Hi Phillip :)
Tested-by: Daniel Almeida <[email protected]> > On 31 Jul 2026, at 05:04, Philipp Stanner <[email protected]> wrote: > > C's dma_fence's are synchronisation primitives that will be needed by all > Rust GPU drivers. > > The dma_fence framework sets a number of rules, notably: > - fences must only be signaled once > - all fences must be signaled at some point > - fence error codes must only be set before signaling > - every pointer to a fence must be backed by a reference > > All those rules are being addressed by these abstractions. > > To cleanly decouple fence issuers and consumers, two types are provided: > - DriverFence: the only fence type that can be signaled and that > carries driver-specific data. > - Fence: the fence type to be shared with other drivers and / or > userspace. The only type callbacks can be registered on. > Cannot be signaled. > > Hereby, a Fence lives in the same chunk of memory as a DriverFence. Both I think “hereby” reads a bit off here, but I am not a native speaker. There’s a few other places where this applies. > share the refcount of the underlying C dma_fence. Since this > implementation does not provide a custom dma_fence_backend_ops.release() > function, the memory is freed by the dma_fence backend once the refcount > drops to 0. > > To create a DriverFence, the user must first allocate a > DriverFenceAllocation, so that the creation of the DriverFence later on > can always succeed. Otherwise, deadlocks could occur if fences need to > be created in a GPU job submission path. > > Synchronization is ensured by the dma_fence backend. > > All DriverFence's created through this abstraction must be signaled by > the creator with an error code. In case a DriverFence drops without > being signaled beforehand, it is signaled with -ECANCELLED as its > error and a warning is printed. This allows the Rust abstraction to very > cleanly decouple fence issuer and consumer by relying on the decoupling > mechanisms in the C backend, which ensures through RCU and the > 'signaled' fence-flag that dma_fence_backend_ops functions cannot > access the potentially unloaded driver code anymore. > > Signalling fences on drop thus grants many advantages. Not signaling > fences on drop would risk deadlock and does not grant real advantages: > By definition only the drivers can ensure that a fence always represents > the hardware's state correctly. > > This implementation models a DmaFenceContext object on which fences are > to be created, thereby ensuring correct sequence numbering according to > the timeline. > > dma_fence supports a variety of callbacks. The mandatory callbacks > (get_timeline_name() and get_driver_name()) are implemented in this > patch. For convenience, they store those name parameters in the fence > context, saving the driver from implementing these two callbacks. > > Support for other callbacks (like for hardware signaling) is prepared > for through the fact that both DriverFence and Fence live in the same > allocation, allowing for usage of container_of from the callback to > access the driver-specific data. > > It is expected that other callbacks, added in the future, also mostly > operate on the generic data in the FenceContext. To make this safe, the > implementation ensures through a lifetime that a DriverFence cannot > outlive its FenceContext. Since this can, currently, not be fully > guaranteed (core::mem::forget() could make the compiler forget about the > memory) in Rust, an additional safety measure is implemented: the > FenceContext keeps track of all unsignaled fences, and should it ever > drop with such a fence present, it will signal it, ensuring full > decoupling. > > Synchronization for dma_fence_ops callbacks is ensured by only running the > Rust deconstructor delayed with call_rcu(), which prevents UAF-bugs > should a DriverFence drop while a Fence callback is currently operating > on the associated driver data. Since they can also operate on the > FenceContext's data, its drop implementation also performs the necessary > delay with rcu_barrier(). > > An additional issue discovered during the review process of this code is > that there is (currently) no mechanism in Rust to prevent someone from > circumventing the DriverFence's FenceContext-reference's lifetime by > "forgetting" the fence, e.g. with core::mem::forget(). Since this > apparently can also happen with recfounting cycles, it's quite likely > that it would enable UAF bugs on the FenceContext. Print warnings if > this or other misuse of the fence API happens. I think cycles are fine, if anything they make things live longer than intended (possibly leaking them forever), but at no point they lead to UAFs. And for the mem::forget() point, there seems to be precedent in other patches pointing to unsafe constructors, where the safety requirement is basically "don't mem::forget() this". In fact, if you mem::forget() in the previous Arc approach, it seems like you leak the context, while mem::forget() on the current solution does seem to allow UAF by ending the borrow as you said yourself: let ctx = .... // FenceContext in some driver queue structure let fence = ctx.fence_alloc(...).new_fence() // DriverFence<'_, T> // borrows ctx mem::forget(fence); // ends the borrow drop(ctx); // DriverFenceData contains a dangling &FenceContext, and that allocation is managed by C versus: let ctx: Arc<FenceCtx<...