[PATCH v7 5/7] xen/9pfs: send requests to the backend

[Stefano Stabellini]

Implement struct p9_trans_module create and close functions by looking
at the available Xen 9pfs frontend-backend connections. We don't expect
many frontend-backend connections, thus walking a list is OK.

Send requests to the backend by copying each request to one of the
available rings (each frontend-backend connection comes with multiple
rings). Handle the ring and notifications following the 9pfs
specification. If there are not enough free bytes on the ring for the
request, wait on the wait_queue: the backend will send a notification
after consuming more requests.

Signed-off-by: Stefano Stabellini <stefano@xxxxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
CC: groug@xxxxxxxx
CC: jgross@xxxxxxxx
CC: Eric Van Hensbergen <ericvh@xxxxxxxxx>
CC: Ron Minnich <rminnich@xxxxxxxxxx>
CC: Latchesar Ionkov <lucho@xxxxxxxxxx>
CC: v9fs-developer@xxxxxxxxxxxxxxxxxxxxx
---
 net/9p/trans_xen.c | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 85 insertions(+), 2 deletions(-)

diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c
index fe3d172..28f30f4 100644
--- a/net/9p/trans_xen.c
+++ b/net/9p/trans_xen.c
@@ -85,22 +85,105 @@ struct xen_9pfs_front_priv {
 static LIST_HEAD(xen_9pfs_devs);
 static DEFINE_RWLOCK(xen_9pfs_lock);
 
+/* We don't currently allow canceling of requests */
 static int p9_xen_cancel(struct p9_client *client, struct p9_req_t *req)
 {
-	return 0;
+	return 1;
 }
 
 static int p9_xen_create(struct p9_client *client, const char *addr, char *args)
 {
-	return 0;
+	struct xen_9pfs_front_priv *priv;
+
+	read_lock(&xen_9pfs_lock);
+	list_for_each_entry(priv, &xen_9pfs_devs, list) {
+		if (!strcmp(priv->tag, addr)) {
+			priv->client = client;
+			read_unlock(&xen_9pfs_lock);
+			return 0;
+		}
+	}
+	read_unlock(&xen_9pfs_lock);
+	return -EINVAL;
 }
 
 static void p9_xen_close(struct p9_client *client)
 {
+	struct xen_9pfs_front_priv *priv;
+
+	read_lock(&xen_9pfs_lock);
+	list_for_each_entry(priv, &xen_9pfs_devs, list) {
+		if (priv->client == client) {
+			priv->client = NULL;
+			read_unlock(&xen_9pfs_lock);
+			return;
+		}
+	}
+	read_unlock(&xen_9pfs_lock);
+}
+
+static bool p9_xen_write_todo(struct xen_9pfs_dataring *ring, RING_IDX size)
+{
+	RING_IDX cons, prod;
+
+	cons = ring->intf->out_cons;
+	prod = ring->intf->out_prod;
+	virt_mb();
+
+	return XEN_9PFS_RING_SIZE -
+		xen_9pfs_queued(prod, cons, XEN_9PFS_RING_SIZE) >= size;
 }
 
 static int p9_xen_request(struct p9_client *client, struct p9_req_t *p9_req)
 {
+	struct xen_9pfs_front_priv *priv = NULL;
+	RING_IDX cons, prod, masked_cons, masked_prod;
+	unsigned long flags;
+	u32 size = p9_req->tc->size;
+	struct xen_9pfs_dataring *ring;
+	int num;
+
+	read_lock(&xen_9pfs_lock);
+	list_for_each_entry(priv, &xen_9pfs_devs, list) {
+		if (priv->client == client)
+			break;
+	}
+	read_unlock(&xen_9pfs_lock);
+	if (!priv || priv->client != client)
+		return -EINVAL;
+
+	num = p9_req->tc->tag % priv->num_rings;
+	ring = &priv->rings[num];
+
+again:
+	while (wait_event_interruptible(ring->wq,
+					p9_xen_write_todo(ring, size)) != 0)
+		;
+
+	spin_lock_irqsave(&ring->lock, flags);
+	cons = ring->intf->out_cons;
+	prod = ring->intf->out_prod;
+	virt_mb();
+
+	if (XEN_9PFS_RING_SIZE - xen_9pfs_queued(prod, cons,
+						 XEN_9PFS_RING_SIZE) < size) {
+		spin_unlock_irqrestore(&ring->lock, flags);
+		goto again;
+	}
+
+	masked_prod = xen_9pfs_mask(prod, XEN_9PFS_RING_SIZE);
+	masked_cons = xen_9pfs_mask(cons, XEN_9PFS_RING_SIZE);
+
+	xen_9pfs_write_packet(ring->data.out, p9_req->tc->sdata, size,
+			      &masked_prod, masked_cons, XEN_9PFS_RING_SIZE);
+
+	p9_req->status = REQ_STATUS_SENT;
+	virt_wmb();			/* write ring before updating pointer */
+	prod += size;
+	ring->intf->out_prod = prod;
+	spin_unlock_irqrestore(&ring->lock, flags);
+	notify_remote_via_irq(ring->irq);
+
 	return 0;
 }
 
-- 
1.9.1