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tcp: Deal with DSACKs, and adjust rescue hole on success.

Description

tcp: Deal with DSACKs, and adjust rescue hole on success.

When a rescue retransmission is successful, rather than
inserting new holes to the left of it, adjust the old
rescue entry to cover the missed sequence space.

Also, as snd_fack may be stale by that point, pull it forward
in order to never create a hole left of snd_una/th_ack.

Finally, with DSACKs, tcp_sack_doack() may be called
with new full ACKs but a DSACK block. Account for this
eventuality properly to keep sacked_bytes >= 0.

MFC after: 3 days
Reviewed By: kbowling, tuexen, transport
Sponsored by: NetApp, Inc.
Differential Revision: https://reviews.freebsd.org/D29835

Details

Provenance
rscheffAuthored on Apr 20 2021, 12:53 PM
Reviewer
transport
Differential Revision
D29835: tcp: Deal with DSACKs, and adjust rescue hole on success.
Parents
R10:9ca874cf740e: Add TCP LRO support for VLAN and VxLAN.
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