Re: [PATCH 2/4] rust: dma: generalize `dma_{read,write}` macro
From: "Benno Lossin" <lossin@kernel.org>
Date: 2026-02-14 10:05:00
Also in:
driver-core, lkml
On Sat Feb 14, 2026 at 6:33 AM CET, Gary Guo wrote:
+ (@parse [$dma:expr] [$($proj:tt)*] [, $val:expr]) => {
+ let ptr = $crate::project_pointer!(
+ mut $crate::dma::CoherentAllocation::as_mut_ptr(&$dma), $($proj)*
+ );
+ let val = $val;
+ // SAFETY: pointer created by projection is within DMA region.
+ unsafe { $crate::dma::CoherentAllocation::field_write(&$dma, ptr, val) }This evaluates `$dma` for a second time (and also places it inside an `unsafe` block).
+ };
Missing surrounding `{}` to allow this in expression position?
+ (@parse [$dma:expr] [$($proj:tt)*] [.$field:tt $($rest:tt)*]) => {
+ $crate::dma_write!(@parse [$dma] [$($proj)* .$field] [$($rest)*])
+ };
+ (@parse [$dma:expr] [$($proj:tt)*] [[$index:expr]? $($rest:tt)*]) => {
+ $crate::dma_write!(@parse [$dma] [$($proj)* [$index]?] [$($rest)*])
+ };
+ (@parse [$dma:expr] [$($proj:tt)*] [[$index:expr] $($rest:tt)*]) => {
+ $crate::dma_write!(@parse [$dma] [$($proj)* [$index]] [$($rest)*])
+ };
+ ($dma:expr, $($rest:tt)*) => {
+ $crate::dma_write!(@parse [$dma] [] [$($rest)*])
};
I'm wondering if this also works:
($dma:expr, $($(.$field:ident)? $([$index:expr])?)*, $val:expr) => {{
let dma = &$dma;
let ptr = $crate::project_pointer!(
mut $crate::dma::CoherentAllocation::as_mut_ptr(dma),
$($(.$field)? $([$index])?)*,
);
let val = $val;
// SAFETY: pointer created by projection is within DMA region.
unsafe { $crate::dma::CoherentAllocation::field_write(dma, ptr, val) }
}}
quoted hunk ↗ jump to hunk
}diff --git a/samples/rust/rust_dma.rs b/samples/rust/rust_dma.rs index 9c45851c876e..b772ada2c65c 100644 --- a/samples/rust/rust_dma.rs +++ b/samples/rust/rust_dma.rs@@ -68,7 +68,7 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> impl PinInit<Self, E CoherentAllocation::alloc_coherent(pdev.as_ref(), TEST_VALUES.len(), GFP_KERNEL)?; for (i, value) in TEST_VALUES.into_iter().enumerate() { - kernel::dma_write!(ca[i] = MyStruct::new(value.0, value.1))?; + kernel::dma_write!(ca, [i]?, MyStruct::new(value.0, value.1)); } let size = 4 * page::PAGE_SIZE;@@ -91,17 +91,17 @@ fn drop(self: Pin<&mut Self>) { dev_info!(self.pdev, "Unload DMA test driver.\n"); for (i, value) in TEST_VALUES.into_iter().enumerate() { - let val0 = kernel::dma_read!(self.ca[i].h); - let val1 = kernel::dma_read!(self.ca[i].b); - assert!(val0.is_ok()); - assert!(val1.is_ok()); + let result = (|| -> Result<_> { + let val0 = kernel::dma_read!(self.ca, [i]?.h); + let val1 = kernel::dma_read!(self.ca, [i]?.b); - if let Ok(val0) = val0 { assert_eq!(val0, value.0); - } - if let Ok(val1) = val1 { assert_eq!(val1, value.1); - } + + Ok(()) + })();
I dislike that we have to reintroduce the budget-try block here. Ideally we could add something like `try` at the beginning of the macro and then automatically add the try block. Feel free to make that a future series. Cheers, Benno
+
+ assert!(result.is_ok());
}
for (i, entry) in self.sgt.iter().enumerate() {