[PATCH 2/2] xen-netback: add module parameter to disable dynamic multicast control

[ChiaHao Hsu <andyhsu@xxxxxxxxxx>]

In order to support live migration of guests between kernels
that do and do not support 'feature-dynamic-multicast-control',
we add a module parameter that allows the feature to be disabled
at run time, instead of using hardcode value.
The default value is enable.

Signed-off-by: ChiaHao Hsu <andyhsu@xxxxxxxxxx>
---
 drivers/net/xen-netback/common.h  |  1 +
 drivers/net/xen-netback/netback.c |  7 +++++++
 drivers/net/xen-netback/xenbus.c  | 14 ++++++++------
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index bfb7a3054917..c166ebb5a81f 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -415,6 +415,7 @@ static inline pending_ring_idx_t nr_pending_reqs(struct 
xenvif_queue *queue)
 irqreturn_t xenvif_interrupt(int irq, void *dev_id);
 
 extern bool control_ring;
+extern bool dynamic_multicast_control;
 extern bool separate_tx_rx_irq;
 extern bool provides_xdp_headroom;
 
diff --git a/drivers/net/xen-netback/netback.c 
b/drivers/net/xen-netback/netback.c
index 20d858f0456a..4c3d92238ae9 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -54,6 +54,13 @@
 bool control_ring = true;
 module_param(control_ring, bool, 0644);
 
+/* Provide an option to extend multicast control protocol. This allows
+ * request-multicast-control to be set by the frontend at any time,
+ * the backend will watch the value and re-sample on watch events.
+ */
+bool dynamic_multicast_control = true;
+module_param(dynamic_multicast_control, bool, 0644);
+
 /* Provide an option to disable split event channels at load time as
  * event channels are limited resource. Split event channels are
  * enabled by default.
diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index 8a9169cff9c5..36c699f99da4 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -1092,12 +1092,14 @@ 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;
+               if (dynamic_multicast_control) {
+                       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);
-- 
2.23.3