[Xen-devel] [PATCH v3 11/13] xen/pvcalls: implement poll command

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

For active sockets, check the indexes and use the inflight_conn_req
waitqueue to wait.

For passive sockets if an accept is outstanding
(PVCALLS_FLAG_ACCEPT_INFLIGHT), check if it has been answered by looking
at bedata->rsp[req_id]. If so, return POLLIN.  Otherwise use the
inflight_accept_req waitqueue.

If no accepts are inflight, send PVCALLS_POLL to the backend. If we have
outstanding POLL requests awaiting for a response 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 sock_mapping from the
poll id (we previously converted struct sock_mapping* 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 | 135 +++++++++++++++++++++++++++++++++++++++++---
 drivers/xen/pvcalls-front.h |   3 +
 2 files changed, 129 insertions(+), 9 deletions(-)

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 635a83a..1c975d6 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -72,6 +72,8 @@ struct sock_mapping {
                 * Only one poll operation can be inflight for a given socket.
                 */
 #define PVCALLS_FLAG_ACCEPT_INFLIGHT 0
+#define PVCALLS_FLAG_POLL_INFLIGHT   1
+#define PVCALLS_FLAG_POLL_RET        2
                        uint8_t flags;
                        uint32_t inflight_req_id;
                        struct sock_mapping *accept_map;
@@ -139,15 +141,32 @@ 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;
-               dst = (uint8_t *)&bedata->rsp[req_id] + sizeof(rsp->req_id);
-               src = (uint8_t *)rsp + 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 sock_mapping *map = (struct sock_mapping *)
+                                                  rsp->u.poll.id;
+
+                       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();
+                       clear_bit(PVCALLS_FLAG_POLL_INFLIGHT,
+                                 (void *)&map->passive.flags);
+               } else {
+                       dst = (uint8_t *)&bedata->rsp[req_id] +
+                             sizeof(rsp->req_id);
+                       src = (uint8_t *)rsp + 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++;
@@ -736,6 +755,104 @@ 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, ret;
+       struct xen_pvcalls_request *req;
+
+       if (test_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
+                    (void *)&map->passive.flags)) {
+               uint32_t req_id = READ_ONCE(map->passive.inflight_req_id);
+               if (req_id != PVCALLS_INVALID_ID &&
+                   READ_ONCE(bedata->rsp[req_id].req_id) == req_id)
+                       return POLLIN;
+
+               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);
+       ret = get_request(bedata, &req_id);
+       if (ret < 0) {
+               spin_unlock(&bedata->pvcallss_lock);
+               return ret;
+       }
+       req = RING_GET_REQUEST(&bedata->ring, req_id);
+       req->req_id = req_id;
+       req->cmd = PVCALLS_POLL;
+       req->u.poll.id = (uint64_t) map;
+
+       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);
+}
+
 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
-- 
1.9.1


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