Re: [PATCH v2 10/13] xen/pvcalls: implement poll command

[Boris Ostrovsky]

On 07/25/2017 05:22 PM, Stefano Stabellini wrote:
> For active sockets, check the indexes and use the inflight_conn_req
> waitqueue to wait.
>
> For passive sockets, send PVCALLS_POLL to the backend. Use the
> inflight_accept_req waitqueue if an accept is outstanding. Otherwise use
> the inflight_req waitqueue: inflight_req is awaken when a new response
> is received; on wakeup we check whether the POLL response is arrived by
> looking at the PVCALLS_FLAG_POLL_RET flag. We set the flag from
> pvcalls_front_event_handler, if the response was for a POLL command.
>
> In pvcalls_front_event_handler, get the struct socket pointer from the
> poll id (we previously converted struct socket* to uint64_t and used it
> as id).
>
> Signed-off-by: Stefano Stabellini <stefano@xxxxxxxxxxx>
> CC: boris.ostrovsky@xxxxxxxxxx
> CC: jgross@xxxxxxxx
> ---
>  drivers/xen/pvcalls-front.c | 134 ++++++++++++++++++++++++++++++++++++++++----
>  drivers/xen/pvcalls-front.h |   3 +
>  2 files changed, 126 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index b4ca569..833b717 100644
> --- a/drivers/xen/pvcalls-front.c
> +++ b/drivers/xen/pvcalls-front.c
> @@ -130,17 +130,35 @@ static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
>  		rsp = RING_GET_RESPONSE(&bedata->ring, bedata->ring.rsp_cons);
>  
>  		req_id = rsp->req_id;
> -		src = (uint8_t *)&bedata->rsp[req_id];
> -		src += sizeof(rsp->req_id);
> -		dst = (uint8_t *)rsp;
> -		dst += sizeof(rsp->req_id);
> -		memcpy(dst, src, sizeof(*rsp) - sizeof(rsp->req_id));
> -		/*
> -		 * First copy the rest of the data, then req_id. It is
> -		 * paired with the barrier when accessing bedata->rsp.
> -		 */
> -		smp_wmb();
> -		WRITE_ONCE(bedata->rsp[req_id].req_id, rsp->req_id);
> +		if (rsp->cmd == PVCALLS_POLL) {
> +			struct socket *sock = (struct socket *) rsp->u.poll.id;
> +			struct sock_mapping *map =
> +				(struct sock_mapping *)
> +				READ_ONCE(sock->sk->sk_send_head);
> +
> +			set_bit(PVCALLS_FLAG_POLL_RET,
> +				(void *)&map->passive.flags);
> +			/*
> +			 * Set RET, then clear INFLIGHT. It pairs with
> +			 * the checks at the beginning of
> +			 * pvcalls_front_poll_passive.
> +			 */
> +			smp_wmb();

virt_wmb() (here, below, and I think I saw it somewhere else)

> +			clear_bit(PVCALLS_FLAG_POLL_INFLIGHT,
> +				  (void *)&map->passive.flags);
> +		} else {
> +			src = (uint8_t *)&bedata->rsp[req_id];
> +			src += sizeof(rsp->req_id);
> +			dst = (uint8_t *)rsp;
> +			dst += sizeof(rsp->req_id);
> +			memcpy(dst, src, sizeof(*rsp) - sizeof(rsp->req_id));
> +			/*
> +			 * First copy the rest of the data, then req_id. It is
> +			 * paired with the barrier when accessing bedata->rsp.
> +			 */
> +			smp_wmb();
> +			WRITE_ONCE(bedata->rsp[req_id].req_id, rsp->req_id);
> +		}
>  
>  		done = 1;
>  		bedata->ring.rsp_cons++;
> @@ -707,6 +725,100 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
>  	return ret;
>  }
>  
> +static unsigned int pvcalls_front_poll_passive(struct file *file,
> +					       struct pvcalls_bedata *bedata,
> +					       struct sock_mapping *map,
> +					       poll_table *wait)
> +{
> +	int notify, req_id;
> +	struct xen_pvcalls_request *req;
> +
> +	if (test_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> +		     (void *)&map->passive.flags)) {
> +		poll_wait(file, &map->passive.inflight_accept_req, wait);
> +		return 0;
> +	}
> +
> +	if (test_and_clear_bit(PVCALLS_FLAG_POLL_RET,
> +			       (void *)&map->passive.flags))
> +		return POLLIN;
> +
> +	/*
> +	 * First check RET, then INFLIGHT. No barriers necessary to
> +	 * ensure execution ordering because of the conditional
> +	 * instructions creating control dependencies.
> +	 */
> +
> +	if (test_and_set_bit(PVCALLS_FLAG_POLL_INFLIGHT,
> +			     (void *)&map->passive.flags)) {
> +		poll_wait(file, &bedata->inflight_req, wait);
> +		return 0;
> +	}
> +
> +	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) {
> +		spin_unlock(&bedata->pvcallss_lock);
> +		return -EAGAIN;
> +	}
> +	req = RING_GET_REQUEST(&bedata->ring, req_id);
> +	req->req_id = req_id;
> +	req->cmd = PVCALLS_POLL;
> +	req->u.poll.id = (uint64_t) map->sock;
> +
> +	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);
> +
> +	poll_wait(file, &bedata->inflight_req, wait);
> +	return 0;
> +}
> +
> +static unsigned int pvcalls_front_poll_active(struct file *file,
> +					      struct pvcalls_bedata *bedata,
> +					      struct sock_mapping *map,
> +					      poll_table *wait)
> +{
> +	unsigned int mask = 0;
> +	int32_t in_error, out_error;
> +	struct pvcalls_data_intf *intf = map->active.ring;
> +
> +	out_error = intf->out_error;
> +	in_error = intf->in_error;
> +
> +	poll_wait(file, &map->active.inflight_conn_req, wait);
> +	if (pvcalls_front_write_todo(map))
> +		mask |= POLLOUT | POLLWRNORM;
> +	if (pvcalls_front_read_todo(map))
> +		mask |= POLLIN | POLLRDNORM;
> +	if (in_error != 0 || out_error != 0)
> +		mask |= POLLERR;
> +
> +	return mask;
> +}
> +
> +unsigned int pvcalls_front_poll(struct file *file, struct socket *sock,
> +			       poll_table *wait)
> +{
> +	struct pvcalls_bedata *bedata;
> +	struct sock_mapping *map;
> +
> +	if (!pvcalls_front_dev)
> +		return POLLNVAL;
> +	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> +
> +	map = (struct sock_mapping *) READ_ONCE(sock->sk->sk_send_head);
> +	if (!map)
> +		return POLLNVAL;
> +	if (map->active_socket)
> +		return pvcalls_front_poll_active(file, bedata, map, wait);
> +	else
> +		return pvcalls_front_poll_passive(file, bedata, map, wait);
> +}

All other routines return an int (0 or error code).  Shouldn't they all
have the same return type? (In fact, where are all these routines called
from?)

-boris

> +
>  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 de24041..25e05b8 100644
> --- a/drivers/xen/pvcalls-front.h
> +++ b/drivers/xen/pvcalls-front.h
> @@ -20,5 +20,8 @@ int pvcalls_front_recvmsg(struct socket *sock,
>  			  struct msghdr *msg,
>  			  size_t len,
>  			  int flags);
> +unsigned int pvcalls_front_poll(struct file *file,
> +				struct socket *sock,
> +				poll_table *wait);
>  
>  #endif