linux-kernel - Re: [PATCH v2 07/13] xen/pvcalls: implement accept command

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Date:   Wed, 26 Jul 2017 16:24:04 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org,
        jgross@...e.com, Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v2 07/13] xen/pvcalls: implement accept command

On Wed, 26 Jul 2017, Boris Ostrovsky wrote:
> On 07/25/2017 05:22 PM, Stefano Stabellini wrote:
> > Send PVCALLS_ACCEPT to the backend. Allocate a new active socket. Make
> > sure that only one accept command is executed at any given time by
> > setting PVCALLS_FLAG_ACCEPT_INFLIGHT and waiting on the
> > inflight_accept_req waitqueue.
> >
> > sock->sk->sk_send_head is not used for ip sockets: reuse the field to
> > store a pointer to the struct sock_mapping corresponding to the socket.
> >
> > Convert the new struct socket pointer into an uint64_t and use it as id
> > for the new socket to pass to the backend.
> >
> > Signed-off-by: Stefano Stabellini <stefano@...reto.com>
> > CC: boris.ostrovsky@...cle.com
> > CC: jgross@...e.com
> > ---
> >  drivers/xen/pvcalls-front.c | 79 +++++++++++++++++++++++++++++++++++++++++++++
> >  drivers/xen/pvcalls-front.h |  3 ++
> >  2 files changed, 82 insertions(+)
> >
> > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> > index 3b5d50e..b8c4538 100644
> > --- a/drivers/xen/pvcalls-front.c
> > +++ b/drivers/xen/pvcalls-front.c
> > @@ -413,6 +413,85 @@ int pvcalls_front_listen(struct socket *sock, int backlog)
> >  	return ret;
> >  }
> >  
> > +int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
> > +{
> > +	struct pvcalls_bedata *bedata;
> > +	struct sock_mapping *map;
> > +	struct sock_mapping *map2 = NULL;
> > +	struct xen_pvcalls_request *req;
> > +	int notify, req_id, ret, evtchn;
> > +
> > +	if (!pvcalls_front_dev)
> > +		return -ENOTCONN;
> > +	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> > +
> > +	map = (struct sock_mapping *) READ_ONCE(sock->sk->sk_send_head);
> > +	if (!map)
> > +		return -ENOTSOCK;
> > +
> > +	if (map->passive.status != PVCALLS_STATUS_LISTEN)
> > +		return -EINVAL;
> > +
> > +	/*
> > +	 * Backend only supports 1 inflight accept request, will return
> > +	 * errors for the others
> > +	 */
> > +	if (test_and_set_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> > +			     (void *)&map->passive.flags)) {
> > +		if (wait_event_interruptible(map->passive.inflight_accept_req,
> > +			!test_and_set_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> > +					  (void *)&map->passive.flags))
> > +			!= 0)
> 
> Unnecessary "!=0".

OK


> > +			return -EINTR;
> > +	}
> > +
> > +
> > +	newsock->sk = kzalloc(sizeof(*newsock->sk), GFP_KERNEL);
> > +	if (newsock->sk == NULL)
> > +		return -ENOMEM;
> > +
> > +	spin_lock(&bedata->pvcallss_lock);
> > +	req_id = bedata->ring.req_prod_pvt & (RING_SIZE(&bedata->ring) - 1);
> > +	if (RING_FULL(&bedata->ring) ||
> > +	    READ_ONCE(bedata->rsp[req_id].req_id) != PVCALLS_INVALID_ID) {
> > +		kfree(newsock->sk);
> > +		spin_unlock(&bedata->pvcallss_lock);
> > +		return -EAGAIN;
> > +	}
> > +
> > +	map2 = create_active(&evtchn);
> > +
> > +	req = RING_GET_REQUEST(&bedata->ring, req_id);
> > +	req->req_id = req_id;
> > +	req->cmd = PVCALLS_ACCEPT;
> > +	req->u.accept.id = (uint64_t) sock;
> > +	req->u.accept.ref = map2->active.ref;
> > +	req->u.accept.id_new = (uint64_t) newsock;
> > +	req->u.accept.evtchn = evtchn;
> > +
> > +	list_add_tail(&map2->list, &bedata->socket_mappings);
> > +	WRITE_ONCE(newsock->sk->sk_send_head, (void *)map2);
> > +	map2->sock = newsock;
> > +
> > +	bedata->ring.req_prod_pvt++;
> > +	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&bedata->ring, notify);
> > +	spin_unlock(&bedata->pvcallss_lock);
> > +	if (notify)
> > +		notify_remote_via_irq(bedata->irq);
> > +
> > +	wait_event(bedata->inflight_req,
> > +		   READ_ONCE(bedata->rsp[req_id].req_id) == req_id);
> > +
> > +	clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT, (void *)&map->passive.flags);
> > +	wake_up(&map->passive.inflight_accept_req);
> > +
> > +	ret = bedata->rsp[req_id].ret;
> > +	/* read ret, then set this rsp slot to be reused */
> > +	smp_mb();
> > +	WRITE_ONCE(bedata->rsp[req_id].req_id, PVCALLS_INVALID_ID);
> > +	return ret;
> > +}
> > +
> >  static const struct xenbus_device_id pvcalls_front_ids[] = {
> >  	{ "pvcalls" },
> >  	{ "" }
> > diff --git a/drivers/xen/pvcalls-front.h b/drivers/xen/pvcalls-front.h
> > index aa8fe10..ab4f1da 100644
> > --- a/drivers/xen/pvcalls-front.h
> > +++ b/drivers/xen/pvcalls-front.h
> > @@ -10,5 +10,8 @@ int pvcalls_front_bind(struct socket *sock,
> >  		       struct sockaddr *addr,
> >  		       int addr_len);
> >  int pvcalls_front_listen(struct socket *sock, int backlog);
> > +int pvcalls_front_accept(struct socket *sock,
> > +			 struct socket *newsock,
> > +			 int flags);
> >  
> >  #endif
>