[libvirt] [PATCH v2 3/3] conf: Allow users to define UUID for devices

Michal Privoznik mprivozn at redhat.com
Tue Oct 31 06:04:35 UTC 2017

On 10/30/2017 11:12 PM, Jim Fehlig wrote:
> On 10/30/2017 03:31 PM, Jim Fehlig wrote:
>> On 10/03/2017 07:53 AM, Daniel P. Berrange wrote:
>>> On Tue, Oct 03, 2017 at 02:11:44PM +0200, Martin Kletzander wrote:
>>>> On Tue, Oct 03, 2017 at 12:58:59PM +0200, Michal Privoznik wrote:
>>>>> https://bugzilla.redhat.com/show_bug.cgi?id=1434451
>>>>> It comes handy for management application to be able to have a
>>>>> per-device label so that it can uniquely identify devices it
>>>>> cares about. The advantage of this approach is that we don't have
>>>>> to generate aliases at define time (non trivial amount of work
>>>>> and problems). The only thing we do is parse the user supplied
>>>>> UUID and format it back. For instance:
>>>>>     <disk type='block' device='disk'>
>>>>>       <driver name='qemu' type='raw'/>
>>>>>       <source dev='/dev/HostVG/QEMUGuest1'/>
>>>>>       <target dev='hda' bus='ide'/>
>>>>>       <uuid>1efaf08b-9317-4b0f-b227-912e4bd9f483</uuid>
>>>>>       <address type='drive' controller='0' bus='0' target='0'
>>>>> unit='0'/>
>>>>>     </disk>
>>>>> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>>>>> ---
>>>>> This is just a very basic implementation. If I get a green light on
>>>>> this, I can
>>>>> implement the feature further, i.e. allow device lookup on the
>>>>> UUID. For
>>>>> instance:
>>>>> virsh domiftune fedora $UUID $bandwidth
>>> <snip>
>>> I'm thinking that part of the problem we're having with agreeing how to
>>> deal with this RFE is that we're over-analysing semantics, by wondering
>>> whether its a unique name or UUID, its relation to alias, whether it has
>>> bearing on APIs.
>>> How about we change tack, and do what we did when we needed application
>>> specific information at the top level - just declare a general purpose
>>> <metadata> element and say it is a completely opaque blob. Libvirt will
>>> *never* do anything with it, other than to preserve it exactly as is.
>>> No API will ever use the metadata in any way. Libvirt will never try to
>>> guarantee uniqueness of metadata for each device. It can be JSON or a
>>> gziped microsoft word document for all we care. Entirely upto the app
>>> developer to decide what metadata is saved and guarantee uniqueness if
>>> they so desired.
>> I vote for the opaque blob since it would be helpful for my use case
>> described here
>> https://www.redhat.com/archives/libvir-list/2017-October/msg01329.html
> I should have read further ahead in my mail backlog, where I would have
> discovered this has already be solved using <alias>. That's fine, but
> I'm curious why the domain of permissible characters is restricted?
> Could it include ():;/ ?

Currently, only: a-zA-Z0-9_- is allowed. This is because in qemu driver
aliases are put onto qemu cmd line where only limited set of characters
is allowed. However, the check for that could be moved to drivers so
that each driver can define its own set of allowed characters.


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