From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [omega-g1:11072] Re: [PATCH] net: configurable sysctl
 parameter "net.core.tcp_lowat" for sk_stream_min_wspace()
Date: Mon, 22 Aug 2011 11:35:44 -0700 (PDT)
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From: "Jun.Kondo" <jun.kondo@ctc-g.co.jp>
Date: Mon, 22 Aug 2011 09:33:52 +0900

> is it (really) network problem ?
> or is wmem not enough free to write?

Oh yes you can indeed make this determination, by using the socket
timeouts via the SO_RCVTIMEO and SO_SNDTIMEO socket options.

Timeouts, when hit, will return -EINTR, whereas lack of buffer space
on a non-blocking socket will return -EAGAIN.

I think you simply are unaware of the facilities available in the BSD
socket API.