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Message-ID: <87v7m2h9bo.fsf@t14s.mail-host-address-is-not-set>
Date: Mon, 01 Sep 2025 10:21:31 +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>, Breno Leitao
<leitao@...ian.org>, linux-block@...r.kernel.org,
rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 15/18] rust: block: add `GenDisk` private data support
"Daniel Almeida" <daniel.almeida@...labora.com> writes:
>> On 22 Aug 2025, at 09:14, Andreas Hindborg <a.hindborg@...nel.org> wrote:
>>
>> Allow users of the rust block device driver API to install private data in
>> the `GenDisk` structure.
>>
>> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
>> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
>> ---
>> drivers/block/rnull/rnull.rs | 8 ++++---
>> rust/kernel/block/mq.rs | 7 +++---
>> rust/kernel/block/mq/gen_disk.rs | 32 ++++++++++++++++++++++----
>> rust/kernel/block/mq/operations.rs | 46 ++++++++++++++++++++++++++++++--------
>> 4 files changed, 74 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
>> index 8690ff5f974f..8255236bc550 100644
>> --- a/drivers/block/rnull/rnull.rs
>> +++ b/drivers/block/rnull/rnull.rs
>> @@ -61,14 +61,16 @@ fn new(
>> .logical_block_size(block_size)?
>> .physical_block_size(block_size)?
>> .rotational(rotational)
>> - .build(fmt!("{}", name.to_str()?), tagset)
>> + .build(fmt!("{}", name.to_str()?), tagset, ())
>> }
>> }
>>
>> #[vtable]
>> impl Operations for NullBlkDevice {
>> + type QueueData = ();
>> +
>> #[inline(always)]
>> - fn queue_rq(rq: ARef<mq::Request<Self>>, _is_last: bool) -> Result {
>> + fn queue_rq(_queue_data: (), rq: ARef<mq::Request<Self>>, _is_last: bool) -> Result {
>> mq::Request::end_ok(rq)
>> .map_err(|_e| kernel::error::code::EIO)
>> // We take no refcounts on the request, so we expect to be able to
>> @@ -79,5 +81,5 @@ fn queue_rq(rq: ARef<mq::Request<Self>>, _is_last: bool) -> Result {
>> Ok(())
>> }
>>
>> - fn commit_rqs() {}
>> + fn commit_rqs(_queue_data: ()) {}
>> }
>> diff --git a/rust/kernel/block/mq.rs b/rust/kernel/block/mq.rs
>> index 98fa0d6bc8f7..6e546f4f3d1c 100644
>> --- a/rust/kernel/block/mq.rs
>> +++ b/rust/kernel/block/mq.rs
>> @@ -69,20 +69,21 @@
>> //!
>> //! #[vtable]
>> //! impl Operations for MyBlkDevice {
>> +//! type QueueData = ();
>> //!
>> -//! fn queue_rq(rq: ARef<Request<Self>>, _is_last: bool) -> Result {
>> +//! fn queue_rq(_queue_data: (), rq: ARef<Request<Self>>, _is_last: bool) -> Result {
>> //! Request::end_ok(rq);
>> //! Ok(())
>> //! }
>> //!
>> -//! fn commit_rqs() {}
>> +//! fn commit_rqs(_queue_data: ()) {}
>> //! }
>> //!
>> //! let tagset: Arc<TagSet<MyBlkDevice>> =
>> //! Arc::pin_init(TagSet::new(1, 256, 1), flags::GFP_KERNEL)?;
>> //! let mut disk = gen_disk::GenDiskBuilder::new()
>> //! .capacity_sectors(4096)
>> -//! .build(format_args!("myblk"), tagset)?;
>> +//! .build(format_args!("myblk"), tagset, ())?;
>> //!
>> //! # Ok::<(), kernel::error::Error>(())
>> //! ```
>> diff --git a/rust/kernel/block/mq/gen_disk.rs b/rust/kernel/block/mq/gen_disk.rs
>> index 6b1b846874db..46ec80269970 100644
>> --- a/rust/kernel/block/mq/gen_disk.rs
>> +++ b/rust/kernel/block/mq/gen_disk.rs
>> @@ -13,6 +13,7 @@
>> static_lock_class,
>> str::NullTerminatedFormatter,
>> sync::Arc,
>> + types::{ForeignOwnable, ScopeGuard},
>> };
>> use core::fmt::{self, Write};
>>
>> @@ -98,7 +99,14 @@ pub fn build<T: Operations>(
>> self,
>> name: fmt::Arguments<'_>,
>> tagset: Arc<TagSet<T>>,
>> + queue_data: T::QueueData,
>> ) -> Result<GenDisk<T>> {
>> + let data = queue_data.into_foreign();
>> + let recover_data = ScopeGuard::new(|| {
>> + // SAFETY: T::QueueData was created by the call to `into_foreign()` above
>> + drop(unsafe { T::QueueData::from_foreign(data) });
>> + });
>> +
>> // SAFETY: `bindings::queue_limits` contain only fields that are valid when zeroed.
