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

[Programmingkid]

On Aug 27, 2015, at 10:02 AM, Eric Blake wrote:

> On 08/27/2015 07:56 AM, Programmingkid wrote:
> 
>>> If we did have auto-generated names, we would need to come up with a
>>> scheme that is not going to clash with any existing naming that users
>>> of QEMU may already be doing, otherwise we risk causing a regression.
>>> Something as simple as what you suggest has non-trivial chance of
>>> clashing.
>> 
>> Actually there is a way to prevent clashing. When QEMU auto-generates a
>> name, it could scan all the ID's to see if there is a clash. If the ID is 
>> already
>> taken, just increment the ID until it is detected to be unique. The previous
>> threads on this subject has patches that did just that. This means that a
>> ID scheme that is just a single number would work without clashes. 
> 
> No, because you cannot predict what FUTURE names the user will request.
> The name generated by qemu must be IMPOSSIBLE to request manually, and
> not just one that happens not to clash at the current moment.

If I add a device with an ID that is taken, QEMU can just say sorry that ID is 
already
taken. I could just increment the ID myself until I find one that is unique. It 
is a
simple algorithm. Maybe you are talking about some program that has hard coded
ID's it depends on. If that is the case, perhaps this management program could 
be
made to be a little flexible. Or use a 160-bit SHA-1 generated ID that is 
virtually
guaranteed to always be unique.

What about this scenario. There are 1 million devices added to QEMU, and I need 
to
add a device with an ID. Each of the 1 million devices already have an ID. If I 
don't want
to try to find a unique ID myself, having QEMU do it for me would make things 
much easier.
How would I find this device's ID? I could issue some kind of monitor command 
that gives me
the ID. This feature doesn't appear to be implemented yet. This will change. A 
future
' info all-devices '  command would probably do it.