This introduces an optional export() callback for GEM objects, which is used to implement the drm_gem_object_funcs->export function. Signed-off-by: Lyude Paul <lyude at redhat.com> --- drivers/gpu/drm/nova/gem.rs | 1 + rust/kernel/drm/gem/mod.rs | 72 +++++++++++++++++++++++++++++++++++- rust/kernel/drm/gem/shmem.rs | 6 ++- 3 files changed, 76 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/nova/gem.rs b/drivers/gpu/drm/nova/gem.rs index 015cb56061a56..bbce6b0f4e6a4 100644 --- a/drivers/gpu/drm/nova/gem.rs +++ b/drivers/gpu/drm/nova/gem.rs @@ -16,6 +16,7 @@ #[pin_data] pub(crate) struct NovaObject {} +#[vtable] impl gem::DriverObject for NovaObject { type Driver = NovaDriver; type Object = gem::Object<Self>; diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs index f9f9727f14e4a..1ac25fc6d527b 100644 --- a/rust/kernel/drm/gem/mod.rs +++ b/rust/kernel/drm/gem/mod.rs @@ -8,7 +8,7 @@ use crate::{ alloc::flags::*, - bindings, + bindings, dma_buf, drm::driver::{AllocImpl, AllocOps}, drm::{self, private::Sealed}, error::{to_result, Result}, @@ -45,6 +45,7 @@ fn as_ref(&self) -> &kernel::drm::gem::OpaqueObject<D> { pub(crate) use impl_as_opaque; /// GEM object functions, which must be implemented by drivers. +#[vtable] pub trait DriverObject: Sync + Send + Sized { /// Parent `Driver` for this object. type Driver: drm::Driver; @@ -69,6 +70,11 @@ fn open(_obj: &Self::Object, _file: &DriverFile<Self>) -> Result { /// Close a handle to an existing object, associated with a File. fn close(_obj: &Self::Object, _file: &DriverFile<Self>) {} + + /// Optional handle for exporting a gem object. + fn export(_obj: &Self::Object, _flags: u32) -> Result<DmaBuf<Self::Object>> { + unimplemented!() + } } /// Trait that represents a GEM object subtype @@ -138,6 +144,21 @@ extern "C" fn close_callback<T: DriverObject>( T::close(obj, file); } +extern "C" fn export_callback<T: DriverObject>( + raw_obj: *mut bindings::drm_gem_object, + flags: i32, +) -> *mut bindings::dma_buf { + // SAFETY: `export_callback` is specified in the AllocOps structure for `Object<T>`, ensuring + // that `raw_obj` is contained within a `Object<T>`. + let obj = unsafe { T::Object::from_raw(raw_obj) }; + + match T::export(obj, flags as u32) { + // DRM takes a hold of the reference + Ok(buf) => buf.into_raw(), + Err(e) => e.to_ptr(), + } +} + impl<T: DriverObject> IntoGEMObject for Object<T> { fn as_raw(&self) -> *mut bindings::drm_gem_object { self.obj.get() @@ -248,7 +269,11 @@ impl<T: DriverObject> Object<T> { open: Some(open_callback::<T>), close: Some(close_callback::<T>), print_info: None, - export: None, + export: if T::HAS_EXPORT { + Some(export_callback::<T>) + } else { + None + }, pin: None, unpin: None, get_sg_table: None, @@ -375,6 +400,49 @@ fn as_raw(&self) -> *mut bindings::drm_gem_object { impl<D: drm::Driver> Sealed for OpaqueObject<D> {} +/// A [`dma_buf::DmaBuf`] which has been exported from a GEM object. +/// +/// The [`dma_buf::DmaBuf`] will be released when this type is dropped. +/// +/// # Invariants +/// +/// - `self.0` points to a valid initialized [`dma_buf::DmaBuf`] for the lifetime of this object. +/// - The GEM object from which this [`dma_buf::DmaBuf`] was exported from is guaranteed to be of +/// type `T`. +pub struct DmaBuf<T: IntoGEMObject>(NonNull<dma_buf::DmaBuf>, PhantomData<T>); + +impl<T: IntoGEMObject> Deref for DmaBuf<T> { + type Target = dma_buf::DmaBuf; + + #[inline] + fn deref(&self) -> &Self::Target { + // SAFETY: This pointer is guaranteed to be valid by our type invariants. + unsafe { self.0.as_ref() } + } +} + +impl<T: IntoGEMObject> Drop for DmaBuf<T> { + #[inline] + fn drop(&mut self) { + // SAFETY: + // - `dma_buf::DmaBuf` is guaranteed to have an identical layout to `struct dma_buf` + // by its type invariants. + // - We hold the last reference to this `DmaBuf`, making it safe to destroy. + unsafe { bindings::drm_gem_dmabuf_release(self.0.cast().as_ptr()) } + } +} + +impl<T: IntoGEMObject> DmaBuf<T> { + /// Leak the reference for this [`DmaBuf`] and return a raw pointer to it. + #[inline] + pub(crate) fn into_raw(self) -> *mut bindings::dma_buf { + let dma_ptr = self.as_raw(); + + core::mem::forget(self); + dma_ptr + } +} + pub(super) const fn create_fops() -> bindings::file_operations { // SAFETY: As by the type invariant, it is safe to initialize `bindings::file_operations` // zeroed. diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs index 1437cda27a22c..b3a70e6001842 100644 --- a/rust/kernel/drm/gem/shmem.rs +++ b/rust/kernel/drm/gem/shmem.rs @@ -66,7 +66,11 @@ impl<T: DriverObject> Object<T> { open: Some(super::open_callback::<T>), close: Some(super::close_callback::<T>), print_info: Some(bindings::drm_gem_shmem_object_print_info), - export: None, + export: if T::HAS_EXPORT { + Some(super::export_callback::<T>) + } else { + None + }, pin: Some(bindings::drm_gem_shmem_object_pin), unpin: Some(bindings::drm_gem_shmem_object_unpin), get_sg_table: Some(bindings::drm_gem_shmem_object_get_sg_table), -- 2.50.0
Daniel Almeida
2025-Sep-05 15:09 UTC
[PATCH v3 13/14] rust: drm: gem: Add export() callback
> On 29 Aug 2025, at 19:35, Lyude Paul <lyude at redhat.com> wrote: > > This introduces an optional export() callback for GEM objects, which is > used to implement the drm_gem_object_funcs->export function. > > Signed-off-by: Lyude Paul <lyude at redhat.com> > --- > drivers/gpu/drm/nova/gem.rs | 1 + > rust/kernel/drm/gem/mod.rs | 72 +++++++++++++++++++++++++++++++++++- > rust/kernel/drm/gem/shmem.rs | 6 ++- > 3 files changed, 76 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/nova/gem.rs b/drivers/gpu/drm/nova/gem.rs > index 015cb56061a56..bbce6b0f4e6a4 100644 > --- a/drivers/gpu/drm/nova/gem.rs > +++ b/drivers/gpu/drm/nova/gem.rs > @@ -16,6 +16,7 @@ > #[pin_data] > pub(crate) struct NovaObject {} > > +#[vtable] > impl gem::DriverObject for NovaObject { > type Driver = NovaDriver; > type Object = gem::Object<Self>; > diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs > index f9f9727f14e4a..1ac25fc6d527b 100644 > --- a/rust/kernel/drm/gem/mod.rs > +++ b/rust/kernel/drm/gem/mod.rs > @@ -8,7 +8,7 @@ > > use crate::{ > alloc::flags::*, > - bindings, > + bindings, dma_buf, > drm::driver::{AllocImpl, AllocOps}, > drm::{self, private::Sealed}, > error::{to_result, Result}, > @@ -45,6 +45,7 @@ fn as_ref(&self) -> &kernel::drm::gem::OpaqueObject<D> { > pub(crate) use impl_as_opaque; > > /// GEM object functions, which must be implemented by drivers. > +#[vtable] > pub trait DriverObject: Sync + Send + Sized { > /// Parent `Driver` for this object. > type Driver: drm::Driver; > @@ -69,6 +70,11 @@ fn open(_obj: &Self::Object, _file: &DriverFile<Self>) -> Result { > > /// Close a handle to an existing object, associated with a File. > fn close(_obj: &Self::Object, _file: &DriverFile<Self>) {} > + > + /// Optional handle for exporting a gem object. > + fn export(_obj: &Self::Object, _flags: u32) -> Result<DmaBuf<Self::Object>> { > + unimplemented!()Shouldn?t this be the vtable-specific build error?