// SPDX-License-Identifier: GPL-2.0 //! This module provides a wrapper for the C `struct request` type.//!//! C header: [`include/linux/blk-mq.h`](srctree/include/linux/blk-mq.h) use crate::{ bindings, block::mq::Operations, error::Result, types::{ARef, AlwaysRefCounted, Opaque},};use core::{ marker::PhantomData, ptr::{addr_of_mut, NonNull}, sync::atomic::{AtomicU64, Ordering},}; /// 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:////// 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 1 and 2 to ensure we fail tag to request conversions for/// requests that are not owned by the driver.////// 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`].////// # Invariants////// * `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()`.////// [`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. /// /// # 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`. /// /// [`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 // reference count that we can pass to `ARef`. unsafe { ARef::from_raw(NonNull::new_unchecked(ptr as *const Self as *mut Self)) } } /// Notify the block layer that a request is going to be processed now. /// /// The block layer uses this hook to do proper initializations such as /// starting the timeout timer. It is a requirement that block device /// drivers call this function when starting to process a request. /// /// # Safety /// /// The caller must have exclusive ownership of `self`, that is /// `self.wrapper_ref().refcount() == 2`. pub(crate) unsafe fn start_unchecked(this: &ARef<Self>) { // SAFETY: By type invariant, `self.0` is a valid `struct request` and // we have exclusive access. unsafe { bindings::blk_mq_start_request(this.0.get()) }; } /// 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`]. /// /// 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( 2, 0, Ordering::Relaxed, Ordering::Relaxed, ) { return Err(this); } let request_ptr = this.0.get(); core::mem::forget(this); Ok(request_ptr) } /// Notify the block layer that the request has been completed without errors. /// /// 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)?; // SAFETY: By type invariant, `this.0` was a valid `struct request`. The // success of the call to `try_set_end` guarantees that there are no // `ARef`s pointing to this request. Therefore it is safe to hand it // back to the block layer. unsafe { bindings::blk_mq_end_request(request_ptr, bindings::BLK_STS_OK as _) }; Ok(()) } /// 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`]. 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 // valid allocation. let wrapper_ptr = unsafe { bindings::blk_mq_rq_to_pdu(request_ptr).cast::<RequestDataWrapper>() }; // SAFETY: By C API contract, wrapper_ptr points to a valid allocation // and is not null. unsafe { NonNull::new_unchecked(wrapper_ptr) } } /// 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, // the private data associated with this request is initialized and // valid. The existence of `&self` guarantees that the private data is // valid as a shared reference. unsafe { Self::wrapper_ptr(self as *const Self as *mut Self).as_ref() } }} /// A wrapper around data stored in the private area of the C [`struct request`].////// [`struct request`]: srctree/include/linux/blk-mq.hpub(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. refcount: AtomicU64,} impl RequestDataWrapper { /// Return a reference to the refcount of the request that is embedding /// `self`. pub(crate) fn refcount(&self) -> &AtomicU64 { &self.refcount } /// Return a pointer to the refcount of the request that is embedding the /// pointee of `this`. /// /// # Safety /// /// - `this` must point to a live allocation of at least the size of `Self`. pub(crate) unsafe fn refcount_ptr(this: *mut Self) -> *mut AtomicU64 { // SAFETY: Because of the safety requirements of this function, the // field projection is safe. unsafe { addr_of_mut!