On Sun, Sep 13 2020 at 8:43pm -0400,
Damien Le Moal <Damien.LeMoal@xxxxxxx> wrote:
> 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 <snitzer@xxxxxxxxxx>
> >> ---
> >> 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 for the additional context, sorry to make you so concerned! ;)
Mike
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