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

[Boris Ostrovsky]

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@xxxxxxxxxxx>
> CC: boris.ostrovsky@xxxxxxxxxx
> CC: jgross@xxxxxxxx
> ---
>  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".

-boris

> +			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