Add a Rust abstraction for the kernel's devres (device resource
management) implementation.
The Devres type acts as a container to manage the lifetime and
accessibility of device bound resources. Therefore it registers a
devres callback and revokes access to the resource on invocation.
Users of the Devres abstraction can simply free the corresponding
resources in their Drop implementation, which is invoked when either the
Devres instance goes out of scope or the devres callback leads to the
resource being revoked, which implies a call to drop_in_place().
Signed-off-by: Danilo Krummrich <d...@kernel.org>
---
MAINTAINERS | 1 +
rust/helpers/device.c | 10 +++
rust/helpers/helpers.c | 1 +
rust/kernel/devres.rs | 178 +++++++++++++++++++++++++++++++++++++++++
rust/kernel/lib.rs | 1 +
5 files changed, 191 insertions(+)
create mode 100644 rust/helpers/device.c
create mode 100644 rust/kernel/devres.rs
diff --git a/MAINTAINERS b/MAINTAINERS
index 0cc69e282889..a9ae2d69f961 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7034,6 +7034,7 @@ F: include/linux/property.h
F: lib/kobj*
F: rust/kernel/device.rs
F: rust/kernel/device_id.rs
+F: rust/kernel/devres.rs
F: rust/kernel/driver.rs
DRIVERS FOR OMAP ADAPTIVE VOLTAGE SCALING (AVS)
diff --git a/rust/helpers/device.c b/rust/helpers/device.c
new file mode 100644
index 000000000000..b2135c6686b0
--- /dev/null
+++ b/rust/helpers/device.c
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/device.h>
+
+int rust_helper_devm_add_action(struct device *dev,
+ void (*action)(void *),
+ void *data)
+{
+ return devm_add_action(dev, action, data);
+}
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 63f9b1da179f..a3b52aa021de 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -12,6 +12,7 @@
#include "build_assert.c"
#include "build_bug.c"
#include "cred.c"
+#include "device.c"
#include "err.c"
#include "fs.c"
#include "io.c"
diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
new file mode 100644
index 000000000000..9c9dd39584eb
--- /dev/null
+++ b/rust/kernel/devres.rs
@@ -0,0 +1,178 @@
+// 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::Device,
+ error::{Error, Result},
+ prelude::*,
+ revocable::Revocable,
+ sync::Arc,
+};
+
+use core::ops::Deref;
+
+#[pin_data]
+struct DevresInner<T> {
+ #[pin]
+ data: Revocable<T>,
+}
+
+/// 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.
+///
+/// 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.
+///
+/// # Example
+///
+/// ```no_run
+/// # use kernel::{bindings, c_str, device::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 _, SIZE as _) };
+/// if addr.is_null() {
+/// return Err(ENOMEM);
+/// }
+///
+/// Ok(IoMem(IoRaw::new(addr as _, 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 _); };
+/// }
+/// }
+///
+/// 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() -> Result<(), Error> {
+/// # // SAFETY: Invalid usage; just for the example to get an `ARef<Device>`
instance.
+/// # let dev = unsafe { Device::get_device(core::ptr::null_mut()) };
+///
+/// // SAFETY: Invalid usage for example purposes.
+/// let iomem = unsafe { IoMem::<{ core::mem::size_of::<u32>()
}>::new(0xBAAAAAAD)? };
+/// let devres = Devres::new(&dev, iomem, GFP_KERNEL)?;
+///
+/// let res = devres.try_access().ok_or(ENXIO)?;
+/// res.writel(0x42, 0x0);
+/// # Ok(())
+/// # }
+/// ```
+pub struct Devres<T>(Arc<DevresInner<T>>);
+
+impl<T> DevresInner<T> {
+ fn new(dev: &Device, data: T, flags: Flags) -> Result<Arc<DevresInner<T>>>
{
+ let inner = Arc::pin_init(
+ pin_init!( DevresInner {
+ data <- Revocable::new(data),
+ }),
+ flags,
+ )?;
+
+ // Convert `Arc<DevresInner>` into a raw pointer and make devres own
this reference until
+ // `Self::devres_callback` is called.
+ let data = inner.clone().into_raw();
+
+ // SAFETY: `devm_add_action` guarantees to call
`Self::devres_callback` once `dev` is
+ // detached.
+ let ret = unsafe {
+ bindings::devm_add_action(dev.as_raw(),
Some(Self::devres_callback), data as _)
+ };
+
+ if ret != 0 {
+ // SAFETY: We just created another reference to `inner` in order
to pass it to
+ // `bindings::devm_add_action`. If `bindings::devm_add_action`
fails, we have to drop
+ // this reference accordingly.
+ let _ = unsafe { Arc::from_raw(data) };
+ return Err(Error::from_errno(ret));
+ }
+
+ Ok(inner)
+ }
+
+ #[allow(clippy::missing_safety_doc)]
+ unsafe extern "C" fn devres_callback(ptr: *mut kernel::ffi::c_void) {
+ let ptr = ptr as *mut DevresInner<T>;
+ // Devres owned this memory; now that we received the callback, drop
the `Arc` and hence the
+ // reference.
+ // SAFETY: Safe, since we leaked an `Arc` reference to
devm_add_action() in
+ // `DevresInner::new`.
+ let inner = unsafe { Arc::from_raw(ptr) };
+
+ inner.data.revoke();
+ }
+}
+
+impl<T> Devres<T> {
+ /// Creates a new [`Devres`] instance of the given `data`. The `data`
encapsulated within the
+ /// returned `Devres` instance' `data` will be revoked once the device is
detached.
+ pub fn new(dev: &Device, data: T, flags: Flags) -> Result<Self> {
+ let inner = DevresInner::new(dev, data, flags)?;
+
+ Ok(Devres(inner))
+ }
+
+ /// Same as [`Devres::new`], but does not return a `Devres` instance.
Instead the given `data`
+ /// is owned by devres and will be revoked / dropped, once the device is
detached.
+ pub fn new_foreign_owned(dev: &Device, data: T, flags: Flags) -> Result {
+ let _ = DevresInner::new(dev, data, flags)?;
+
+ Ok(())
+ }
+}
+
+impl<T> Deref for Devres<T> {
+ type Target = Revocable<T>;
+
+ fn deref(&self) -> &Self::Target {
+ &self.0.data
+ }
+}
+
+impl<T> Drop for Devres<T> {
+ fn drop(&mut self) {
+ // Revoke the data, such that it gets dropped already and the actual
resource is freed.
+ //
+ // `DevresInner` has to stay alive until the devres callback has been
called. This is
+ // necessary since we don't know when `Devres` is dropped and calling
+ // `devm_remove_action()` instead could race with
`devres_release_all()`.
+ //
+ // SAFETY: When `drop` runs, it's guaranteed that nobody is accessing
the revocable data
+ // anymore, hence it is safe not to wait for the grace period to
finish.
+ unsafe { self.revoke_nosync() };
+ }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 6c836ab73771..2b61bf99d1ee 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -41,6 +41,7 @@
pub mod cred;
pub mod device;
pub mod device_id;
+pub mod devres;
pub mod driver;
pub mod error;
#[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
--
2.47.1
