On Tue, Mar 07, 2023 at 11:25:26PM +0900, 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@xxxxxxxxxxxxx> A bunch of thoughts/questions: - You have the pub functions to create ioctl numbers, but it looks like most drivers just do this in the C uapi headers instead and then use the direct number from the bindings? I wonder whether we shouldn't just use that as standard way, since in the end we do need the C headers for userspace to use the ioctls/structs. Or could we generate the headers from rust? - More type safety would be nice. You have the one for device, but not yet for DrmFile. At least if I read the examples in asahi/vgem right. Also the FIXME for how to make sure you generate the table for the right kind of driver would be nice to fix. - Type safety against the size of the struct an ioctl number is great! - I wonder whether we could adjust the type according to _IOR/W/RW, i.e. if you have W then your ioctl function is Result<Struct>, if not then Result<()> since it's just errno, and you get the paramater only when you have R set. We had in the past confusions where people got this wrong and wondered why their parameters don't make it to userspace. - There's also the question of drm_ioctl() zero-extending the ioctl parameter struct both ways (i.e. kernel kernel or newer userspace). I think trying to encode that with Some() is overkill, but maybe worth a thought. - It would be _really_ great if rust ioctl abstractions enforce https://dri.freedesktop.org/docs/drm/process/botching-up-ioctls.html at the type level, i.e. everything naturally aligned, no gaps, all that stuff. This would also hold for get/put_user and all these things (I didn't look into that stuff yet in the drivers when you pull in entire arrays). Cheers, Daniel > --- > 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> > > /* `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), > +/// } > +/// ``` > +/// > +#[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>() == $crate::ioctl::_IOC_SIZE(cmd)); > + let i: u32 = i + 1; > + )* > + }; > + > + let ioctls = &[$( > + $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; > > -- > 2.35.1 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
