kernel/
devres.rs

1// SPDX-License-Identifier: GPL-2.0
2
3//! Devres abstraction
4//!
5//! [`Devres`] represents an abstraction for the kernel devres (device resource management)
6//! implementation.
7
8use crate::{
9    alloc::Flags,
10    bindings,
11    device::{
12        Bound,
13        Device, //
14    },
15    error::to_result,
16    prelude::*,
17    revocable::{
18        Revocable,
19        RevocableGuard, //
20    },
21    sync::{
22        aref::ARef,
23        rcu,
24        Completion, //
25    },
26    types::{
27        ForeignOwnable,
28        Opaque,
29        ScopeGuard, //
30    },
31};
32
33use pin_init::Wrapper;
34
35/// [`Devres`] inner data accessed from [`Devres::callback`].
36#[pin_data]
37struct Inner<T: Send> {
38    #[pin]
39    data: Revocable<T>,
40    /// Tracks whether [`Devres::callback`] has been completed.
41    #[pin]
42    devm: Completion,
43    /// Tracks whether revoking [`Self::data`] has been completed.
44    #[pin]
45    revoke: Completion,
46}
47
48/// This abstraction is meant to be used by subsystems to containerize [`Device`] bound resources to
49/// manage their lifetime.
50///
51/// [`Device`] bound resources should be freed when either the resource goes out of scope or the
52/// [`Device`] is unbound respectively, depending on what happens first. In any case, it is always
53/// guaranteed that revoking the device resource is completed before the corresponding [`Device`]
54/// is unbound.
55///
56/// To achieve that [`Devres`] registers a devres callback on creation, which is called once the
57/// [`Device`] is unbound, revoking access to the encapsulated resource (see also [`Revocable`]).
58///
59/// After the [`Devres`] has been unbound it is not possible to access the encapsulated resource
60/// anymore.
61///
62/// [`Devres`] users should make sure to simply free the corresponding backing resource in `T`'s
63/// [`Drop`] implementation.
64///
65/// # Examples
66///
67/// ```no_run
68/// use kernel::{
69///     bindings,
70///     device::{
71///         Bound,
72///         Device,
73///     },
74///     devres::Devres,
75///     io::{
76///         Io,
77///         IoRaw,
78///         PhysAddr,
79///     },
80/// };
81/// use core::ops::Deref;
82///
83/// // See also [`pci::Bar`] for a real example.
84/// struct IoMem<const SIZE: usize>(IoRaw<SIZE>);
85///
86/// impl<const SIZE: usize> IoMem<SIZE> {
87///     /// # Safety
88///     ///
89///     /// [`paddr`, `paddr` + `SIZE`) must be a valid MMIO region that is mappable into the CPUs
90///     /// virtual address space.
91///     unsafe fn new(paddr: usize) -> Result<Self>{
92///         // SAFETY: By the safety requirements of this function [`paddr`, `paddr` + `SIZE`) is
93///         // valid for `ioremap`.
94///         let addr = unsafe { bindings::ioremap(paddr as PhysAddr, SIZE) };
95///         if addr.is_null() {
96///             return Err(ENOMEM);
97///         }
98///
99///         Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
100///     }
101/// }
102///
103/// impl<const SIZE: usize> Drop for IoMem<SIZE> {
104///     fn drop(&mut self) {
105///         // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
106///         unsafe { bindings::iounmap(self.0.addr() as *mut c_void); };
107///     }
108/// }
109///
110/// impl<const SIZE: usize> Deref for IoMem<SIZE> {
111///    type Target = Io<SIZE>;
112///
113///    fn deref(&self) -> &Self::Target {
114///         // SAFETY: The memory range stored in `self` has been properly mapped in `Self::new`.
115///         unsafe { Io::from_raw(&self.0) }
116///    }
117/// }
118/// # fn no_run(dev: &Device<Bound>) -> Result<(), Error> {
119/// // SAFETY: Invalid usage for example purposes.
120/// let iomem = unsafe { IoMem::<{ core::mem::size_of::<u32>() }>::new(0xBAAAAAAD)? };
121/// let devres = KBox::pin_init(Devres::new(dev, iomem), GFP_KERNEL)?;
122///
123/// let res = devres.try_access().ok_or(ENXIO)?;
124/// res.write8(0x42, 0x0);
125/// # Ok(())
126/// # }
127/// ```
128///
129/// # Invariants
130///
131/// `Self::inner` is guaranteed to be initialized and is always accessed read-only.
132#[pin_data(PinnedDrop)]
133pub struct Devres<T: Send> {
134    dev: ARef<Device>,
135    /// Pointer to [`Self::devres_callback`].
136    ///
137    /// Has to be stored, since Rust does not guarantee to always return the same address for a
138    /// function. However, the C API uses the address as a key.
139    callback: unsafe extern "C" fn(*mut c_void),
140    /// Contains all the fields shared with [`Self::callback`].
141    // TODO: Replace with `UnsafePinned`, once available.
142    //
143    // Subsequently, the `drop_in_place()` in `Devres::drop` and `Devres::new` as well as the
144    // explicit `Send` and `Sync' impls can be removed.