>> = ...; // same as above, assume refcount==1 let fence = ctx.new_fence_allocation(..).new_fence(); // ctx refcount==2 mem::forget(fence); // ctx refcount==2 drop(ctx) //ctx refcount==1 I noticed that you added a counter to catch the first case, but that assumes that signaled fences won’t reach into the context anymore, IIUC? More on that below. > > Add abstractions for dma_fence in Rust. > > Signed-off-by: Philipp Stanner <[email protected]> > --- > rust/bindings/bindings_helper.h | 1 + > rust/helpers/dma_fence.c | 48 ++ > rust/helpers/helpers.c | 1 + > rust/kernel/dma_buf/dma_fence.rs | 995 +++++++++++++++++++++++++++++++ > rust/kernel/dma_buf/mod.rs | 14 + > rust/kernel/lib.rs | 1 + > 6 files changed, 1060 insertions(+) > create mode 100644 rust/helpers/dma_fence.c > create mode 100644 rust/kernel/dma_buf/dma_fence.rs > create mode 100644 rust/kernel/dma_buf/mod.rs > > diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h > index 1124785e210b..54b62d952e01 100644 > --- a/rust/bindings/bindings_helper.h > +++ b/rust/bindings/bindings_helper.h > @@ -53,6 +53,7 @@ > #include <linux/debugfs.h> > #include <linux/device/faux.h> > #include <linux/dma-direction.h> > +#include <linux/dma-fence.h> > #include <linux/dma-mapping.h> > #include <linux/dma-resv.h> > #include <linux/errname.h> > diff --git a/rust/helpers/dma_fence.c b/rust/helpers/dma_fence.c > new file mode 100644 > index 000000000000..0e08411098fa > --- /dev/null > +++ b/rust/helpers/dma_fence.c > @@ -0,0 +1,48 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +#include <linux/dma-fence.h> > + > +__rust_helper void rust_helper_dma_fence_get(struct dma_fence *f) > +{ > + dma_fence_get(f); > +} > + > +__rust_helper void rust_helper_dma_fence_put(struct dma_fence *f) > +{ > + dma_fence_put(f); > +} > + > +__rust_helper bool rust_helper_dma_fence_begin_signalling(void) > +{ > + return dma_fence_begin_signalling(); > +} > + > +__rust_helper void rust_helper_dma_fence_end_signalling(bool cookie) > +{ > + dma_fence_end_signalling(cookie); > +} > + > +__rust_helper bool rust_helper_dma_fence_is_signaled(struct dma_fence *f) > +{ > + return dma_fence_is_signaled(f); > +} > + > +__rust_helper bool rust_helper_dma_fence_test_signaled_flag(struct dma_fence > *f) > +{ > + return dma_fence_test_signaled_flag(f); > +} > + > +__rust_helper void rust_helper_dma_fence_lock_irqsave(struct dma_fence *f, > unsigned long *flags) > +{ > + dma_fence_lock_irqsave(f, *flags); > +} > + > +__rust_helper void rust_helper_dma_fence_unlock_irqrestore(struct dma_fence > *f, unsigned long *flags) > +{ > + dma_fence_unlock_irqrestore(f, *flags); > +} > + > +__rust_helper void rust_helper_dma_fence_set_error(struct dma_fence *f, int > error) > +{ > + dma_fence_set_error(f, error); > +} > diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c > index 998e31052e66..4ab8aa9da7e7 100644 > --- a/rust/helpers/helpers.c > +++ b/rust/helpers/helpers.c > @@ -58,6 +58,7 @@ > #include "cred.c" > #include "device.c" > #include "dma.c" > +#include "dma_fence.c" > #include "dma-resv.c" > #include "drm.c" > #include "drm_gpuvm.c" > diff --git a/rust/kernel/dma_buf/dma_fence.rs > b/rust/kernel/dma_buf/dma_fence.rs > new file mode 100644 > index 000000000000..d6322e062faf > --- /dev/null > +++ b/rust/kernel/dma_buf/dma_fence.rs > @@ -0,0 +1,995 @@ > +// SPDX-License-Identifier: GPL-2.0 SPDX is being used here, > + > +/* > + * Copyright (C) 2025, 2026 Red Hat Inc.: > + * Author: Philipp Stanner <[email protected]> > + */ So perhaps SPDX-CopyrightText should be used here? > + > +//! DriverFence support. > +//! > +//! Reference: <https://docs.kernel.org/driver-api/dma-buf.html#c.dma_fence> > +//! > +//! header: [`include/linux/dma-fence.h`](srctree/include/linux/dma-fence.h) > + > +use crate::{ > + alloc::AllocError, > + bindings, > + container_of, > + error::to_result, > + prelude::*, > + types::ForeignOwnable, > + types::Opaque, // > +}; > + > +use core::{ > + marker::PhantomData, > + mem::ManuallyDrop, > + ops::Deref, > + ptr, > + ptr::{ > + drop_in_place, > + NonNull, // > + }, // > +}; > + > +use kernel::{ > + str::CString, > + sync::{ > + aref::{ > + ARef, > + AlwaysRefCounted, // > + }, > + atomic::{ > + Atomic, > + Relaxed, // > + }, > + rcu::rcu_barrier, // > + }, // > +}; > + > +/// VTable for dma_fence backend_ops callbacks. > +// > +// Mandatory dma_fence backend_ops are implemented implicitly through > +// [`FenceContext`]. Additional ones shall get implemented on this trait. > +pub trait FenceContextOps { > + /// The generic payload data for [`DriverFence`]s created on this fctx. > + type FenceDataType: Send + Sync; > +} > + > +/// A dma-fence context. A fence context takes care of associating related > fences > +/// with each other, providing each with raising sequence numbers and a > common > +/// identifier. > +#[pin_data(PinnedDrop)] > +pub struct FenceContext<T: FenceContextOps + Send + Sync> { > + /// The fence context number. > + nr: u64, > + /// The sequence number for the next fence created. > + seqno: Atomic<u64>, > + // The name parameters can be accessed by the dma_fence backend_ops. UAF > + // errors are prevented by the `call_rcu()` in > `drop_driver_fence_data()`. > + /// The name of the driver this FenceContext's fences belong to. > + driver_name: CString, > + /// The name of the timeline this FenceContext's fences belong to. > + timeline_name: CString, > + /// The number of all unsignaled fences on this context. > + // Used to warn about forgotten fences. > + // > + // The life-time on `DriverFence`s should typically prevent this from Lifetime is a single word. > + // happening. > + // > + // However, we cannot fully guarantee in Rust that `DriverFence`s will > not > + // be forgotten, e.g., through refcounting. This could circumvent the > + // lifetime which intends to enforce that all fences disappear before > their > + // context. > + nr_of_unsignaled_fences: Atomic<u64>, Why are we tracking the number of unsignaled fences, specifically? Is it not possible for the C side (which controls the actual allocation) to reach back into the Rust side via the callbacks even after the context drops, regardless of their signaled status? And in any case, even side stepping this signaled vs unsignaled dilemma that this counter is trying to check, the end result seems to be "sorry, you misused the API and now a UAF is possible". In this specific sense, it doesn't sound that much better than what we are trying to move away from in C. The more I think about this borrow design, the more I believe a simple refcount would be way safer. I mean, this field would go away to begin with, IIUC, and that’s not even considering the point above. > + /// The user's data. > + #[pin] > + data: T, > +} > + > +impl<'a, T: Send + Sync + FenceContextOps> FenceContext<T> { > + // This can later be extended as a vtable in case other parties need > support > + // for the more "exotic" callbacks. > + const OPS: bindings::dma_fence_ops = bindings::dma_fence_ops { > + get_driver_name: Some(Self::get_driver_name), > + get_timeline_name: Some(Self::get_timeline_name), > + enable_signaling: None, > + signaled: None, > + wait: None, > + release: None, > + set_deadline: None, > + }; > + > + /// Create a new `FenceContext`. > + pub fn new<E>( > + initial_seqno: u64, > + driver_name: CString, > + timeline_name: CString, > + data: impl PinInit<T, E>, > + ) -> impl PinInit<Self, Error> > + where > + Error: From<E>, > + { > + try_pin_init!