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

["Stephen C. Tweedie" <sct@xxxxxxxxxx>]

Hi,

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':
        start_xenstored()
        start_consoled()
        start_blktapctrl()
        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.

--Stephen



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