rust/kernel/devres.rs - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0

 //! Devres abstraction
 //!
 //! [`Devres`] represents an abstraction for the kernel devres (device resource management)
 //! implementation.

 use crate::{
     alloc::Flags,
     bindings,
     device::{Bound, Device},
     error::{to_result, Error, Result},
     ffi::c_void,
     prelude::*,
     revocable::{Revocable, RevocableGuard},
     sync::{rcu, Completion},
     types::{ARef, ForeignOwnable, Opaque, ScopeGuard},
 };

 use pin_init::Wrapper;

 /// [`Devres`] inner data accessed from [`Devres::callback`].
 #[pin_data]
 struct Inner<T: Send> {
     #[pin]
     data: Revocable<T>,
     /// Tracks whether [`Devres::callback`] has been completed.
     #[pin]
     devm: Completion,
     /// Tracks whether revoking [`Self::data`] has been completed.
     #[pin]
     revoke: Completion,
 }

 /// This abstraction is meant to be used by subsystems to containerize [`Device`] bound resources to
 /// manage their lifetime.
 ///
 /// [`Device`] bound resources should be freed when either the resource goes out of scope or the
 /// [`Device`] is unbound respectively, depending on what happens first. In any case, it is always
 /// guaranteed that revoking the device resource is completed before the corresponding [`Device`]
 /// is unbound.
 ///
 /// To achieve that [`Devres`] registers a devres callback on creation, which is called once the
 /// [`Device`] is unbound, revoking access to the encapsulated resource (see also [`Revocable`]).
 ///
 /// After the [`Devres`] has been unbound it is not possible to access the encapsulated resource
 /// anymore.
 ///
 /// [`Devres`] users should make sure to simply free the corresponding backing resource in `T`'s
 /// [`Drop`] implementation.
 ///
 /// # Examples
 ///
 /// ```no_run
 /// # use kernel::{bindings, device::{Bound, Device}, devres::Devres, io::{Io, IoRaw}};
 /// # use core::ops::Deref;
 ///
 /// // See also [`pci::Bar`] for a real example.
 /// struct IoMem<const SIZE: usize>(IoRaw<SIZE>);
 ///
 /// impl<const SIZE: usize> IoMem<SIZE> {
 ///     /// # Safety
 ///     ///
 ///     /// [`paddr`, `paddr` + `SIZE`) must be a valid MMIO region that is mappable into the CPUs
 ///     /// virtual address space.
 ///     unsafe fn new(paddr: usize) -> Result<Self>{
 ///         // SAFETY: By the safety requirements of this function [`paddr`, `paddr` + `SIZE`) is
 ///         // valid for `ioremap`.
 ///         let addr = unsafe { bindings::ioremap(paddr as bindings::phys_addr_t, SIZE) };
 ///         if addr.is_null() {
 ///             return Err(ENOMEM);
 ///         }
 ///
 ///         Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
 ///     }
 /// }
 ///
 /// impl<const SIZE: usize> Drop for IoMem<SIZE> {
 ///     fn drop(&mut self) {
 ///         // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
 ///         unsafe { bindings::iounmap(self.0.addr() as *mut c_void); };
 ///     }
 /// }
 ///
 /// impl<const SIZE: usize> Deref for IoMem<SIZE> {
 ///    type Target = Io<SIZE>;
 ///
 ///    fn deref(&self) -> &Self::Target {
 ///         // SAFETY: The memory range stored in `self` has been properly mapped in `Self::new`.
 ///         unsafe { Io::from_raw(&self.0) }
 ///    }
 /// }
 /// # fn no_run(dev: &Device<Bound>) -> Result<(), Error> {
 /// // SAFETY: Invalid usage for example purposes.
 /// let iomem = unsafe { IoMem::<{ core::mem::size_of::<u32>() }>::new(0xBAAAAAAD)? };
 /// let devres = KBox::pin_init(Devres::new(dev, iomem), GFP_KERNEL)?;
 ///
 /// let res = devres.try_access().ok_or(ENXIO)?;
 /// res.write8(0x42, 0x0);
 /// # Ok(())
 /// # }
 /// ```
 ///
 /// # Invariants
 ///
 /// [`Self::inner`] is guaranteed to be initialized and is always accessed read-only.
 #[pin_data(PinnedDrop)]
 pub struct Devres<T: Send> {
     dev: ARef<Device>,
     /// Pointer to [`Self::devres_callback`].
     ///
     /// Has to be stored, since Rust does not guarantee to always return the same address for a
     /// function. However, the C API uses the address as a key.
     callback: unsafe extern "C" fn(*mut c_void),
     /// Contains all the fields shared with [`Self::callback`].
     // TODO: Replace with `UnsafePinned`, once available.
     //
     // Subsequently, the `drop_in_place()` in `Devres::drop` and the explicit `Send` and `Sync'
     // impls can be removed.
     #[pin]
     inner: Opaque<Inner<T>>,
 }

