Re: [PATCH net v2 2/2] selftests: net: check timestamp echo after an old ACK

[Eric Dumazet]

On Fri, Sep 25, 2026 at 12:45 AM Jeff Jo <jeffjo@xxxxxxxxxx> wrote:
>
> Add a regression test for a gap-filling packet whose acknowledgment has
> become old. Linux first sends data to the peer. Deliver two peer data
> packets out of order: the later packet acknowledges Linux's data, while
> the delayed packet still carries the earlier acknowledgment.
>
> Require the ACK that closes the receive gap to echo the delayed packet's
> timestamp, 301000. Without the fix, Linux accepts the data but still echoes
> the previously saved timestamp, 1000. Also check that the application can
> read all 34 bytes.
>
> Use a large jump in peer timestamps to represent the idle interval, with
> no real wait, loss or retransmission. The test directly checks the outgoing
> timestamp echo. It requires packetdrill's merged TSecr verification fix
> (linked below); older tools incorrectly pass on an unfixed kernel.
>
> Use the existing packetdrill selftest runner for IPv4, IPv6 and
> IPv4-mapped IPv6.
>
> Link: https://github.com/google/packetdrill/commit/83f72d3f9085d0e26eb4d206fe4d7cfab5b6d872
> Assisted-by: LLM
> Signed-off-by: Jeff Jo <jeffjo@xxxxxxxxxx>

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>

Thanks!