DynamicWindow Patch

[Markus Friedl]

On Wed, Jul 07, 2004 at 02:51:53PM -0400, Michael Stevens wrote:
> We have developed a patch that enables changing the SSH window size
> using the tcp window size as the source. This allows SSH to obtain
> maximum use of the bandwidth on high BDP links.
> 
> We also have a page that describes the changes and performance.
> http://www.psc.edu/~rapier/hpn-ssh/
> 
> The patch against CVS is included here.

> -	if (len > 0x100000)
> +	if (!buffer->unlimited && len > 0x100000)
>  		fatal("buffer_append_space: len %u not supported", len);

that's dangerous, is it really necessary? we could
crank the 0x100000.

> +		u_int32_t tcpwinsz = 0;
> +		socklen_t optsz = sizeof(tcpwinsz);
> +		int ret = -1;
> +		u_int32_t addition = 0;
> +		if (c->dynamic_window)
> +			ret = getsockopt(packet_get_connection_in(), 
> +				SOL_SOCKET, SO_RCVBUF, &tcpwinsz, &optsz);
> +		if (c->dynamic_window && (ret == 0) && 
> +		    (tcpwinsz > c->local_window_max)) {
> +			addition = 2 * tcpwinsz - c->local_window_max;
> +			c->local_window_max += addition;
> +		}

why do you need to do this here? why not just announce a bigger
window when the channel is created?

does SO_RCVBUF change during the session? otherwise we could do
this instead.  but i agree, we should really improve the WINDOW_ADJUST
handling.

Index: ssh.c
===================================================================
RCS file: /cvs/src/usr.bin/ssh/ssh.c,v
retrieving revision 1.222
diff -u -r1.222 ssh.c
--- ssh.c	23 Jun 2004 14:31:01 -0000	1.222
+++ ssh.c	7 Jul 2004 21:21:53 -0000
@@ -1096,6 +1096,8 @@
 {
 	Channel *c;
 	int window, packetmax, in, out, err;
+	u_int32_t tcpwinsz = 0;
+	socklen_t optsz = sizeof(tcpwinsz);
 
 	if (stdin_null_flag) {
 		in = open(_PATH_DEVNULL, O_RDONLY);
@@ -1122,6 +1124,10 @@
 		window >>= 1;
 		packetmax >>= 1;
 	}
+	if (getsockopt(packet_get_connection_in(),SOL_SOCKET, SO_RCVBUF,
+	    &tcpwinsz, &optsz) == 0) 
+		window = 2 * tcpwinsz;
+
 	c = channel_new(
 	    "session", SSH_CHANNEL_OPENING, in, out, err,
 	    window, packetmax, CHAN_EXTENDED_WRITE,