 impl<T: Send> Devres<T> {
     /// Creates a new [`Devres`] instance of the given `data`.
     ///
     /// The `data` encapsulated within the returned `Devres` instance' `data` will be
     /// (revoked)[`Revocable`] once the device is detached.
     pub fn new<'a, E>(
         dev: &'a Device<Bound>,
         data: impl PinInit<T, E> + 'a,
     ) -> impl PinInit<Self, Error> + 'a
     where
         T: 'a,
         Error: From<E>,
     {
         let callback = Self::devres_callback;

         try_pin_init!(&this in Self {
             dev: dev.into(),
             callback,
             // INVARIANT: `inner` is properly initialized.
             inner <- {
                 // SAFETY: `this` is a valid pointer to uninitialized memory.
                 let inner = unsafe { &raw mut (*this.as_ptr()).inner };

                 // SAFETY:
                 // - `dev.as_raw()` is a pointer to a valid bound device.
                 // - `inner` is guaranteed to be a valid for the duration of the lifetime of `Self`.
                 // - `devm_add_action()` is guaranteed not to call `callback` until `this` has been
                 //    properly initialized, because we require `dev` (i.e. the *bound* device) to
                 //    live at least as long as the returned `impl PinInit<Self, Error>`.
                 to_result(unsafe {
                     bindings::devm_add_action(dev.as_raw(), Some(callback), inner.cast())
                 })?;

                 Opaque::pin_init(try_pin_init!(Inner {
                     devm <- Completion::new(),
                     revoke <- Completion::new(),
                     data <- Revocable::new(data),
                 }))
             },
         })
     }

     fn inner(&self) -> &Inner<T> {
         // SAFETY: By the type invairants of `Self`, `inner` is properly initialized and always
         // accessed read-only.
         unsafe { &*self.inner.get() }
     }

     fn data(&self) -> &Revocable<T> {
         &self.inner().data
     }

     #[allow(clippy::missing_safety_doc)]
     unsafe extern "C" fn devres_callback(ptr: *mut kernel::ffi::c_void) {
         // SAFETY: In `Self::new` we've passed a valid pointer to `Inner` to `devm_add_action()`,
         // hence `ptr` must be a valid pointer to `Inner`.
         let inner = unsafe { &*ptr.cast::<Inner<T>>() };

         // Ensure that `inner` can't be used anymore after we signal completion of this callback.
         let inner = ScopeGuard::new_with_data(inner, |inner| inner.devm.complete_all());

         if !inner.data.revoke() {
             // If `revoke()` returns false, it means that `Devres::drop` already started revoking
             // `data` for us. Hence we have to wait until `Devres::drop` signals that it
             // completed revoking `data`.
             inner.revoke.wait_for_completion();
         }
     }

     fn remove_action(&self) -> bool {
         // SAFETY:
         // - `self.dev` is a valid `Device`,
         // - the `action` and `data` pointers are the exact same ones as given to
         //   `devm_add_action()` previously,
         (unsafe {
             bindings::devm_remove_action_nowarn(
                 self.dev.as_raw(),
                 Some(self.callback),
                 core::ptr::from_ref(self.inner()).cast_mut().cast(),
             )
         } == 0)
     }

