On Tue, 2023-03-07 at 23:25 +0900, Asahi Lina wrote:
> 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@xxxxxxxxxxxxx>
> ---
> 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_fi
> le.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) });
Maybe you can help educate me a bit here... This feels like a really
sketchy pattern. We're creating a Device from a pointer, an operation
which inherently consumes a reference but then marking it ManuallyDrop
so drm_device_put() never gets called. It took me a while but I think
I figured out what you're trying to do: Make it so all the Rust stuff
works with Device, not drm_device but it still feels really wrong. It
works, it just feels like there's a lot of unsafe abstraction juggling
happening here and I expect this operation is going to be pretty common
in the Rust abstraction layer.
Am I missing something?
~Faith
> + // 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;
>
