Subject: Re: A kexec approach to hibernation
From: Xavier Bestel <xavier.bestel@free.fr>
To: Jeremy Maitin-Shepard <jbms@cmu.edu>
Cc: nigel@nigel.suspend2.net, "Rafael J. Wysocki" <rjw@sisk.pl>,
       linux-kernel@vger.kernel.org, Linus Torvalds <torvalds@osdl.org>,
       Pavel Machek <pavel@ucw.cz>
In-Reply-To: <87r6oimqva.fsf@jbms.ath.cx>
References: <878xb3l888.fsf@jbms.ath.cx> <200706020114.37245.rjw@sisk.pl>
	 <87odjz9qo9.fsf@jbms.ath.cx> <200706020233.44509.rjw@sisk.pl>
	 <87k5un9l4n.fsf@jbms.ath.cx> <1181533248.17758.55.camel@nigel.suspend2.net>
	 <87abv6o7qo.fsf@jbms.ath.cx>
	 <1181576723.11365.45.camel@frg-rhel40-em64t-04>
	 <87r6oimqva.fsf@jbms.ath.cx>
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Date: Mon, 11 Jun 2007 18:03:28 +0200
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On Mon, 2007-06-11 at 11:51 -0400, Jeremy Maitin-Shepard wrote:
> Xavier Bestel <xavier.bestel@free.fr> writes:
> 
> > On Mon, 2007-06-11 at 11:01 -0400, Jeremy Maitin-Shepard wrote:
> >> >> You might claim then that the solution is to simply keep the network
> >> >> driver quiesced or stopped.  But then it is impossible to write the
> >> >> image over the network.  The way to get around this problem is to write
> >> >> the image over the network using a fresh network stack.
> >> 
> >> > Or teach the driver stack about the difference/reset it. Remember that
> >> > even if you get a fresh network stack, you'll still be getting packets
> >> > for the old stack. Getting a new ip (assuming one is available) won't
> >> > stop other connections getting killed, either because we send resets
> >> > from the kexec'd kernel, or because they timeout looking for the old
> >> > ip.
> >> 
> >> I could be mistaken, but I think that bringing up the network interface
> >> with a different IP address would prevent it from reseting existing TCP
> >> connections, because it would never receive the packets for those
> >> existing connections.  
> 
> > That can't work. There are networks where the client must have a fixed
> > IP, or must accept the adress given by dhcp in order to talk to
> > fileservers. And you still have the same mac adress, which may cause
> > problems.
> 
> I wasn't suggesting that using a different IP address would be a general
> solution.  It might be a solution for a few people.
> 
> In general, I'd imagine that most people would not bring up the network
> interface at all, and most of the people that do would bring it up with
> the same IP address, causing some existing TCP connections to possibly
> be reset.
> 
> I think that causing connections to be reset is, however, far better
> than acking packets that are then silently thrown away.

If I were helping you coding I'd suggest to only concentrate on having
your project work on standard filesystems, and then when it works maybe
think about suspending on crypto-over-loop-over-fuse-over-vpn-over-wifi.
But talk is cheap so I'm shutting up. Right now. :)

	Xav


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