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

[Karol Herbst <kherbst@redhat.com>]

On Tue, Mar 7, 2023 at 3:48 PM Karol Herbst <kherbst@redhat.com> wrote:
>
> On Tue, Mar 7, 2023 at 3:27 PM Asahi Lina <lina@asahilina.net> 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.
> >
> > +# Rust abstractions cannot be built as modules currently, so force them as
> > +# bool by using these intermediate symbols. In the future these could be
> > +# tristate once abstractions themselves can be built as modules.
> > +config RUST_DRM
> > +       bool "Rust support for the DRM subsystem"
> > +       depends on DRM=y
> > +
> >  config DRM_MIPI_DBI
> >         tristate
> >         depends on DRM
> > diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> > index 91bb7906ca5a..2687bef1676f 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 <linux/delay.h>
> >  #include <linux/device.h>
> >  #include <linux/dma-mapping.h>
> > @@ -23,6 +24,7 @@
> >  #include <linux/sysctl.h>
> >  #include <linux/timekeeping.h>
> >  #include <linux/xarray.h>
> > +#include <uapi/drm/drm.h>
> >
>
> might make more sense to add this chunk to the patch actually needing it
>

ehh, ignore this comment please :)

> >  /* `bindgen` gets confused at certain things. */
> >  const gfp_t BINDINGS_GFP_KERNEL = GFP_KERNEL;
> > diff --git a/rust/kernel/drm/ioctl.rs b/rust/kernel/drm/ioctl.rs
> > new file mode 100644
> > index 000000000000..10304efbd5f1
> > --- /dev/null
> > +++ b/rust/kernel/drm/ioctl.rs
> > @@ -0,0 +1,147 @@
> > +// SPDX-License-Identifier: GPL-2.0 OR MIT
> > +#![allow(non_snake_case)]
> > +
> > +//! DRM IOCTL definitions.
> > +//!
> > +//! C header: [`include/linux/drm/drm_ioctl.h`](../../../../include/linux/drm/drm_ioctl.h)
> > +
> > +use crate::ioctl;
> > +
> > +const BASE: u32 = bindings::DRM_IOCTL_BASE as u32;
> > +
> > +/// Construct a DRM ioctl number with no argument.
> > +pub const fn IO(nr: u32) -> u32 {
> > +    ioctl::_IO(BASE, nr)
> > +}
> > +
> > +/// Construct a DRM ioctl number with a read-only argument.
> > +pub const fn IOR<T>(nr: u32) -> u32 {
> > +    ioctl::_IOR::<T>(BASE, nr)
> > +}
> > +
> > +/// Construct a DRM ioctl number with a write-only argument.
> > +pub const fn IOW<T>(nr: u32) -> u32 {
> > +    ioctl::_IOW::<T>(BASE, nr)
> > +}
> > +
> > +/// Construct a DRM ioctl number with a read-write argument.
> > +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;
> > +
> > +/// Whether drm_ioctl_desc.func should be called with the DRM BKL held or not. Enforced as the
> > +/// default for all modern drivers, hence there should never be a need to set this flag.
> > +///
> > +/// Do not use anywhere else than for the VBLANK_WAIT IOCTL, which is the only legacy IOCTL which
> > +/// needs this.
> > +pub const UNLOCKED: u32 = bindings::drm_ioctl_flags_DRM_UNLOCKED;
> > +
> > +/// 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;
> > +
> > +/// 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),
> > +/// }
>
> I am wondering.. couldn't we make it a proc_macro and just tag all the
> functions instead? Though I also see the point of having a central
> list of all ioctls... Maybe we should have some higher level
> discussions around on _how_ we want things to look like.
>
> > +/// ```
> > +///
> > +#[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.
> > +                $(
> > +                    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>() == $crate::ioctl::_IOC_SIZE(cmd));
>
> ::core::mem::size_of
>
> > +                    let i: u32 = i + 1;
> > +                )*
> > +            };
> > +
> > +            let ioctls = &[$(
> > +                $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 {
>
> ::core
>
> > +                            // 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 $func(&*dev, data, &file) {
> > +                                Err(e) => e.to_kernel_errno(),
> > +                                Ok(i) => i.try_into().unwrap_or(ERANGE.to_kernel_errno()),
>
> need to specify the namespace on ERANGE, no?
>
> > +                            }
> > +                        }
> > +                        Some($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;
> >
> > --
> > 2.35.1
> >