Question regarding do_tcp_sendpages, tcp_current_mss and eff_sacks

From: Ashvin Goel
Date: Sat Apr 17 2004 - 15:05:20 EST

I am trying to use do_tcp_sendpages() to stream some data from within the Linux Redhat kernel 2.4.20 (it is an smp kernel running on a uniprocessor). After a while this function returns an error value of -512. This error value makes no sense to me. A little debugging showed that tcp_current_mss() returns negative values. In particular, for the socket to which do_tcp_sendpages() is sending data, tp->eff_sacks has the value 200. This makes the value returned by tcp_current_mss be -156 (1448 - 4 - 200 * 8). Is this value reasonable? I think this value is causing do_tcp_sendpages() to return a large negative value.

Thanks for any help/suggestions. Please CC your post to me personally.

Ashvin Goel
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