On Wed, 05 Mar 2008 09:21:24 -0600
James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 2008-03-05 at 14:51 +0100, Jens Axboe wrote:
> > On Wed, Mar 05 2008, Tejun Heo wrote:
> > > This is getting insanely subtle. Let's say there's PIO driver which
> > > transfer certain sized chunks at a time and completes request partially
> > > after completing each chunk and the driver uses draining to eat up
> > > whatever excess data, which seems like a legit use case to me. But it
> > > won't work because __end_that_request_first() will terminate when it
> > > reaches reaches the 'true' transfer size. That's just broken API. FWIW,
> > >
> > > Nacked-by: Tejun Heo <htejun@xxxxxxxxx>
> >
> > Yeah, I think I may have gone a bit overboard in applying this so
> > quickly. It's just not a good interface, silently adding the extra
> > length if asked to complete more. It may even happen right now, for a
> > driver that does no padding (it probably wont do any harm here either,
> > but still).
> >
> > I'll try and see if I can come up with something cleaner.
> >
> > My basic design paradigm for this is that the _driver_ (or mid layer, if
> > SCSI wants to handle it) should care about the padding. So make it easy
> > for them to pad, but have it 'unrolled' by completion time. We should
> > NOT need any extra_len checks or additions in the block/ directory,
> > period.
>
> Right, that's why my original proposal was to do nothing for padding
> (other than ensure the driver could adjust the length if it wanted to)
> and to add an extra element always for draining, which the driver could
> ignore. It basically pushed the use paradigm onto the driver.
>
> If we want the use paradigm shared between block and driver, then I
> think the best approach is to keep all the bios the same (so not adjust
> for padding), but do adjust in the blk_rq_map_sg(). That way we have
> the padding and draining unwind information by comparing with the bio.
Adjusting only sg in blk_rq_map_sg (like drain) looks much
better. This works with libata for me.
diff --git a/block/blk-map.c b/block/blk-map.c
index c07d9c8..e949969 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -140,26 +140,6 @@ int blk_rq_map_user(struct request_queue *q, struct request *rq,
ubuf += ret;
}
- /*
- * __blk_rq_map_user() copies the buffers if starting address
- * or length isn't aligned to dma_pad_mask. As the copied
- * buffer is always page aligned, we know that there's enough
- * room for padding. Extend the last bio and update
- * rq->data_len accordingly.
- *
- * On unmap, bio_uncopy_user() will use unmodified
- * bio_map_data pointed to by bio->bi_private.
- */
- if (len & q->dma_pad_mask) {
- unsigned int pad_len = (q->dma_pad_mask & ~len) + 1;
- struct bio *tail = rq->biotail;
-
- tail->bi_io_vec[tail->bi_vcnt - 1].bv_len += pad_len;
- tail->bi_size += pad_len;
-
- rq->extra_len += pad_len;
- }
-
rq->buffer = rq->data = NULL;
return 0;
unmap_rq:
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 0f58616..2a81c87 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -220,6 +220,13 @@ new_segment:
bvprv = bvec;
} /* segments in rq */
+ if (sg && (q->dma_pad_mask & rq->data_len)) {
+ unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1;
+
+ sg->length += pad_len;
+ rq->extra_len += pad_len;
+ }
+
if (q->dma_drain_size && q->dma_drain_needed(rq)) {
if (rq->cmd_flags & REQ_RW)
memset(q->dma_drain_buffer, 0, q->dma_drain_size);
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index e5c6f6a..fecba05 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -757,7 +757,7 @@ void scsi_finish_command(struct scsi_cmnd *cmd)
"Notifying upper driver of completion "
"(result %x)\n", cmd->result));
- good_bytes = scsi_bufflen(cmd) + cmd->request->extra_len;
+ good_bytes = scsi_bufflen(cmd);
if (cmd->request->cmd_type != REQ_TYPE_BLOCK_PC) {
drv = scsi_cmd_to_driver(cmd);
if (drv->done)
--
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