On 10/24/2012 05:54 AM, Itamar Heim wrote:
On 10/23/2012 10:52 PM, Ayal Baron wrote:


----- Original Message -----
On Tue, Oct 23, 2012 at 05:53:20AM -0400, Doron Fediuck wrote:


----- Original Message -----
From: "Livnat Peer" <lp...@redhat.com>
To: "Dan Kenigsberg" <dan...@redhat.com>
Cc: engine-de...@ovirt.org, "Genadi Chereshnya"
<gcher...@redhat.com>, vdsm-de...@fedorahosted.org
Sent: Monday, October 22, 2012 8:29:20 AM
Subject: Re: [Engine-devel] [vdsm] unmanaged devices thrown into
'custom' feature

On 21/10/12 23:49, Dan Kenigsberg wrote:
On Sun, Oct 21, 2012 at 11:57:10AM -0400, Eli Mesika wrote:


----- Original Message -----
From: "Yair Zaslavsky" <yzasl...@redhat.com>
To: "Livnat Peer" <lp...@redhat.com>
Cc: "Genadi Chereshnya" <gcher...@redhat.com>,
engine-de...@ovirt.org, vdsm-de...@fedorahosted.org
Sent: Sunday, October 21, 2012 5:38:54 PM
Subject: Re: [Engine-devel] unmanaged devices thrown into
'custom' feature



----- Original Message -----
From: "Livnat Peer" <lp...@redhat.com>
To: "Dan Kenigsberg" <dan...@redhat.com>
Cc: "Genadi Chereshnya" <gcher...@redhat.com>,
engine-de...@ovirt.org, vdsm-de...@fedorahosted.org
Sent: Sunday, October 21, 2012 5:18:31 PM
Subject: Re: [Engine-devel] unmanaged devices thrown into
'custom'
feature

On 21/10/12 16:42, Dan Kenigsberg wrote:
I have just noticed that when a VM is started for the
second
time,
Engine
issues the "create" vdsm verb with some information
regarding
"unmanaged" devices (an example is shown below[1]) in the
'custom'
propery bag.

I'm surprised about this, as I was not aware of this usage
of
the
'custom' dictionary, and Vdsm is not doing anything with
the
data.


If I recall correctly the idea of passing the unmanaged
devices
data
in
the custom property was to enable managing stable device
addresses
in
the hooks (to devices that were added to the VM via hooks
from
the
first
place), so this info is there not for VDSM use.
For example if you add a device in a hook it will be kept in
the
engine
as a non managed device. later when starting the VM again
you
would
like
to assign the same device address to your device, and you
can do
so
because you have access to the original address in the
custom
properties
of the VM.

This is exactly what Eli has explained Gendai and Dan today.

(I was asking here because I did not understand the verbal
explanation.)


This is taken from the Stable Device Address design in
http://wiki.ovirt.org/wiki/Features/Design/StableDeviceAddresses

Unmanaged Device
-----------------
Unmanaged Device will be supported in the new format and will
include all unhandled devices as sound/controller/etc and
future
devices. Those devices will be persistent and will have Type ,
SubType (device specific) and an Address. For 3.1 an unmanaged
Device is not exposed to any GUI/REST API. Unmanaged devices
are
passed to vdsm inside a Custom property. VDSM in it turn is
passing this as is for possible hook processing.

Thanks for the elaboration. Too bad that I've missed this issue
before.

Are you aware of any hook making use of this?  I hope that hook
writers
are not using APIs that are not documented in vdsmd(8).

It seems as a classic case where a generic bag interface is
coerced
into
an awkward partially-documented interface.

I think that a better approach would have been to pass all
devices
(managed and unmanaged alike) in the 'devices' property, and
let
vdsm
expose whatever is needed to the before_vm_start hook.

Maybe we can still do this.

That was the original idea but Ayal objected and I think Igor did
not
like it as well...


+2.
The original design had an 'unmanaged' (or generic) device type,
and all
devices should have been normalized. But as explained, this was
strongly
rejected in the VDSM side, causing Eli write some special handling
for this anomaly.

Can someone (Ayal?) explain the rejection on Vdsm side?
Hiding part of the API in the custom propery bag requires strong
reasoning indeed.

It's not hiding anything.
Today vdsm passes the libvirt xml to the hooks + the custom properties.
If you pass 'non-managed devices' through the devices API then basically you're saying to vdsm 'here is a bunch of things I want you to ignore but be a sport and pass it on to the hooks'. Last I checked, that mechanism is custom properties. I don't see any reason to add another one.

1. this means hooks don't actually get the unmanaged devices today?

Yes they do, in the custom properties.

2. custom property are to pass parameters to the hook user can reasonably control. device management should not be part of that if not strictly related to the hook (from user's side).

No problem, then we should not pass these devices at all.

3. I'm guessing (didn't get this first time i read your answer), you are hinting the unmanaged devices should be passed as a custom property to vdsm, auto generated by engine?
I'm not saying this is what *should* happen, I'm saying this is what *is* happening.
vdsm passes to hooks 2 things:
1. libvirt xml (which obviously would not contain 'unmanaged devices')
2. whatever is passed in 'custom properties' by engine (afaik engine passes the entire bag of properties to all hooks, relevant or not). For some reason someone insisted on being able to pass all the devices engine gets back from the vm back to the hooks even if these were not passed by engine when starting up the VM (iirc the idea was that if a hook adds a device in this way it is able to know what address the device got on previous run and maintain stable device addresses). What I opposed originally was the ability when running a VM to pass in the devices section a list of devices that should not be attached to the vm (i.e. 'here is a list of devices that I don't want you to use devices in the vm'). I think it's self evident why I was against this and why I still oppose the idea. If you want a bag of rubbish to pass to hooks then that is 'custom properties'. No need to make the API any uglier. Personally, I think that any hook that adds devices should be able to manage addresses (e.g. choose an empty address, or add a post hook for running VMs and persist the info). In fact, this is just another case where hooks are used in the entirely wrong place. The place to do this is in the engine with an engine side pre-run vm hook and then any devices you want to add to the VM become 'managed' as far as vdsm is concerned.

Note that from what I could understand, Dan was really trying to understand why we don't 'manage' these devices (actually passing them to libvirt on subsequent runs of the VM).


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