(Self { > + // SAFETY: `dma_fence_context_alloc()` merely works on a global > + // atomic. Parameter `1` is the number of contexts we want to > + // allocate. > + nr: unsafe { bindings::dma_fence_context_alloc(1) }, > + seqno: Atomic::new(initial_seqno), > + driver_name, > + timeline_name, > + nr_of_unsignaled_fences: Atomic::new(0), > + data <- data, > + }) > + } > + > + fn get_next_seqno(&self) -> u64 { > + self.seqno.fetch_add(1, Relaxed) > + } Can we get rid of the “get” prefix here? I hardly see “get” in Rust accessors. > + > + /// Allocate the memory for a [`DriverFence`] and already store `data` > inside. > + /// > + /// This is needed because many times, creation of a [`DriverFence`] > must not > + /// fail, and allocating might deadlock in some situations. > + /// > + /// The `data` you pass here must not perform any operations that are > illegal > + /// in atomic context in its [`Drop`] implementation. > + pub fn fence_alloc(&self, data: T::FenceDataType) -> > Result<DriverFenceAllocation<'_, T>> { ^ In the same spirit as the last iteration, can we please rename this? We don’t need to shorten methods and types IMHO. We can just say “new_allocation” or a some other variation without “alloc”. > + let fence_data = DriverFenceData { > + rcu_head: Default::default(), > + // `inner` remains uninitialized until a `DriverFence` takes > over. > + inner: Fence { > + inner: Opaque::uninit(), > + }, > + fctx: self, > + data, > + }; > + > + // In order to support the C dma_fence callbacks, it is necessary for > + // a `Fence` and a `DriverFence` to live in the same allocation, > + // because the C backend passes a dma_fence, from which the driver > most > + // likely wants to be able to access its `data` in `DriverFence`. > + // > + // Hence, we need the manage the memory manually. It will be freed > by the > + // C backend automatically once the refcount within `Fence` drops to > 0. > + let data = KBox::new(fence_data, GFP_KERNEL | __GFP_ZERO)?; > + > + Ok(DriverFenceAllocation { > + data, > + ops: &Self::OPS, > + }) > + } > + > + extern "C" fn get_driver_name(ptr: *mut bindings::dma_fence) -> *const > c_char { > + // SAFETY: The C backend only invokes this callback with `ptr` > pointing > + // to a valid, unsignaled `bindings::dma_fence`. All fences created > in > + // this module always reside within `Fence` which always resides in a > + // `DriverFenceData`, thus satisfying the function's safety > + // requirements. > + let fctx = unsafe { Self::from_raw_fence(ptr) }; > + > + fctx.driver_name.as_char_ptr() > + } > + > + extern "C" fn get_timeline_name(ptr: *mut bindings::dma_fence) -> *const > c_char { > + // SAFETY: The C backend only invokes this callback with `ptr` > pointing > + // to a valid, unsignaled `bindings::dma_fence`. All fences created > in > + // this module always reside within `Fence` which always resides in a > + // `DriverFenceData`, thus satisfying the function's safety > + // requirements. > + let fctx = unsafe { Self::from_raw_fence(ptr) }; > + > + fctx.timeline_name.as_char_ptr() > + } > + > + /// Create a [`FenceContext`] from an associated [`bindings::dma_fence`]. > + /// > + /// # Safety > + /// > + /// `ptr` must be a valid pointer to a [`bindings::dma_fence`] which > resides > + /// within a [`Fence`], which in turn resides in a [`DriverFenceData`]. > + unsafe fn from_raw_fence(ptr: *mut bindings::dma_fence) -> &'a Self { > + let opaque_fence = Opaque::cast_from(ptr); > + > + // SAFETY: Safe due to the function's overall safety requirements. > + let fence_ptr = unsafe { container_of!(opaque_fence, Fence, inner) }; > + > + // CAST: `DriverFenceData` is repr(C) and a `Fence` is its first > member. > + let fence_data_ptr = fence_ptr as *mut DriverFenceData<'a, T>; > + > + // SAFETY: Safe because of the comments directly above. > + let fence_data = unsafe { &*fence_data_ptr }; > + > + fence_data.fctx > + } > +} > + > +// FenceContext's drop() ensures that the driver cannot unload while there > are > +// still dma_fence callbacks running. This also prevents UAF problems with > +// `fctx.driver_name` and `fctx.timeline_name`. > +// > +// DriverFence data gets dropped through `call_rcu()` in `DriverFence::drop`. > +// This `rcu_barrier()` also serves to wait for their completion. > +#[pinned_drop] > +impl<T: FenceContextOps + Send + Sync> PinnedDrop for FenceContext<T> { > + fn drop(self: Pin<&mut Self>) { > + if self.nr_of_unsignaled_fences.load(Relaxed) > 0 { > + pr_err!("Unsignaled DriverFence(s) left in FenceContext. UAF > possible.\n"); > + } > + > + // TODO: > + // It would be even more robust if the fence context signals all > + // forgotten fences itself. To do so, it would keep a list of > unsignaled > + // fences. That list members would have to be pre-allocated (see > + // `FenceCallback::fence_alloc()`). > + > + rcu_barrier(); > + } > +} > + > +/// Error type for fence callback registration. > +/// > +/// Generic over `T` so that `AlreadySignaled` can return the callback to the > +/// caller, allowing it to reclaim any resources owned by the callback (e.g., > +/// a fence handle that needs to be signaled). > +#[derive(Debug)] > +pub enum CallbackError<T = ()> { > + /// The fence was already signaled. The callback is returned so the > caller > + /// can extract owned resources without losing them. > + AlreadySignaled(T), > + /// Some other error occurred during registration. > + Other(Error), > +} > + > +impl<T> From<CallbackError<T>> for Error { > + fn from(err: CallbackError<T>) -> Self { > + match err { > + CallbackError::AlreadySignaled(_) => ENOENT, > + CallbackError::Other(e) => e, > + } > + } > +} > + > +impl<T> From<AllocError> for CallbackError<T> { > + fn from(e: AllocError) -> Self { > + CallbackError::Other(Error::from(e)) > + } > +} > + > +/// Trait for callbacks that can be registered on fences. > +/// > +/// When the fence signals, the callback will be invoked. > +/// > +/// # Example > +/// > +/// ```rust > +/// use kernel::dma_buf::FenceCallback; > +/// > +/// struct MyCallback { > +/// // Your callback state here > +/// } > +/// > +/// impl FenceCallback for MyCallback { > +/// fn called(&mut self) { > +/// pr_info!