[ovirt-devel] feature review - ReportGuestDisksLogicalDeviceName

[Michal Skrivanek]

On Sep 2, 2014, at 21:03 , Nir Soffer <nsoffer at redhat.com> wrote:

> ----- Original Message -----
>> From: "Michal Skrivanek" <mskrivan at redhat.com>
>> To: "Liron Aravot" <laravot at redhat.com>, "Dan Kenigsberg" <danken at redhat.com>, "Federico Simoncelli"
>> <fsimonce at redhat.com>, "Vinzenz Feenstra" <vfeenstr at redhat.com>
>> Cc: users at ovirt.org, devel at ovirt.org
>> Sent: Tuesday, September 2, 2014 3:29:57 PM
>> Subject: Re: [ovirt-devel] feature review - ReportGuestDisksLogicalDeviceName
>> 
>> 
>> On Sep 2, 2014, at 13:11 , Liron Aravot <laravot at redhat.com> wrote:
>> 
>>> 
>>> 
>>> ----- Original Message -----
>>>> From: "Federico Simoncelli" <fsimonce at redhat.com>
>>>> To: devel at ovirt.org
>>>> Cc: "Liron Aravot" <laravot at redhat.com>, users at ovirt.org,
>>>> smizrahi at redhat.com, "Michal Skrivanek"
>>>> <mskrivan at redhat.com>, "Vinzenz Feenstra" <vfeenstr at redhat.com>, "Allon
>>>> Mureinik" <amureini at redhat.com>, "Dan
>>>> Kenigsberg" <danken at redhat.com>
>>>> Sent: Tuesday, September 2, 2014 12:50:28 PM
>>>> Subject: Re: feature review - ReportGuestDisksLogicalDeviceName
>>>> 
>>>> ----- Original Message -----
>>>>> From: "Dan Kenigsberg" <danken at redhat.com>
>>>>> To: "Liron Aravot" <laravot at redhat.com>
>>>>> Cc: users at ovirt.org, devel at ovirt.org, smizrahi at redhat.com,
>>>>> fsimonce at redhat.com, "Michal Skrivanek"
>>>>> <mskrivan at redhat.com>, "Vinzenz Feenstra" <vfeenstr at redhat.com>, "Allon
>>>>> Mureinik" <amureini at redhat.com>
>>>>> Sent: Monday, September 1, 2014 11:23:45 PM
>>>>> Subject: Re: feature review - ReportGuestDisksLogicalDeviceName
>>>>> 
>>>>> On Sun, Aug 31, 2014 at 07:20:04AM -0400, Liron Aravot wrote:
>>>>>> Feel free to review the the following feature.
>>>>>> 
>>>>>> http://www.ovirt.org/Features/ReportGuestDisksLogicalDeviceName
>>>>> 
>>>>> Thanks for posting this feature page. Two things worry me about this
>>>>> feature. The first is timing. It is not reasonable to suggest an API
>>>>> change, and expect it to get to ovirt-3.5.0. We are two late anyway.
>>>>> 
>>>>> The other one is the suggested API. You suggest placing volatile and
>>>>> optional infomation in getVMList. It won't be the first time that we
>>>>> have it (guestIPs, guestFQDN, clientIP, and displayIP are there) but
>>>>> it's foreign to the notion of "conf" reported by getVMList() - the set
>>>>> of parameters needed to recreate the VM.
>>> 
>>> The fact is that today we return guest information in list(Full=true), We
>>> decide on it's notion
>>> and it seems like we already made our minds when guest info was added there
>>> :) . I don't see any harm in returning the disk mapping there
>>> and if we'll want to extract the guest info out, we can extract all of it
>>> in later version (4?) without need for BC. Having
>>> the information spread between different verbs is no better imo.
>>>> 
>>>> At first sight this seems something belonging to getVmStats (which
>>>> is reporting already other guest agent information).
>>>> 
>>> 
>>> Fede, I've mentioned in the wiki, getVmStats is called by the engine every
>>> few seconds and therefore that info
>>> wasn't added there but to list() which is called only when the hash is
>>> changed. If everyone is in for that simple
>>> solution i'm fine with that, but Michal/Vincenz preferred it that way.
>> 
>> yes, that was the main reason me and Vinzenz suggested to use list(). 15s is
>> a reasonable compromise, IMHO.
>> And since it's also reported by guest agent in a similar manner (and actually
>> via the same vdsm<->ga API call) as other guest information I think it
>> should sit alongside guestIPs, FQDN, etc…
>> 
>> Maybe not the best place, but I would leave that for a bigger discussion
>> if/when we want to refactor reporting of the guest agent information
> 
> Given that we are late, adding disk mapping where other guest info is
> in a backward compatible way looks reasonable.
> 
> Did you consider adding a new verb for getting guest information?
> This 
> verb can be called once after starting/recovering a vm, and then only when
> guest info hash changes (like the xml hash).

yes, was considered but turned down. 
Main reason is an additional overhead and pollution of the API for a tiny little item which is in the same group of guest agent reported items. It doesn't make sense to introduce an inconsistency just this one item.
Refactoring of the frequency of what we report is indeed long overdue, but we shouldn't start here…(the first and most offending is still the application list)

Thanks,
michal

> 
> Nir
> 
>