[PATCH v2 08/13] xen/pvcalls: implement sendmsg

[Stefano Stabellini <sstabellini@kernel.org>]

Send data to an active socket by copying data to the "out" ring. Take
the active socket out_mutex so that only one function can access the
ring at any given time.

If not enough room is available on the ring, rather than returning
immediately or sleep-waiting, spin for up to 5000 cycles. This small
optimization turns out to improve performance significantly.

Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
CC: boris.ostrovsky@oracle.com
CC: jgross@suse.com
---
 drivers/xen/pvcalls-front.c | 109 ++++++++++++++++++++++++++++++++++++++++++++
 drivers/xen/pvcalls-front.h |   3 ++
 2 files changed, 112 insertions(+)

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index b8c4538..d8ed280 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -29,6 +29,7 @@
 #define PVCALLS_INVALID_ID (UINT_MAX)
 #define RING_ORDER XENBUS_MAX_RING_GRANT_ORDER
 #define PVCALLS_NR_REQ_PER_RING __CONST_RING_SIZE(xen_pvcalls, XEN_PAGE_SIZE)
+#define PVCALLS_FRONT_MAX_SPIN 5000
 
 struct pvcalls_bedata {
 	struct xen_pvcalls_front_ring ring;
@@ -79,6 +80,22 @@ struct sock_mapping {
 	};
 };
 
+static int pvcalls_front_write_todo(struct sock_mapping *map)
+{
+	struct pvcalls_data_intf *intf = map->active.ring;
+	RING_IDX cons, prod, size = XEN_FLEX_RING_SIZE(intf->ring_order);
+	int32_t error;
+
+	cons = intf->out_cons;
+	prod = intf->out_prod;
+	error = intf->out_error;
+	if (error == -ENOTCONN)
+		return 0;
+	if (error != 0)
+		return error;
+	return size - pvcalls_queued(prod, cons, size);
+}
+
 static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
 {
 	struct xenbus_device *dev = dev_id;
@@ -309,6 +326,98 @@ int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
 	return ret;
 }
 
+static int __write_ring(struct pvcalls_data_intf *intf,
+			struct pvcalls_data *data,
+			struct iov_iter *msg_iter,
+			size_t len)
+{
+	RING_IDX cons, prod, size, masked_prod, masked_cons;
+	RING_IDX array_size = XEN_FLEX_RING_SIZE(intf->ring_order);
+	int32_t error;
+
+	cons = intf->out_cons;
+	prod = intf->out_prod;
+	error = intf->out_error;
+	/* read indexes before continuing */
+	virt_mb();
+
+	if (error < 0)
+		return error;
+
+	size = pvcalls_queued(prod, cons, array_size);
+	if (size >= array_size)
+		return 0;
+	if (len > array_size - size)
+		len = array_size - size;
+
+	masked_prod = pvcalls_mask(prod, array_size);
+	masked_cons = pvcalls_mask(cons, array_size);
+
+	if (masked_prod < masked_cons) {
+		copy_from_iter(data->out + masked_prod, len, msg_iter);
+	} else {
+		if (len > array_size - masked_prod) {
+			copy_from_iter(data->out + masked_prod,
+				       array_size - masked_prod, msg_iter);
+			copy_from_iter(data->out,
+				       len - (array_size - masked_prod),
+				       msg_iter);
+		} else {
+			copy_from_iter(data->out + masked_prod, len, msg_iter);
+		}
+	}
+	/* write to ring before updating pointer */
+	virt_wmb();
+	intf->out_prod += len;
+
+	return len;
+}
+
+int pvcalls_front_sendmsg(struct socket *sock, struct msghdr *msg,
+			  size_t len)
+{
+	struct pvcalls_bedata *bedata;
+	struct sock_mapping *map;
+	int sent = 0, tot_sent = 0;
+	int count = 0, flags;
+
+	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;
+
+	flags = msg->msg_flags;
+	if (flags & (MSG_CONFIRM|MSG_DONTROUTE|MSG_EOR|MSG_OOB))
+		return -EOPNOTSUPP;
+
+	mutex_lock(&map->active.out_mutex);
+	if ((flags & MSG_DONTWAIT) && !pvcalls_front_write_todo(map)) {
+		mutex_unlock(&map->active.out_mutex);
+		return -EAGAIN;
+	}
+
+again:
+	count++;
+	sent = __write_ring(map->active.ring,
+			    &map->active.data, &msg->msg_iter,
+			    len);
+	if (sent > 0) {
+		len -= sent;
+		tot_sent += sent;
+		notify_remote_via_irq(map->active.irq);
+	}
+	if (sent >= 0 && len > 0 && count < PVCALLS_FRONT_MAX_SPIN)
+		goto again;
+	if (sent < 0)
+		tot_sent = sent;
+
+	mutex_unlock(&map->active.out_mutex);
+	return tot_sent;
+}
+
 int pvcalls_front_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
 {
 	struct pvcalls_bedata *bedata;
diff --git a/drivers/xen/pvcalls-front.h b/drivers/xen/pvcalls-front.h
index ab4f1da..d937c24 100644
--- a/drivers/xen/pvcalls-front.h
+++ b/drivers/xen/pvcalls-front.h
@@ -13,5 +13,8 @@ int pvcalls_front_bind(struct socket *sock,
 int pvcalls_front_accept(struct socket *sock,
 			 struct socket *newsock,
 			 int flags);
+int pvcalls_front_sendmsg(struct socket *sock,
+			  struct msghdr *msg,
+			  size_t len);
 
 #endif
-- 
1.9.1