Allow users of the rust block device driver API to install private data in
the `GenDisk` structure.
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
drivers/block/rnull/rnull.rs | 8 ++++---
rust/kernel/block/mq.rs | 7 +++---
rust/kernel/block/mq/gen_disk.rs | 36 +++++++++++++++++++++++++----
rust/kernel/block/mq/operations.rs | 46 ++++++++++++++++++++++++++++++--------
4 files changed, 78 insertions(+), 19 deletions(-)
diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
index d09bc77861e4..a012c59ecb3c 100644
--- a/drivers/block/rnull/rnull.rs
+++ b/drivers/block/rnull/rnull.rs
@@ -62,14 +62,16 @@ 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
@@ -80,5 +82,5 @@ 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..988e0ba63693 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 +99,16 @@ 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(|| {
+ drop(
+ // SAFETY: T::QueueData was created by the call to `into_foreign()` above
+ 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 +123,7 @@ pub fn build<T: Operations>(
bindings::__blk_mq_alloc_disk(
tagset.raw_tag_set(),
&mut lim,
- core::ptr::null_mut(),
+ data.cast(),
static_lock_class!().as_ptr(),
)
})?;
@@ -167,8 +177,12 @@ 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 +194,10 @@ 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 +209,22 @@ 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) };
+
+ drop(
+ // 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.
+ 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..a6c1ee2190a1 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
+ // call to `ForeignOwnable::into_pointer()` 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.cast()) };
+
// 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`.
+ // `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.cast()) };
+ T::commit_rqs(queue_data)
}
/// This function is called by the C kernel. It is not currently
--
2.47.2On Tue, Aug 12, 2025 at 10:44:30AM +0200, Andreas Hindborg wrote:
> Allow users of the rust block device driver API to install private data in
> the `GenDisk` structure.
>
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
Overall LGTM.
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> 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(|| {
> + drop(
> + // SAFETY: T::QueueData was created by the call to `into_foreign()` above
> + unsafe { T::QueueData::from_foreign(data) },
> + );
This is usually formatted as:
// SAFETY: T::QueueData was created by the call to `into_foreign()` above
drop(unsafe { T::QueueData::from_foreign(data) });
> 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) };
> +
> + drop(
> + // 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.
> + unsafe { T::QueueData::from_foreign(queue_data) },
> + );
Ditto here.
> // 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
> + // call to `ForeignOwnable::into_pointer()` 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.cast()) };
Is this cast necessary? Is it not a void pointer?
> @@ -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`.
> + // `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.cast()) };
Ditto here.
Alice
"Alice Ryhl" <aliceryhl@google.com> writes:
> On Tue, Aug 12, 2025 at 10:44:30AM +0200, Andreas Hindborg wrote:
>> Allow users of the rust block device driver API to install private data in
>> the `GenDisk` structure.
>>
>> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
>
> Overall LGTM.
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
>
>> 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(|| {
>> + drop(
>> + // SAFETY: T::QueueData was created by the call to `into_foreign()` above
>> + unsafe { T::QueueData::from_foreign(data) },
>> + );
>
> This is usually formatted as:
>
> // SAFETY: T::QueueData was created by the call to `into_foreign()` above
> drop(unsafe { T::QueueData::from_foreign(data) });
I don't really have a preference, my optimization function was to
minimize distance to the unsafe block. Are there any rust guidelines on this?
>
>> 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) };
>> +
>> + drop(
>> + // 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.
>> + unsafe { T::QueueData::from_foreign(queue_data) },
>> + );
>
> Ditto here.
>
>> // 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
>> + // call to `ForeignOwnable::into_pointer()` 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.cast()) };
>
> Is this cast necessary? Is it not a void pointer?
Leftover from old `ForeignOwnable` I think. I'll remove it.
Best regards,
Andreas Hindborg
On Wed, Aug 13, 2025 at 3:47 PM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>
> "Alice Ryhl" <aliceryhl@google.com> writes:
>
> > On Tue, Aug 12, 2025 at 10:44:30AM +0200, Andreas Hindborg wrote:
> >> Allow users of the rust block device driver API to install private data in
> >> the `GenDisk` structure.
> >>
> >> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> >
> > Overall LGTM.
> > Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> >
> >> 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(|| {
> >> + drop(
> >> + // SAFETY: T::QueueData was created by the call to `into_foreign()` above
> >> + unsafe { T::QueueData::from_foreign(data) },
> >> + );
> >
> > This is usually formatted as:
> >
> > // SAFETY: T::QueueData was created by the call to `into_foreign()` above
> > drop(unsafe { T::QueueData::from_foreign(data) });
>
> I don't really have a preference, my optimization function was to
> minimize distance to the unsafe block. Are there any rust guidelines on this?
I would say that the unsafe keyword just has to be on the next line
from the safety comment. Optimizing further than that leads to wonky
formatting. A similar example that I also think is going too far:
let var =
// SAFETY: bla bla
unsafe { value };
Alice
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