Re: [PATCH] Add timeout to xenconsole to fix race condition in xm create -c

[Anthony Liguori <aliguori@us.ibm.com>]

Christian Limpach wrote:

>On 8/30/05, Anthony Liguori <aliguori@us.ibm.com> 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/<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
>tree.
>  
>
Rusty had some objections to this originally--this is why its not there 
now.  Rusty?

Regards,

Anthony Liguori

>    christian
>
>  
>