qdisc: allow setting default queuing discipline

By default, the pfifo_fast queue discipline has been used by default
for all devices. But we have better choices now.

This patch allow setting the default queueing discipline with sysctl.
This allows easy use of better queueing disciplines on all devices
without having to use tc qdisc scripts. It is intended to allow
an easy path for distributions to make fq_codel or sfq the default
qdisc.

This patch also makes pfifo_fast more of a first class qdisc, since
it is now possible to manually override the default and explicitly
use pfifo_fast. The behavior for systems who do not use the sysctl
is unchanged, they still get pfifo_fast

Also removes leftover random # in sysctl net core.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 66 insertions, 7 deletions

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 51b968d3febb..812e57900591 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -131,6 +131,11 @@ static DEFINE_RWLOCK(qdisc_mod_lock);
  ************************************************/
 
 
+/* Qdisc to use by default */
+
+const struct Qdisc_ops *default_qdisc_ops = &pfifo_fast_ops;
+EXPORT_SYMBOL(default_qdisc_ops);
+
 /* The list of all installed queueing disciplines. */
 
 static struct Qdisc_ops *qdisc_base;
@@ -200,6 +205,58 @@ int unregister_qdisc(struct Qdisc_ops *qops)
 }
 EXPORT_SYMBOL(unregister_qdisc);
 
+/* Get default qdisc if not otherwise specified */
+void qdisc_get_default(char *name, size_t len)
+{
+        read_lock(&qdisc_mod_lock);
+        strlcpy(name, default_qdisc_ops->id, len);
+        read_unlock(&qdisc_mod_lock);
+}
+
+static struct Qdisc_ops *qdisc_lookup_default(const char *name)
+{
+        struct Qdisc_ops *q = NULL;
+
+        for (q = qdisc_base; q; q = q->next) {
+                if (!strcmp(name, q->id)) {
+                        if (!try_module_get(q->owner))
+                                q = NULL;
+                        break;
+                }
+        }
+
+        return q;
+}
+
+/* Set new default qdisc to use */
+int qdisc_set_default(const char *name)
+{
+        const struct Qdisc_ops *ops;
+
+        if (!capable(CAP_NET_ADMIN))
+                return -EPERM;
+
+        write_lock(&qdisc_mod_lock);
+        ops = qdisc_lookup_default(name);
+        if (!ops) {
+                /* Not found, drop lock and try to load module */
+                write_unlock(&qdisc_mod_lock);
+                request_module("sch_%s", name);
+                write_lock(&qdisc_mod_lock);
+
+                ops = qdisc_lookup_default(name);
+        }
+
+        if (ops) {
+                /* Set new default */
+                module_put(default_qdisc_ops->owner);
+                default_qdisc_ops = ops;
+        }
+        write_unlock(&qdisc_mod_lock);
+
+        return ops ? 0 : -ENOENT;
+}
+
 /* We know handle. Find qdisc among all qdisc's attached to device
    (root qdisc, all its children, children of children etc.)
  */
@@ -1854,6 +1911,7 @@ static int __init pktsched_init(void)
                 return err;
         }
 
+        register_qdisc(&pfifo_fast_ops);
         register_qdisc(&pfifo_qdisc_ops);
         register_qdisc(&bfifo_qdisc_ops);
         register_qdisc(&pfifo_head_drop_qdisc_ops);
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 48be3d5c0d92..5078e0c5db8d 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -530,7 +530,6 @@ struct Qdisc_ops pfifo_fast_ops __read_mostly = {
         .dump           =       pfifo_fast_dump,
         .owner          =       THIS_MODULE,
 };
-EXPORT_SYMBOL(pfifo_fast_ops);
 
 static struct lock_class_key qdisc_tx_busylock;
 
@@ -583,6 +582,9 @@ struct Qdisc *qdisc_create_dflt(struct netdev_queue *dev_queue,
 {
         struct Qdisc *sch;
 
+        if (!try_module_get(ops->owner))
+                goto errout;
+
         sch = qdisc_alloc(dev_queue, ops);
         if (IS_ERR(sch))
                 goto errout;
@@ -686,7 +688,7 @@ static void attach_one_default_qdisc(struct net_device *dev,
 
         if (dev->tx_queue_len) {
                 qdisc = qdisc_create_dflt(dev_queue,
-                                          &pfifo_fast_ops, TC_H_ROOT);
+                                          default_qdisc_ops, TC_H_ROOT);
                 if (!qdisc) {
                         netdev_info(dev, "activation failed\n");
                         return;
@@ -739,9 +741,8 @@ void dev_activate(struct net_device *dev)
         int need_watchdog;
 
         /* No queueing discipline is attached to device;
-           create default one i.e. pfifo_fast for devices,
-           which need queueing and noqueue_qdisc for
-           virtual interfaces
+         * create default one for devices, which need queueing
+         * and noqueue_qdisc for virtual interfaces
          */
 
         if (dev->qdisc == &noop_qdisc)
diff --git a/net/sched/sch_mq.c b/net/sched/sch_mq.c
index 5da78a19ac9a..2e56185736d6 100644
--- a/net/sched/sch_mq.c
+++ b/net/sched/sch_mq.c
@@ -57,7 +57,7 @@ static int mq_init(struct Qdisc *sch, struct nlattr *opt)
 
         for (ntx = 0; ntx < dev->num_tx_queues; ntx++) {
                 dev_queue = netdev_get_tx_queue(dev, ntx);
-                qdisc = qdisc_create_dflt(dev_queue, &pfifo_fast_ops,
+                qdisc = qdisc_create_dflt(dev_queue, default_qdisc_ops,
                                           TC_H_MAKE(TC_H_MAJ(sch->handle),
                                                     TC_H_MIN(ntx + 1)));
                 if (qdisc == NULL)
diff --git a/net/sched/sch_mqprio.c b/net/sched/sch_mqprio.c
index accec33c454c..d44c868cb537 100644
--- a/net/sched/sch_mqprio.c
+++ b/net/sched/sch_mqprio.c
@@ -124,7 +124,7 @@ static int mqprio_init(struct Qdisc *sch, struct nlattr *opt)
 
         for (i = 0; i < dev->num_tx_queues; i++) {
                 dev_queue = netdev_get_tx_queue(dev, i);
-                qdisc = qdisc_create_dflt(dev_queue, &pfifo_fast_ops,
+                qdisc = qdisc_create_dflt(dev_queue, default_qdisc_ops,
                                           TC_H_MAKE(TC_H_MAJ(sch->handle),
                                                     TC_H_MIN(i + 1)));
                 if (qdisc == NULL) {