     /// Return a reference of the [`Device`] this [`Devres`] instance has been created with.
     pub fn device(&self) -> &Device {
         &self.dev
     }

     /// Obtain `&'a T`, bypassing the [`Revocable`].
     ///
     /// This method allows to directly obtain a `&'a T`, bypassing the [`Revocable`], by presenting
     /// a `&'a Device<Bound>` of the same [`Device`] this [`Devres`] instance has been created with.
     ///
     /// # Errors
     ///
     /// An error is returned if `dev` does not match the same [`Device`] this [`Devres`] instance
     /// has been created with.
     ///
     /// # Examples
     ///
     /// ```no_run
     /// # #![cfg(CONFIG_PCI)]
     /// # use kernel::{device::Core, devres::Devres, pci};
     ///
     /// fn from_core(dev: &pci::Device<Core>, devres: Devres<pci::Bar<0x4>>) -> Result {
     ///     let bar = devres.access(dev.as_ref())?;
     ///
     ///     let _ = bar.read32(0x0);
     ///
     ///     // might_sleep()
     ///
     ///     bar.write32(0x42, 0x0);
     ///
     ///     Ok(())
     /// }
     /// ```
     pub fn access<'a>(&'a self, dev: &'a Device<Bound>) -> Result<&'a T> {
         if self.dev.as_raw() != dev.as_raw() {
             return Err(EINVAL);
         }

         // SAFETY: `dev` being the same device as the device this `Devres` has been created for
         // proves that `self.data` hasn't been revoked and is guaranteed to not be revoked as long
         // as `dev` lives; `dev` lives at least as long as `self`.
         Ok(unsafe { self.data().access() })
     }

     /// [`Devres`] accessor for [`Revocable::try_access`].
     pub fn try_access(&self) -> Option<RevocableGuard<'_, T>> {
         self.data().try_access()
     }

     /// [`Devres`] accessor for [`Revocable::try_access_with`].
     pub fn try_access_with<R, F: FnOnce(&T) -> R>(&self, f: F) -> Option<R> {
         self.data().try_access_with(f)
     }

     /// [`Devres`] accessor for [`Revocable::try_access_with_guard`].
     pub fn try_access_with_guard<'a>(&'a self, guard: &'a rcu::Guard) -> Option<&'a T> {
         self.data().try_access_with_guard(guard)
     }
 }

 // SAFETY: `Devres` can be send to any task, if `T: Send`.
 unsafe impl<T: Send> Send for Devres<T> {}

 // SAFETY: `Devres` can be shared with any task, if `T: Sync`.
 unsafe impl<T: Send + Sync> Sync for Devres<T> {}

 #[pinned_drop]
 impl<T: Send> PinnedDrop for Devres<T> {
     fn drop(self: Pin<&mut Self>) {
         // SAFETY: When `drop` runs, it is guaranteed that nobody is accessing the revocable data
         // anymore, hence it is safe not to wait for the grace period to finish.
         if unsafe { self.data().revoke_nosync() } {
             // We revoked `self.data` before the devres action did, hence try to remove it.
             if !self.remove_action() {
                 // We could not remove the devres action, which means that it now runs concurrently,
                 // hence signal that `self.data` has been revoked by us successfully.
                 self.inner().revoke.complete_all();

                 // Wait for `Self::devres_callback` to be done using this object.
                 self.inner().devm.wait_for_completion();
             }
         } else {
             // `Self::devres_callback` revokes `self.data` for us, hence wait for it to be done
             // using this object.
             self.inner().devm.wait_for_completion();
         }

         // INVARIANT: At this point it is guaranteed that `inner` can't be accessed any more.
         //
         // SAFETY: `inner` is valid for dropping.
         unsafe { core::ptr::drop_in_place(self.inner.get()) };
     }
 }