((*this).refcount) } }} // SAFETY: Exclusive access is thread-safe for `Request`. `Request` has no `&mut// self` methods and `&self` methods that mutate `self` are internally// synchronized.unsafe impl<T: Operations> Send for Request<T> {} // SAFETY: Shared access is thread-safe for `Request`. `&self` methods that// mutate `self` are internally synchronized`unsafe impl<T: Operations> Sync for Request<T> {} /// Store the result of `op(target.load())` in target, returning new value of/// target.fn atomic_relaxed_op_return(target: &AtomicU64, op: impl Fn(u64) -> u64) -> u64 { let old = target.fetch_update(Ordering::Relaxed, Ordering::Relaxed, |x| Some(op(x))); // SAFETY: Because the operation passed to `fetch_update` above always // return `Some`, `old` will always be `Ok`. let old = unsafe { old.unwrap_unchecked() }; op(old)} /// Store the result of `op(target.load)` in `target` if `target.load() !=/// 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| { if x == pred { None } else { Some(op(x)) } }) .is_ok()} // SAFETY: All instances of `Request<T>` are reference counted. This// implementation of `AlwaysRefCounted` ensure that increments to the ref count// keeps the object alive in memory at least until a matching reference count// decrement is executed.unsafe impl<T: Operations> AlwaysRefCounted for Request<T> { fn inc_ref(&self) { let refcount = &self.wrapper_ref().refcount(); #[cfg_attr(not(CONFIG_DEBUG_MISC), allow(unused_variables))] let updated = atomic_relaxed_op_unless(refcount, |x| x + 1, 0); #[cfg(CONFIG_DEBUG_MISC)] if !updated { panic!("Request refcount zero on clone") } } unsafe fn dec_ref(obj: core::ptr::NonNull<Self>) { // SAFETY: The type invariants of `ARef` guarantee that `obj` is valid // for read. let wrapper_ptr = unsafe { Self::wrapper_ptr(obj.as_ptr()).as_ptr() }; // SAFETY: The type invariant of `Request` guarantees that the private // data area is initialized and valid. let refcount = unsafe { &*RequestDataWrapper::refcount_ptr(wrapper_ptr) }; #[cfg_attr(not(CONFIG_DEBUG_MISC), allow(unused_variables))] let new_refcount = atomic_relaxed_op_return(refcount, |x| x - 1); #[cfg(CONFIG_DEBUG_MISC)] if new_refcount == 0 { panic!("Request reached refcount zero in Rust abstractions"); } }}
// SPDX-License-Identifier: GPL-2.0
//! This module provides a wrapper for the C `struct request` type.
//!
//! C header: [`include/linux/blk-mq.h`](srctree/include/linux/blk-mq.h)
use crate::{
bindings,
block::mq::Operations,
error::Result,
types::{ARef, AlwaysRefCounted, Opaque},
};
use core::{
marker::PhantomData,
ptr::{addr_of_mut, NonNull},
sync::atomic::{AtomicU64, Ordering},
};
/// 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:
///
/// 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 1 and 2 to ensure we fail tag to request conversions for
/// requests that are not owned by the driver.
///
/// 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`].
///
/// # Invariants
///
/// * `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()`.
///
/// [`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.
///
/// # 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`.
///
/// [`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
// reference count that we can pass to `ARef`.
unsafe { ARef::from_raw(NonNull::new_unchecked(ptr as *const Self as *mut Self)) }
}
/// Notify the block layer that a request is going to be processed now.
///
/// The block layer uses this hook to do proper initializations such as
/// starting the timeout timer. It is a requirement that block device
/// drivers call this function when starting to process a request.
///
/// # Safety
///
/// The caller must have exclusive ownership of `self`, that is
/// `self.wrapper_ref().refcount() == 2`.
pub(crate) unsafe fn start_unchecked(this: &ARef<Self>) {
// SAFETY: By type invariant, `self.0` is a valid `struct request` and
// we have exclusive access.
unsafe { bindings::blk_mq_start_request(this.0.get()) };
}
/// 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`].
///
/// 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(
2,
0,
Ordering::Relaxed,
Ordering::Relaxed,
) {
return Err(this);
}
let request_ptr = this.0.get();
core::mem::forget(this);
Ok(request_ptr)
}
/// Notify the block layer that the request has been completed without errors.
///
/// 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)?;
// SAFETY: By type invariant, `this.0` was a valid `struct request`. The
// success of the call to `try_set_end` guarantees that there are no
// `ARef`s pointing to this request. Therefore it is safe to hand it
// back to the block layer.
unsafe { bindings::blk_mq_end_request(request_ptr, bindings::BLK_STS_OK as _) };
Ok(())
}
/// 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`].
