[ovs-dev] Combining monitor2 and monitor_cond methods

[Andy Zhou]

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.