tcp: mptcp: use mptcp receive buffer space to select rcv window
In MPTCP, the receive window is shared across all subflows, because it refers to the mptcp-level sequence space. MPTCP receivers already place incoming packets on the mptcp socket receive queue and will charge it to the mptcp socket rcvbuf until userspace consumes the data. Update __tcp_select_window to use the occupancy of the parent/mptcp socket instead of the subflow socket in case the tcp socket is part of a logical mptcp connection. This commit doesn't change choice of initial window for passive or active connections. While it would be possible to change those as well, this adds complexity (especially when handling MP_JOIN requests). Furthermore, the MPTCP RFC specifically says that a MPTCP sender 'MUST NOT use the RCV.WND field of a TCP segment at the connection level if it does not also carry a DSS option with a Data ACK field.' SYN/SYNACK packets do not carry a DSS option with a Data ACK field. Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: David S. Miller <davem@davemloft.net>
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