("Fence signaled!"); > +/// // Handle fence completion > +/// } > +/// } > +/// ``` > +pub trait FenceCallback: Send + 'static { > + /// Called when the fence is signaled. > + /// > + /// This is called from the fence signaling path, which may be in > interrupt > + /// context or with locks held, which is why `self` is only borrowed, so > that > + /// it cannot drop. Implementations must not sleep or perform > + /// long-running operations. > + /// > + /// An implementation likely wants to inform itself (e.g., through a > work item) > + /// within this callback that the associated > [`FenceCallbackRegistration`] > + /// can now be dropped. > + fn called(&mut self); > +} > + > +/// A callback registration on a fence. > +/// > +/// When this object is dropped, the callback is automatically removed if it > +/// hasn't been called yet. > +#[pin_data(PinnedDrop)] > +pub struct FenceCallbackRegistration<T: FenceCallback + 'static> { > + #[pin] > + callback_foreign: Opaque<bindings::dma_fence_cb>, > + callback: ManuallyDrop<T>, > + fence: ARef<Fence>, > +} > + > +impl<T: FenceCallback> FenceCallbackRegistration<T> { > + /// Create a [`PinInit`] closure for registering a callback on a fence. > + /// > + /// The actual attempt at registering the callback will take place once > you > + /// call an allocator's `pin_init()` function. > + /// > + /// On success the callback is pinned in place and will fire when the > fence > + /// signals. On `AlreadySignaled` the callback is returned to the caller > so > + /// that owned resources can be reclaimed. > + pub fn new<'a>(fence: &'a Fence, callback: T) -> impl PinInit<Self, > CallbackError<T>> + 'a > + where > + T: 'a, > + { > + try_pin_init!(Self { > + // We need to fully initialize the fence because after > + // `dma_fence_add_callback()` ran, the callback might immediately > + // get invoked. > + callback: ManuallyDrop::new(callback), > + fence: ARef::from(fence), > + callback_foreign <- Opaque::try_ffi_init(|ptr| { > + // SAFETY: `fence.inner.get()` is a valid, initialized > `struct > + // dma_fence`. `ptr` points to the `struct dma_fence_cb` > field > + // within the pinned allocation, so it remains valid until > + // `dma_fence_remove_callback()` in `PinnedDrop` or until the > + // callback fires. > + let ret = unsafe { > + to_result(bindings::dma_fence_add_callback( > + fence.inner.get(), > + ptr, > + Some(Self::dma_fence_callback), > + )) > + }; > + match ret { > + Ok(()) => Ok(()), > + Err(e) => { > + // SAFETY: We could not register the callback. Thus, > + // C will not use it. So we can just take it back > + // and pass it to the user again. > + let cb_back = unsafe { ManuallyDrop::take(callback) > }; > + if e == ENOENT { > + Err(CallbackError::AlreadySignaled(cb_back)) > + } else { > + Err(CallbackError::Other(e)) > + } > + }, > + } > + }), > + }? CallbackError<T>) > + } > + > + /// Raw dma fence callback that is called by the C code. > + /// > + /// # Safety > + /// > + /// This is only called by the dma_fence subsystem with valid pointers. > + unsafe extern "C" fn dma_fence_callback( > + _fence: *mut bindings::dma_fence, > + callback_foreign: *mut bindings::dma_fence_cb, > + ) { > + let ptr = Opaque::cast_from(callback_foreign).cast_mut(); > + > + // SAFETY: All `cb` we can receive here have been created in such a > way > + // that they are embedded into a `FenceCallbackRegistration`. The > + // backend ensures synchronisation so whoever holds the registration > + // object cannot drop it while this code is running. See > + // `FenceCallbackRegistration::drop`. > + unsafe { > + let reg: *mut Self = container_of!(ptr, Self, callback_foreign); > + > + (*reg).callback.called(); > + } > + } > + > + /// Returns a reference to the fence this callback is registered on. > + pub fn fence(self: Pin<&Self>) -> &Fence { > + &self.get_ref().fence > + } > +} > + > +#[pinned_drop] > +impl<T: FenceCallback> PinnedDrop for FenceCallbackRegistration<T> { > + fn drop(self: Pin<&mut Self>) { > + // Always call dma_fence_remove_callback, even if `callback` has > already > + // been taken by `dma_fence_callback`. This is necessary for > + // synchronization: `dma_fence_remove_callback` acquires > `fence->lock`, > + // which ensures that any in-flight `dma_fence_signal` (which calls > our > + // callback while holding the same lock) has completed before we free > + // the struct. > + // > + // Without this, Drop can race with a concurrent signal: > + // CPU0 (signal, lock held): take() -> signaled(fence_ref) (in > progress) > + // CPU1 (drop): sees is_some()==false -> skips lock -> frees struct > + // CPU0: accesses fence_ref -> use-after-free > + // > + // When the callback has already fired, the signal path detached the > + // list node via INIT_LIST_HEAD, so dma_fence_remove_callback just > sees > + // an empty node and returns false — the lock acquisition is the only > + // thing that matters. > + // > + // SAFETY: The fence pointer is valid and the cb was initialized by > + // dma_fence_add_callback during construction. > + unsafe { > + bindings::dma_fence_remove_callback(self.fence.as_raw(), > self.callback_foreign.get()); > + } > + > + // SAFETY: This is literally the drop implementation, so no one has > + // dropped this so far; so we can do it now. > + unsafe { ManuallyDrop::<T>::drop(self.project().callback) }; > + } > +} > + > +// SAFETY: FenceCallbackRegistration can be sent between threads. > +unsafe impl<T: FenceCallback> Send for FenceCallbackRegistration<T> {} > + > +// SAFETY: &FenceCallbackRegistration can be shared between threads if &T > can. > +unsafe impl<T: FenceCallback> Sync for FenceCallbackRegistration<T> where T: > Sync {} > + > +/// The receiving counterpart of a [`DriverFence`]. > +/// > +/// The