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tc/skbmod: Introduce SKBMOD_F_ECN option 

Recently we added SKBMOD_F_ECN option support to the kernel; support it in
the tc-skbmod(8) front end, and update its man page accordingly.

The 2 least significant bits of the Traffic Class field in IPv4 and IPv6
headers are used to represent different ECN states [1]:

	0b00: "Non ECN-Capable Transport", Non-ECT
	0b10: "ECN Capable Transport", ECT(0)
	0b01: "ECN Capable Transport", ECT(1)
	0b11: "Congestion Encountered", CE

This new option, "ecn", marks ECT(0) and ECT(1) IPv{4,6} packets as CE,
which is useful for ECN-based rate limiting.  For example:

	$ tc filter add dev eth0 parent 1: protocol ip prio 10 \
		u32 match ip protocol 1 0xff flowid 1:2 \
		action skbmod \
		ecn

The updated tc-skbmod SYNOPSIS looks like the following:

	tc ... action skbmod { set SETTABLE | swap SWAPPABLE | ecn } ...

Only one of "set", "swap" or "ecn" shall be used in a single tc-skbmod
command.  Trying to use more than one of them at a time is considered
undefined behavior; pipe multiple tc-skbmod commands together instead.
"set" and "swap" only affect Ethernet packets, while "ecn" only affects
IP packets.

Depends on kernel patch "net/sched: act_skbmod: Add SKBMOD_F_ECN option
support", as well as iproute2 patch "tc/skbmod: Remove misinformation
about the swap action".

[1] https://en.wikipedia.org/wiki/Explicit_Congestion_Notification

Reviewed-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Signed-off-by: David Ahern <dsahern@kernel.org>
This commit is contained in:
Peilin Ye 2021-08-04 11:15:16 -07:00 committed by Stephen Hemminger
parent 86c596ed91
commit 7e7270bb1f
2 changed files with 36 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
man/man8/tc-skbmod.8
View File

@ -8,7 +8,8 @@ skbmod - user-friendly packet editor action
.BR tc " ... " "action skbmod " "{ " "set "
.IR SETTABLE " | "
.BI swap " SWAPPABLE"
.RI " } [ " CONTROL " ] [ "
.RB " | " ecn
.RI "} [ " CONTROL " ] [ "
.BI index " INDEX "
]
@ -37,6 +38,12 @@ action. Instead of having to manually edit 8-, 16-, or 32-bit chunks of an
ethernet header,
.B skbmod
allows complete substitution of supported elements.
Action must be one of
.BR set ", " swap " and " ecn "."
.BR set " and " swap
only affect Ethernet packets, while
.B ecn
only affects IP packets.
.SH OPTIONS
.TP
.BI dmac " DMAC"
@ -51,6 +58,10 @@ Change the ethertype to the specified value.
.BI mac
Used to swap mac addresses.
.TP
.B ecn
Used to mark ECN Capable Transport (ECT) IP packets as Congestion Encountered (CE).
Does not affect Non ECN-Capable Transport (Non-ECT) packets.
.TP
.I CONTROL
The following keywords allow to control how the tree of qdisc, classes,
filters and actions is further traversed after this action.
@ -115,7 +126,7 @@ tc filter add dev eth5 parent 1: protocol ip prio 10 \\
.EE
.RE
Finally, swap the destination and source mac addresses in the header:
To swap the destination and source mac addresses in the Ethernet header:
.RS
.EX
@ -126,13 +137,22 @@ tc filter add dev eth3 parent 1: protocol ip prio 10 \\
.EE
.RE
However, trying to
.B set
and
.B swap
in a single
.B skbmod
command will cause undefined behavior.
Finally, to mark the CE codepoint in the IP header for ECN Capable Transport (ECT) packets:
.RS
.EX
tc filter add dev eth0 parent 1: protocol ip prio 10 \\
u32 match ip protocol 1 0xff flowid 1:2 \\
action skbmod \\
ecn
.EE
.RE
Only one of
.BR set ", " swap " and " ecn
shall be used in a single command.
Trying to use more than one of them in a single command is considered undefined behavior; pipe
multiple commands together instead.
.SH SEE ALSO
.BR tc (8),

8
tc/m_skbmod.c
View File

@ -28,7 +28,7 @@
static void skbmod_explain(void)
{
fprintf(stderr,
"Usage:... skbmod { set <SETTABLE> | swap <SWAPPABLE> } [CONTROL] [index INDEX]\n"
"Usage:... skbmod { set <SETTABLE> | swap <SWAPPABLE> | ecn } [CONTROL] [index INDEX]\n"
"where SETTABLE is: [dmac DMAC] [smac SMAC] [etype ETYPE]\n"
"where SWAPPABLE is: \"mac\" to swap mac addresses\n"
"\tDMAC := 6 byte Destination MAC address\n"
@ -111,6 +111,9 @@ static int parse_skbmod(struct action_util *a, int *argc_p, char ***argv_p,
p.flags |= SKBMOD_F_SMAC;
fprintf(stderr, "src MAC address <%s>\n", saddr);
ok += 1;
} else if (matches(*argv, "ecn") == 0) {
p.flags |= SKBMOD_F_ECN;
ok += 1;
} else if (matches(*argv, "help") == 0) {
skbmod_usage();
} else {
@ -211,6 +214,9 @@ static int print_skbmod(struct action_util *au, FILE *f, struct rtattr *arg)
if (p->flags & SKBMOD_F_SWAPMAC)
fprintf(f, "swap mac ");
if (p->flags & SKBMOD_F_ECN)
fprintf(f, "ecn ");
fprintf(f, "\n\t index %u ref %d bind %d", p->index, p->refcnt,
p->bindcnt);
if (show_stats) {