Re: [PATCH RFC 01/18] rust: drm: ioctl: Add DRM ioctl abstraction

["Maíra Canal" <mcanal@igalia.com>]

On 3/7/23 11:25, Asahi Lina wrote:
> DRM drivers need to be able to declare which driver-specific ioctls they
> support. This abstraction adds the required types and a helper macro to
> generate the ioctl definition inside the DRM driver.
> 
> Note that this macro is not usable until further bits of the
> abstraction are in place (but it will not fail to compile on its own, if
> not called).
> 
> Signed-off-by: Asahi Lina <lina@asahilina.net>
> ---
>   drivers/gpu/drm/Kconfig         |   7 ++
>   rust/bindings/bindings_helper.h |   2 +
>   rust/kernel/drm/ioctl.rs        | 147 ++++++++++++++++++++++++++++++++++++++++
>   rust/kernel/drm/mod.rs          |   5 ++
>   rust/kernel/lib.rs              |   2 +
>   5 files changed, 163 insertions(+)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index dc0f94f02a82..dab8f0f9aa96 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -27,6 +27,13 @@ menuconfig DRM
>   	  details.  You should also select and configure AGP
>   	  (/dev/agpgart) support if it is available for your platform.
>   

[...]

> +
> +/// Declare the DRM ioctls for a driver.
> +///
> +/// Each entry in the list should have the form:
> +///
> +/// `(ioctl_number, argument_type, flags, user_callback),`
> +///
> +/// `argument_type` is the type name within the `bindings` crate.
> +/// `user_callback` should have the following prototype:
> +///
> +/// ```
> +/// fn foo(device: &kernel::drm::device::Device<Self>,
> +///        data: &mut bindings::argument_type,
> +///        file: &kernel::drm::file::File<Self::File>,
> +/// )
> +/// ```
> +/// where `Self` is the drm::drv::Driver implementation these ioctls are being declared within.
> +///
> +/// # Examples
> +///
> +/// ```
> +/// kernel::declare_drm_ioctls! {
> +///     (FOO_GET_PARAM, drm_foo_get_param, ioctl::RENDER_ALLOW, my_get_param_handler),
> +/// }
> +/// ```
> +///
> +#[macro_export]
> +macro_rules! declare_drm_ioctls {
> +    ( $(($cmd:ident, $struct:ident, $flags:expr, $func:expr)),* $(,)? ) => {
> +        const IOCTLS: &'static [$crate::drm::ioctl::DrmIoctlDescriptor] = {
> +            const _:() = {
> +                let i: u32 = $crate::bindings::DRM_COMMAND_BASE;
> +                // Assert that all the IOCTLs are in the right order and there are no gaps,
> +                // and that the sizeof of the specified type is correct.

I believe that not necessarily the IOCTLs need to be in the right order and
with no gaps. For example, armada_drm.h has a gap in between 0x00 and
0x02 and exynos_drm.h also have gaps. Moreover, some drivers, like vgem and
virtgpu, start their IOCTLs with 0x01.

Best Regards,
- Maíra Canal

> +                $(
> +                    let cmd: u32 = $crate::macros::concat_idents!($crate::bindings::DRM_IOCTL_, $cmd);
> +                    ::core::assert!(i == $crate::ioctl::_IOC_NR(cmd));
> +                    ::core::assert!(core::mem::size_of::<$crate::bindings::$struct>() == $crate::ioctl::_IOC_SIZE(cmd));
> +                    let i: u32 = i + 1;
> +                )*
> +            };
> +
> +            let ioctls = &[$(
> +                $crate::bindings::drm_ioctl_desc {
> +                    cmd: $crate::macros::concat_idents!($crate::bindings::DRM_IOCTL_, $cmd) as u32,
> +                    func: {
> +                        #[allow(non_snake_case)]
> +                        unsafe extern "C" fn $cmd(
> +                                raw_dev: *mut $crate::bindings::drm_device,
> +                                raw_data: *mut ::core::ffi::c_void,
> +                                raw_file_priv: *mut $crate::bindings::drm_file,
> +                        ) -> core::ffi::c_int {
> +                            // SAFETY: We never drop this, and the DRM core ensures the device lives
> +                            // while callbacks are being called.
> +                            //
> +                            // FIXME: Currently there is nothing enforcing that the types of the
> +                            // dev/file match the current driver these ioctls are being declared
> +                            // for, and it's not clear how to enforce this within the type system.
> +                            let dev = ::core::mem::ManuallyDrop::new(unsafe {
> +                                $crate::drm::device::Device::from_raw(raw_dev)
> +                            });
> +                            // SAFETY: This is just the ioctl argument, which hopefully has the right type
> +                            // (we've done our best checking the size).
> +                            let data = unsafe { &mut *(raw_data as *mut $crate::bindings::$struct) };
> +                            // SAFETY: This is just the DRM file structure
> +                            let file = unsafe { $crate::drm::file::File::from_raw(raw_file_priv) };
> +
> +                            match $func(&*dev, data, &file) {
> +                                Err(e) => e.to_kernel_errno(),
> +                                Ok(i) => i.try_into().unwrap_or(ERANGE.to_kernel_errno()),
> +                            }
> +                        }
> +                        Some($cmd)
> +                    },
> +                    flags: $flags,
> +                    name: $crate::c_str!(::core::stringify!($cmd)).as_char_ptr(),
> +                }
> +            ),*];
> +            ioctls
> +        };
> +    };
> +}
> diff --git a/rust/kernel/drm/mod.rs b/rust/kernel/drm/mod.rs
> new file mode 100644
> index 000000000000..9ec6d7cbcaf3
> --- /dev/null
> +++ b/rust/kernel/drm/mod.rs
> @@ -0,0 +1,5 @@
> +// SPDX-License-Identifier: GPL-2.0 OR MIT
> +
> +//! DRM subsystem abstractions.
> +
> +pub mod ioctl;
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 7903490816bf..cb23d24c6718 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -37,6 +37,8 @@ mod build_assert;
>   pub mod delay;
>   pub mod device;
>   pub mod driver;
> +#[cfg(CONFIG_RUST_DRM)]
> +pub mod drm;
>   pub mod error;
>   pub mod io_buffer;
>   pub mod io_mem;
>