Re: [Xen-devel] [PATCH v3 03/13] xen/pvcalls: connect to the backend

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 11 Aug 2017, Boris Ostrovsky wrote:
> On 07/31/2017 06:57 PM, Stefano Stabellini wrote:
> > Implement the probe function for the pvcalls frontend. Read the
> > supported versions, max-page-order and function-calls nodes from
> > xenstore.
> >
> > Only one frontend<->backend connection is supported at any given time
> > for a guest. Store the active frontend device to a static pointer.
> >
> > Introduce a stub functions for the event handler.
> >
> > Signed-off-by: Stefano Stabellini <stefano@xxxxxxxxxxx>
> > CC: boris.ostrovsky@xxxxxxxxxx
> > CC: jgross@xxxxxxxx
> > ---
> >  drivers/xen/pvcalls-front.c | 130 
> > ++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 130 insertions(+)
> >
> > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> > index a126195..2afe36d 100644
> > --- a/drivers/xen/pvcalls-front.c
> > +++ b/drivers/xen/pvcalls-front.c
> > @@ -84,12 +84,142 @@ static int pvcalls_front_remove(struct xenbus_device 
> > *dev)
> >  static int pvcalls_front_probe(struct xenbus_device *dev,
> >                       const struct xenbus_device_id *id)
> >  {
> > +   int ret = -ENOMEM, evtchn, i;
> > +   unsigned int max_page_order, function_calls, len;
> > +   char *versions;
> > +   grant_ref_t gref_head = 0;
> > +   struct xenbus_transaction xbt;
> > +   struct pvcalls_bedata *bedata = NULL;
> > +   struct xen_pvcalls_sring *sring;
> > +
> > +   if (pvcalls_front_dev != NULL) {
> > +           dev_err(&dev->dev, "only one PV Calls connection supported\n");
> > +           return -EINVAL;
> > +   }
> > +
> > +   versions = xenbus_read(XBT_NIL, dev->otherend, "versions", &len);
> > +   if (!len)
> > +           return -EINVAL;
> > +   if (strcmp(versions, "1")) {
> > +           kfree(versions);
> > +           return -EINVAL;
> > +   }
> > +   kfree(versions);
> > +   max_page_order = xenbus_read_unsigned(dev->otherend,
> > +                                         "max-page-order", 0);
> > +   if (max_page_order < PVCALLS_RING_ORDER)
> > +           return -ENODEV;
> > +   function_calls = xenbus_read_unsigned(dev->otherend,
> > +                                         "function-calls", 0);
> > +   if (function_calls != 1)
> 
> XENBUS_FUNCTIONS_CALLS

XENBUS_FUNCTIONS_CALLS is actually defined as "1". I'll add a comment
instead.


> > +           return -ENODEV;
> > +   pr_info("%s max-page-order is %u\n", __func__, max_page_order);
> > +
> > +   bedata = kzalloc(sizeof(struct pvcalls_bedata), GFP_KERNEL);
> > +   if (!bedata)
> > +           return -ENOMEM;
> > +
> > +   dev_set_drvdata(&dev->dev, bedata);
> > +   pvcalls_front_dev = dev;
> > +   init_waitqueue_head(&bedata->inflight_req);
> > +   for (i = 0; i < PVCALLS_NR_REQ_PER_RING; i++)
> > +           bedata->rsp[i].req_id = PVCALLS_INVALID_ID;
> > +
> > +   sring = (struct xen_pvcalls_sring *) __get_free_page(GFP_KERNEL |
> > +                                                        __GFP_ZERO);
> > +   if (!sring)
> > +           goto error;
> > +   SHARED_RING_INIT(sring);
> > +   FRONT_RING_INIT(&bedata->ring, sring, XEN_PAGE_SIZE);
> > +
> > +   ret = xenbus_alloc_evtchn(dev, &evtchn);
> > +   if (ret)
> > +           goto error;
> > +
> > +   bedata->irq = bind_evtchn_to_irqhandler(evtchn,
> > +                                           pvcalls_front_event_handler,
> > +                                           0, "pvcalls-frontend", dev);
> > +   if (bedata->irq < 0) {
> 
> In the previous patch you free up irq if it is strictly >0. Should have
> been >=0.

OK


> > +           ret = bedata->irq;
> > +           goto error;
> > +   }
> > +
> > +   ret = gnttab_alloc_grant_references(1, &gref_head);
> > +   if (ret < 0)
> > +           goto error;
> > +   bedata->ref = gnttab_claim_grant_reference(&gref_head);
> > +   if (bedata->ref < 0) {
> > +           ret = bedata->ref;
> > +           goto error;
> > +   }
> > +   gnttab_grant_foreign_access_ref(bedata->ref, dev->otherend_id,
> > +                                   virt_to_gfn((void *)sring), 0);
> > +
> > + again:
> > +   ret = xenbus_transaction_start(&xbt);
> > +   if (ret) {
> > +           xenbus_dev_fatal(dev, ret, "starting transaction");
> > +           goto error;
> > +   }
> > +   ret = xenbus_printf(xbt, dev->nodename, "version", "%u", 1);
> > +   if (ret)
> > +           goto error_xenbus;
> > +   ret = xenbus_printf(xbt, dev->nodename, "ring-ref", "%d", bedata->ref);
> > +   if (ret)
> > +           goto error_xenbus;
> > +   ret = xenbus_printf(xbt, dev->nodename, "port", "%u",
> > +                       evtchn);
> > +   if (ret)
> > +           goto error_xenbus;
> > +   ret = xenbus_transaction_end(xbt, 0);
> > +   if (ret) {
> > +           if (ret == -EAGAIN)
> > +                   goto again;
> > +           xenbus_dev_fatal(dev, ret, "completing transaction");
> > +           goto error;
> > +   }
> > +
> > +   INIT_LIST_HEAD(&bedata->socket_mappings);
> > +   INIT_LIST_HEAD(&bedata->socketpass_mappings);
> > +   spin_lock_init(&bedata->pvcallss_lock);
> > +   xenbus_switch_state(dev, XenbusStateInitialised);
> > +
> >     return 0;
> > +
> > + error_xenbus:
> > +   xenbus_transaction_end(xbt, 1);
> > +   xenbus_dev_fatal(dev, ret, "writing xenstore");
> > + error:
> > +   pvcalls_front_remove(dev);
> 
> Going back to the previous patch --- it seems to me that on some error
> paths certain structures may not be usable in pvcalls_front_remove().
> For example, socket_mappings list is definitely not initialized.

You are right, I'll fix that.
 
 
> > +   return ret;
> >  }
> >  
> >  static void pvcalls_front_changed(struct xenbus_device *dev,
> >                         enum xenbus_state backend_state)
> >  {
> > +   switch (backend_state) {
> > +   case XenbusStateReconfiguring:
> > +   case XenbusStateReconfigured:
> > +   case XenbusStateInitialising:
> > +   case XenbusStateInitialised:
> > +   case XenbusStateUnknown:
> > +           break;
> > +
> > +   case XenbusStateInitWait:
> > +           break;
> > +
> > +   case XenbusStateConnected:
> > +           xenbus_switch_state(dev, XenbusStateConnected);
> > +           break;
> > +
> > +   case XenbusStateClosed:
> > +           if (dev->state == XenbusStateClosed)
> > +                   break;
> > +           /* Missed the backend's CLOSING state -- fallthrough */
> > +   case XenbusStateClosing:
> > +           xenbus_frontend_closed(dev);
> > +           break;
> > +   }
> >  }
> >  
> >  static struct xenbus_driver pvcalls_front_driver = {
> 

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