In the TCP stack, the hhook(9) framework provides hooks for kernel modules

to add actions that run when a TCP frame is sent or received on a TCP
session in the ESTABLISHED state. In the base tree, this functionality is
only used for the h_ertt module, which is used by the cc_cdg, cc_chd, cc_hd,
and cc_vegas congestion control modules.

Presently, we incur overhead to check for hooks each time a TCP frame is
sent or received on an ESTABLISHED TCP session.

This change adds a new compile-time option (TCP_HHOOK) to determine whether
to include the hhook(9) framework for TCP. To retain backwards
compatibility, I added the TCP_HHOOK option to every configuration file that
already defined "options INET". (Therefore, this patch introduces no
functional change. In order to see a functional difference, you need to
compile a custom kernel without the TCP_HHOOK option.) This change will
allow users to easily exclude this functionality from their kernel, should
they wish to do so.

Note that any users who use a custom kernel configuration and use one of the
congestion control modules listed above will need to add the TCP_HHOOK
option to their kernel configuration.

Reviewed by:	rrs, lstewart, hiren (previous version), sjg (makefiles only)
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D8185

1 files changed, 5 insertions, 0 deletions

diff --git a/UPDATING b/UPDATING
index 970401bff532..b6e6bf61eaa0 100644
--- a/UPDATING
+++ b/UPDATING
@@ -31,6 +31,11 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 12.x IS SLOW:
 	disable the most expensive debugging functionality run
 	"ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20161008:
+	Use of the cc_cdg, cc_chd, cc_hd, or cc_vegas congestion control
+	modules now requires that the kernel configuration contain the
+	TCP_HHOOK option. (This option is included in the GENERIC kernel.)
+
 20161003:
 	The WITHOUT_ELFCOPY_AS_OBJCOPY src.conf(5) knob has been retired.
 	ELF Tool Chain's elfcopy is always installed as /usr/bin/objcopy.