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

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Date:   Thu, 11 Mar 2021 23:00:35 +0000
From:   ChiaHao Hsu <andyhsu@...zon.com>
To:     <netdev@...r.kernel.org>
CC:     <wei.liu@...nel.org>, <paul@....org>, <davem@...emloft.net>,
        <kuba@...nel.org>, <andyhsu@...zon.com>,
        <xen-devel@...ts.xenproject.org>
Subject: [net-next 2/2] xen-netback: add module parameter to disable dynamic multicast control

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@...zon.com>
---
 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 a119ae673862..d369428ea5bb 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 9801b8d10239..a7f487289bec 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -1094,12 +1094,14 @@ 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