 /// Consume `data` and [`Drop::drop`] `data` once `dev` is unbound.
 fn register_foreign<P>(dev: &Device<Bound>, data: P) -> Result
 where
     P: ForeignOwnable + Send + 'static,
 {
     let ptr = data.into_foreign();

     #[allow(clippy::missing_safety_doc)]
     unsafe extern "C" fn callback<P: ForeignOwnable>(ptr: *mut kernel::ffi::c_void) {
         // SAFETY: `ptr` is the pointer to the `ForeignOwnable` leaked above and hence valid.
         drop(unsafe { P::from_foreign(ptr.cast()) });
     }

     // SAFETY:
     // - `dev.as_raw()` is a pointer to a valid and bound device.
     // - `ptr` is a valid pointer the `ForeignOwnable` devres takes ownership of.
     to_result(unsafe {
         // `devm_add_action_or_reset()` also calls `callback` on failure, such that the
         // `ForeignOwnable` is released eventually.
         bindings::devm_add_action_or_reset(dev.as_raw(), Some(callback::<P>), ptr.cast())
     })
 }

 /// Encapsulate `data` in a [`KBox`] and [`Drop::drop`] `data` once `dev` is unbound.
 ///
 /// # Examples
 ///
 /// ```no_run
 /// use kernel::{device::{Bound, Device}, devres};
 ///
 /// /// Registration of e.g. a class device, IRQ, etc.
 /// struct Registration;
 ///
 /// impl Registration {
 ///     fn new() -> Self {
 ///         // register
 ///
 ///         Self
 ///     }
 /// }
 ///
 /// impl Drop for Registration {
 ///     fn drop(&mut self) {
 ///        // unregister
 ///     }
 /// }
 ///
 /// fn from_bound_context(dev: &Device<Bound>) -> Result {
 ///     devres::register(dev, Registration::new(), GFP_KERNEL)
 /// }
 /// ```
 pub fn register<T, E>(dev: &Device<Bound>, data: impl PinInit<T, E>, flags: Flags) -> Result
 where
     T: Send + 'static,
     Error: From<E>,
 {
     let data = KBox::pin_init(data, flags)?;

     register_foreign(dev, data)
 }
	// SPDX-License-Identifier: GPL-2.0

	//! Devres abstraction
	//!
	//! [`Devres`] represents an abstraction for the kernel devres (device resource management)
	//! implementation.

	use crate::{
	alloc::Flags,
	bindings,
	device::{Bound, Device},
	error::{to_result, Error, Result},
	ffi::c_void,
	prelude::*,
	revocable::{Revocable, RevocableGuard},
	sync::{rcu, Completion},
	types::{ARef, ForeignOwnable, Opaque, ScopeGuard},
	};

	use pin_init::Wrapper;

	/// [`Devres`] inner data accessed from [`Devres::callback`].
	#[pin_data]
	struct Inner<T: Send> {
	#[pin]
	data: Revocable<T>,
	/// Tracks whether [`Devres::callback`] has been completed.
	#[pin]
	devm: Completion,
	/// Tracks whether revoking [`Self::data`] has been completed.
	#[pin]
	revoke: Completion,
	}

