From a674fefd17324fc467f043568e738b80ca22f2b4 Mon Sep 17 00:00:00 2001 From: Danilo Krummrich Date: Tue, 18 Jun 2024 17:48:34 +0200 Subject: [PATCH] rust: add abstraction for struct device Add an (always) reference-counted abstraction for a generic C `struct device`. This abstraction encapsulates existing `struct device` instances and manages its reference count. Subsystems may use this abstraction as a base to abstract subsystem specific device instances based on a generic `struct device`, such as `struct pci_dev`. Co-developed-by: Wedson Almeida Filho Signed-off-by: Wedson Almeida Filho Signed-off-by: Danilo Krummrich Link: https://lore.kernel.org/r/20240618154841.6716-2-dakr@redhat.com Signed-off-by: Greg Kroah-Hartman --- rust/helpers.c | 1 + rust/kernel/device.rs | 102 ++++++++++++++++++++++++++++++++++++++++++ rust/kernel/lib.rs | 1 + 3 files changed, 104 insertions(+) create mode 100644 rust/kernel/device.rs diff --git a/rust/helpers.c b/rust/helpers.c index 2c37a0f5d7a8..0e02b2c64c72 100644 --- a/rust/helpers.c +++ b/rust/helpers.c @@ -23,6 +23,7 @@ #include #include #include +#include #include #include #include diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs new file mode 100644 index 000000000000..e445e87fb7d7 --- /dev/null +++ b/rust/kernel/device.rs @@ -0,0 +1,102 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Generic devices that are part of the kernel's driver model. +//! +//! C header: [`include/linux/device.h`](srctree/include/linux/device.h) + +use crate::{ + bindings, + types::{ARef, Opaque}, +}; +use core::ptr; + +/// A reference-counted device. +/// +/// This structure represents the Rust abstraction for a C `struct device`. This implementation +/// abstracts the usage of an already existing C `struct device` within Rust code that we get +/// passed from the C side. +/// +/// An instance of this abstraction can be obtained temporarily or permanent. +/// +/// A temporary one is bound to the lifetime of the C `struct device` pointer used for creation. +/// A permanent instance is always reference-counted and hence not restricted by any lifetime +/// boundaries. +/// +/// For subsystems it is recommended to create a permanent instance to wrap into a subsystem +/// specific device structure (e.g. `pci::Device`). This is useful for passing it to drivers in +/// `T::probe()`, such that a driver can store the `ARef` (equivalent to storing a +/// `struct device` pointer in a C driver) for arbitrary purposes, e.g. allocating DMA coherent +/// memory. +/// +/// # Invariants +/// +/// The pointer stored in `Self` is non-null and valid for the lifetime of the `ARef` instance. In +/// particular, the `ARef` instance owns an increment on the underlying object’s reference count. +/// +/// `bindings::device::release` is valid to be called from any thread, hence `ARef` can be +/// dropped from any thread. +#[repr(transparent)] +pub struct Device(Opaque); + +impl Device { + /// Creates a new reference-counted abstraction instance of an existing `struct device` pointer. + /// + /// # Safety + /// + /// Callers must ensure that `ptr` is valid, non-null, and has a non-zero reference count, + /// i.e. it must be ensured that the reference count of the C `struct device` `ptr` points to + /// can't drop to zero, for the duration of this function call. + /// + /// It must also be ensured that `bindings::device::release` can be called from any thread. + /// While not officially documented, this should be the case for any `struct device`. + pub unsafe fn from_raw(ptr: *mut bindings::device) -> ARef { + // SAFETY: By the safety requirements, ptr is valid. + // Initially increase the reference count by one to compensate for the final decrement once + // this newly created `ARef` instance is dropped. + unsafe { bindings::get_device(ptr) }; + + // CAST: `Self` is a `repr(transparent)` wrapper around `bindings::device`. + let ptr = ptr.cast::(); + + // SAFETY: By the safety requirements, ptr is valid. + unsafe { ARef::from_raw(ptr::NonNull::new_unchecked(ptr)) } + } + + /// Obtain the raw `struct device *`. + pub(crate) fn as_raw(&self) -> *mut bindings::device { + self.0.get() + } + + /// Convert a raw C `struct device` pointer to a `&'a Device`. + /// + /// # Safety + /// + /// Callers must ensure that `ptr` is valid, non-null, and has a non-zero reference count, + /// i.e. it must be ensured that the reference count of the C `struct device` `ptr` points to + /// can't drop to zero, for the duration of this function call and the entire duration when the + /// returned reference exists. + pub unsafe fn as_ref<'a>(ptr: *mut bindings::device) -> &'a Self { + // SAFETY: Guaranteed by the safety requirements of the function. + unsafe { &*ptr.cast() } + } +} + +// SAFETY: Instances of `Device` are always reference-counted. +unsafe impl crate::types::AlwaysRefCounted for Device { + fn inc_ref(&self) { + // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. + unsafe { bindings::get_device(self.as_raw()) }; + } + + unsafe fn dec_ref(obj: ptr::NonNull) { + // SAFETY: The safety requirements guarantee that the refcount is non-zero. + unsafe { bindings::put_device(obj.cast().as_ptr()) } + } +} + +// SAFETY: As by the type invariant `Device` can be sent to any thread. +unsafe impl Send for Device {} + +// SAFETY: `Device` can be shared among threads because all immutable methods are protected by the +// synchronization in `struct device`. +unsafe impl Sync for Device {} diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index fbd91a48ff8b..dd1207f1a873 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -28,6 +28,7 @@ extern crate self as kernel; pub mod alloc; mod build_assert; +pub mod device; pub mod error; pub mod init; pub mod ioctl;