On Tue, Dec 04, 2012 at 03:10:00PM -0600, Adam Litke wrote:
> On Tue, Dec 04, 2012 at 12:32:34PM -0500, Antoni Segura Puimedon wrote:
> > Hi list!
> > 
> > We are working on the new 3.2 feature for adding support for updating VM
> > devices, more specifically at the moment network devices.
> > 
> > There is one point of the design which is not yet consensual and we'd 
> > need to agree on a proper and clean design that would satisfy us all:
> > 
> > My current proposal, as reflected by patch:
> >    http://gerrit.ovirt.org/#/c/9560/5/vdsm_api/vdsmapi-schema.json
> > and its parent is to have a linkActive boolean that is true for link
> > status 'up' and false for link status 'down'.
> > 
> > We want to support a none (dummy) network that is used to dissociate vnics
> > from any real network. The semantics, as you can see in the patch are that
> > unless you specify a network, updateDevice will place the interface on that
> > network. However, Adam Litke argues that not specifying a network should
> > keep the vnic on the network it currently is, as network is an optional
> > parameter and 'linkActive' is also optional and has this "preserve current
> > state" semantics.
> > 
> > I can certainly see the merit of what Adam proposes, and the implementation
> > would be that linkActive becomes an enum like so:
> > 
> > {'enum': 'linkState'/* or linkActive */ , 'data': ['up', 'down', 
> > 'disconnected']}
> > 
> > With this change, network would only be changed if one different than the 
> > current
> > one is specified and the vnic would be taken to the dummy bridge when the 
> > linkState
> > would be set to 'disconnected'.
> > 
> > There is also an objection, raised by Adam about the semantics of 
> > portMirroring.
> > The current behavior from my patch is:
> > 
> > portMirroring is None or is not set -> No action taken.
> > portMirroring = [] -> No action taken.
> > portMirroring = [a,b,z] -> Set port mirroring for nets a,b and z to the 
> > specified vnic.
> > 
> > His proposal is:
> > portMirroring is None or is not set -> No action taken.
> > portMirroring = [] -> Unset port mirroring to the vnic that is currently 
> > set.
> > portMirroring = [a,b,z] -> Set port mirroring for nets a,b and z to the 
> > specified vnic.
> > 
> > I would really welcome comments on this to have finally an agreement to the 
> > api for this
> > feature.

ack for portMirroring semantics. [] must mean "no networks are mirrored
to this nic".

I am less sure about allowing a "No action taken" semantics, as it
add the current state to the API and complicates it. I'd also like to
keep the updateDevice API as similar as possible to vmCreate one.

However, we already have defaults in vmCreate (for pci address
allocation, portmirroring off) so I suppose I can join Adam here.

But this does not mean we should allow a default everywhere. I find it
unintuitive to have a linkState=disconnected, as setting this attribute
should clear the network attribute - they become non-orthogonal. So in
my opinion, a missing network should mean "nic is connected to no
network" rather than "keep current connection".

Dan.
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