Re: [PATCH net-next v2] tcp: enable mid stream window clamp
From: Eric Dumazet <hidden>
Date: 2021-08-25 02:45:05
On 8/19/21 12:54 PM, Neil Spring wrote:
quoted hunk ↗ jump to hunk
The TCP_WINDOW_CLAMP socket option is defined in tcp(7) to "Bound the size of the advertised window to this value." Window clamping is distributed across two variables, window_clamp ("Maximal window to advertise" in tcp.h) and rcv_ssthresh ("Current window clamp"). This patch updates the function where the window clamp is set to also reduce the current window clamp, rcv_sshthresh, if needed. With this, setting the TCP_WINDOW_CLAMP option has the documented effect of limiting the window. Signed-off-by: Neil Spring <redacted> --- v2: - fix email formatting net/ipv4/tcp.c | 2 ++ 1 file changed, 2 insertions(+)diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index f931def6302e..2dc6212d5888 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c@@ -3338,6 +3338,8 @@ int tcp_set_window_clamp(struct sock *sk, int val) } else { tp->window_clamp = val < SOCK_MIN_RCVBUF / 2 ? SOCK_MIN_RCVBUF / 2 : val; + tp->rcv_ssthresh = min(tp->rcv_ssthresh, + tp->window_clamp);
This fits in a single line I think. tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
} return 0; }
Hi Neil Can you provide a packetdrill test showing the what the new expected behavior is ? It is not really clear why you need this. Also if we are unable to increase tp->rcv_ssthresh, this means the following sequence will not work as we would expect : +0 setsockopt(5, IPPROTO_TCP, TCP_WINDOW_CLAMP, [10000], 4) = 0 +0 setsockopt(5, IPPROTO_TCP, TCP_WINDOW_CLAMP, [100000], 4) = 0 Thanks.