145    #[pin]
146    inner: Opaque<Inner<T>>,
147    _add_action: (),
148}
149
150impl<T: Send> Devres<T> {
151    /// Creates a new [`Devres`] instance of the given `data`.
152    ///
153    /// The `data` encapsulated within the returned `Devres` instance' `data` will be
154    /// (revoked)[`Revocable`] once the device is detached.
155    pub fn new<'a, E>(
156        dev: &'a Device<Bound>,
157        data: impl PinInit<T, E> + 'a,
158    ) -> impl PinInit<Self, Error> + 'a
159    where
160        T: 'a,
161        Error: From<E>,
162    {
163        try_pin_init!(&this in Self {
164            dev: dev.into(),
165            callback: Self::devres_callback,
166            // INVARIANT: `inner` is properly initialized.
167            inner <- Opaque::pin_init(try_pin_init!(Inner {
168                    devm <- Completion::new(),
169                    revoke <- Completion::new(),
170                    data <- Revocable::new(data),
171            })),
172            // TODO: Replace with "initializer code blocks" [1] once available.
173            //
174            // [1] https://github.com/Rust-for-Linux/pin-init/pull/69
175            _add_action: {
176                // SAFETY: `this` is a valid pointer to uninitialized memory.
177                let inner = unsafe { &raw mut (*this.as_ptr()).inner };
178
179                // SAFETY:
180                // - `dev.as_raw()` is a pointer to a valid bound device.
181                // - `inner` is guaranteed to be a valid for the duration of the lifetime of `Self`.
182                // - `devm_add_action()` is guaranteed not to call `callback` until `this` has been
183                //    properly initialized, because we require `dev` (i.e. the *bound* device) to
184                //    live at least as long as the returned `impl PinInit<Self, Error>`.
185                to_result(unsafe {
186                    bindings::devm_add_action(dev.as_raw(), Some(*callback), inner.cast())
187                }).inspect_err(|_| {
188                    let inner = Opaque::cast_into(inner);
189
190                    // SAFETY: `inner` is a valid pointer to an `Inner<T>` and valid for both reads
191                    // and writes.
192                    unsafe { core::ptr::drop_in_place(inner) };
193                })?;
194            },
195        })
196    }
197
198    fn inner(&self) -> &Inner<T> {
199        // SAFETY: By the type invairants of `Self`, `inner` is properly initialized and always
200        // accessed read-only.
201        unsafe { &*self.inner.get() }
202    }
203
204    fn data(&self) -> &Revocable<T> {
205        &self.inner().data
206    }
207
208    #[allow(clippy::missing_safety_doc)]
209    unsafe extern "C" fn devres_callback(ptr: *mut kernel::ffi::c_void) {
210        // SAFETY: In `Self::new` we've passed a valid pointer to `Inner` to `devm_add_action()`,
211        // hence `ptr` must be a valid pointer to `Inner`.
212        let inner = unsafe { &*ptr.cast::<Inner<T>>() };
213
214        // Ensure that `inner` can't be used anymore after we signal completion of this callback.
215        let inner = ScopeGuard::new_with_data(inner, |inner| inner.devm.complete_all());
216
217        if !inner.data.revoke() {
218            // If `revoke()` returns false, it means that `Devres::drop` already started revoking
219            // `data` for us. Hence we have to wait until `Devres::drop` signals that it
220            // completed revoking `data`.
221            inner.revoke.wait_for_completion();
222        }
223    }
224
225    fn remove_action(&self) -> bool {
226        // SAFETY:
227        // - `self.dev` is a valid `Device`,
228        // - the `action` and `data` pointers are the exact same ones as given to
229        //   `devm_add_action()` previously,
230        (unsafe {
231            bindings::devm_remove_action_nowarn(
232                self.dev.as_raw(),
233                Some(self.callback),
234                core::ptr::from_ref(self.inner()).cast_mut().cast(),
235            )
236        } == 0)
237    }
238
239    /// Return a reference of the [`Device`] this [`Devres`] instance has been created with.
240    pub fn device(&self) -> &Device {
241        &self.dev
242    }
243
244    /// Obtain `&'a T`, bypassing the [`Revocable`].
245    ///
246    /// This method allows to directly obtain a `&'a T`, bypassing the [`Revocable`], by presenting
247    /// a `&'a Device<Bound>` of the same [`Device`] this [`Devres`] instance has been created with.
248    ///
249    /// # Errors
250    ///
251    /// An error is returned if `dev` does not match the same [`Device`] this [`Devres`] instance
252    /// has been created with.
