c06d313d86
Currently man 8 tc-skbmod says that "...the swap action will occur after
any smac/dmac substitutions are executed, if they are present."
This is false. In fact, trying to "set" and "swap" in a single skbmod
command causes the "set" part to be completely ignored. As an example:
$ tc filter add dev eth0 parent 1: protocol ip prio 10 \
matchall action skbmod \
set dmac AA:AA:AA:AA:AA:AA smac BB:BB:BB:BB:BB:BB \
swap mac
The above command simply does a "swap", without setting DMAC or SMAC to
AA's or BB's. The root cause of this is in the kernel, see
net/sched/act_skbmod.c:tcf_skbmod_init():
parm = nla_data(tb[TCA_SKBMOD_PARMS]);
index = parm->index;
if (parm->flags & SKBMOD_F_SWAPMAC)
lflags = SKBMOD_F_SWAPMAC;
^^^^^^^^^^^^^^^^^^^^^^^^^^
Doing a "=" instead of "|=" clears all other "set" flags when doing a
"swap". Discourage using "set" and "swap" in the same command by
documenting it as undefined behavior, and update the "SYNOPSIS" section
as well as tc -help text accordingly.
If one really needs to e.g. "set" DMAC to all AA's then "swap" DMAC and
SMAC, one should do two separate commands and "pipe" them together.
Reviewed-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
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| man8 | ||
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