	/// This abstraction is meant to be used by subsystems to containerize [`Device`] bound resources to
	/// manage their lifetime.
	///
	/// [`Device`] bound resources should be freed when either the resource goes out of scope or the
	/// [`Device`] is unbound respectively, depending on what happens first. In any case, it is always
	/// guaranteed that revoking the device resource is completed before the corresponding [`Device`]
	/// is unbound.
	///
	/// To achieve that [`Devres`] registers a devres callback on creation, which is called once the
	/// [`Device`] is unbound, revoking access to the encapsulated resource (see also [`Revocable`]).
	///
	/// After the [`Devres`] has been unbound it is not possible to access the encapsulated resource
	/// anymore.
	///
	/// [`Devres`] users should make sure to simply free the corresponding backing resource in `T`'s
	/// [`Drop`] implementation.
	///
	/// # Examples
	///
	/// ```no_run
	/// # use kernel::{bindings, device::{Bound, Device}, devres::Devres, io::{Io, IoRaw}};
	/// # use core::ops::Deref;
	///
	/// // See also [`pci::Bar`] for a real example.
	/// struct IoMem<const SIZE: usize>(IoRaw<SIZE>);
	///
	/// impl<const SIZE: usize> IoMem<SIZE> {
	/// /// # Safety
	/// ///
	/// /// [`paddr`, `paddr` + `SIZE`) must be a valid MMIO region that is mappable into the CPUs
	/// /// virtual address space.
	/// unsafe fn new(paddr: usize) -> Result<Self>{
	/// // SAFETY: By the safety requirements of this function [`paddr`, `paddr` + `SIZE`) is
	/// // valid for `ioremap`.
	/// let addr = unsafe { bindings::ioremap(paddr as bindings::phys_addr_t, SIZE) };
	/// if addr.is_null() {
	/// return Err(ENOMEM);
	/// }
	///
	/// Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
	/// }
	/// }
	///
	/// impl<const SIZE: usize> Drop for IoMem<SIZE> {
	/// fn drop(&mut self) {
	/// // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
	/// unsafe { bindings::iounmap(self.0.addr() as *mut c_void); };
	/// }
	/// }
	///
	/// impl<const SIZE: usize> Deref for IoMem<SIZE> {
	/// type Target = Io<SIZE>;
	///
	/// fn deref(&self) -> &Self::Target {
	/// // SAFETY: The memory range stored in `self` has been properly mapped in `Self::new`.
	/// unsafe { Io::from_raw(&self.0) }
	/// }
	/// }
	/// # fn no_run(dev: &Device<Bound>) -> Result<(), Error> {
	/// // SAFETY: Invalid usage for example purposes.
	/// let iomem = unsafe { IoMem::<{ core::mem::size_of::<u32>() }>::new(0xBAAAAAAD)? };
	/// let devres = KBox::pin_init(Devres::new(dev, iomem), GFP_KERNEL)?;
	///
	/// let res = devres.try_access().ok_or(ENXIO)?;
	/// res.write8(0x42, 0x0);
	/// # Ok(())
	/// # }
	/// ```
	///
	/// # Invariants
	///
	/// [`Self::inner`] is guaranteed to be initialized and is always accessed read-only.
	#[pin_data(PinnedDrop)]
	pub struct Devres<T: Send> {
	dev: ARef<Device>,
	/// Pointer to [`Self::devres_callback`].
	///
	/// Has to be stored, since Rust does not guarantee to always return the same address for a
	/// function. However, the C API uses the address as a key.
	callback: unsafe extern "C" fn(*mut c_void),
	/// Contains all the fields shared with [`Self::callback`].
	// TODO: Replace with `UnsafePinned`, once available.
	//
	// Subsequently, the `drop_in_place()` in `Devres::drop` and the explicit `Send` and `Sync'
	// impls can be removed.
	#[pin]
	inner: Opaque<Inner<T>>,
	}

	impl<T: Send> Devres<T> {
	/// Creates a new [`Devres`] instance of the given `data`.
	///
	/// The `data` encapsulated within the returned `Devres` instance' `data` will be
	/// (revoked)[`Revocable`] once the device is detached.
	pub fn new<'a, E>(
	dev: &'a Device<Bound>,
	data: impl PinInit<T, E> + 'a,
	) -> impl PinInit<Self, Error> + 'a
	where
	T: 'a,
	Error: From<E>,
	{
	let callback = Self::devres_callback;

	try_pin_init!(&this in Self {
	dev: dev.into(),
	callback,
	// INVARIANT: `inner` is properly initialized.
	inner <- {
	// SAFETY: `this` is a valid pointer to uninitialized memory.
	let inner = unsafe { &raw mut (*this.as_ptr()).inner };

