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Re: [Xen-devel] [PATCH] Add timeout to xenconsole to fix race condition

To: Anthony Liguori <aliguori@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Add timeout to xenconsole to fix race condition in xm create -c
From: Christian Limpach <christian.limpach@xxxxxxxxx>
Date: Wed, 31 Aug 2005 11:31:43 +0100
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 8/30/05, Anthony Liguori <aliguori@xxxxxxxxxx> wrote:
> This should address the problems people are having now.
> Wait a little bit for tty to appear.  There is a race condition that
> occurs after xend creates a domain.  Since no event triggers consoled to
> re-examine existing domains, we'll often not see the new pty by the time
> we're here.  Since consoled sleeps for 2 second periods, a 5 second
> timeout should keep us covered.

I've applied this with slighly changed comments since xenconsoled now
uses watches and should setup the tty almost immediately.  The race
still exists though.

> A xenstore watch isn't much better since we don't want to block forever
> if given an invalid domain or worse yes, a domain that someone else has
> connected to.

It would improve the responsiveness but a timeout is still needed for
the reasons you pointed out.

Finally, there's still an issue with storing the console tty
information in /console/<domid> -- there might be stale data from a
previous domain having the same domid and the client might run before
the console daemon has rewritten the tty entry.  I think this is best
fixed by moving the console tty information into the domain's /domain


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