[PATCH v3 net-next 2/3] netem: add uapi to express delay and jitter in nanoseconds

[Dave Taht]

netem userspace has long relied on a horrible /proc/net/psched hack
to translate the current notion of "ticks" to nanoseconds.

Expressing latency and jitter instead, in well defined nanoseconds,
increases the dynamic range of emulated delays and jitter in netem.

It will also ease a transition where reducing a tick to nsec
equivalence would constrain the max delay in prior versions of
netem to only 4.3 seconds.

Signed-off-by: Dave Taht <dave.t...@gmail.com>
Suggested-by: Eric Dumazet <eduma...@google.com>
Reviewed-by: Eric Dumazet <eduma...@google.com>
---
 include/uapi/linux/pkt_sched.h |  2 ++
 net/sched/sch_netem.c          | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 6a2c5ea..8fe6d18 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -537,6 +537,8 @@ enum {
        TCA_NETEM_ECN,
        TCA_NETEM_RATE64,
        TCA_NETEM_PAD,
+       TCA_NETEM_LATENCY64,
+       TCA_NETEM_JITTER64,
        __TCA_NETEM_MAX,
 };
 
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index e64e0e0..47d6dec 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -819,6 +819,8 @@ static const struct nla_policy netem_policy[TCA_NETEM_MAX + 
1] = {
        [TCA_NETEM_LOSS]        = { .type = NLA_NESTED },
        [TCA_NETEM_ECN]         = { .type = NLA_U32 },
        [TCA_NETEM_RATE64]      = { .type = NLA_U64 },
+       [TCA_NETEM_LATENCY64]   = { .type = NLA_S64 },
+       [TCA_NETEM_JITTER64]    = { .type = NLA_S64 },
 };
 
 static int parse_attr(struct nlattr *tb[], int maxtype, struct nlattr *nla,
@@ -916,6 +918,12 @@ static int netem_change(struct Qdisc *sch, struct nlattr 
*opt)
                q->rate = max_t(u64, q->rate,
                                nla_get_u64(tb[TCA_NETEM_RATE64]));
 
+       if (tb[TCA_NETEM_LATENCY64])
+               q->latency = nla_get_s64(tb[TCA_NETEM_LATENCY64]);
+
+       if (tb[TCA_NETEM_JITTER64])
+               q->jitter = nla_get_s64(tb[TCA_NETEM_JITTER64]);
+
        if (tb[TCA_NETEM_ECN])
                q->ecn = nla_get_u32(tb[TCA_NETEM_ECN]);
 
@@ -1020,6 +1028,12 @@ static int netem_dump(struct Qdisc *sch, struct sk_buff 
*skb)
        if (nla_put(skb, TCA_OPTIONS, sizeof(qopt), &qopt))
                goto nla_put_failure;
 
+       if (nla_put(skb, TCA_NETEM_LATENCY64, sizeof(q->latency), &q->latency))
+               goto nla_put_failure;
+
+       if (nla_put(skb, TCA_NETEM_JITTER64, sizeof(q->jitter), &q->jitter))
+               goto nla_put_failure;
+
        cor.delay_corr = q->delay_cor.rho;
        cor.loss_corr = q->loss_cor.rho;
        cor.dup_corr = q->dup_cor.rho;
-- 
2.7.4