>> let mut lim: bindings::queue_limits = unsafe { core::mem::zeroed() };
>>
>> @@ -113,7 +121,7 @@ pub fn build<T: Operations>(
>> bindings::__blk_mq_alloc_disk(
>> tagset.raw_tag_set(),
>> &mut lim,
>> - core::ptr::null_mut(),
>> + data,
>> static_lock_class!().as_ptr(),
>> )
>> })?;
>> @@ -167,8 +175,12 @@ pub fn build<T: Operations>(
>> },
>> )?;
>>
>> + recover_data.dismiss();
>> +
>> // INVARIANT: `gendisk` was initialized above.
>> // INVARIANT: `gendisk` was added to the VFS via `device_add_disk` above.
>> + // INVARIANT: `gendisk.queue.queue_data` is set to `data` in the call to
>> + // `__blk_mq_alloc_disk` above.
>> Ok(GenDisk {
>> _tagset: tagset,
>> gendisk,
>> @@ -180,9 +192,10 @@ pub fn build<T: Operations>(
>> ///
>> /// # Invariants
>> ///
>> -/// - `gendisk` must always point to an initialized and valid `struct gendisk`.
>> -/// - `gendisk` was added to the VFS through a call to
>> -/// `bindings::device_add_disk`.
>> +/// - `gendisk` must always point to an initialized and valid `struct gendisk`.
>> +/// - `gendisk` was added to the VFS through a call to
>> +/// `bindings::device_add_disk`.
>> +/// - `self.gendisk.queue.queuedata` is initialized by a call to `ForeignOwnable::into_foreign`.
>> pub struct GenDisk<T: Operations> {
>> _tagset: Arc<TagSet<T>>,
>> gendisk: *mut bindings::gendisk,
>> @@ -194,9 +207,20 @@ unsafe impl<T: Operations + Send> Send for GenDisk<T> {}
>>
>> impl<T: Operations> Drop for GenDisk<T> {
>> fn drop(&mut self) {
>> + // SAFETY: By type invariant of `Self`, `self.gendisk` points to a valid
>> + // and initialized instance of `struct gendisk`, and, `queuedata` was
>> + // initialized with the result of a call to
>> + // `ForeignOwnable::into_foreign`.
>> + let queue_data = unsafe { (*(*self.gendisk).queue).queuedata };
>> +
>> // SAFETY: By type invariant, `self.gendisk` points to a valid and
>> // initialized instance of `struct gendisk`, and it was previously added
>> // to the VFS.
>> unsafe { bindings::del_gendisk(self.gendisk) };
>> +
>> + // SAFETY: `queue.queuedata` was created by `GenDiskBuilder::build` with
>> + // a call to `ForeignOwnable::into_foreign` to create `queuedata`.
>> + // `ForeignOwnable::from_foreign` is only called here.
>> + drop(unsafe { T::QueueData::from_foreign(queue_data) });
>> }
>> }
>> diff --git a/rust/kernel/block/mq/operations.rs b/rust/kernel/block/mq/operations.rs
>> index c2b98f507bcb..6fb256f55acc 100644
>> --- a/rust/kernel/block/mq/operations.rs
>> +++ b/rust/kernel/block/mq/operations.rs
>> @@ -6,14 +6,15 @@
>>
>> use crate::{
>> bindings,
>> - block::mq::request::RequestDataWrapper,
>> - block::mq::Request,
>> + block::mq::{request::RequestDataWrapper, Request},
>> error::{from_result, Result},
>> prelude::*,
>> - types::ARef,
>> + types::{ARef, ForeignOwnable},
>> };
>> use core::{marker::PhantomData, sync::atomic::AtomicU64, sync::atomic::Ordering};
>>
>> +type ForeignBorrowed<'a, T> = <T as ForeignOwnable>::Borrowed<'a>;
>> +
>> /// Implement this trait to interface blk-mq as block devices.
