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

[Abdiel Janulgue <abdiel.janulgue@gmail.com>]

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@kernel.org>
>> Signed-off-by: Abdiel Janulgue <abdiel.janulgue@gmail.com>
>> ---
>>   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