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Re: [Qemu-devel] Should we auto-generate IDs?
From: |
Programmingkid |
Subject: |
Re: [Qemu-devel] Should we auto-generate IDs? |
Date: |
Thu, 27 Aug 2015 11:58:22 -0400 |
On Aug 27, 2015, at 11:40 AM, Jeff Cody wrote:
> On Thu, Aug 27, 2015 at 11:20:20AM -0400, Programmingkid wrote:
>>
>> On Aug 27, 2015, at 10:42 AM, Daniel P. Berrange wrote:
>>
>>> On Thu, Aug 27, 2015 at 10:34:05AM -0400, Programmingkid wrote:
>>>>
>>>> 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.
>>>
>>> If breaking existing apps was OK, we would just mandate that users always
>>> provide an ID which trivially avoids the problem of not having an ID to
>>> use when deleting the object. We want to /avoid/ breaking existing apps
>>> though, so saying an app should change the way it works in order to cope
>>> with QEMU's ID generation is not appropriate. Hence any use of
>>> auto-generated
>>> IDs, must use a separate namespace to avoid such clashes.
>>
>> This is making the assumption that an auto-generated ID system would break
>> any existing
>> application. We don't know this. In fact, I predict a future patch would
>> allow existing
>> applications to continue running without modification. The patch would be a
>> win-win
>> for both users and any management application.
>>
>
> Daniel's assumption is spot on. The idea of "QEMU can just say sorry
> that ID is already taken" will break existing applications.
>
> But we are all striving to make your prediction true, with this very
> conversation.
Ok, it sounds like some are concerned that Libvirt would not be able to work
with this
feature. Let me ask you this: does Libvirt interact with QEMU before the user
has a
chance to do so? If the answer is yes, then that means Libvirt will have
finished
creating all its devices with their ID's long before the user has a chance to
enter
his own devices.
- Re: [Qemu-devel] Should we auto-generate IDs?, (continued)
- Re: [Qemu-devel] Should we auto-generate IDs?, Programmingkid, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Daniel P. Berrange, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Programmingkid, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Eric Blake, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Programmingkid, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Daniel P. Berrange, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Programmingkid, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Jeff Cody, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?,
Programmingkid <=
- Re: [Qemu-devel] Should we auto-generate IDs?, Daniel P. Berrange, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Programmingkid, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Daniel P. Berrange, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Programmingkid, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Programmingkid, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Jeff Cody, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Eric Blake, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Jeff Cody, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Daniel P. Berrange, 2015/08/27
- Re: [Qemu-devel] Should we auto-generate IDs?, Programmingkid, 2015/08/27