rust: block: fix formatting of `kernel::block::mq::request` module

    sync::atomic::{AtomicU64, Ordering},

};

/// A wrapper around a blk-mq `struct request`. This represents an IO request.

/// A wrapper around a blk-mq [`struct request`]. This represents an IO request.

///

/// # Implementation details

///

/// There are four states for a request that the Rust bindings care about:

///

/// A) Request is owned by block layer (refcount 0)

/// B) Request is owned by driver but with zero `ARef`s in existence

///    (refcount 1)

/// C) Request is owned by driver with exactly one `ARef` in existence

///    (refcount 2)

/// D) Request is owned by driver with more than one `ARef` in existence

///    (refcount > 2)

/// 1. Request is owned by block layer (refcount 0).

/// 2. Request is owned by driver but with zero [`ARef`]s in existence

///    (refcount 1).

/// 3. Request is owned by driver with exactly one [`ARef`] in existence

///    (refcount 2).

/// 4. Request is owned by driver with more than one [`ARef`] in existence

///    (refcount > 2).

///

///

/// We need to track A and B to ensure we fail tag to request conversions for

/// We need to track 1 and 2 to ensure we fail tag to request conversions for

/// requests that are not owned by the driver.

///

/// We need to track C and D to ensure that it is safe to end the request and hand

/// We need to track 3 and 4 to ensure that it is safe to end the request and hand

/// back ownership to the block layer.

///

/// The states are tracked through the private `refcount` field of

/// `RequestDataWrapper`. This structure lives in the private data area of the C

/// `struct request`.

/// [`struct request`].

///

/// # Invariants

///

/// * `self.0` is a valid `struct request` created by the C portion of the kernel.

/// * `self.0` is a valid [`struct request`] created by the C portion of the

///   kernel.

/// * The private data area associated with this request must be an initialized

///   and valid `RequestDataWrapper<T>`.

/// * `self` is reference counted by atomic modification of

///   self.wrapper_ref().refcount().

///   `self.wrapper_ref().refcount()`.

///

/// [`struct request`]: srctree/include/linux/blk-mq.h

///

#[repr(transparent)]

pub struct Request<T: Operations>(Opaque<bindings::request>, PhantomData<T>);

impl<T: Operations> Request<T> {

    /// Create an `ARef<Request>` from a `struct request` pointer.

    /// Create an [`ARef<Request>`] from a [`struct request`] pointer.

    ///

    /// # Safety

    ///

    /// * The caller must own a refcount on `ptr` that is transferred to the

    ///   returned `ARef`.

    /// * The type invariants for `Request` must hold for the pointee of `ptr`.

    ///   returned [`ARef`].

    /// * The type invariants for [`Request`] must hold for the pointee of `ptr`.

    ///

    /// [`struct request`]: srctree/include/linux/blk-mq.h

    pub(crate) unsafe fn aref_from_raw(ptr: *mut bindings::request) -> ARef<Self> {

        // INVARIANT: By the safety requirements of this function, invariants are upheld.

        // SAFETY: By the safety requirement of this function, we own a

    }

    /// Try to take exclusive ownership of `this` by dropping the refcount to 0.

    /// This fails if `this` is not the only `ARef` pointing to the underlying

    /// `Request`.

    /// This fails if `this` is not the only [`ARef`] pointing to the underlying

    /// [`Request`].

    ///

    /// If the operation is successful, `Ok` is returned with a pointer to the

    /// C `struct request`. If the operation fails, `this` is returned in the

    /// `Err` variant.

    /// If the operation is successful, [`Ok`] is returned with a pointer to the

    /// C [`struct request`]. If the operation fails, `this` is returned in the

    /// [`Err`] variant.

    ///

    /// [`struct request`]: srctree/include/linux/blk-mq.h

    fn try_set_end(this: ARef<Self>) -> Result<*mut bindings::request, ARef<Self>> {

        // We can race with `TagSet::tag_to_rq`

        if let Err(_old) = this.wrapper_ref().refcount().compare_exchange(

    /// Notify the block layer that the request has been completed without errors.

    ///

    /// This function will return `Err` if `this` is not the only `ARef`

    /// This function will return [`Err`] if `this` is not the only [`ARef`]

    /// referencing the request.

    pub fn end_ok(this: ARef<Self>) -> Result<(), ARef<Self>> {

        let request_ptr = Self::try_set_end(this)?;

        Ok(())

    }

    /// Return a pointer to the `RequestDataWrapper` stored in the private area

    /// Return a pointer to the [`RequestDataWrapper`] stored in the private area

    /// of the request structure.

    ///

    /// # Safety

    ///

    /// - `this` must point to a valid allocation of size at least size of

    ///   `Self` plus size of `RequestDataWrapper`.

    ///   [`Self`] plus size of [`RequestDataWrapper`].

    pub(crate) unsafe fn wrapper_ptr(this: *mut Self) -> NonNull<RequestDataWrapper> {

        let request_ptr = this.cast::<bindings::request>();

        // SAFETY: By safety requirements for this function, `this` is a

        unsafe { NonNull::new_unchecked(wrapper_ptr) }

    }

    /// Return a reference to the `RequestDataWrapper` stored in the private

    /// Return a reference to the [`RequestDataWrapper`] stored in the private

    /// area of the request structure.

    pub(crate) fn wrapper_ref(&self) -> &RequestDataWrapper {

        // SAFETY: By type invariant, `self.0` is a valid allocation. Further,

    }

}

/// A wrapper around data stored in the private area of the C `struct request`.

/// A wrapper around data stored in the private area of the C [`struct request`].

///

/// [`struct request`]: srctree/include/linux/blk-mq.h

pub(crate) struct RequestDataWrapper {

    /// The Rust request refcount has the following states:

    ///

    /// - 0: The request is owned by C block layer.

    /// - 1: The request is owned by Rust abstractions but there are no ARef references to it.

    /// - 2+: There are `ARef` references to the request.

    /// - 1: The request is owned by Rust abstractions but there are no [`ARef`] references to it.

    /// - 2+: There are [`ARef`] references to the request.

    refcount: AtomicU64,

}

}

/// Store the result of `op(target.load)` in `target` if `target.load() !=

/// pred`, returning true if the target was updated.

/// pred`, returning [`true`] if the target was updated.

fn atomic_relaxed_op_unless(target: &AtomicU64, op: impl Fn(u64) -> u64, pred: u64) -> bool {

    target

        .fetch_update(Ordering::Relaxed, Ordering::Relaxed, |x| {