Date:   Wed, 26 Jul 2017 09:35:29 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org
Cc:     linux-kernel@...r.kernel.org, jgross@...e.com,
        Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v2 02/13] xen/pvcalls: connect to the backend



On 7/25/2017 5:21 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.
>
> Introduce a data structure named pvcalls_bedata. It contains pointers to
> the command ring, the event channel, a list of active sockets and a list
> of passive sockets. Lists accesses are protected by a spin_lock.
>
> Introduce a waitqueue to allow waiting for a response on commands sent
> to the backend.
>
> Introduce an array of struct xen_pvcalls_response to store commands
> responses.
>
> 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@...reto.com>
> CC: boris.ostrovsky@...cle.com
> CC: jgross@...e.com
> ---
>   drivers/xen/pvcalls-front.c | 153 ++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 153 insertions(+)
>
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index a8d38c2..5e0b265 100644
> --- a/drivers/xen/pvcalls-front.c
> +++ b/drivers/xen/pvcalls-front.c
> @@ -20,6 +20,29 @@
>   #include <xen/xenbus.h>
>   #include <xen/interface/io/pvcalls.h>
>   
> +#define PVCALLS_INVALID_ID (UINT_MAX)

Unnecessary parentheses

> +#define RING_ORDER XENBUS_MAX_RING_GRANT_ORDER

PVCALLS_RING_ORDER?

> +#define PVCALLS_NR_REQ_PER_RING __CONST_RING_SIZE(xen_pvcalls, XEN_PAGE_SIZE)
> +
> +struct pvcalls_bedata {
> +	struct xen_pvcalls_front_ring ring;
> +	grant_ref_t ref;
> +	int irq;
> +
> +	struct list_head socket_mappings;
> +	struct list_head socketpass_mappings;
> +	spinlock_t pvcallss_lock;
> +
> +	wait_queue_head_t inflight_req;
> +	struct xen_pvcalls_response rsp[PVCALLS_NR_REQ_PER_RING];
> +};
> +struct xenbus_device *pvcalls_front_dev;

static

> +
> +static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
> +{
> +	return IRQ_HANDLED;
> +}
> +
>   static const struct xenbus_device_id pvcalls_front_ids[] = {
>   	{ "pvcalls" },
>   	{ "" }
> @@ -33,12 +56,142 @@ 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 = -EFAULT, evtchn, ref = -1, 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);
> +	ret = xenbus_scanf(XBT_NIL, dev->otherend,
> +			   "max-page-order", "%u", &max_page_order);
> +	if (ret <= 0)
> +		return -ENODEV;
> +	if (max_page_order < RING_ORDER)
> +		return -ENODEV;
> +	ret = xenbus_scanf(XBT_NIL, dev->otherend,
> +			   "function-calls", "%u", &function_calls);
> +	if (ret <= 0 || function_calls != 1)
> +		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;
> +
> +	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) {
> +		ret = bedata->irq;
> +		goto error;
> +	}
> +
> +	ret = gnttab_alloc_grant_references(1, &gref_head);
> +	if (ret < 0)
> +		goto error;
> +	bedata->ref = ref = gnttab_claim_grant_reference(&gref_head);

Is ref really needed?

> +	if (ref < 0)
> +		goto error;
> +	gnttab_grant_foreign_access_ref(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", 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);
> +	dev_set_drvdata(&dev->dev, bedata);
> +	pvcalls_front_dev = dev;
> +	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);

I think patch 12 (where you implement cleanup) could be moved before 
this one.

I also think you are leaking bedata on error paths.

-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 = {

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