[newlib 57/65] tcp: Add support for DSACK based reordering window to rack.

Sebastian Huber sebastian.huber at embedded-brains.de
Thu Jul 7 11:59:04 UTC 2022

From: Randall Stewart <rrs at FreeBSD.org>

The rack stack, with respect to the rack bits in it, was originally built based
on an early I-D of rack. In fact at that time the TLP bits were in a separate
I-D. The dynamic reordering window based on DSACK events was not present
in rack at that time. It is now part of the RFC and we need to update our stack
to include these features. However we want to have a way to control the feature
so that we can, if the admin decides, make it stay the same way system wide as
well as via socket option. The new sysctl and socket option has the following
meaning for setting:

00 (0) - Keep the old way, i.e. reordering window is 1 and do not use DSACK bytes to add to reorder window
01 (1) - Change the Reordering window to 1/4 of an RTT but do not use DSACK bytes to add to reorder window
10 (2) - Keep the reordering window as 1, but do use SACK bytes to add additional 1/4 RTT delay to the reorder window
11 (3) - reordering window is 1/4 of an RTT and add additional DSACK bytes to increase the reordering window (RFC behavior)

The default currently in the sysctl is 3 so we get standards based behavior.
Reviewed by: tuexen
Sponsored by: Netflix Inc.
Differential Revision: https://reviews.freebsd.org/D31506
 newlib/libc/sys/rtems/include/netinet/tcp.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/newlib/libc/sys/rtems/include/netinet/tcp.h b/newlib/libc/sys/rtems/include/netinet/tcp.h
index a79dbeaad..29c1e376c 100644
--- a/newlib/libc/sys/rtems/include/netinet/tcp.h
+++ b/newlib/libc/sys/rtems/include/netinet/tcp.h
@@ -309,6 +309,7 @@ struct tcphdr {
 #define TCP_RACK_PACING_BETA 1138	/* Changing the beta for pacing */
 #define TCP_RACK_PACING_BETA_ECN 1139	/* Changing the beta for ecn with pacing */
 #define TCP_RACK_TIMER_SLOP 1140	/* Set or get the timer slop used */
+#define TCP_RACK_DSACK_OPT 1141		/* How do we setup rack timer DSACK options bit 1/2 */
 /* Start of reserved space for third-party user-settable options. */

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