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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 >>>>> --- >>>>> 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(wri= ter.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 al= so needs >> to return `Ok` so it's not like that you can use `?`. > > Is it clearer? The `checked_sub` is efficient and makes it clear the > code won't panic. And `ok_or` takes care of converting to the right > error nicely. There's no error here. Best, Gary