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
// valid allocation.
let wrapper_ptr =
unsafe { bindings::blk_mq_rq_to_pdu(request_ptr).cast::<RequestDataWrapper>() };
// SAFETY: By C API contract, wrapper_ptr points to a valid allocation
// and is not null.
unsafe { NonNull::new_unchecked(wrapper_ptr) }
}
/// 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,
// the private data associated with this request is initialized and
// valid. The existence of `&self` guarantees that the private data is
// valid as a shared reference.
unsafe { Self::wrapper_ptr(self as *const Self as *mut Self).as_ref() }
}
}
/// 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.
refcount: AtomicU64,
}
impl RequestDataWrapper {
/// Return a reference to the refcount of the request that is embedding
/// `self`.
pub(crate) fn refcount(&self) -> &AtomicU64 {
&self.refcount
}
/// Return a pointer to the refcount of the request that is embedding the
/// pointee of `this`.
///
/// # Safety
///
/// - `this` must point to a live allocation of at least the size of `Self`.
pub(crate) unsafe fn refcount_ptr(this: *mut Self) -> *mut AtomicU64 {
// SAFETY: Because of the safety requirements of this function, the
// field projection is safe.
unsafe { addr_of_mut!((*this).refcount) }
}
}
// SAFETY: Exclusive access is thread-safe for `Request`. `Request` has no `&mut
// self` methods and `&self` methods that mutate `self` are internally
// synchronized.
unsafe impl<T: Operations> Send for Request<T> {}
// SAFETY: Shared access is thread-safe for `Request`. `&self` methods that
// mutate `self` are internally synchronized`
unsafe impl<T: Operations> Sync for Request<T> {}
/// Store the result of `op(target.load())` in target, returning new value of
/// target.
fn atomic_relaxed_op_return(target: &AtomicU64, op: impl Fn(u64) -> u64) -> u64 {
let old = target.fetch_update(Ordering::Relaxed, Ordering::Relaxed, |x| Some(op(x)));
// SAFETY: Because the operation passed to `fetch_update` above always
// return `Some`, `old` will always be `Ok`.
let old = unsafe { old.unwrap_unchecked() };
op(old)
}
/// Store the result of `op(target.load)` in `target` if `target.load() !=
/// 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| {
if x == pred {
None
} else {
Some(op(x))
}
})
.is_ok()
}
// SAFETY: All instances of `Request<T>` are reference counted. This
// implementation of `AlwaysRefCounted` ensure that increments to the ref count
// keeps the object alive in memory at least until a matching reference count
// decrement is executed.
unsafe impl<T: Operations> AlwaysRefCounted for Request<T> {
fn inc_ref(&self) {
let refcount = &self.wrapper_ref().refcount();
#[cfg_attr(not(CONFIG_DEBUG_MISC), allow(unused_variables))]
let updated = atomic_relaxed_op_unless(refcount, |x| x + 1, 0);
#[cfg(CONFIG_DEBUG_MISC)]
if !updated {
panic!("Request refcount zero on clone")
}
}
unsafe fn dec_ref(obj: core::ptr::NonNull<Self>) {
// SAFETY: The type invariants of `ARef` guarantee that `obj` is valid
// for read.
let wrapper_ptr = unsafe { Self::wrapper_ptr(obj.as_ptr()).as_ptr() };
// SAFETY: The type invariant of `Request` guarantees that the private
// data area is initialized and valid.
let refcount = unsafe { &*RequestDataWrapper::refcount_ptr(wrapper_ptr) };
#[cfg_attr(not(CONFIG_DEBUG_MISC), allow(unused_variables))]
let new_refcount = atomic_relaxed_op_return(refcount, |x| x - 1);
#[cfg(CONFIG_DEBUG_MISC)]
if new_refcount == 0 {
panic!("Request reached refcount zero in Rust abstractions");
}
}
}