Requesting comments.

So, bacically commit 56b765b79 (htb: improved accuracy at high rates),
broke the "linklayer atm" handling.  As it didn't update the iproute tc util.

Treating this as a regression fix, this is the smallest and least
intrusive solution I could come up with.

I'm basically restoring the "linklayer atm" handling, by using the
__reserved field in struct tc_ratespec, to convey the chosen
linklayer option.


KERNEL patch:
=============

[PATCH RFC] net_sched: restore "linklayer atm" handling

From: Jesper Dangaard Brouer <redacted>

commit 56b765b79 ("htb: improved accuracy at high rates")
broke the "linklayer atm" handling.

 tc class add ... htb rate X ceil Y linklayer atm

This patch restores the "linklayer atm" handling, by using the
__reserved field in struct tc_ratespec, to convey the choosen
linklayer option.

This requires a corrosponding iproute2 tc fix, that updates this
field.  Older tc binaries can be detected by the kernel, as the
field would be zero.

Request-For-Comments-by: Jesper Dangaard Brouer [off-list ref]
---

 include/net/sch_generic.h      |    8 +++++++-
 include/uapi/linux/pkt_sched.h |   11 ++++++++++-
 net/sched/sch_generic.c        |    4 ++++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index e7f4e21..c9916b1 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h

@@ -682,13 +682,18 @@ struct psched_ratecfg {
 	u64	rate_bps;
 	u32	mult;
 	u16	overhead;
+	u8	linklayer;
 	u8	shift;
 };
 
 static inline u64 psched_l2t_ns(const struct psched_ratecfg *r,
 				unsigned int len)
 {
-	return ((u64)(len + r->overhead) * r->mult) >> r->shift;
+	u64 pkt_len = len + r->overhead;
+
+	if (r->linklayer == TC_LINKLAYER_ATM)
+		pkt_len = DIV_ROUND_UP(pkt_len,48)*53;