[Xen-devel] [PATCH net-next v3] xen-netback: implement dynamic multicast control

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

My recent patch to the Xen Project documents a protocol for 'dynamic
multicast control' in netif.h. This extends the previous multicast control
protocol to not require a shared ring reconnection to turn the feature off.
Instead the backend watches the "request-multicast-control" key in xenstore
and turns the feature off if the key value is written to zero.

This patch adds support for dynamic multicast control in xen-netback.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
---

v3:
 - Log (rate limited) error when watch is already registered

v2:
 - Log error on failure to allocate memory for multicast watch
---
 drivers/net/xen-netback/common.h |  1 +
 drivers/net/xen-netback/xenbus.c | 89 ++++++++++++++++++++++++++++++++++++----
 2 files changed, 82 insertions(+), 8 deletions(-)

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 0333ab0..1128252 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -251,6 +251,7 @@ struct xenvif {
        unsigned int stalled_queues;
 
        struct xenbus_watch credit_watch;
+       struct xenbus_watch mcast_ctrl_watch;
 
        spinlock_t lock;
 
diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index 56ebd82..39a303d 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -327,7 +327,7 @@ static int netback_probe(struct xenbus_device *dev,
                        goto abort_transaction;
                }
 
-               /* We support multicast-control. */
+               /* We support dynamic multicast-control. */
                err = xenbus_printf(xbt, dev->nodename,
                                    "feature-multicast-control", "%d", 1);
                if (err) {
@@ -335,6 +335,14 @@ static int netback_probe(struct xenbus_device *dev,
                        goto abort_transaction;
                }
 
+               err = xenbus_printf(xbt, dev->nodename,
+                                   "feature-dynamic-multicast-control",
+                                   "%d", 1);
+               if (err) {
+                       message = "writing feature-dynamic-multicast-control";
+                       goto abort_transaction;
+               }
+
                err = xenbus_transaction_end(xbt, 0);
        } while (err == -EAGAIN);
 
@@ -683,7 +691,8 @@ static void xen_net_rate_changed(struct xenbus_watch *watch,
        }
 }
 
-static int xen_register_watchers(struct xenbus_device *dev, struct xenvif *vif)
+static int xen_register_credit_watch(struct xenbus_device *dev,
+                                    struct xenvif *vif)
 {
        int err = 0;
        char *node;
@@ -708,7 +717,7 @@ static int xen_register_watchers(struct xenbus_device *dev, 
struct xenvif *vif)
        return err;
 }
 
-static void xen_unregister_watchers(struct xenvif *vif)
+static void xen_unregister_credit_watch(struct xenvif *vif)
 {
        if (vif->credit_watch.node) {
                unregister_xenbus_watch(&vif->credit_watch);
@@ -717,6 +726,75 @@ static void xen_unregister_watchers(struct xenvif *vif)
        }
 }
 
+static void xen_mcast_ctrl_changed(struct xenbus_watch *watch,
+                                  const char **vec, unsigned int len)
+{
+       struct xenvif *vif = container_of(watch, struct xenvif,
+                                         mcast_ctrl_watch);
+       struct xenbus_device *dev = xenvif_to_xenbus_device(vif);
+       int val;
+
+       if (xenbus_scanf(XBT_NIL, dev->otherend,
+                        "request-multicast-control", "%d", &val) < 0)
+               val = 0;
+       vif->multicast_control = !!val;
+}
+
+static int xen_register_mcast_ctrl_watch(struct xenbus_device *dev,
+                                        struct xenvif *vif)
+{
+       int err = 0;
+       char *node;
+       unsigned maxlen = strlen(dev->otherend) +
+               sizeof("/request-multicast-control");
+
+       if (vif->mcast_ctrl_watch.node) {
+               pr_err_ratelimited("Watch is already registered\n");
+               return -EADDRINUSE;
+       }
+
+       node = kmalloc(maxlen, GFP_KERNEL);
+       if (!node) {
+               pr_err("Failed to allocate memory for watch\n");
+               return -ENOMEM;
+       }
+       snprintf(node, maxlen, "%s/request-multicast-control",
+                dev->otherend);
+       vif->mcast_ctrl_watch.node = node;
+       vif->mcast_ctrl_watch.callback = xen_mcast_ctrl_changed;
+       err = register_xenbus_watch(&vif->mcast_ctrl_watch);
+       if (err) {
+               pr_err("Failed to set watcher %s\n",
+                      vif->mcast_ctrl_watch.node);
+               kfree(node);
+               vif->mcast_ctrl_watch.node = NULL;
+               vif->mcast_ctrl_watch.callback = NULL;
+       }
+       return err;
+}
+
+static void xen_unregister_mcast_ctrl_watch(struct xenvif *vif)
+{
+       if (vif->mcast_ctrl_watch.node) {
+               unregister_xenbus_watch(&vif->mcast_ctrl_watch);
+               kfree(vif->mcast_ctrl_watch.node);
+               vif->mcast_ctrl_watch.node = NULL;
+       }
+}
+
+static void xen_register_watchers(struct xenbus_device *dev,
+                                 struct xenvif *vif)
+{
+       xen_register_credit_watch(dev, vif);
+       xen_register_mcast_ctrl_watch(dev, vif);
+}
+
+static void xen_unregister_watchers(struct xenvif *vif)
+{
+       xen_unregister_mcast_ctrl_watch(vif);
+       xen_unregister_credit_watch(vif);
+}
+
 static void unregister_hotplug_status_watch(struct backend_info *be)
 {
        if (be->have_hotplug_status_watch) {
@@ -1030,11 +1108,6 @@ static int read_xenbus_vif_flags(struct backend_info *be)
                val = 0;
        vif->ipv6_csum = !!val;
 
-       if (xenbus_scanf(XBT_NIL, dev->otherend, "request-multicast-control",
-                        "%d", &val) < 0)
-               val = 0;
-       vif->multicast_control = !!val;
-
        return 0;
 }
 
-- 
2.1.4


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