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;