[PATCH RFC 03/18] rust: drm: file: Add File abstraction

Asahi Lina
2023-03-07T14:32:08Z

A DRM File is the DRM counterpart to a kernel file structure,
representing an open DRM file descriptor. Add a Rust abstraction to
allow drivers to implement their own File types that implement the
DriverFile trait.

Signed-off-by: Asahi Lina <lina@asahilina.net>
---
rust/bindings/bindings_helper.h | 1 +
rust/kernel/drm/drv.rs | 7 ++-
rust/kernel/drm/file.rs | 113 ++++++++++++++++++++++++++++++++++++++++
rust/kernel/drm/mod.rs | 1 +
4 files changed, 120 insertions(+), 2 deletions(-)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 2a999138c4ae..7d7828faf89c 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -8,6 +8,7 @@

#include <drm/drm_device.h>
#include <drm/drm_drv.h>
+#include <drm/drm_file.h>
#include <drm/drm_ioctl.h>
#include <linux/delay.h>
#include <linux/device.h>
diff --git a/rust/kernel/drm/drv.rs b/rust/kernel/drm/drv.rs
index 29a465515dc9..1dcb651e1417 100644
--- a/rust/kernel/drm/drv.rs
+++ b/rust/kernel/drm/drv.rs
@@ -144,6 +144,9 @@ pub trait Driver {
/// Should be either `drm::gem::Object<T>` or `drm::gem::shmem::Object<T>`.
type Object: AllocImpl;

+ /// The type used to represent a DRM File (client)
+ type File: drm::file::DriverFile;
+
/// Driver metadata
const INFO: DriverInfo;

@@ -213,8 +216,8 @@ macro_rules! drm_device_register {
impl<T: Driver> Registration<T> {
const VTABLE: bindings::drm_driver = drm_legacy_fields! {
load: None,
- open: None, // TODO: File abstraction
- postclose: None, // TODO: File abstraction
+ open: Some(drm::file::open_callback::<T::File>),
+ postclose: Some(drm::file::postclose_callback::<T::File>),
lastclose: None,
unload: None,
release: None,
diff --git a/rust/kernel/drm/file.rs b/rust/kernel/drm/file.rs
new file mode 100644
index 000000000000..48751e93c38a
--- /dev/null
+++ b/rust/kernel/drm/file.rs
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+//! DRM File objects.
+//!
+//! C header: [`include/linux/drm/drm_file.h`](../../../../include/linux/drm/drm_file.h)
+
+use crate::{bindings, drm, error::Result};
+use alloc::boxed::Box;
+use core::marker::PhantomData;
+use core::ops::Deref;
+
+/// Trait that must be implemented by DRM drivers to represent a DRM File (a client instance).
+pub trait DriverFile {
+ /// The parent `Driver` implementation for this `DriverFile`.
+ type Driver: drm::drv::Driver;
+
+ /// Open a new file (called when a client opens the DRM device).
+ fn open(device: &drm::device::Device<Self::Driver>) -> Result<Box<Self>>;
+}
+
+/// An open DRM File.
+///
+/// # Invariants
+/// `raw` is a valid pointer to a `drm_file` struct.
+#[repr(transparent)]
+pub struct File<T: DriverFile> {
+ raw: *mut bindings::drm_file,
+ _p: PhantomData<T>,
+}
+
+pub(super) unsafe extern "C" fn open_callback<T: DriverFile>(
+ raw_dev: *mut bindings::drm_device,
+ raw_file: *mut bindings::drm_file,
+) -> core::ffi::c_int {
+ let drm = core::mem::ManuallyDrop::new(unsafe { drm::device::Device::from_raw(raw_dev) });
+ // SAFETY: This reference won't escape this function
+ let file = unsafe { &mut *raw_file };
+
+ let inner = match T::open(&drm) {
+ Err(e) => {
+ return e.to_kernel_errno();
+ }
+ Ok(i) => i,
+ };
+
+ file.driver_priv = Box::into_raw(inner) as *mut _;
+
+ 0
+}
+
+pub(super) unsafe extern "C" fn postclose_callback<T: DriverFile>(
+ _dev: *mut bindings::drm_device,
+ raw_file: *mut bindings::drm_file,
+) {
+ // SAFETY: This reference won't escape this function
+ let file = unsafe { &*raw_file };
+
+ // Drop the DriverFile
+ unsafe { Box::from_raw(file.driver_priv as *mut T) };
+}
+
+impl<T: DriverFile> File<T> {
+ // Not intended to be called externally, except via declare_drm_ioctls!()
+ #[doc(hidden)]
+ pub unsafe fn from_raw(raw_file: *mut bindings::drm_file) -> File<T> {
+ File {
+ raw: raw_file,
+ _p: PhantomData,
+ }
+ }
+
+ #[allow(dead_code)]
+ /// Return the raw pointer to the underlying `drm_file`.
+ pub(super) fn raw(&self) -> *const bindings::drm_file {
+ self.raw
+ }
+
+ /// Return an immutable reference to the raw `drm_file` structure.
+ pub(super) fn file(&self) -> &bindings::drm_file {
+ unsafe { &*self.raw }
+ }
+}
+
+impl<T: DriverFile> Deref for File<T> {
+ type Target = T;
+
+ fn deref(&self) -> &T {
+ unsafe { &*(self.file().driver_priv as *const T) }
+ }
+}
+
+impl<T: DriverFile> crate::private::Sealed for File<T> {}
+
+/// Generic trait to allow users that don't care about driver specifics to accept any File<T>.
+///
+/// # Safety
+/// Must only be implemented for File<T> and return the pointer, following the normal invariants
+/// of that type.
+pub unsafe trait GenericFile: crate::private::Sealed {
+ /// Returns the raw const pointer to the `struct drm_file`
+ fn raw(&self) -> *const bindings::drm_file;
+ /// Returns the raw mut pointer to the `struct drm_file`
+ fn raw_mut(&mut self) -> *mut bindings::drm_file;
+}
+
+unsafe impl<T: DriverFile> GenericFile for File<T> {
+ fn raw(&self) -> *const bindings::drm_file {
+ self.raw
+ }
+ fn raw_mut(&mut self) -> *mut bindings::drm_file {
+ self.raw
+ }
+}
diff --git a/rust/kernel/drm/mod.rs b/rust/kernel/drm/mod.rs
index 69376b3c6db9..a767942d0b52 100644
--- a/rust/kernel/drm/mod.rs
+++ b/rust/kernel/drm/mod.rs
@@ -4,4 +4,5 @@

pub mod device;
pub mod drv;
+pub mod file;
pub mod ioctl;

--
2.35.1