[ovs-dev] Combining monitor2 and monitor_cond methods

[Liran Schour]

Andy Zhou <azhou at nicira.com> wrote on 09/11/2015 10:50:25 PM:

> 
> On Mon, Nov 9, 2015 at 11:04 AM, Liran Schour <LIRANS at il.ibm.com> wrote:
> > 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.
> That's fine. Are you going to OVS CON? if you do, we can also meet and
> discuss more if you'd like.
> 

Yes I will be at the OVS CON. I will be glad to meet and discuss.