K 10
svn:author
V 5
shurd
K 8
svn:date
V 27
2019-01-25T18:30:12.552764Z
K 7
svn:log
V 863
MFC r343047:

Fix window update issue when scaling disabled

When the TCP window scale option is not used, and the window
opens up enough in one soreceive, a window update will not be sent.

For example, if recwin == 65535, so->so_rcv.sb_hiwat >= 262144, and
so->so_rcv.sb_hiwat <= 524272, the window update will never be sent.
This is because recwin and adv are clamped to TCP_MAXWIN << tp->rcv_scale,
and so will never be >= so->so_rcv.sb_hiwat / 4
or <= so->so_rcv.sb_hiwat / 8.

This patch ensures a window update is sent if the window opens by
TCP_MAXWIN << tp->rcv_scale, which should only happen when the window
size goes from zero to the max expressible.

This issue looks like it was introduced in r306769 when recwin was clamped
to TCP_MAXWIN << tp->rcv_scale.

Sponsored by:	Limelight Networks
Differential Revision:	https://reviews.freebsd.org/D18821

END