[ovs-dev] Combining monitor2 and monitor_cond methods

Liran Schour LIRANS at il.ibm.com
Mon Nov 9 19:04:48 UTC 2015


Andy Zhou <azhou at nicira.com> wrote on 09/11/2015 07:49:37 PM:
>
> >> On Wed, Nov 4, 2015 at 5:22 AM, Liran Schour <LIRANS at il.ibm.com> 
wrote:
> >> > In order not to have 2 new monitor methods, maybe we should combine 
them
> >> > into a single method.
> >> >
> >> > However, as I thought on this, monitor_cond without any conditions
> >> > should
> >> > not send any updates at all. A typical usage will be in OVN when
> >> > ovn-controller will open a monitor_cond session with empty
> >> > "where"condition
> >> > array and when VMs are deployed on this host, it will add 
conditions by
> >> > monitor_cond_change method and by that will get all the updates 
relevant
> >> > to
> >> > that specific host.
> >> >
> >> > As I see it, we have here 2 options:
> >> > 1. monitor_cond without any "where" value will behave as the 
proposed
> >> > monitor2 method - send updates upon all rows using update2
> >> > notifications.
> >> >     monitor_cond with "where" value that is an empty array will not 
send
> >> > any
> >> > updates at all till conditions are added by monitor_cond_change 
method.
> >> >
> >> This can work, but the API seems subtle. So I'd prefer to explore the
> >> next option more.
> >>
> >> > 2. monitor_cond always sends updates. If there is no "where" value 
or it
> >> > is
> >> > an empty array, updates on all rows will be sent using update2
> >> > notifications. In this case a client will not be able to open a 
monitor
> >> > session and expect no updates at all like written in the usage 
above.
> >> >
> >>
> >> This seems natural.
> >>
> >> If no updates are expected at the beginning, could we come up with a
> >> where condition that
> >> will not generate any updates? Like "where false".
> >>
> >
> > It can work if we can define "where" to be an array of <condition> and
> > boolean values. For example: "where" : [false, <condition>*]. Since 
the
> > monitor_cond will monitor any row that match at least one of the 
conditions,
> > if we will have "where" : [false] no row will be monitored.
> 
> This solution looks good to me. May be we can define <condition> as 
either
> a 3-element array or a JSON boolean. For completeness, we can define
> where : [] to be the same as where : [true]
> 

OK, I will work on a combined patch series based on your monitor2 branch 
with the
Bug fix. However it seems that I will not be able to make it till after 
the OVS 
conference.




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