Re: [PATCH v2 0/6] rust / dma_buf: Add abstractions for dma_fence

[Philipp Stanner <phasta@mailbox.org>]

On Tue, 2026-06-16 at 13:02 +0200, Danilo Krummrich wrote:
> On Tue Jun 16, 2026 at 10:28 AM CEST, Philipp Stanner wrote:
> > Changes since v1:
> 
> It seems that some of the comments from v1 [1][2] are not addressed, did you
> forget them?

yeah, a bunch of stuff might have slipped me. Mea culpa. Need to
address some more issues in v3 anyways; but wanted to present the rough
RCU idea here as a heads-up.

> 
> In particular the pin_init_from_closure() looks unnecessary and can probably
> replaced with something like (untested):
> 
> 	let mut callback = Some(callback);
> 	
> 	try_pin_init!(Self {
> 	    cb <- 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) => {
> 	                let cb_back = callback.take().expect("success path did not run");
> 	                if e == ENOENT {
> 	                    Err(CallbackError::AlreadySignaled(cb_back))
> 	                } else {
> 	                    Err(CallbackError::Other(e))
> 	                }
> 	            }
> 	        }
> 	    }),
> 	    callback: callback.take().expect("error path did not run"),
> 	    fence: ARef::from(fence),
> 	}? CallbackError<T>)
> 
> Please also see my previous comments regarding DriverFenceBorrow, it still seems
> to miss the lifetime and it should probably use ManuallyDrop<DriverFence>.

ACK.

> 
> It also seems the patch series was created without --base, what's the base
> revision?

Branched out from drm-misc-next for development purposes (since it
heavily relies on dma-fence.c)

I can rebase on drm-rust-next for the next revision.

> 
> [1] https://lore.kernel.org/all/DIW3ZK5NLKU3.1QYMQB0ISHFBG@kernel.org/
> [2] https://lore.kernel.org/all/DIW42TO5HY6H.2RLL8V8H48A5A@kernel.org/