Re: [PATCH v2 1/8] rust: drm: ioctl: Add DRM ioctl abstraction

[Daniel Vetter <daniel.vetter@ffwll.ch>]

On Wed, Jun 19, 2024 at 01:31:37AM +0200, Danilo Krummrich wrote:
> From: Asahi Lina <lina@asahilina.net>
> 
> DRM drivers need to be able to declare which driver-specific ioctls they
> support. Add an abstraction implementing 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>
> Signed-off-by: Danilo Krummrich <dakr@redhat.com>

Aside from the fixme commments in here I also had a bit a wishlist/ideas
compilation of my own:

https://lore.kernel.org/dri-devel/ZDfKLjKOfDHkEc1V@phenom.ffwll.local/#t

Not sure where/how we want to record all these, and when we should try to
fix them?
-Sima

> ---
>  rust/bindings/bindings_helper.h |   1 +
>  rust/kernel/drm/ioctl.rs        | 153 ++++++++++++++++++++++++++++++++
>  rust/kernel/drm/mod.rs          |   5 ++
>  rust/kernel/lib.rs              |   2 +
>  rust/uapi/uapi_helper.h         |   1 +
>  5 files changed, 162 insertions(+)
>  create mode 100644 rust/kernel/drm/ioctl.rs
>  create mode 100644 rust/kernel/drm/mod.rs
> 
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 30ad2a0e22d7..ed25b686748e 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -6,6 +6,7 @@
>   * Sorted alphabetically.
>   */
>  
> +#include <drm/drm_ioctl.h>
>  #include <kunit/test.h>
>  #include <linux/errname.h>
>  #include <linux/ethtool.h>
> diff --git a/rust/kernel/drm/ioctl.rs b/rust/kernel/drm/ioctl.rs
> new file mode 100644
> index 000000000000..09ca7a8e7583
> --- /dev/null
> +++ b/rust/kernel/drm/ioctl.rs
> @@ -0,0 +1,153 @@
> +// SPDX-License-Identifier: GPL-2.0 OR MIT
> +#![allow(non_snake_case)]
> +
> +//! DRM IOCTL definitions.
> +//!
> +//! C header: [`include/linux/drm/drm_ioctl.h`](srctree/include/linux/drm/drm_ioctl.h)
> +
> +use crate::ioctl;
> +
> +const BASE: u32 = uapi::DRM_IOCTL_BASE as u32;
> +
> +/// Construct a DRM ioctl number with no argument.
> +#[inline(always)]
> +pub const fn IO(nr: u32) -> u32 {
> +    ioctl::_IO(BASE, nr)
> +}
> +
> +/// Construct a DRM ioctl number with a read-only argument.
> +#[inline(always)]
> +pub const fn IOR<T>(nr: u32) -> u32 {
> +    ioctl::_IOR::<T>(BASE, nr)
> +}
> +
> +/// Construct a DRM ioctl number with a write-only argument.
> +#[inline(always)]
> +pub const fn IOW<T>(nr: u32) -> u32 {
> +    ioctl::_IOW::<T>(BASE, nr)
> +}
> +
> +/// Construct a DRM ioctl number with a read-write argument.
> +#[inline(always)]
> +pub const fn IOWR<T>(nr: u32) -> u32 {
> +    ioctl::_IOWR::<T>(BASE, nr)
> +}
> +
> +/// Descriptor type for DRM ioctls. Use the `declare_drm_ioctls!{}` macro to construct them.
> +pub type DrmIoctlDescriptor = bindings::drm_ioctl_desc;
> +
> +/// This is for ioctl which are used for rendering, and require that the file descriptor is either
> +/// for a render node, or if it’s a legacy/primary node, then it must be authenticated.
> +pub const AUTH: u32 = bindings::drm_ioctl_flags_DRM_AUTH;
> +
> +/// This must be set for any ioctl which can change the modeset or display state. Userspace must
> +/// call the ioctl through a primary node, while it is the active master.
> +///
> +/// Note that read-only modeset ioctl can also be called by unauthenticated clients, or when a
> +/// master is not the currently active one.
> +pub const MASTER: u32 = bindings::drm_ioctl_flags_DRM_MASTER;
> +
> +/// Anything that could potentially wreak a master file descriptor needs to have this flag set.
> +///
> +/// Current that’s only for the SETMASTER and DROPMASTER ioctl, which e.g. logind can call to
> +/// force a non-behaving master (display compositor) into compliance.
> +///
> +/// This is equivalent to callers with the SYSADMIN capability.