>> ///
>> /// To implement a block device driver, implement this trait as described in the
>> @@ -26,12 +27,20 @@
>> /// [module level documentation]: kernel::block::mq
>> #[macros::vtable]
>> pub trait Operations: Sized {
>> + /// 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 queue a request with the driver. If `is_last` is
>> /// `false`, the driver is allowed to defer committing the request.
>> - fn queue_rq(rq: ARef<Request<Self>>, is_last: bool) -> Result;
>> + fn queue_rq(
>> + queue_data: ForeignBorrowed<'_, Self::QueueData>,
>> + rq: ARef<Request<Self>>,
>> + is_last: bool,
>> + ) -> Result;
>>
>> /// Called by the kernel to indicate that queued requests should be submitted.
>> - fn commit_rqs();
>> + fn commit_rqs(queue_data: ForeignBorrowed<'_, Self::QueueData>);
>>
>> /// Called by the kernel to poll the device for completed requests. Only
>> /// used for poll queues.
>> @@ -70,7 +79,7 @@ impl<T: Operations> OperationsVTable<T> {
>> /// promise to not access the request until the driver calls
>> /// `bindings::blk_mq_end_request` for the request.
>> unsafe extern "C" fn queue_rq_callback(
>> - _hctx: *mut bindings::blk_mq_hw_ctx,
>> + hctx: *mut bindings::blk_mq_hw_ctx,
>> bd: *const bindings::blk_mq_queue_data,
>> ) -> bindings::blk_status_t {
>> // SAFETY: `bd.rq` is valid as required by the safety requirement for
>> @@ -88,10 +97,20 @@ impl<T: Operations> OperationsVTable<T> {
>> // reference counted by `ARef` until then.
>> let rq = unsafe { Request::aref_from_raw((*bd).rq) };
>>
>> + // SAFETY: `hctx` is valid as required by this function.
>> + let queue_data = unsafe { (*(*hctx).queue).queuedata };
>> +
>> + // SAFETY: `queue.queuedata` was created by `GenDisk::try_new()` with a
>
> isn’t this set on build() ?
Yes, you are right. Refactoring happened.
>
>> + // call to `ForeignOwnable::into_pointer()` to create `queuedata`.
>
> into_pointer() ?
Should be `into_foreign`, will fix.
>
>> + // `ForeignOwnable::from_foreign()` is only called when the tagset is
>> + // dropped, which happens after we are dropped.
>> + let queue_data = unsafe { T::QueueData::borrow(queue_data) };
>> +
>> // SAFETY: We have exclusive access and we just set the refcount above.
>> unsafe { Request::start_unchecked(&rq) };
>>
>> let ret = T::queue_rq(
>> + queue_data,
>> rq,
>> // SAFETY: `bd` is valid as required by the safety requirement for
>> // this function.
>> @@ -110,9 +129,18 @@ impl<T: Operations> OperationsVTable<T> {
>> ///
>> /// # Safety
>> ///
>> - /// This function may only be called by blk-mq C infrastructure.
>> - unsafe extern "C" fn commit_rqs_callback(_hctx: *mut bindings::blk_mq_hw_ctx) {
>> - T::commit_rqs()
>> + /// This function may only be called by blk-mq C infrastructure. The caller
>> + /// must ensure that `hctx` is valid.
>> + unsafe extern "C" fn commit_rqs_callback(hctx: *mut bindings::blk_mq_hw_ctx) {
>> + // SAFETY: `hctx` is valid as required by this function.
>> + let queue_data = unsafe { (*(*hctx).queue).queuedata };
>> +
>> + // SAFETY: `queue.queuedata` was created by `GenDisk::try_new()` with a
>> + // call to `ForeignOwnable::into_pointer()` to create `queuedata`.
>
> into_foreign()?
Yep, thanks.
>
>> + // `ForeignOwnable::from_foreign()` is only called when the tagset is
>> + // dropped, which happens after we are dropped.
>> + let queue_data = unsafe { T::QueueData::borrow(queue_data) };
>> + T::commit_rqs(queue_data)
>> }
>>
>> /// This function is called by the C kernel. It is not currently
>>
>> --
>> 2.47.2
>>
>>
>>
>
> Reviewed-by: Daniel Almeida <daniel.almeida@...labora.com>
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