Re: [PATCH v8 3/7] rust: dma: implement BinaryWriter for CoherentAllocation<u8>

["Alexandre Courbot" <acourbot@nvidia.com>]

On Sat Mar 14, 2026 at 11:05 AM JST, Timur Tabi wrote:
> On Fri, 2026-03-13 at 11:11 +0900, Alexandre Courbot wrote:
>> > +        if offset.is_negative() {
>> > +            return Err(EINVAL);
>> > +        }
>> 
>> Won't the `try_into` right below also reject negative values?
>> 
>> > +
>> > +        let offset_val: usize = (*offset).try_into().map_err(|_| EINVAL)?;
>
> Well, yes, but there's actually a bigger problem, now that you point this out.  If usize is 32
> bits, the try_into() could fail if *offset is too large.  In that case, it should return Ok(0)
> instead of EINVAL.
>
> So actually, we need to keep the is_negative() check, but should modify the try_into() to return
> Ok(0) instead of EINVAL.
>
> let Ok(offset_val) = usize::try_from(*offset) else {
>     return Ok(0);  // offset too large for usize = past EOF
> };
>
> Are we going to assume CONFIG_64BIT forever, and just ignore any possible errors if usize is 32
> bits?

This is not Nova, so we cannot assume CONFIG_64BIT. I guess we have to
do as you described above.