> +pub const ROOT_ONLY: u32 = bindings::drm_ioctl_flags_DRM_ROOT_ONLY;
> +
> +/// This is used for all ioctl needed for rendering only, for drivers which support render nodes.
> +/// This should be all new render drivers, and hence it should be always set for any ioctl with
> +/// `AUTH` set. Note though that read-only query ioctl might have this set, but have not set
> +/// DRM_AUTH because they do not require authentication.
> +pub const RENDER_ALLOW: u32 = bindings::drm_ioctl_flags_DRM_RENDER_ALLOW;
> +
> +/// Internal structures used by the `declare_drm_ioctls!{}` macro. Do not use directly.
> +#[doc(hidden)]
> +pub mod internal {
> +    pub use bindings::drm_device;
> +    pub use bindings::drm_file;
> +    pub use bindings::drm_ioctl_desc;
> +}
> +
> +/// 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:
> +///
> +/// ```ignore
> +/// 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
> +///
> +/// ```ignore
> +/// 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] = {
> +            use $crate::uapi::*;
> +            const _:() = {
> +                let i: u32 = $crate::uapi::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.
> +                $(
> +                    let cmd: u32 = $crate::macros::concat_idents!(DRM_IOCTL_, $cmd);
> +                    ::core::assert!(i == $crate::ioctl::_IOC_NR(cmd));
> +                    ::core::assert!(core::mem::size_of::<$crate::uapi::$struct>() ==
> +                                    $crate::ioctl::_IOC_SIZE(cmd));
> +                    let i: u32 = i + 1;
> +                )*
> +            };
> +
> +            let ioctls = &[$(
> +                $crate::drm::ioctl::internal::drm_ioctl_desc {
> +                    cmd: $crate::macros::concat_idents!(DRM_IOCTL_, $cmd) as u32,
> +                    func: {
> +                        #[allow(non_snake_case)]
> +                        unsafe extern "C" fn $cmd(
> +                                raw_dev: *mut $crate::drm::ioctl::internal::drm_device,
> +                                raw_data: *mut ::core::ffi::c_void,
> +                                raw_file_priv: *mut $crate::drm::ioctl::internal::drm_file,
> +                        ) -> core::ffi::c_int {
> +                            // SAFETY: 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 = $crate::drm::device::Device::borrow(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 $crate::uapi::$struct) };
> +                            // SAFETY: This is just the DRM file structure
> +                            let file = unsafe { $crate::drm::file::File::from_raw(raw_file_priv) };
> +
> +                            match $func(dev, data, &file) {
> +                                Err(e) => e.to_errno(),
> +                                Ok(i) => i.try_into()
> +                                            .unwrap_or($crate::error::code::ERANGE.to_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 4a02946dbbd9..5a68b9a5fe03 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -33,6 +33,8 @@
>  pub mod device_id;
>  pub mod devres;
>  pub mod driver;
> +#[cfg(CONFIG_DRM = "y")]
> +pub mod drm;
>  pub mod error;
>  #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
>  pub mod firmware;
> diff --git a/rust/uapi/uapi_helper.h b/rust/uapi/uapi_helper.h
> index 08f5e9334c9e..ed42a456da2e 100644
> --- a/rust/uapi/uapi_helper.h
> +++ b/rust/uapi/uapi_helper.h
> @@ -7,5 +7,6 @@
>   */
>  
>  #include <uapi/asm-generic/ioctl.h>
> +#include <uapi/drm/drm.h>
>  #include <uapi/linux/mii.h>
>  #include <uapi/linux/ethtool.h>
> -- 
> 2.45.1
> 

-- 
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch