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Re: [Xen-devel] Re: blktap race against xenstore startup

To: Anthony Liguori <aliguori@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: blktap race against xenstore startup
From: "Stephen C. Tweedie" <sct@xxxxxxxxxx>
Date: Fri, 29 Sep 2006 00:23:58 +0100
Cc: Andrew Warfield <andrew.warfield@xxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Julian Chesterfield <jac90@xxxxxxxxx>
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On Thu, 2006-09-28 at 17:45 -0500, Anthony Liguori wrote:

> > Ugh.  There has got to be a better way to synchronise with the initial
> > population of the dom0 information into xenstore, surely?  Has no other
> > component of the Xen stack ever seen this before?
> I don't know how blktap is launched right now, but the same problem has 
> occurred in the past for other daemons (like xenconsoled).
> xenstored won't close standard output until it's ready to receive 
> connections.  xend start will wait to start the other daemons until 
> xenstored is ready.  How does blktap get spawned?

It (the blktapctrl userland daemon) gets execve'd by xend:

    elif sys.argv[1] == 'start':
        return daemon.start()

The problem is not that xenstored is dead: it's alive and running, it
just hasn't had the /local/domain tree filled in, so it returns ENOENT.
xenstored *is* ready, but that's not enough.


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