Re: [RFC] FC pass thru - Rev IV

FUJITA Tomonori
2008-11-28T02:23:02Z

On Thu, 27 Nov 2008 20:01:41 -0600
James Bottomley <James.Bottomley@HansenPartnership.com> wrote:

> On Thu, 2008-11-27 at 18:53 +0900, FUJITA Tomonori wrote:
> > > + blk_end_bidi_request(job->req, err, blk_rq_bytes(job->req), bytes_requested);
> > >
> > > The residual count is left in req->data_len. Does bsg have a way to return the
> > > residual to user-mode? It must, since Pete was using that for sure. Note that
> > > you are looking for the bidi_read residual count.
> >
> > Yeah, bsg has. struct sg_io_v4 has:
> >
> > __s32 din_resid; /* [o] din_xfer_len - actual_din_xfer_len */
> > __s32 dout_resid; /* [o] dout_xfer_len - actual_dout_xfer_len */
> >
> >
> > > As was said by people. You must complete ALL bytes on both sides. Residual information
> > > is passed through req->data_len. Other wise the request is still active.
> > >
> > > (And yes blk_end_request uses blk_end_bidi_request internally)
> >
> > We always complete all bytes on both sides. So why we do something
> > like:
> >
> > int blk_end_request(struct request *rq, int error, unsigned int nr_bytes)
> > {
> > unsigned int bidi_bytes = 0;
> >
> > if (blk_bidi_rq(rq))
> > bidi_bytes = req->next_rq->data_len;
> >
> > return blk_end_io(rq, error, nr_bytes, bidi_bytes, NULL);
> > }
>
> That looks good ... care to patch it up (including conversion of all the
> users) and send it to Jens for consideration?

Sure, I'll do.

> > The callers can do something like:
> >
> > blk_end_request(rq, err, rq->data_len);
> > rq-->next_rq->data_len = resid;
>
> Um ... I see what you're trying to do, but I don't think it works like
> this. The residual could be collected in the end_io call back which is
> inline in the blk_end_request().

Yeah, you are right. bsg doesn't though. But after calling
blk_end_request, bsg can touch (or free) rq any time. So the callers
can't touch rq in the above way after calling blk_end_request (it's
racy).

As Boaz said, we must (and can) set resid before blk_end_request.