From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [PATCH] Add timeout to xenconsole to fix race condition in xm create -c Date: Wed, 31 Aug 2005 15:42:52 -0500 Message-ID: <4316164C.4050509@us.ibm.com> References: <4314D5CC.3020107@us.ibm.com> <3d8eece20508310331244b808@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <3d8eece20508310331244b808@mail.gmail.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Christian.Limpach@cl.cam.ac.uk Cc: Rusty Russell , xen-devel List-Id: xen-devel@lists.xenproject.org Christian Limpach wrote: >On 8/30/05, Anthony Liguori 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. > > Yes, what we really want is a event-dispatch mechanism. It's something we've talked about a bit here but without flushing out any sort of actual design. >>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/ -- 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 >tree. > > Rusty had some objections to this originally--this is why its not there now. Rusty? Regards, Anthony Liguori > christian > > >