	// SAFETY:
	// - `dev.as_raw()` is a pointer to a valid bound device.
	// - `inner` is guaranteed to be a valid for the duration of the lifetime of `Self`.
	// - `devm_add_action()` is guaranteed not to call `callback` until `this` has been
	// properly initialized, because we require `dev` (i.e. the bound device) to
	// live at least as long as the returned `impl PinInit<Self, Error>`.
	to_result(unsafe {
	bindings::devm_add_action(dev.as_raw(), Some(callback), inner.cast())
	})?;

	Opaque::pin_init(try_pin_init!(Inner {
	devm <- Completion::new(),
	revoke <- Completion::new(),
	data <- Revocable::new(data),
	}))
	},
	})
	}

	fn inner(&self) -> &Inner<T> {
	// SAFETY: By the type invairants of `Self`, `inner` is properly initialized and always
	// accessed read-only.
	unsafe { &*self.inner.get() }
	}

	fn data(&self) -> &Revocable<T> {
	&self.inner().data
	}

	#[allow(clippy::missing_safety_doc)]
	unsafe extern "C" fn devres_callback(ptr: *mut kernel::ffi::c_void) {
	// SAFETY: In `Self::new` we've passed a valid pointer to `Inner` to `devm_add_action()`,
	// hence `ptr` must be a valid pointer to `Inner`.
	let inner = unsafe { &*ptr.cast::<Inner<T>>() };

	// Ensure that `inner` can't be used anymore after we signal completion of this callback.
	let inner = ScopeGuard::new_with_data(inner, \|inner\| inner.devm.complete_all());

	if !inner.data.revoke() {
	// If `revoke()` returns false, it means that `Devres::drop` already started revoking
	// `data` for us. Hence we have to wait until `Devres::drop` signals that it
	// completed revoking `data`.
	inner.revoke.wait_for_completion();
	}
	}

	fn remove_action(&self) -> bool {
	// SAFETY:
	// - `self.dev` is a valid `Device`,
	// - the `action` and `data` pointers are the exact same ones as given to
	// `devm_add_action()` previously,
	(unsafe {
	bindings::devm_remove_action_nowarn(
	self.dev.as_raw(),
	Some(self.callback),
	core::ptr::from_ref(self.inner()).cast_mut().cast(),
	)
	} == 0)
	}

	/// Return a reference of the [`Device`] this [`Devres`] instance has been created with.
	pub fn device(&self) -> &Device {
	&self.dev
	}

	/// Obtain `&'a T`, bypassing the [`Revocable`].
	///
	/// This method allows to directly obtain a `&'a T`, bypassing the [`Revocable`], by presenting
	/// a `&'a Device<Bound>` of the same [`Device`] this [`Devres`] instance has been created with.
	///
	/// # Errors
	///
	/// An error is returned if `dev` does not match the same [`Device`] this [`Devres`] instance
	/// has been created with.
	///
	/// # Examples
	///
	/// ```no_run
	/// # #![cfg(CONFIG_PCI)]
	/// # use kernel::{device::Core, devres::Devres, pci};
	///
	/// fn from_core(dev: &pci::Device<Core>, devres: Devres<pci::Bar<0x4>>) -> Result {
	/// let bar = devres.access(dev.as_ref())?;
	///
	/// let _ = bar.read32(0x0);
	///
	/// // might_sleep()
	///
	/// bar.write32(0x42, 0x0);
	///
	/// Ok(())
	/// }
	/// ```
	pub fn access<'a>(&'a self, dev: &'a Device<Bound>) -> Result<&'a T> {
	if self.dev.as_raw() != dev.as_raw() {
	return Err(EINVAL);
	}

	// SAFETY: `dev` being the same device as the device this `Devres` has been created for
	// proves that `self.data` hasn't been revoked and is guaranteed to not be revoked as long
	// as `dev` lives; `dev` lives at least as long as `self`.
	Ok(unsafe { self.data().access() })
	}

	/// [`Devres`] accessor for [`Revocable::try_access`].
	pub fn try_access(&self) -> Option<RevocableGuard<'_, T>> {
	self.data().try_access()
	}

