[9fans] PPPoE

[Zoltan Jarai <jarai@mail.tvnet.hu>]

I had to make the following modifications to Russ Cox's pppoe.c to get
it work with my ADSL provider (TVnet) here in Hungary.  TVnet does not
use PPP framing, so I did not need the -F (nor -f) option.  The buf[0]
at the end is a correction of a typo in the hexdump routine, useful
when debugging.

diff pppoe-orig.c pppoe.c
236c236
< 	char e[ERRMAX], path[64];
---
> 	char e[ERRLEN], path[64];
239c239
< 		rerrstr(e, sizeof e);
---
> 		errstr(e);
511d510
< 	argv[argc++] = "-F";
687a687
> 			buf[0] = '\0';

Still, I had problems viewing web pages and connecting to FTP sites.
So I checked out Roaring Penguin's PPPoE client for Linux.  As they
explain it (http://www.roaringpenguin.com/pppoe/als-pppoe-paper.pdf
section 4.5) they modify the MSS value in the TCP header of packets.
First, I tried to implement their trick (see among their sources
rp-pppoe-3.3/src/common.c:/^clampMSS) but I did not succeed, not
surprisingly, since I know next to nothing about TCP.  But then
lowering the default MSS to 1412 (value suggested by them) in the
kernel (/sys/src/9/ip/tcp.c:/DEF_MSS) helped.

Hope this helps.

Zoltan