sch_red: generalize accurate MAX_P support to RED/GRED/CHOKE

Now RED uses a Q0.32 number to store max_p (max probability), allow
RED/GRED/CHOKE to use/report full resolution at config/dump time.

Old tc binaries are non aware of new attributes, and still set/get Plog.

New tc binary set/get both Plog and max_p for backward compatibility,
they display "probability value" if they get max_p from new kernels.

# tc -d  qdisc show dev ...
...
qdisc red 10: parent 1:1 limit 360Kb min 30Kb max 90Kb ecn ewma 5
probability 0.09 Scell_log 15

Make sure we avoid potential divides by 0 in reciprocal_value(), if
(max_th - min_th) is big.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 18 insertions, 4 deletions

diff --git a/net/sched/sch_gred.c b/net/sched/sch_gred.c
index b9493a09a870..a1b7407ac2a4 100644
--- a/net/sched/sch_gred.c
+++ b/net/sched/sch_gred.c
@@ -34,7 +34,7 @@ struct gred_sched;
 
 struct gred_sched_data {
 	u32		limit;		/* HARD maximal queue length	*/
-	u32      	DP;		/* the drop pramaters */
+	u32		DP;		/* the drop parameters */
 	u32		bytesin;	/* bytes seen on virtualQ so far*/
 	u32		packetsin;	/* packets seen on virtualQ so far*/
 	u32		backlog;	/* bytes on the virtualQ */
@@ -379,7 +379,8 @@ static inline int gred_change_table_def(struct Qdisc *sch, struct nlattr *dps)
 }
 
 static inline int gred_change_vq(struct Qdisc *sch, int dp,
-				 struct tc_gred_qopt *ctl, int prio, u8 *stab)
+				 struct tc_gred_qopt *ctl, int prio,
+				 u8 *stab, u32 max_P)
 {
 	struct gred_sched *table = qdisc_priv(sch);
 	struct gred_sched_data *q;
@@ -400,7 +401,7 @@ static inline int gred_change_vq(struct Qdisc *sch, int dp,
 
 	red_set_parms(&q->parms,
 		      ctl->qth_min, ctl->qth_max, ctl->Wlog, ctl->Plog,
-		      ctl->Scell_log, stab);
+		      ctl->Scell_log, stab, max_P);
 
 	return 0;
 }
@@ -409,6 +410,7 @@ static const struct nla_policy gred_policy[TCA_GRED_MAX + 1] = {
 	[TCA_GRED_PARMS]	= { .len = sizeof(struct tc_gred_qopt) },
 	[TCA_GRED_STAB]		= { .len = 256 },
 	[TCA_GRED_DPS]		= { .len = sizeof(struct tc_gred_sopt) },
+	[TCA_GRED_MAX_P]	= { .type = NLA_U32 },
 };
 
 static int gred_change(struct Qdisc *sch, struct nlattr *opt)
@@ -418,6 +420,7 @@ static int gred_change(struct Qdisc *sch, struct nlattr *opt)
 	struct nlattr *tb[TCA_GRED_MAX + 1];
 	int err, prio = GRED_DEF_PRIO;
 	u8 *stab;
+	u32 max_P;
 
 	if (opt == NULL)
 		return -EINVAL;
@@ -433,6 +436,8 @@ static int gred_change(struct Qdisc *sch, struct nlattr *opt)
 	    tb[TCA_GRED_STAB] == NULL)
 		return -EINVAL;
 
+	max_P = tb[TCA_GRED_MAX_P] ? nla_get_u32(tb[TCA_GRED_MAX_P]) : 0;
+
 	err = -EINVAL;
 	ctl = nla_data(tb[TCA_GRED_PARMS]);
 	stab = nla_data(tb[TCA_GRED_STAB]);
@@ -457,7 +462,7 @@ static int gred_change(struct Qdisc *sch, struct nlattr *opt)
 
 	sch_tree_lock(sch);
 
-	err = gred_change_vq(sch, ctl->DP, ctl, prio, stab);
+	err = gred_change_vq(sch, ctl->DP, ctl, prio, stab, max_P);
 	if (err < 0)
 		goto errout_locked;
 
@@ -498,6 +503,7 @@ static int gred_dump(struct Qdisc *sch, struct sk_buff *skb)
 	struct gred_sched *table = qdisc_priv(sch);
 	struct nlattr *parms, *opts = NULL;
 	int i;
+	u32 max_p[MAX_DPs];
 	struct tc_gred_sopt sopt = {
 		.DPs	= table->DPs,
 		.def_DP	= table->def,
@@ -509,6 +515,14 @@ static int gred_dump(struct Qdisc *sch, struct sk_buff *skb)
 	if (opts == NULL)
 		goto nla_put_failure;
 	NLA_PUT(skb, TCA_GRED_DPS, sizeof(sopt), &sopt);
+
+	for (i = 0; i < MAX_DPs; i++) {
+		struct gred_sched_data *q = table->tab[i];
+
+		max_p[i] = q ? q->parms.max_P : 0;
+	}
+	NLA_PUT(skb, TCA_GRED_MAX_P, sizeof(max_p), max_p);
+
 	parms = nla_nest_start(skb, TCA_GRED_PARMS);
 	if (parms == NULL)
 		goto nla_put_failure;