	/// [`Devres`] accessor for [`Revocable::try_access_with`].
	pub fn try_access_with<R, F: FnOnce(&T) -> R>(&self, f: F) -> Option<R> {
	self.data().try_access_with(f)
	}

	/// [`Devres`] accessor for [`Revocable::try_access_with_guard`].
	pub fn try_access_with_guard<'a>(&'a self, guard: &'a rcu::Guard) -> Option<&'a T> {
	self.data().try_access_with_guard(guard)
	}
	}

	// SAFETY: `Devres` can be send to any task, if `T: Send`.
	unsafe impl<T: Send> Send for Devres<T> {}

	// SAFETY: `Devres` can be shared with any task, if `T: Sync`.
	unsafe impl<T: Send + Sync> Sync for Devres<T> {}

	#[pinned_drop]
	impl<T: Send> PinnedDrop for Devres<T> {
	fn drop(self: Pin<&mut Self>) {
	// SAFETY: When `drop` runs, it is guaranteed that nobody is accessing the revocable data
	// anymore, hence it is safe not to wait for the grace period to finish.
	if unsafe { self.data().revoke_nosync() } {
	// We revoked `self.data` before the devres action did, hence try to remove it.
	if !self.remove_action() {
	// We could not remove the devres action, which means that it now runs concurrently,
	// hence signal that `self.data` has been revoked by us successfully.
	self.inner().revoke.complete_all();

	// Wait for `Self::devres_callback` to be done using this object.
	self.inner().devm.wait_for_completion();
	}
	} else {
	// `Self::devres_callback` revokes `self.data` for us, hence wait for it to be done
	// using this object.
	self.inner().devm.wait_for_completion();
	}

	// INVARIANT: At this point it is guaranteed that `inner` can't be accessed any more.
	//
	// SAFETY: `inner` is valid for dropping.
	unsafe { core::ptr::drop_in_place(self.inner.get()) };
	}
	}

	/// Consume `data` and [`Drop::drop`] `data` once `dev` is unbound.
	fn register_foreign<P>(dev: &Device<Bound>, data: P) -> Result
	where
	P: ForeignOwnable + Send + 'static,
	{
	let ptr = data.into_foreign();

	#[allow(clippy::missing_safety_doc)]
	unsafe extern "C" fn callback<P: ForeignOwnable>(ptr: *mut kernel::ffi::c_void) {
	// SAFETY: `ptr` is the pointer to the `ForeignOwnable` leaked above and hence valid.
	drop(unsafe { P::from_foreign(ptr.cast()) });
	}

	// SAFETY:
	// - `dev.as_raw()` is a pointer to a valid and bound device.
	// - `ptr` is a valid pointer the `ForeignOwnable` devres takes ownership of.
	to_result(unsafe {
	// `devm_add_action_or_reset()` also calls `callback` on failure, such that the
	// `ForeignOwnable` is released eventually.
	bindings::devm_add_action_or_reset(dev.as_raw(), Some(callback::<P>), ptr.cast())
	})
	}

	/// Encapsulate `data` in a [`KBox`] and [`Drop::drop`] `data` once `dev` is unbound.
	///
	/// # Examples
	///
	/// ```no_run
	/// use kernel::{device::{Bound, Device}, devres};
	///
	/// /// Registration of e.g. a class device, IRQ, etc.
	/// struct Registration;
	///
	/// impl Registration {
	/// fn new() -> Self {
	/// // register
	///
	/// Self
	/// }
	/// }
	///
	/// impl Drop for Registration {
	/// fn drop(&mut self) {
	/// // unregister
	/// }
	/// }
	///
	/// fn from_bound_context(dev: &Device<Bound>) -> Result {
	/// devres::register(dev, Registration::new(), GFP_KERNEL)
	/// }
	/// ```
	pub fn register<T, E>(dev: &Device<Bound>, data: impl PinInit<T, E>, flags: Flags) -> Result
	where
	T: Send + 'static,
	Error: From<E>,
	{
	let data = KBox::pin_init(data, flags)?;

	register_foreign(dev, data)
	}