Rust DMA fence implementation has a dualistic design: > [`DriverFence`]s > +/// are the producer-side, intended to be always owned by only one party. > That > +/// party has the monopoly on signalling the fence. > +/// > +/// A [`Fence`] is the counterpart for consumers. Thus, [`Fence`]s are always > +/// refcounted and can shared with an arbitrary number of parties, including > +/// userspace. Hereby, a [`Fence`] can only be used for actions such as > checking > +/// the fence's status or for registering callbacks on it. > +/// > +/// Once the associated [`DriverFence`] signals, all > +/// [`FenceCallbackRegistration`]s registered on the [`Fence`] will be > executed. > +/// > +/// A [`Fence`] can arbitrarily outlive its [`DriverFence`] and the > +/// [`FenceContext`]. Signalling a [`DriverFence`] decouples it from its > +/// [`Fence`]s. > +#[repr(transparent)] > +pub struct Fence { > + /// The actual dma_fence passed to C. > + inner: Opaque<bindings::dma_fence>, > +} > + > +/// Guard helper for locking within this module. Is this new? Needs a bit more documentation. OTOH I think we shouldn’t come up with a new guard type. IIRC from Lyude’s et al previous work, there’s already a way to build a Rust lock from a C lock (Lock::from_raw()). In fact, I think this whole implementation can boil down to: pub fn lock(&self) -> SpinLockIrqGuard<‘_, ()> { let ptr = unsafe {bindings::dma_fence_spinlock(…)}; unsafe { SpinLockIrq::<()>::from_raw(ptr)}.lock() } This has a few advantages: a) doesn’t introduce its own guard type, instead reusing something that was previously tested, b) you get the right behavior with the included NotThreadSafe token. c) the guard is now borrowed. Your guard is owned, which can easily lead to UB because the lifetime is detached from the &self that originated it. > +struct FenceGuard { > + inner: *mut bindings::dma_fence, > + flags: usize, > +} > + > +impl Deref for FenceGuard { > + type Target = *mut bindings::dma_fence; > + > + fn deref(&self) -> &Self::Target { > + &self.inner > + } > +} > + > +impl Drop for FenceGuard { > + fn drop(&mut self) { > + // SAFETY: `fence` is valid because `self` is valid. `flag_ptr` is > + // merely a pointer to an integer, which lives as long as this > function. > + // When a `FenceGuard` exists, the lock has been taken by definition. > + unsafe { bindings::dma_fence_unlock_irqrestore(self.inner, &raw mut > self.flags) }; > + } > +} > + > +// SAFETY: Fences are literally designed to be shared between threads. > +unsafe impl Send for Fence {} > +// SAFETY: Fences are literally designed to be shared between threads. > +unsafe impl Sync for Fence {} > + > +impl Fence { > + /// Check whether the fence was signaled at the moment of the function > call. > + /// > + /// Note that this can return `true` for a [`Fence`] whose > [`DriverFence`] > + /// has not yet been dropped. The reason is that the fence ops callbacks > can > + /// cause the fence to get signaled by the C backend. > + pub fn is_signaled(&self) -> bool { > + // We should not use `dma_fence_is_signaled_locked()` here, because > + // according to the C backend's recommendations, that function is > + // problematic and we should avoid calling that function with a lock > + // held. > + > + // SAFETY: `fence` stems from `self`, which is valid by definition. > + let ret = unsafe { bindings::dma_fence_is_signaled(self.as_raw()) }; > + > + // To be as robust as possible for the future we guarantee that an > API > + // caller can 100% rely on the signalling being completed (i.e., all > + // fence callbacks ran), so we have to take the lock. > + // > + // The reason is that the C dma_fence backend currently does not > + // carefully synchronize the `dma_fence_is_signaled()` function with > the > + // proper spinlock. This can lead to the function returning `true` > while > + // fence callbacks are still being executed. This can be mitigated by > + // guarding the entire function with the spinlock. > + // > + // The fundamental reason is that the C backend currently does guard > + // setting of the fence's signaled-bit with the fence's spinlock, but > + // reading is done locklessly. > + // > + // See commit c8a5d5ea3ba6a. > + > + let _ = self.lock(); > + > + ret > + } > + > + fn lock(&self) -> FenceGuard { > + let mut guard = FenceGuard { > + inner: self.as_raw(), > + flags: 0, > + }; > + > + // SAFETY: `fence` is valid because `self` is valid. `flag_ptr` is > + // merely a pointer to an integer, whose lifetime is tied to the > guard > + // object. > + unsafe { bindings::dma_fence_lock_irqsave(guard.inner, &raw mut > guard.flags) }; > + > + guard > + } > + > + /// Get the fence's sequence number. > + pub fn get_seqno(&self) -> u64 { I recommend removing the “get” prefix from this too. Just “seqno”. > + // SAFETY: Valid because `self` is valid. > + unsafe { (*self.as_raw()).seqno } > + } > + > + fn as_raw(&self) -> *mut bindings::dma_fence { > + self.inner.get() > + } > + > + /// Create a [`Fence`] from a raw C [`bindings::dma_fence`]. > + /// > + /// # Safety > + /// > + /// `ptr` must point to an initialized fence that is embedded into a > [`Fence`]. > + pub unsafe fn from_raw<'a>(ptr: *mut bindings::dma_fence) -> &'a Self { > + // SAFETY: Safe as per the function's overall safety requirements. > + unsafe { &*ptr.cast() } > + } > +} > + > +// SAFETY: These implement the C backends refcounting methods which are > proven > +// to work correctly. > +unsafe impl AlwaysRefCounted for Fence { > + fn inc_ref(&self) { > + // SAFETY: `self.as_raw()` is a pointer to a valid `struct > dma_fence`. > + unsafe { bindings::dma_fence_get(self.as_raw()) } > + } > + > + /// # Safety > + /// > + /// `ptr`must be a valid pointer to a [`DriverFence`]. > + unsafe fn dec_ref(ptr: NonNull<Self>) { > + // SAFETY: `ptr` is never a NULL pointer; and when `dec_ref()` is > called > + // the fence is by definition still valid. > + let fence = unsafe { (*ptr.as_ptr()).inner.get() }; > + > + // SAFETY: `fence` was created validly above. When `dec_ref()` is > called, > + // there is by definition still a reference alive that can be put. > + unsafe { bindings::dma_fence_put(fence) } > + } > +} > + > +// Necessary to guarantee