netdev - Re: Add a SOCK_DESTROY operation to close sockets from userspace

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Message-ID: <1447859760.22599.149.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 18 Nov 2015 07:16:00 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Lorenzo Colitti <lorenzo@...gle.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
	Erik Kline <ek@...gle.com>,
	Maciej Żenczykowski <maze@...gle.com>,
	Dmitry Torokhov <dtor@...gle.com>
Subject: Re: Add a SOCK_DESTROY operation to close sockets from userspace

On Wed, 2015-11-18 at 15:56 +0100, Hannes Frederic Sowa wrote:
> On Wed, Nov 18, 2015, at 15:45, Lorenzo Colitti wrote:
> > On Wed, Nov 18, 2015 at 10:31 PM, Hannes Frederic Sowa
> > <hannes@...essinduktion.org> wrote:
> > > I was not saying using tcp_close literally, sorry for not making that
> > > clear, but just model the state transitions after tcp_close. At least it
> > > seems like a normal close to me.
> > 
> > But it shouldn't be a normal close. Consider calling SOCK_DESTROY on a
> > socket that is streaming data to a peer. If SOCK_DESTROY results in
> > the kernel sending a FIN, the remote side might think that the sender
> > closed the connection gracefully, even though the local side aborted
> > the connection.
> 
> Oh, yes, I understand. The connection wasn't closed by the application
> but by the administrator forcefully. So we should never indicate a
> successful TCP shutdown with FIN but with RST. A TIME_WAIT period
> actuallty still seems useful to me, maybe with different semantics, only
> RST incoming data?

There is some confusion.

TIME_WAIT are used to be able to send ACK packets to incoming valid
packets.

To send RST, you need nothing at all.

TIME_WAIT are hints for normal ending connections, to handle old packets
(and or duplicates)



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