Re: Re: blktap race against xenstore startup

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

Stephen C. Tweedie wrote:
> 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.
>   

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

Regards,

Anthony Liguori

> --Stephen
>
>
>