rust: block: add GenDisk private data support

Allow users of the rust block device driver API to install private data in
the `GenDisk` structure.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250902-rnull-up-v6-16-v7-14-b5212cc89b98@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Andreas Hindborg

drivers/block/rnull/rnull.rs

@@ -61,14 +61,16 @@ impl NullBlkDevice {
             .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 @@ impl Operations for NullBlkDevice {
         Ok(())
     }
 
-    fn commit_rqs() {}
+    fn commit_rqs(_queue_data: ()) {}
 }

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>(())
 //! ```

rust/kernel/block/mq/gen_disk.rs

@@ -13,6 +13,7 @@ use crate::{
     static_lock_class,
     str::NullTerminatedFormatter,
     sync::Arc,
+    types::{ForeignOwnable, ScopeGuard},
 };
 use core::fmt::{self, Write};
 
@@ -98,7 +99,14 @@ impl GenDiskBuilder {
         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 @@ impl GenDiskBuilder {
             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 @@ impl GenDiskBuilder {
             },
         )?;
 
+        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 @@ impl GenDiskBuilder {
 ///
 /// # 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) });
     }
 }

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 @@ use core::{marker::PhantomData, sync::atomic::AtomicU64, sync::atomic::Ordering}
 /// [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 `GenDiskBuilder::build` with
+        // a call to `ForeignOwnable::into_foreign` to create `queuedata`.
+        // `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_foreign()` to create `queuedata`.
+        // `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