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

[Stefano Stabellini]

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)
+			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
-- 
1.9.1