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[Xen-devel] Re: problem restarting xenstored

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 
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.


Anthony Liguori

Thanks, Jan

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