Re: [PATCH v2 3/3] rust: dma: add as_slice/write functions for CoherentAllocation

[Abdiel Janulgue]

On 10/04/2025 12:57, Alexandre Courbot wrote:
> Hi Abdiel,
>
> On Thu Apr 10, 2025 at 5:58 PM JST, Abdiel Janulgue wrote:
> > Add unsafe accessors for the region for reading or writing large
> > blocks of data.
> >
> > Reviewed-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
> > Signed-off-by: Abdiel Janulgue <abdiel.janulgue@xxxxxxxxx>
> > ---
> >   rust/kernel/dma.rs | 85 ++++++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 85 insertions(+)
> >
> > diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
> > index a61da5eeb017..880f6f04ba86 100644
> > --- a/rust/kernel/dma.rs
> > +++ b/rust/kernel/dma.rs
> > @@ -218,6 +218,91 @@ pub fn dma_handle(&self) -> bindings::dma_addr_t {
> >           self.dma_handle
> >       }
> >   
> > +    /// Returns the data from the region starting from `offset` as a slice.
> > +    /// `offset` and `count` are in units of `T`, not the number of bytes.
> > +    ///
> > +    /// For ringbuffer type of r/w access or use-cases where the pointer to the live data is needed,
> > +    /// [`CoherentAllocation::start_ptr`] or [`CoherentAllocation::start_ptr_mut`] could be used instead.
> > +    ///
> > +    /// # Safety
> > +    ///
> > +    /// * Callers must ensure that the device does not read/write to/from memory while the returned
> > +    ///   slice is live.
> > +    /// * Callers must ensure that this call does not race with a write to the same region while
> > +    ///   while the returned slice is live.
> > +    pub unsafe fn as_slice(&self, offset: usize, count: usize) -> Result<&[T]> {
> > +        let end = offset.checked_add(count).ok_or(EOVERFLOW)?;
> > +        if end >= self.count {
> > +            return Err(EINVAL);
> > +        }
>
> Not sure if you have overlooked my comment on the previous iteration or
> if I completely missed the mark, but my understanding if that the bound
> check should be `if end > self.count`. Also applies to the other methods
> of this patch.
Ah sorry about that, just missed that part! But will definitely do a 
follow-up that includes this (with other changes if needed).

/Abdiel