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

To: "Stephen C. Tweedie" <sct@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: blktap race against xenstore startup
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Thu, 28 Sep 2006 20:15:46 -0500
Cc: Andrew Warfield <andrew.warfield@xxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Julian Chesterfield <jac90@xxxxxxxxx>
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Stephen C. Tweedie wrote:

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.

Ah, I see. So it sounds like blktapctrl ought to be setting a watch for /local/domain.


Anthony Liguori


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