net/sched: sch_cake: Add cake_mq qdisc for using cake on mq devices

Add a cake_mq qdisc which installs cake instances on each hardware
queue on a multi-queue device.

This is just a copy of sch_mq that installs cake instead of the default
qdisc on each queue. Subsequent commits will add sharing of the config
between cake instances, as well as a multi-queue aware shaper algorithm.

Reviewed-by: Willem de Bruijn <[e-mail]>
Signed-off-by: Toke Høiland-Jørgensen <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

net/sched/sch_cake.c

···
 #include <linux/if_vlan.h>
 #include <net/gso.h>
 #include <net/pkt_sched.h>
+#include <net/sch_priv.h>
 #include <net/pkt_cls.h>
 #include <net/tcp.h>
 #include <net/flow_dissector.h>
···
 };
 MODULE_ALIAS_NET_SCH("cake");
 
+struct cake_mq_sched {
+	struct mq_sched mq_priv; /* must be first */
+};
+
+static void cake_mq_destroy(struct Qdisc *sch)
+{
+	mq_destroy_common(sch);
+}
+
+static int cake_mq_init(struct Qdisc *sch, struct nlattr *opt,
+			struct netlink_ext_ack *extack)
+{
+	int ret;
+
+	ret = mq_init_common(sch, opt, extack, &cake_qdisc_ops);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int cake_mq_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+	mq_dump_common(sch, skb);
+	return 0;
+}
+
+static int cake_mq_change(struct Qdisc *sch, struct nlattr *opt,
+			  struct netlink_ext_ack *extack)
+{
+	return -EOPNOTSUPP;
+}
+
+static int cake_mq_graft(struct Qdisc *sch, unsigned long cl, struct Qdisc *new,
+			 struct Qdisc **old, struct netlink_ext_ack *extack)
+{
+	NL_SET_ERR_MSG(extack, "can't replace cake_mq sub-qdiscs");
+	return -EOPNOTSUPP;
+}
+
+static const struct Qdisc_class_ops cake_mq_class_ops = {
+	.select_queue	= mq_select_queue,
+	.graft		= cake_mq_graft,
+	.leaf		= mq_leaf,
+	.find		= mq_find,
+	.walk		= mq_walk,
+	.dump		= mq_dump_class,
+	.dump_stats	= mq_dump_class_stats,
+};
+
+static struct Qdisc_ops cake_mq_qdisc_ops __read_mostly = {
+	.cl_ops		=	&cake_mq_class_ops,
+	.id		=	"cake_mq",
+	.priv_size	=	sizeof(struct cake_mq_sched),
+	.init		=	cake_mq_init,
+	.destroy	=	cake_mq_destroy,
+	.attach		=	mq_attach,
+	.change		=	cake_mq_change,
+	.change_real_num_tx = mq_change_real_num_tx,
+	.dump		=	cake_mq_dump,
+	.owner		=	THIS_MODULE,
+};
+MODULE_ALIAS_NET_SCH("cake_mq");
+
 static int __init cake_module_init(void)
 {
-	return register_qdisc(&cake_qdisc_ops);
+	int ret;
+
+	ret = register_qdisc(&cake_qdisc_ops);
+	if (ret)
+		return ret;
+
+	ret = register_qdisc(&cake_mq_qdisc_ops);
+	if (ret)
+		unregister_qdisc(&cake_qdisc_ops);
+
+	return ret;
 }
 
 static void __exit cake_module_exit(void)
 {
 	unregister_qdisc(&cake_qdisc_ops);
+	unregister_qdisc(&cake_mq_qdisc_ops);
 }
 
 module_init(cake_module_init)
···
 MODULE_AUTHOR("Jonathan Morton");
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_DESCRIPTION("The CAKE shaper.");
+MODULE_IMPORT_NS("NET_SCHED_INTERNAL");