253    ///
254    /// # Examples
255    ///
256    /// ```no_run
257    /// # #![cfg(CONFIG_PCI)]
258    /// # use kernel::{device::Core, devres::Devres, pci};
259    ///
260    /// fn from_core(dev: &pci::Device<Core>, devres: Devres<pci::Bar<0x4>>) -> Result {
261    ///     let bar = devres.access(dev.as_ref())?;
262    ///
263    ///     let _ = bar.read32(0x0);
264    ///
265    ///     // might_sleep()
266    ///
267    ///     bar.write32(0x42, 0x0);
268    ///
269    ///     Ok(())
270    /// }
271    /// ```
272    pub fn access<'a>(&'a self, dev: &'a Device<Bound>) -> Result<&'a T> {
273        if self.dev.as_raw() != dev.as_raw() {
274            return Err(EINVAL);
275        }
276
277        // SAFETY: `dev` being the same device as the device this `Devres` has been created for
278        // proves that `self.data` hasn't been revoked and is guaranteed to not be revoked as long
279        // as `dev` lives; `dev` lives at least as long as `self`.
280        Ok(unsafe { self.data().access() })
281    }
282
283    /// [`Devres`] accessor for [`Revocable::try_access`].
284    pub fn try_access(&self) -> Option<RevocableGuard<'_, T>> {
285        self.data().try_access()
286    }
287
288    /// [`Devres`] accessor for [`Revocable::try_access_with`].
289    pub fn try_access_with<R, F: FnOnce(&T) -> R>(&self, f: F) -> Option<R> {
290        self.data().try_access_with(f)
291    }
292
293    /// [`Devres`] accessor for [`Revocable::try_access_with_guard`].
294    pub fn try_access_with_guard<'a>(&'a self, guard: &'a rcu::Guard) -> Option<&'a T> {
295        self.data().try_access_with_guard(guard)
296    }
297}
298
299// SAFETY: `Devres` can be send to any task, if `T: Send`.
300unsafe impl<T: Send> Send for Devres<T> {}
301
302// SAFETY: `Devres` can be shared with any task, if `T: Sync`.
303unsafe impl<T: Send + Sync> Sync for Devres<T> {}
304
305#[pinned_drop]
306impl<T: Send> PinnedDrop for Devres<T> {
307    fn drop(self: Pin<&mut Self>) {
308        // SAFETY: When `drop` runs, it is guaranteed that nobody is accessing the revocable data
309        // anymore, hence it is safe not to wait for the grace period to finish.
310        if unsafe { self.data().revoke_nosync() } {
311            // We revoked `self.data` before the devres action did, hence try to remove it.
312            if !self.remove_action() {
313                // We could not remove the devres action, which means that it now runs concurrently,
314                // hence signal that `self.data` has been revoked by us successfully.
315                self.inner().revoke.complete_all();
316
317                // Wait for `Self::devres_callback` to be done using this object.
318                self.inner().devm.wait_for_completion();
319            }
320        } else {
321            // `Self::devres_callback` revokes `self.data` for us, hence wait for it to be done
322            // using this object.
323            self.inner().devm.wait_for_completion();
324        }
325
326        // INVARIANT: At this point it is guaranteed that `inner` can't be accessed any more.
327        //
328        // SAFETY: `inner` is valid for dropping.
329        unsafe { core::ptr::drop_in_place(self.inner.get()) };
330    }
331}
332
333/// Consume `data` and [`Drop::drop`] `data` once `dev` is unbound.
334fn register_foreign<P>(dev: &Device<Bound>, data: P) -> Result
335where
336    P: ForeignOwnable + Send + 'static,
337{
338    let ptr = data.into_foreign();
339
340    #[allow(clippy::missing_safety_doc)]
341    unsafe extern "C" fn callback<P: ForeignOwnable>(ptr: *mut kernel::ffi::c_void) {
342        // SAFETY: `ptr` is the pointer to the `ForeignOwnable` leaked above and hence valid.
343        drop(unsafe { P::from_foreign(ptr.cast()) });
344    }
345
346    // SAFETY:
347    // - `dev.as_raw()` is a pointer to a valid and bound device.
348    // - `ptr` is a valid pointer the `ForeignOwnable` devres takes ownership of.
349    to_result(unsafe {
350        // `devm_add_action_or_reset()` also calls `callback` on failure, such that the
351        // `ForeignOwnable` is released eventually.
352        bindings::devm_add_action_or_reset(dev.as_raw(), Some(callback::<P>), ptr.cast())
353    })
354}
355
356/// Encapsulate `data` in a [`KBox`] and [`Drop::drop`] `data` once `dev` is unbound.
357///
358/// # Examples
359///
360/// ```no_run
361/// use kernel::{device::{Bound, Device}, devres};
362///
363/// /// Registration of e.g. a class device, IRQ, etc.
364/// struct Registration;
365///
366/// impl Registration {
367///     fn new() -> Self {
368///         // register
369///
370///         Self
371///     }
372/// }
373///
374/// impl Drop for Registration {
375///     fn drop(&mut self) {
376///        // unregister
377///     }
378/// }
379///
380/// fn from_bound_context(dev: &Device<Bound>) -> Result {
381///     devres::register(dev, Registration::new(), GFP_KERNEL)
382/// }
383/// ```
384pub fn register<T, E>(dev: &Device<Bound>, data: impl PinInit<T, E>, flags: Flags) -> Result
385where
386    T: Send + 'static,
387    Error: From<E>,
388{
389    let data = KBox::pin_init(data, flags)?;
390
391    register_foreign(dev, data)
392}
kernel/devres.rs

kernel/
devres.rs
