[PATCH] rust: dma: return zero for Coherent reads past EOF

[Younes Akhouayri via B4 Relay]

From: Younes Akhouayri <git@xxxxxxxxx>

Coherent<T>::write_to_slice() calculates a zero-byte copy when the file
offset is beyond the allocation, but still calls
UserSliceWriter::write_dma(). The latter rejects offsets beyond the
allocation even when the copy length is zero, so a debugfs read past EOF
returns -ERANGE.

Return before calling write_dma() when the offset is at or beyond the
allocation, matching simple_read_from_buffer() EOF semantics.

Fixes: 016818513936 ("rust: dma: implement BinaryWriter for Coherent<[u8]>")
Signed-off-by: Younes Akhouayri <git@xxxxxxxxx>
---
 rust/kernel/dma.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
index 200def84fb69..36b72fb9ab46 100644
--- a/rust/kernel/dma.rs
+++ b/rust/kernel/dma.rs
@@ -1005,6 +1005,10 @@ fn write_to_slice(
             return Ok(0);
         };
 
+        if offset_val >= self.size() {
+            return Ok(0);
+        }
+
         let count = self.size().saturating_sub(offset_val).min(writer.len());
 
         writer.write_dma(self, offset_val, count)?;

---
base-commit: 880c43b185ca52239e75bc546cc4f4d9154d0fed
change-id: 20260720-fix-dma-coherent-eof-d0d08c91e013

Best regards,
--  
Younes Akhouayri <git@xxxxxxxxx>