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On Fri, Mar 4, 2016 at 1:34 PM, Valeriy Ponomaryov
<vponomaryov at mirantis.com> wrote:
> John,
>
> each instance of manila-share service will perform "ensure_share" operation
> for each "share instance" that is located at
> "hostname at driver_config_group_name".
> So, only one driver is expected to run "ensure_share" for some "share
> instance", because each instance of a driver will have its own unique value
> of "hostname at driver_config_group_name".

Thanks - so if I understand you correctly, each share instance is
uniquely associated with a single instance of the driver at one time,
right?  So while I might have two concurrent calls to ensure_share,
they are guaranteed to be for different shares?

Is this true for the whole driver interface?  Two instances of the
driver will never both be asked to do operations on the same share at
the same time?

John



> Valeriy
>
> On Fri, Mar 4, 2016 at 3:15 PM, John Spray <jspray at redhat.com> wrote:
>>
>> On Fri, Mar 4, 2016 at 12:11 PM, Shinobu Kinjo <shinobu.kj at gmail.com>
>> wrote:
>> > What are you facing?
>>
>> In this particular instance, I'm dealing with a case where we may add
>> some metadata in ceph that will get updated by the driver, and I need
>> to know how I'm going to be called.  I need to know whether e.g. I can
>> expect that ensure_share will only be called once at a time per share,
>> or whether it might be called multiple times in parallel, resulting in
>> a need for me to do more synchronisation a lower level.
>>
>> This is more complicated than locking, because where we update more
>> than one thing at a time we also have to deal with recovery (e.g.
>> manila crashed halfway through updating something in ceph and now I'm
>> recovering it), especially whether the places we do recovery will be
>> called concurrently or not.
>>
>> My very favourite answer here would be a pointer to some
>> documentation, but I'm guessing much this stuff is still at a "word of
>> mouth" stage.
>>
>> John
>>
>> > On Fri, Mar 4, 2016 at 9:06 PM, John Spray <jspray at redhat.com> wrote:
>> >> Hi,
>> >>
>> >> What expectations should driver authors have about multiple instances
>> >> of the driver being instantiated within different instances of
>> >> manila-share?
>> >>
>> >> For example, should I assume that when one instance of a driver is
>> >> having ensure_share called during startup, another instance of the
>> >> driver might be going through the same process on the same share at
>> >> the same time?  Are there any rules at all?
>> >>
>> >> Thanks,
>> >> John
>> >>
>> >>
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>> >
>> >
>> > --
>> > Email:
>> > shinobu at linux.com
>> > GitHub:
>> > shinobu-x
>> > Blog:
>> > Life with Distributed Computational System based on OpenSource
>> >
>> >
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>
>
>
> --
> Kind Regards
> Valeriy Ponomaryov
> www.mirantis.com
> vponomaryov at mirantis.com
>
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