that `inner` always comes first and can be freed > by C. > +// Also useful for using casts instead of container_of(). > +#[repr(C)] > +#[pin_data] > +struct DriverFenceData<'a, T: Send + Sync + FenceContextOps> { > + #[pin] > + /// The inner fence. > + // Must always be the first member so that unsafe casting works; but also > + // necessary so that the C backend can free the allocation (coming from > our > + // Rust code) with kfree_rcu(). > + inner: Fence, > + /// Callback head for dropping this in a deferred manner through RCU. > + rcu_head: bindings::callback_head, > + /// Reference to access the FenceContext. Useful for obtaining name > parameters. > + fctx: &'a FenceContext<T>, > + /// The API user's data. It is essential that the data only performs > + /// operations legal in atomic context in its [`Drop`] implementation. > + #[pin] > + data: T::FenceDataType, > +} > + > +/// A synchronization primitive mainly for GPU drivers. > +/// > +/// The Rust DMA fence implementation has a dualistic design: > [`DriverFence`]s > +/// are the producer-side, intended to be always owned by only one party. > That > +/// party has the monopoly on signalling the fence. > +/// > +/// A [`Fence`] is the counterpart for consumers. Thus, [`Fence`]s are always > +/// refcounted and can shared with an arbitrary number of parties, including > +/// userspace. Hereby, a [`Fence`] can only be used for actions such as > checking > +/// the fence's status or for registering callbacks on it. > +/// > +/// Once the associated [`DriverFence`] signals, all > +/// [`FenceCallbackRegistration`]s registered on a [`Fence`] will be > executed. > +/// > +/// A [`Fence`] can arbitrarily outlive its [`DriverFence`] and the > +/// [`FenceContext`]. Signalling a [`DriverFence`] decouples it from its > +/// [`Fence`]s. > +/// > +/// It is crucial that a [`DriverFence`] always correctly represents the > state > +/// of the associated job on the hardware. Especially, it is strictly > necessary > +/// that the owner ensures that all [`DriverFence`]s eventually get signaled. > +/// As a last ressort, a [`DriverFence`] will signal itself if it drops Typo in resort > +/// unsignaled and print a warning. > +/// > +/// This design intends to implement the [`bindings::dma_fence_ops`] in such > a > +/// way that the driver-data necessary to implement the callback's > functionality > +/// resides in the [`FenceContext`]. Thus, a [`DriverFence`] contains a > +/// reference to the context, which can be accessed in the callbacks. The > +/// implementation, therefore, ensures that a [`DriverFence`] cannot outlive > its > +/// [`FenceContext`]. Unfortunately, this can be circumvented under certain > +/// circumstances in Rust (e.g., usage of [`core::mem::forget`]). > +/// > +/// In the unlikely case of such violations, error warnings are printed. > +/// > +/// # Examples > +/// > +/// ``` > +/// use kernel::dma_buf::{ > +/// DriverFence, > +/// FenceContext, > +/// FenceContextOps, > +/// FenceCallback, > +/// FenceCallbackRegistration, // > +/// }; > +/// use kernel::str::CString; > +/// use kernel::sync::aref::ARef; > +/// use core::fmt::Display; > +/// > +/// struct CallbackData { } > +/// > +/// impl FenceCallback for CallbackData { > +/// fn called(&mut self) { > +/// pr_info!("DmaFence callback executed.\n"); > +/// } > +/// } > +/// > +/// #[pin_data] > +/// struct FenceContextData {} > +/// > +/// impl FenceContextData { > +/// fn new() -> impl PinInit<Self> { > +/// pin_init!(Self {}) > +/// } > +/// } > +/// > +/// impl FenceContextOps for FenceContextData { > +/// type FenceDataType = FenceData; > +/// } > +/// > +/// let fctx_data = FenceContextData::new(); > +/// > +/// let driver_name = CString::try_from_fmt(fmt!("dummy_driver"))?; > +/// let timeline_name = CString::try_from_fmt(fmt!("dummy_timeline"))?; > +/// > +/// let mut fctx = KBox::pin_init(FenceContext::new(0, driver_name, > timeline_name, fctx_data), GFP_KERNEL)?; Missing rustfmt? > +/// > +/// struct FenceData { > +/// data: CString, > +/// } > +/// > +/// let data = CString::try_from_fmt(fmt!("dummy_data"))?; > +/// let fence_data = FenceData { data }; > +/// > +/// let fence_alloc = fctx.fence_alloc(fence_data)?; > +/// let mut fence = fence_alloc.new_fence(); > +/// > +/// let cb_data = CallbackData { }; > +/// let waiting_fence = ARef::from(fence.as_fence()); > +/// let cb_reg = FenceCallbackRegistration::new(&waiting_fence, cb_data); > +/// let cb_reg = KBox::pin_init(cb_reg, GFP_KERNEL)?; > +/// > +/// // TODO signalling guards > +/// fence.signal(Ok(())); > +/// assert_eq!(waiting_fence.is_signaled(), true); > +/// > +/// Ok::<(), Error>(()) > +/// ``` > +pub struct DriverFence<'a, T: Send + Sync + FenceContextOps> { > + /// The actual content of the fence. Lives in a [`NonNull`] so that its > + /// memory can be managed independently. Valid until both the > [`DriverFence`] > + /// and all associated [`Fence`]s have disappeared. > + data: NonNull<DriverFenceData<'a, T>>, > +} > + > +/// A pre-prepared DMA fence, carrying the user's data and the memory it and > the > +/// fence reside in. Only useful for creating a [`DriverFence`]. Splitting > +/// allocation and full initialization is necessary because fences cannot be > +/// allocated dynamically in some circumstances (deadlock). > +pub struct DriverFenceAllocation<'a, T: Send + Sync + FenceContextOps> { > + /// The memory for the actual content of the fence. > + /// Handed over to a [`DriverFence`], or deallocated once the > + /// [`DriverFenceAllocation`] drops. > + data: KBox<DriverFenceData<'a, T>>, > + /// Pointer for the ops for the associated [`FenceContext`] > + ops: *const bindings::dma_fence_ops, > +} > + > +impl<'a, T: Send + Sync + FenceContextOps> DriverFenceAllocation<'a, T> { > + /// Create a new fence, consuming `data`. > + /// > + /// This increments the sequence number in the associated > [`FenceContext`]. > + pub fn new_fence(self) -> DriverFence<'a, T> { > + // We feed the C dma_fence backend a NULL for the spinlock so that it > + // uses per-fence locks automatically. > + let null_ptr: *mut bindings::spinlock = ptr::null_mut(); > + let seqno = self.data.fctx.get_next_seqno(); > + let