[net-next PATCH] taprio: don't reject same mqprio settings

[Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>]

The taprio qdisc allows to set mqprio setting but only once. In case
if mqprio settings are provided next time the error is returned as
it's not allowed to change traffic class mapping in-flignt and that
is normal. But if configuration is absolutely the same - no need to
return error. It allows to provide same command couple times,
changing only base time for instance, or changing only scheds maps,
but leaving mqprio setting w/o modification. It more corresponds the
message: "Changing the traffic mapping of a running schedule is not
supported", so reject mqprio if it's really changed.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
---
 net/sched/sch_taprio.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 7cd68628c637..bd844f2cbf7a 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1347,6 +1347,26 @@ static int taprio_parse_clockid(struct Qdisc *sch, struct nlattr **tb,
 	return err;
 }
 
+static int taprio_mqprio_cmp(struct net_device *dev,
+			     struct tc_mqprio_qopt *mqprio)
+{
+	int i;
+
+	if (mqprio->num_tc != dev->num_tc)
+		return -1;
+
+	for (i = 0; i < mqprio->num_tc; i++)
+		if (dev->tc_to_txq[i].count != mqprio->count[i] ||
+		    dev->tc_to_txq[i].offset != mqprio->offset[i])
+			return -1;
+
+	for (i = 0; i < TC_BITMASK + 1; i++)
+		if (dev->prio_tc_map[i] != mqprio->prio_tc_map[i])
+			return -1;
+
+	return 0;
+}
+
 static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
 			 struct netlink_ext_ack *extack)
 {
@@ -1398,6 +1418,10 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
 	admin = rcu_dereference(q->admin_sched);
 	rcu_read_unlock();
 
+	/* no changes - no new mqprio settings */
+	if (mqprio && !taprio_mqprio_cmp(dev, mqprio))
+		mqprio = NULL;
+
 	if (mqprio && (oper || admin)) {
 		NL_SET_ERR_MSG(extack, "Changing the traffic mapping of a running schedule is not supported");
 		err = -ENOTSUPP;
-- 
2.20.1