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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

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


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