netdev - Antw: Re: Q: need effective backlog for listen()

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Message-Id: <5486AC64020000A1000183D0@gwsmtp1.uni-regensburg.de>
Date:	Tue, 09 Dec 2014 08:01:40 +0100
From:	"Ulrich Windl" <Ulrich.Windl@...uni-regensburg.de>
To:	<phil@...i.org>
Cc:	<netdev@...r.kernel.org>
Subject: Antw: Re: Q: need effective backlog for listen()

>>> Philippe Troin <phil@...i.org> schrieb am 08.12.2014 um 17:35 in Nachricht
<1418056540.384.5.camel@...bium.home.fifi.org>:
> On Mon, 2014-12-08 at 13:51 +0100, Ulrich Windl wrote:
>> (not subscribed to the list, plese keep me on CC:)
>> 
>> I have a problem I could not find the answer. I suspect the problem
>> arises from Linux derivating from standard functionality...
>> 
>> I have written a server that should accept n TCP connections at most.
>> I was expecting that the backlog parameter of listen will cause extra
>> connection requests either
>> 1) to be refused
>> or
>> 2) to time out eventually
>> 
>> (The standard seems to say that extra connections are refused)
> 
> The argument to listen() specifies how many connections the system is
> allow to keep waiting to be accept()ed.
> As soon as you accept() the connection, the count is decremented.
> So that won't help for your use case.
> 
>> However none of the above see ms true. Even if my server delays
>> accept()ing new connections, no client ever sees a "connection
>> refused" or "connection timed out". Is there any chance to signal the
>> client that no more connections are accepted at the moment?
> 
> Close the listening socket.  No new connections will be accepted.
> When you reopen the socket for accepting new connections, you may have
> to use SO_REUSEADDR before bind()ing to the port.

This is what I had done, but those connections who are waiting to be accepted: If I close the listening socket, will the clients see a connection abort, or will they see a connection refused?
Connection aborts could confuse clients.

Ulrich


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