From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cornelia Huck <cornelia.huck@de.ibm.com>
Subject: Re: [Qemu-devel] [PATCH v6 10/13] s390x/css: introduce and realize
 ccw-request callback
Date: Wed, 3 May 2017 13:14:32 +0200
Message-ID: <20170503131432.1a2ecf40.cornelia.huck@de.ibm.com>
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        <20170502180407.33a8f468.cornelia.huck@de.ibm.com>
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To: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Cc: linux-s390@vger.kernel.org, kvm@vger.kernel.org, borntraeger@de.ibm.com, qemu-devel@nongnu.org, Auger Eric <eric.auger@redhat.com>, alex.williamson@redhat.com, Xiao Feng Ren <renxiaof@linux.vnet.ibm.com>, agraf@suse.com
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On Wed, 3 May 2017 10:18:50 +0800
Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com> wrote:

> * Cornelia Huck <cornelia.huck@de.ibm.com> [2017-05-02 18:04:07 +0200]:
> 
> > On Tue, 2 May 2017 10:15:19 +0800
> > Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com> wrote:
> > 
> > > * Auger Eric <eric.auger@redhat.com> [2017-05-01 19:28:23 +0200]:
> > 
> > > > >  static void vfio_ccw_io_notifier_handler(void *opaque)
> > > > >  {
> > > > >      VFIOCCWDevice *vcdev = opaque;
> > > > > +    struct ccw_io_region *region = vcdev->io_region;
> > > > > +    S390CCWDevice *cdev = S390_CCW_DEVICE(vcdev);
> > > > > +    CcwDevice *ccw_dev = CCW_DEVICE(cdev);
> > > > > +    SubchDev *sch = ccw_dev->sch;
> > > > > +    SCSW *s = &sch->curr_status.scsw;
> > > > > +    IRB irb;
> > > > >  
> > > > >      if (!event_notifier_test_and_clear(&vcdev->io_notifier)) {
> > > > >          return;
> > > > >      }
> > > > > +
> > > > > +    if (pread(vcdev->vdev.fd, region,
> > > > > +              vcdev->io_region_size, vcdev->io_region_offset) == -1) {
> > > > is it possible to read less bytes than requested?
> > > Currently, impossible. The kernel side returns either the full region,
> > > or an error.
> > > But we surely could make it more friendly for a partial return. I will
> > > add a check for that case, and generate a channel program check for it.
> > 
> > I think a channel-control check would be more appropriate here.
> 
> Hi Conny,
> 
> After reading PoP 14-43, I think you are right.

(...)

> So I decide to add this piece of code:
> if (size != vcdev->io_region_size) {
>     /* Information transfer error, generate channel-control check. */
>     s->ctrl &= ~SCSW_ACTL_START_PEND;
>     s->cstat = SCSW_CSTAT_CHN_CTRL_CHK;
>     s->ctrl &= ~SCSW_CTRL_MASK_STCTL;
>     s->ctrl |= SCSW_STCTL_PRIMARY | SCSW_STCTL_SECONDARY |
>                SCSW_STCTL_ALERT | SCSW_STCTL_STATUS_PEND;
>     goto read_err;
> }

Looks good.