On 2020/09/12 22:53, Ming Lei wrote:
> On Fri, Sep 11, 2020 at 05:53:36PM -0400, Mike Snitzer wrote:
>> blk_queue_get_max_sectors() has been trained for REQ_OP_WRITE_SAME and
>> REQ_OP_WRITE_ZEROES yet blk_rq_get_max_sectors() didn't call it for
>> those operations.
>
> Actually WRITE_SAME & WRITE_ZEROS are handled by the following if
> chunk_sectors is set:
>
> return min(blk_max_size_offset(q, offset),
> blk_queue_get_max_sectors(q, req_op(rq)));
>
>> Also, there is no need to avoid blk_max_size_offset() if
>> 'chunk_sectors' isn't set because it falls back to 'max_sectors'.
>>
>> Signed-off-by: Mike Snitzer <snit...@redhat.com>
>> ---
>> include/linux/blkdev.h | 19 +++++++++++++------
>> 1 file changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index bb5636cc17b9..453a3d735d66 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -1070,17 +1070,24 @@ static inline unsigned int
>> blk_rq_get_max_sectors(struct request *rq,
>> sector_t offset)
>> {
>> struct request_queue *q = rq->q;
>> + int op;
>> + unsigned int max_sectors;
>>
>> if (blk_rq_is_passthrough(rq))
>> return q->limits.max_hw_sectors;
>>
>> - if (!q->limits.chunk_sectors ||
>> - req_op(rq) == REQ_OP_DISCARD ||
>> - req_op(rq) == REQ_OP_SECURE_ERASE)
>> - return blk_queue_get_max_sectors(q, req_op(rq));
>> + op = req_op(rq);
>> + max_sectors = blk_queue_get_max_sectors(q, op);
>>
>> - return min(blk_max_size_offset(q, offset),
>> - blk_queue_get_max_sectors(q, req_op(rq)));
>> + switch (op) {
>> + case REQ_OP_DISCARD:
>> + case REQ_OP_SECURE_ERASE:
>> + case REQ_OP_WRITE_SAME:
>> + case REQ_OP_WRITE_ZEROES:
>> + return max_sectors;
>> + }>> +
>> + return min(blk_max_size_offset(q, offset), max_sectors);
>> }
>
> It depends if offset & chunk_sectors limit for WRITE_SAME & WRITE_ZEROS
> needs to be considered.
That limit is needed for zoned block devices to ensure that *any* write request,
no matter the command, do not cross zone boundaries. Otherwise, the write would
be immediately failed by the device.
>
>
> Thanks,
> Ming
>
>
--
Damien Le Moal
Western Digital Research
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