fence_ptr = self.as_raw(); > + // SAFETY: `fence_ptr` has been created directly above. It will live > + // at least as long as `Self`. The same applies to `&Self::OPS`. > + unsafe { > + bindings::dma_fence_init(fence_ptr, self.ops, null_ptr, > self.data.fctx.nr, seqno) > + }; > + > + self.data.fctx.nr_of_unsignaled_fences.fetch_add(1, Relaxed); > + > + // A `DriverFenceAllocation`'s purpose is to carry allocated memory, > so that > + // `DriverFence`s can always be created without allocating. In this > + // method, ownership over that memory is transferred to the new > + // `DriverFence` and managed through refcounting. The C dma_fence > + // backend will ultimately free the memory once the refcount reaches > 0. > + let ptr = KBox::into_raw(self.data); > + // SAFETY: `ptr` was just created validly directly above. > + let ptr = unsafe { NonNull::new_unchecked(ptr) }; > + > + DriverFence { data: ptr } > + } > + > + fn as_raw(&self) -> *mut bindings::dma_fence { > + self.data.inner.inner.get() > + } > +} > + > +impl<'a, T: Send + Sync + FenceContextOps> DriverFence<'a, T> { > + fn as_raw(&self) -> *mut bindings::dma_fence { > + // SAFETY: Valid because `self` is valid. > + let fence_data = unsafe { &*self.data.as_ptr() }; > + > + fence_data.inner.inner.get() > + } > + > + /// Create a [`DriverFence`] from a raw pointer to a > [`bindings::dma_fence`]. > + /// > + /// # Safety > + /// > + /// `ptr` must be a valid pointer to a `dma_fence` that was obtained > through > + /// a [`DriverFence`] with matching generic data for both fence and > associated > + /// [`FenceContext`]. > + unsafe fn from_raw(ptr: *mut bindings::dma_fence) -> Self { > + let opaque_fence = Opaque::cast_from(ptr); > + > + // SAFETY: Safe due to the function's overall safety requirements. > + let fence_ptr = unsafe { container_of!(opaque_fence, Fence, inner) }; > + > + // DriverFenceData is repr(C) and a Fence is its first member. > + let fence_data_ptr = fence_ptr as *mut DriverFenceData<'a, T>; > + > + // SAFETY: `fence_data_ptr` was created validly above. > + let data = unsafe { NonNull::new_unchecked(fence_data_ptr) }; > + > + Self { data } > + } > + > + /// Return the underlying [`Fence`]. > + pub fn as_fence(&self) -> &Fence { > + // SAFETY: `self` is by definition still valid, and it cannot drop > until > + // this new reference is gone. > + unsafe { Fence::from_raw(self.as_raw()) } > + } > + > + /// Signal the fence. This will invoke all registered callbacks. > + pub fn signal(self, res: Result) { > + let fence = self.as_fence().lock(); > + > + // SAFETY: `fence` is valid because `self` is valid. The lock must be > + // held, which we acquired directly above. > + if !unsafe { bindings::dma_fence_test_signaled_flag(*fence.deref()) > } { > + if let Err(err) = res { > + // SAFETY: `fence` is valid because `self` is valid. The > fence > + // must not have been signaled yet, which we check directly > above. > + unsafe { bindings::dma_fence_set_error(*fence.deref(), > err.to_errno()) }; > + } > + // SAFETY: `fence` is valid because `self` is valid. The lock > must > + // be held, which we acquired above. > + unsafe { bindings::dma_fence_signal_locked(*fence.deref()) }; > + } > + > + // SAFETY: `self.data` is valid because `self` is valid. > + let fctx = unsafe { self.data.as_ref().fctx }; > + let _ = fctx.nr_of_unsignaled_fences.fetch_sub(1, Relaxed); > + } > +} > + > +// SAFETY: Fences are literally designed to be shared between threads. > +unsafe impl<'a, T: Send + Sync + FenceContextOps> Send for DriverFence<'a, > T> {} > +// SAFETY: Fences are literally designed to be shared between threads. > +unsafe impl<'a, T: Send + Sync + FenceContextOps> Sync for DriverFence<'a, > T> {} > + > +impl<'a, T: Send + Sync + FenceContextOps> Deref for DriverFence<'a, T> { > + type Target = T::FenceDataType; > + > + fn deref(&self) -> &Self::Target { > + // SAFETY: Thanks to refcounting, `data` is always valid as long as > `self` is. > + let data = unsafe { &*self.data.as_ptr() }; > + > + &data.data > + } > +} > + > +/// A borrow wrapper for [`DriverFence`]. Implements [`Deref`]. > +pub struct DriverFenceBorrow<'a, T: Send + Sync + FenceContextOps> { > + driver_fence: ManuallyDrop<DriverFence<'a, T>>, > + _lifetime: PhantomData<&'a T>, > +} > + > +impl<'a, T: Send + Sync + FenceContextOps> Deref for DriverFenceBorrow<'a, > T> { > + type Target = DriverFence<'a, T>; > + > + fn deref(&self) -> &Self::Target { > + self.driver_fence.deref() > + } > +} > + > +// SAFETY: The Rust dma_fence abstractions are already designed around the > inner > +// C `dma_fence`, which can serve safely as the identification point when > being > +// owned by C. Moreover, safety is ensured by not dropping `DriverFence` and > by > +// only allowing operations without side effects on the Borrowed type. > +unsafe impl<T: Send + Sync + FenceContextOps + 'static> ForeignOwnable for > DriverFence<'_, T> { > + type Borrowed<'a> > + = DriverFenceBorrow<'a, T> > + where > + Self: 'a; > + type BorrowedMut<'a> > + = DriverFenceBorrow<'a, T> > + where > + Self: 'a; > + > + const FOREIGN_ALIGN: usize = > core::mem::align_of::<bindings::dma_fence>(); > + > + fn into_foreign(self) -> *mut c_void { > + let fence = self; > + > + let ptr = fence.as_raw(); > + > + // DriverFence must not drop. > + let _ = ManuallyDrop::new(fence); > + > + ptr.cast() > + } > + > + unsafe fn from_foreign(ptr: *mut c_void) -> Self { > + // SAFETY: Safe because the trait implementation only invokes this > with > + // a valid `ptr`, associated to a `DriverFence` with matching > generic data. > + unsafe { Self::from_raw(ptr.cast()) } > + } > + > + unsafe fn borrow<'a>(ptr: *mut c_void) -> Self::Borrowed<'a> > + where > + Self: 'a, > + { > + // SAFETY: The trait implementation ensures that `ptr` always resides > + // within a [`Fence`] within a [`DriverFenceData`]. > + let driver_fence = unsafe { Self::from_raw(ptr.cast()) }; > + > + let driver_fence = ManuallyDrop::new(driver_fence); > + > + DriverFenceBorrow { > + driver_fence, > + _lifetime: PhantomData, > + } > + } > + > + unsafe fn borrow_mut<'a>(ptr: *mut c_void) -> Self::BorrowedMut<'a> > + // FIXME: The bound below and the one above in `borrow` should