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

[Boris Ostrovsky]

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

> +		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.

> +		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.

-boris


> +	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 = {