> + } > } > > /// Trait that represents a GEM object subtype > @@ -138,6 +144,21 @@ extern "C" fn close_callback<T: DriverObject>( > T::close(obj, file); > } > > +extern "C" fn export_callback<T: DriverObject>( > + raw_obj: *mut bindings::drm_gem_object, > + flags: i32, > +) -> *mut bindings::dma_buf { > + // SAFETY: `export_callback` is specified in the AllocOps structure for `Object<T>`, ensuring > + // that `raw_obj` is contained within a `Object<T>`. > + let obj = unsafe { T::Object::from_raw(raw_obj) }; > + > + match T::export(obj, flags as u32) { > + // DRM takes a hold of the reference > + Ok(buf) => buf.into_raw(), > + Err(e) => e.to_ptr(), > + } > +} > + > impl<T: DriverObject> IntoGEMObject for Object<T> { > fn as_raw(&self) -> *mut bindings::drm_gem_object { > self.obj.get() > @@ -248,7 +269,11 @@ impl<T: DriverObject> Object<T> { > open: Some(open_callback::<T>), > close: Some(close_callback::<T>), > print_info: None, > - export: None, > + export: if T::HAS_EXPORT { > + Some(export_callback::<T>) > + } else { > + None > + }, > pin: None, > unpin: None, > get_sg_table: None, > @@ -375,6 +400,49 @@ fn as_raw(&self) -> *mut bindings::drm_gem_object { > > impl<D: drm::Driver> Sealed for OpaqueObject<D> {} > > +/// A [`dma_buf::DmaBuf`] which has been exported from a GEM object. > +/// > +/// The [`dma_buf::DmaBuf`] will be released when this type is dropped. > +/// > +/// # Invariants > +/// > +/// - `self.0` points to a valid initialized [`dma_buf::DmaBuf`] for the lifetime of this object. > +/// - The GEM object from which this [`dma_buf::DmaBuf`] was exported from is guaranteed to be of > +/// type `T`. > +pub struct DmaBuf<T: IntoGEMObject>(NonNull<dma_buf::DmaBuf>, PhantomData<T>); > + > +impl<T: IntoGEMObject> Deref for DmaBuf<T> { > + type Target = dma_buf::DmaBuf; > + > + #[inline] > + fn deref(&self) -> &Self::Target { > + // SAFETY: This pointer is guaranteed to be valid by our type invariants. > + unsafe { self.0.as_ref() }> + } > +} > + > +impl<T: IntoGEMObject> Drop for DmaBuf<T> { > + #[inline] > + fn drop(&mut self) { > + // SAFETY: > + // - `dma_buf::DmaBuf` is guaranteed to have an identical layout to `struct dma_buf` > + // by its type invariants. > + // - We hold the last reference to this `DmaBuf`, making it safe to destroy.How can we be sure of this?> + unsafe { bindings::drm_gem_dmabuf_release(self.0.cast().as_ptr()) } > + } > +} > + > +impl<T: IntoGEMObject> DmaBuf<T> { > + /// Leak the reference for this [`DmaBuf`] and return a raw pointer to it. > + #[inline] > + pub(crate) fn into_raw(self) -> *mut bindings::dma_buf {Then this should perhaps be called leak()? At least if we?re following the std nomenclature.> + let dma_ptr = self.as_raw(); > + > + core::mem::forget(self); > + dma_ptr > + } > +} > + > pub(super) const fn create_fops() -> bindings::file_operations { > // SAFETY: As by the type invariant, it is safe to initialize `bindings::file_operations` > // zeroed. > diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs > index 1437cda27a22c..b3a70e6001842 100644 > --- a/rust/kernel/drm/gem/shmem.rs > +++ b/rust/kernel/drm/gem/shmem.rs > @@ -66,7 +66,11 @@ impl<T: DriverObject> Object<T> { > open: Some(super::open_callback::<T>), > close: Some(super::close_callback::<T>), > print_info: Some(bindings::drm_gem_shmem_object_print_info), > - export: None, > + export: if T::HAS_EXPORT { > + Some(super::export_callback::<T>) > + } else { > + None > + }, > pin: Some(bindings::drm_gem_shmem_object_pin), > unpin: Some(bindings::drm_gem_shmem_object_unpin), > get_sg_table: Some(bindings::drm_gem_shmem_object_get_sg_table), > -- > 2.50.0 >