ///
> + /// To be able to handle accessing this data from interrupt context, this
> + /// data must be `Sync`.
> + ///
> + /// The `RequestData` object is initialized when the requests are allocated
> + /// during queue initialization, and it is are dropped when the requests are
> + /// dropped during queue teardown.
> + type RequestData: Sized + Sync;

It was surprising to me that `request` is reused over many requests. I
think it could be a bit more obvious in the wording.

> /// Data associated with the `struct request_queue` that is allocated for
> /// the `GenDisk` associated with this `Operations` implementation.
> type QueueData: ForeignOwnable;
>
> + /// Called by the kernel to get an initializer for a `Pin<&mut RequestData>`.
> + fn new_request_data() -> impl PinInit<Self::RequestData>;
> +
> /// Called by the kernel to queue a request with the driver. If `is_last` is
> /// `false`, the driver is allowed to defer committing the request.
> fn queue_rq(
> @@ -236,6 +251,13 @@ impl<T: Operations> OperationsVTable<T> {
> // it is valid for writes.
> unsafe { RequestDataWrapper::refcount_ptr(pdu.as_ptr()).write(Refcount::new(0)) };
>
> + let initializer = T::new_request_data();
> +
> + // SAFETY: `pdu` is a valid pointer as established above. We do not
> + // touch `pdu` if `__pinned_init` returns an error. We promise ot to

typo

> diff --git a/rust/kernel/block/mq/tag_set.rs b/rust/kernel/block/mq/tag_set.rs
> index c3cf56d52beec..46481754b1335 100644
> --- a/rust/kernel/block/mq/tag_set.rs
> +++ b/rust/kernel/block/mq/tag_set.rs
> @@ -41,7 +41,7 @@ pub fn new(
> // SAFETY: `blk_mq_tag_set` only contains integers and pointers, which
> // all are allowed to be 0.
> let tag_set: bindings::blk_mq_tag_set = unsafe { core::mem::zeroed() };
> - let tag_set: Result<_> = core::mem::size_of::<RequestDataWrapper>()
> + let tag_set: Result<_> = core::mem::size_of::<RequestDataWrapper<T>>()

size_of in prelude.

Alice