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authorHagen Paul Pfeifer <hagen@jauu.net>2010-08-19 06:33:05 +0000
committerDavid S. Miller <davem@davemloft.net>2010-08-22 21:42:54 -0700
commite88c64f0a42575e01c7ace903d0570bc0b7fcf85 (patch)
treea3e4a4165f978c68823b2453591ea46a3b7a525e /net
parentc2368e795cec561229ef66a04ac51629b918a9e8 (diff)
tcp: allow effective reduction of TCP's rcv-buffer via setsockopt
Via setsockopt it is possible to reduce the socket RX buffer (SO_RCVBUF). TCP method to select the initial window and window scaling option in tcp_select_initial_window() currently misbehaves and do not consider a reduced RX socket buffer via setsockopt. Even though the server's RX buffer is reduced via setsockopt() to 256 byte (Initial Window 384 byte => 256 * 2 - (256 * 2 / 4)) the window scale option is still 7: 192.168.1.38.40676 > 78.47.222.210.5001: Flags [S], seq 2577214362, win 5840, options [mss 1460,sackOK,TS val 338417 ecr 0,nop,wscale 0], length 0 78.47.222.210.5001 > 192.168.1.38.40676: Flags [S.], seq 1570631029, ack 2577214363, win 384, options [mss 1452,sackOK,TS val 2435248895 ecr 338417,nop,wscale 7], length 0 192.168.1.38.40676 > 78.47.222.210.5001: Flags [.], ack 1, win 5840, options [nop,nop,TS val 338421 ecr 2435248895], length 0 Within tcp_select_initial_window() the original space argument - a representation of the rx buffer size - is expanded during tcp_select_initial_window(). Only sysctl_tcp_rmem[2], sysctl_rmem_max and window_clamp are considered to calculate the initial window. This patch adjust the window_clamp argument if the user explicitly reduce the receive buffer. Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net> Cc: David S. Miller <davem@davemloft.net> Cc: Patrick McHardy <kaber@trash.net> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/tcp_output.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index de3bd8458588..01b94b8d9ec9 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2429,6 +2429,12 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
__u8 rcv_wscale;
/* Set this up on the first call only */
req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
+
+ /* limit the window selection if the user enforce a smaller rx buffer */
+ if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
+ (req->window_clamp > tcp_full_space(sk) || req->window_clamp == 0))
+ req->window_clamp = tcp_full_space(sk);
+
/* tcp_full_space because it is guaranteed to be the first packet */
tcp_select_initial_window(tcp_full_space(sk),
mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
@@ -2555,6 +2561,11 @@ static void tcp_connect_init(struct sock *sk)
tcp_initialize_rcv_mss(sk);
+ /* limit the window selection if the user enforce a smaller rx buffer */
+ if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
+ (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
+ tp->window_clamp = tcp_full_space(sk);
+
tcp_select_initial_window(tcp_full_space(sk),
tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
&tp->rcv_wnd,

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