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The latter rejects offsets beyond the >>> allocation even when the copy length is zero, so a debugfs read past EO= F >>> 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<[u= 8]>") >>> Signed-off-by: Younes Akhouayri >>> --- >>> 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); >>> }; >>> =20 >>> + if offset_val >=3D self.size() { >>> + return Ok(0); >>> + } >>> + >>> let count =3D self.size().saturating_sub(offset_val).min(write= r.len()); >> >> This saturating_sub is redundant now and should just use -. > > Or even better, you could use `checked_sub` to perform the test and the > subtraction in one go, while avoiding potentially panicking operands. I think the code is clearer with separate EOF check length calc. This also = needs to return `Ok` so it's not like that you can use `?`. Best, Gary