actually > be > + // unnecessary since the compiler should be able to completely derive all > + // necessary information automatically. There is currently a compiler bug > + // preventing that, though: > + // > + // https://github.com/rust-lang/rust/issues/155430. > + // > + // (Help to) fix the compiler bug and remove the bounds afterwards. > + where > + Self: 'a, > + { > + // SAFETY: The trait implementation ensures that `ptr` always resides > + // within a [`Fence`] within a [`DriverFenceData`]. > + let driver_fence = unsafe { Self::from_raw(ptr.cast()) }; > + > + let driver_fence = ManuallyDrop::new(driver_fence); > + > + DriverFenceBorrow { > + driver_fence, > + _lifetime: PhantomData, > + } > + } > +} > + > +impl<'a, T: Send + Sync + FenceContextOps> Drop for DriverFence<'a, T> { > + fn drop(&mut self) { > + let guard = self.as_fence().lock(); > + > + // Use dma_fence_test_signaled_flag() instead of > + // dma_fence_is_signaled_locked() because the C backend wants to get > rid > + // of the latter. > + > + // SAFETY: `guard` is valid until the `call_rcu()` below. > + let signaled: bool = unsafe { > bindings::dma_fence_test_signaled_flag(*guard.deref()) }; > + if !signaled { > + pr_err!("DriverFence drops unsignaled. Danger of memory > corruption!\n"); > + // SAFETY: `guard` is valid until the `call_rcu()` below. The > fence > + // must not have been signaled yet, which we check directly > above. > + unsafe { bindings::dma_fence_set_error(*guard.deref(), > ECANCELED.to_errno()) }; > + // SAFETY: `guard` is valid until the `call_rcu()` below. The > lock > + // must be held, which we acquired above. > + unsafe { bindings::dma_fence_signal_locked(*guard.deref()) }; > + > + // SAFETY: `self.data` is valid because `self` is valid. > + let fctx = unsafe { self.data.as_ref().fctx }; > + let _ = fctx.nr_of_unsignaled_fences.fetch_sub(1, Relaxed); > + } > + drop(guard); > + > + // SAFETY: Valid because `self` is valid. > + let rcu_head_ptr = unsafe { &raw mut (*self.data.as_ptr()).rcu_head > }; > + > + // `DriverFenceData` but could be accessed through some dma_fence > + // callbacks right now. Access is being revoked in principle above by > + // signalling the fence, but since the C backend does not guarantee > + // perfect full synchronization, we have to wait for one grace > period to > + // ensure that all accessors of `DriverFenceData` (through the > + // dma_fence_ops accessible through a `Fence`) are gone. > + > + // SAFETY: `call_rcu()` is always safe to be called. `rcu_head_ptr` > was > + // created validly above. The module must perform a > `synchronize_rcu()` > + // or `rcu_barrier()` call to guard against module unload. > + unsafe { bindings::call_rcu(rcu_head_ptr, > Some(drop_driver_fence_data::<T>)) }; > + } > +} > + > +// TODO: > +// The entire call_rcu() mechanism in the drop above and the code below > would be > +// unnecessary if C's dma_fence_signal() could be reworked in a way that > after it > +// ran, the caller knows that no fence_ops callbacks can be running anymore. > +// In other words, if the dma_fence backend would use its spinlock for full > +// synchronization. > +// > +// Then we could move the drop_in_place() and dma_fence_put() upwards into > the > +// drop() implementation and call it a day. > + > +/// Finally really drop this `DriverFence<T>` > +/// > +/// # Safety > +/// > +/// `head` references the `rcu_head` field of an `DriverFenceData<T>`. All > +/// accessors to that `DriverFenceData<T>` must be gone by now. This must be > +/// ensured by signalling the associated `DriverFence<T>` and then waiting > +/// for a grace period until calling this function here. > +unsafe extern "C" fn drop_driver_fence_data<T: Send + Sync + > FenceContextOps>( > + head: *mut bindings::callback_head, > +) { > + // SAFETY: Caller provides a pointer to the `rcu_head` field of a > `DriverFenceData<C>`. > + let fence_data = unsafe { container_of!(head, DriverFenceData<'_, T>, > rcu_head) }; > + > + // SAFETY: `fence_data` was created validly above. All the fence's data > will > + // only drop below, but the raw pointer to the raw C `dma_fence` remains > + // valid because the reference count is only decremented at the end of > the > + // function. > + let fence = unsafe { (*fence_data).inner.inner.get() }; > + > + // SAFETY: `fence_data` was created validly above. A grace period has > passed. > + // All callbacks which might have had access to the `fctx` are gone now. > + unsafe { drop_in_place(&raw mut (*fence_data).fctx) }; > + > + // SAFETY: `fence_data` was created validly above. The user has already > + // dropped the only conventional accessor to the user data, the > `DriverFence`, > + // one grace period ago. All accessors are gone now. > + unsafe { drop_in_place(&raw mut (*fence_data).data) }; > + > + // The inner `Fence` explicitly does not get dropped because there may be > + // many more users / consumers, each holding their own reference. > + > + // SAFETY: Once a `DriverFence` is initialized, the inner `fence` is > + // valid and initialized. It is valid until the refcount drops > + // to 0, which can earliest happen once we drop the `DriverFence`'s > reference > + // here. > + unsafe { bindings::dma_fence_put(fence) }; > + > + // The actual memory the data associated with a `DriverFence` lives in > + // gets freed by the C dma_fence backend once the fence's refcount > reaches 0. > +} > diff --git a/rust/kernel/dma_buf/mod.rs b/rust/kernel/dma_buf/mod.rs > new file mode 100644 > index 000000000000..4764a828642e > --- /dev/null > +++ b/rust/kernel/dma_buf/mod.rs > @@ -0,0 +1,14 @@ > +// SPDX-License-Identifier: GPL-2.0 OR MIT > + > +//! DMA-buf subsystem abstractions. > + > +pub mod dma_fence; > + > +pub use self::dma_fence::{ > + DriverFence, > + Fence, > + FenceCallback, > + FenceCallbackRegistration, > + FenceContext, > + FenceContextOps, // > +}; > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs > index 68f4d9a3425d..6221ebfe71df 100644 > --- a/rust/kernel/lib.rs > +++ b/rust/kernel/lib.rs > @@ -67,6 +67,7 @@ > pub mod device_id; > pub mod devres; > pub mod dma; > +pub mod dma_buf; > pub mod driver; > #[cfg(CONFIG_DRM = "y")] > pub mod drm; > -- > 2.55.0 > >
