[Xen-devel] Re: problem restarting xenstored

[Anthony Liguori <anthony@xxxxxxxxxxxxx>]

Jan Beulich wrote:
> As any other daemon, I'd assume it should be possible to restart xenstored (i.e.
> if it crashed or if, during development, a fix was made to it that needs to be
> tested). However, as I learned after over a day of digging, things don't work
> anymore after doing so: Since the watches are transient, they're lost with the
> daemon going away.
> Right now I specifically need this in already mentioned scenarios where I want
> to not touch the base installation of a system or need parallel versions 
> installed,
> but as described above I see the general issue broader (e.g. it obviously
> doesn't make sense to try to start xenstored from 'xend restart' because of
> described problems).
> For some reason, this wasn't a big problem when the base installation was
> 3.0.2-based - apparently something else prevented xenbus' event channel
> handler to get triggered when the 3.0.2 xenstored loaded, and hence all the
> needed watches got installed only when the proper version was loaded the
> first time, giving the impression that things work as expected (until perhaps
> reloading it a second time).
>
> Any suggestions on how to overcome that would be very welcome.
Watches have to become persistent in XenStore.  This has been a TODO 
since the very beginning that noone has ever tackled.  Currently watches 
are only stored in memory so if you restart XenStore any active watch 
will never be fired.
How much of an effect this has on your system depends on the state any 
running domains are in and what functions you use.
Regards,

Anthony Liguori

> Thanks, Jan

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