Re: [Xen-devel] [PATCH v4 12/18] xen/pvcalls: implement poll command

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

> @@ -499,6 +521,55 @@ static int pvcalls_back_accept(struct xenbus_device *dev,
>  static int pvcalls_back_poll(struct xenbus_device *dev,
>                            struct xen_pvcalls_request *req)
>  {
> +     struct pvcalls_fedata *fedata;
> +     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;
> +
> +     fedata = dev_get_drvdata(&dev->dev);
> +
> +     mappass = radix_tree_lookup(&fedata->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);

What is the purpose of the queue lock here?

-boris

> +     if (data) {
> +             mappass->reqcopy.cmd = 0;
> +             ret = 0;
> +             goto out;
> +     }
> +     spin_unlock_irqrestore(&mappass->copy_lock, flags);
> +
> +     /* Tell the caller we don't need to send back a notification yet */
> +     return -1;
>


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