Re: [Qemu-devel] Should we auto-generate IDs?

[Programmingkid]

On Aug 27, 2015, at 10:01 AM, Eric Blake wrote:

> On 08/27/2015 07:51 AM, Daniel P. Berrange wrote:
>> On Thu, Aug 27, 2015 at 09:39:10AM -0400, Programmingkid wrote:
>>> 
>>>> Better still might be fixing things to where we add a global command
>>>> line option that outright fails any attempt to create an unnamed object.
>>>> The option would be off by default for back-compat.  But management
>>>> apps like libvirt can turn it on once they are prepared to name every
>>>> object they create (which in turn may imply fixing any remaining
>>>> interfaces that cannot name an object to add in that ability for
>>>> management to pass in a name).  Then there would be no unnamed objects,
>>>> no ambiguity, and no need to generate names.
>>> 
>>> I do agree with giving every device an ID, but I don't think failing if the 
>>> user
>>> forgets to give one is necessary. If libvirt doesn't give devices and ID, it
>>> would probably benefit from having QEMU do it for libvirt.
> 
> No, you're misunderstanding our argument. The moment there is more than
> one device with an auto-assigned name is the moment that management
> doesn't know which device got which name, so it's better for management
> to pick a name in the first place.

Ok.  I see. You might be assuming that QEMU will be the only one to give a 
device
an ID. The ID will ONLY be given if the user or libvirt *doesn't* give it. So 
libvirt would
be able to function just fine with an ID generating system. 

>> 
>> Libvirt always gives an explicit ID.
> 
> Except it doesn't, yet.  Libvirt still needs to be taught to name all
> node devices (and I'm slowly trying to work on patches towards that goal).

Well if Libvirt doesn't give an ID to a device, then it won't be able to use 
monitor
commands that depend on the ID. This sounds like a completely different problem.

> 
>>    It is impossible to rely on QEMU
>> assigning IDs, because there is no reliable way to identify what ID
>> QEMU assigned to each device after the fact. Other management apps
>> would have the same problem, so auto-generated IDs are pretty useless
>> in that respect.
> 
> It's not to say that auto-generated names would be useless when running
> qemu manually from the command line, but I agree that management
> probably can't safely rely on auto-generated names, and therefore
> solving the issue of auto-generating names is less important.

What if we change this so that management applications could actually query
devices and their properties. I'm thinking some kind of JSON-like output.
Something like 'info all-devices'. It prints the device name, location, and ID.
This list should be easy to parse by Libvirt.