netdev - Re: sendfile()? Re: SO_LINGER dead: I get an immediate RST on 2.6.24?

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Message-ID: <Pine.LNX.4.64.0901121111420.24748@wrl-59.cs.helsinki.fi>
Date:	Mon, 12 Jan 2009 11:18:48 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Bill Fink <billfink@...dspring.com>
cc:	Evgeniy Polyakov <zbr@...emap.net>,
	bert hubert <bert.hubert@...herlabs.nl>,
	"H. Willstrand" <h.willstrand@...il.com>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: sendfile()? Re: SO_LINGER dead: I get an immediate RST on 2.6.24?

On Sun, 11 Jan 2009, Bill Fink wrote:

> On Mon, 12 Jan 2009, Evgeniy Polyakov wrote:
> 
> > On Mon, Jan 12, 2009 at 12:08:24AM +0100, bert hubert (bert.hubert@...herlabs.nl) wrote:
> > > I fully understand. Sometimes I have to talk to stupid devices though. What
> > > I do find is the TCP_INFO ioctl, which offers this field in struct tcp_info:
> > > 
> > >         __u32   tcpi_unacked;
> > > 
> > > Which comes from:
> > > 
> > > struct tcp_sock {
> > > ...
> > >         u32     packets_out;    /* Packets which are "in flight"        */
> > > ...
> > > }
> > > 
> > > If this becomes 0, perhaps this might tell me everything I sent was acked?
> > 
> > 0 means that there are noin-flight packets, which is effectively number
> > of unacked packets. So if your application waits for this field to
> > become zero, it will wait for all sent packets to be acked.
> 
> I use this type of strategy in nuttcp, and it seems to work fine.
> I have a loop with a small delay and a check of tcpi_unacked, and
> break out of the loop if tcpi_unacked becomes 0 or a defined timeout
> period has passed.

Checking tcpi_unacked alone won't be reliable. The peer might be slow 
enough to advertize zero window for a short period of time and during 
that period you would have packets_out zero...


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