Re: [PATCH net-next v2] mptcp: normalize seq numbers reported in mptcp_info

[Matthieu Baerts <matttbe@kernel.org>]

Hi Kalpan,

On 27/08/2026 06:10, Kalpan Jani wrote:
> mptcpi_write_seq, mptcpi_snd_una and mptcpi_rcv_nxt report the raw
> 64-bit data sequence numbers, seeded from the connection's IDSN/IASN.
> Since the IDSN/IASN come from mptcp_crypto_key_sha(), these fields
> carry an effectively random offset and are not useful to userspace as
> absolute values: a caller has to snapshot two getsockopt(MPTCP_INFO)
> calls and subtract to get anything meaningful, which is exactly what
> tools/testing/selftests/net/mptcp/mptcp_sockopt.c already does.
> 
> mptcp_info also reports mptcpi_bytes_sent, mptcpi_bytes_received and
> mptcpi_bytes_acked, which give the same information as a plain byte
> count starting at 0. The snapshot-and-diff workaround for the seq
> fields is redundant once those are available.

Thank you for looking at this!

> Cache the local and remote initial sequence numbers on the
> mptcp_sock the same way ->token already is, and subtract them in
> mptcp_diag_fill_info(), so mptcpi_write_seq, mptcpi_snd_una and
> mptcpi_rcv_nxt also start near 0 for a freshly established
> connection.
Not to increase msk's size for these fields only used in the diag side
(under the msk lock I think), couldn't you get the info from the first
subflow instead? It should always be available (except when being
disconnected, but the other fields should be 0 in this case, no?)

Cheers,
Matt
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