[PATCH v4 05/11] block: Add core atomic write support

[Ritesh Harjani (IBM)]

Ritesh Harjani (IBM) <ritesh.list at gmail.com> writes:

> John Garry <john.g.garry at oracle.com> writes:
>
>> +
>> +	mask = boundary - 1;
>> +
>> +	/* start/end are boundary-aligned, so cannot be crossing */
>> +	if (!(start & mask) || !(end & mask))
>> +		return false;
>> +
>> +	imask = ~mask;
>> +
>> +	/* Top bits are different, so crossed a boundary */
>> +	if ((start & imask) != (end & imask))
>> +		return true;
>
> The last condition looks wrong. Shouldn't it be end - 1?
>
>> +
>> +	return false;
>> +}
>
> Can we do something like this?
>
> static bool rq_straddles_atomic_write_boundary(struct request *rq,
> 					       unsigned int start_adjust,
> 					       unsigned int end_adjust)
> {
> 	unsigned int boundary = queue_atomic_write_boundary_bytes(rq->q);
> 	unsigned long boundary_mask;
> 	unsigned long start_rq_pos, end_rq_pos;
>
> 	if (!boundary)
> 		return false;
>
> 	start_rq_pos = blk_rq_pos(rq) << SECTOR_SHIFT;
> 	end_rq_pos = start_rq_pos + blk_rq_bytes(rq);

my bad. I meant this...

   end_rq_pos = start_rq_pos + blk_rq_bytes(rq) - 1;
>
> 	start_rq_pos -= start_adjust;
> 	end_rq_pos += end_adjust;
>
> 	boundary_mask = boundary - 1;
>
> 	if ((start_rq_pos | boundary_mask) != (end_rq_pos | boundary_mask))
> 		return true;
>
> 	return false;
> }
>
> I was thinking this check should cover all cases? Thoughts?
>
>

-ritesh