linux-kernel - Re: [PATCH v3 12/18] xen/pvcalls: implement poll command

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Date:   Tue, 13 Jun 2017 17:47:31 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Juergen Gross <jgross@...e.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org,
        boris.ostrovsky@...cle.com,
        Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v3 12/18] xen/pvcalls: implement poll command

On Tue, 13 Jun 2017, Juergen Gross wrote:
> On 02/06/17 21:31, Stefano Stabellini wrote:
> > Implement poll on passive sockets by requesting a delayed response with
> > mappass->reqcopy, and reply back when there is data on the passive
> > socket.
> > 
> > Poll on active socket is unimplemented as by the spec, as the frontend
> > should just wait for events and check the indexes on the indexes page.
> > 
> > Only support one outstanding poll (or accept) request for every passive
> > socket at any given time.
> > 
> > Signed-off-by: Stefano Stabellini <stefano@...reto.com>
> > CC: boris.ostrovsky@...cle.com
> > CC: jgross@...e.com
> > ---
> >  drivers/xen/pvcalls-back.c | 75 ++++++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 73 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> > index f1173f4..82f350d 100644
> > --- a/drivers/xen/pvcalls-back.c
> > +++ b/drivers/xen/pvcalls-back.c
> > @@ -344,11 +344,33 @@ static void __pvcalls_back_accept(struct work_struct *work)
> >  static void pvcalls_pass_sk_data_ready(struct sock *sock)
> >  {
> >  	struct sockpass_mapping *mappass = sock->sk_user_data;
> > +	struct pvcalls_fedata *priv;
> > +	struct xen_pvcalls_response *rsp;
> > +	unsigned long flags;
> > +	int notify;
> >  
> >  	if (mappass == NULL)
> >  		return;
> >  
> > -	queue_work(mappass->wq, &mappass->register_work);
> > +	priv = mappass->priv;
> > +	spin_lock_irqsave(&mappass->copy_lock, flags);
> > +	if (mappass->reqcopy.cmd == PVCALLS_POLL) {
> > +		rsp = RING_GET_RESPONSE(&priv->ring, priv->ring.rsp_prod_pvt++);
> > +		rsp->req_id = mappass->reqcopy.req_id;
> > +		rsp->u.poll.id = mappass->reqcopy.u.poll.id;
> > +		rsp->cmd = mappass->reqcopy.cmd;
> > +		rsp->ret = 0;
> > +
> > +		mappass->reqcopy.cmd = 0;
> > +		spin_unlock_irqrestore(&mappass->copy_lock, flags);
> > +
> > +		RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&priv->ring, notify);
> > +		if (notify)
> > +			notify_remote_via_irq(mappass->priv->irq);
> > +	} else {
> > +		spin_unlock_irqrestore(&mappass->copy_lock, flags);
> > +		queue_work(mappass->wq, &mappass->register_work);
> > +	}
> >  }
> >  
> >  static int pvcalls_back_bind(struct xenbus_device *dev,
> > @@ -493,7 +515,56 @@ static int pvcalls_back_accept(struct xenbus_device *dev,
> >  static int pvcalls_back_poll(struct xenbus_device *dev,
> >  			     struct xen_pvcalls_request *req)
> >  {
> > -	return 0;
> > +	struct pvcalls_fedata *priv;
> > +	struct sockpass_mapping *mappass;
> > +	struct xen_pvcalls_response *rsp;
> > +	struct inet_connection_sock *icsk;
> > +	struct request_sock_queue *queue;
> > +	unsigned long flags;
> > +	int ret;
> > +	bool data;
> > +
> > +	priv = dev_get_drvdata(&dev->dev);
> > +
> > +	mappass = radix_tree_lookup(&priv->socketpass_mappings, req->u.poll.id);
> > +	if (mappass == NULL)
> > +		return -EINVAL;
> > +
> > +	/*
> > +	 * Limitation of the current implementation: only support one
> > +	 * concurrent accept or poll call on one socket.
> > +	 */
> > +	spin_lock_irqsave(&mappass->copy_lock, flags);
> > +	if (mappass->reqcopy.cmd != 0) {
> > +		ret = -EINTR;
> > +		goto out;
> > +	}
> > +
> > +	mappass->reqcopy = *req;
> > +	icsk = inet_csk(mappass->sock->sk);
> > +	queue = &icsk->icsk_accept_queue;
> > +	spin_lock(&queue->rskq_lock);
> > +	data = queue->rskq_accept_head != NULL;
> > +	spin_unlock(&queue->rskq_lock);
> > +	if (data) {
> > +		mappass->reqcopy.cmd = 0;
> > +		ret = 0;
> > +		goto out;
> > +	}
> > +	spin_unlock_irqrestore(&mappass->copy_lock, flags);

I'll also need to change these mappass->reqcopy.cmd accesses to
ACCESS_ONCE to be consistent with the changes to the previous patch
(need to become atomic)


> > +	/* Tell the caller we don't need to send back a notification yet */
> > +	return -1;
> > +
> > +out:
> > +	spin_unlock_irqrestore(&mappass->copy_lock, flags);
> > +
> > +	rsp = RING_GET_RESPONSE(&priv->ring, priv->ring.rsp_prod_pvt++);
> > +	rsp->req_id = req->req_id;
> > +	rsp->cmd = req->cmd;
> > +	rsp->u.poll.id = req->u.poll.id;
> > +	rsp->ret = ret;
> > +	return ret;
> 
> return 0;

Yes