hi,
thanks for the detailed explanation!
YAMAMOTO Takashi
> Sure.
>
> Here's a sample vdi_create call:
>
> <methodCall>
> <methodName>vdi_create</methodName>
> <params>
> <param>
> <value>
> <struct>
> <member>
> <name>host_ref</name>
> <value>OpaqueRef:1a69645b-8981-b076-3439-ae40715168cb</value>
> </member>
> <member>
> <name>command</name>
> <value>vdi_create</value>
> </member>
> <member>
> <name>args</name>
> <value>
> <array>
> <data>
> <value>104857600</value>
> </data>
> </array>
> </value>
> </member>
> <member>
> <name>device_config</name>
> <value>
> <struct>
> <member>
> <name>SRmaster</name>
> <value>true</value>
> </member>
> <member>
> <name>device</name>
> <value>/dev/sda3</value>
> </member>
> </struct>
> </value>
> </member>
> <member>
> <name>session_ref</name>
> <value>OpaqueRef:bb4ba642-1427-513d-f398-d07a07b56157</value>
> </member>
> <member>
> <name>sr_ref</name>
> <value>OpaqueRef:2fa93049-ee45-284c-e657-067e0c181789</value>
> </member>
> <member>
> <name>sr_uuid</name>
> <value>668da5be-32e8-1fac-6d1f-7590e2fa1c09</value>
> </member>
> <member>
> <name>vdi_sm_config</name>
> <value>
> <struct/>
> </value>
> </member>
> <member>
> <name>subtask_of</name>
> <value>OpaqueRef:cb7e281b-8430-1979-e36a-5dd17dab5c72</value>
> </member>
> </struct>
> </value>
> </param>
> </params>
> </methodCall>
>
> There is only a sr_uuid here, and no vdi_uuid at all.
>
> The way it works is:
>
> 1. Xapi receives a VDI.create XenAPI call
> 2. Xapi checks the SR, figures out which host should do the operation, checks
> it has its PBD attached and various other checks
> 3. On the host in question, Xapi calls out to the SM backend to do a
> vdi_create operation. It only tells the SM backend the size of the disk and
> the 'sm_config' map.
> 4. The SM backend creates the actual object - a vhd, or an ISO, or an LVM
> partition or whatever
> 5. The SM backend then introduces a VDI record using the XenAPI call
> 'VDI.db_introduce' - this API call takes a uuid which was made up by the SM
> backend. Xapi ensures that the uuid is globally unique and that the location
> field is unique within the SR.
> 6. The SM backend returns control to Xapi, returning a small structure
> containing the uuid that it has just made up as well as the location.
> 7. Xapi looks up the VDI by uuid, and then overwrites several of the fields
> (including name_label) with the parameters of the XenAPI VDI.create call
> (from step 1).
> 8. The VDI.create call finishes, returning the reference of the VDI object.
>
> On all subsequent calls to the backend associated with this VDI (vdi_attach,
> vdi_clone, etc.), Xapi will always pass in the reference, uuid and location
> of the VDI:
>
> ...
> <member>
> <name>vdi_ref</name>
> <value>OpaqueRef:67b70c91-8d6d-7c09-2a68-21aa5b3e3d07</value>
> </member>
> <member>
> <name>vdi_location</name>
> <value>f6397206-9dcb-f649-f893-a54de0ec60e4</value>
> </member>
> <member>
> <name>vdi_uuid</name>
> <value>1399962e-76d1-9303-86e5-98ae75708116</value>
> </member>
> ...
>
> The idea is that the location field is used to identify which VDI xapi is
> talking about. For you, in the vdi_create call, the _db_introduce function
> would create
> the VDI record with your 32 bit id in the location field. All subsequent
> calls about that VDI will contain that location field as well as the VDI's
> uuid, so the uuid isn't
> really important as far as your backend is concerned - all you need is the
> location to identify your VDI. You *could* base the uuid of the VDI on your
> 32 bit id, but it's not necessary.
>
> Hope this helps,
>
> Jon
>
>
> On 20 May 2010, at 02:46, YAMAMOTO Takashi wrote:
>
>> hi,
>>
>>>>>> i'm writing a python sr plugin for our product and have a few questions.
>>>>>>
>>>>>> - our product has 32-bit id, not uuid, for each volumes, which i want to
>>>>>> map
>>>>>> to xcp's vdi. i generate name-based uuid from the 32-bit id in sr.scan
>>>>>> and
>>>>>> vdi.create. is this a reasonable approach?
>>>>>>
>>>>>
>>>>> You can use the 'location' field in the VDI to contain your 32 bit id -
>>>>> then the uuid is irrelevant. I'd like to move more of the storage
>>>>> backends in this direction - currently I believe only the ISO SR does it
>>>>> this way.
>>>>
>>>> ok. in that case, xapi generates random uuids for me, right?
>>>>
>>>
>>> Actually the backends are responsible for creating the uuid.
>>
>> then, what is vdi_create's uuid argument for?
>> (my current plugin code simply ignores the argument and
>> return generated uuid via vdi_info. is it ok?)
>>
>> our product itself doesn't provide uuids at all. so someone should
>> generate ones so that xapi can use them.
>> i plan to make my sr plugin generate name-based uuid from our product's
>> 32-bit id. does it sound ok for you?
>>
>> i'm not sure how your suggestion to use vdi location is related to
>> the uuid issue. can you please elaborate a bit?
>>
>> YAMAMOTO Takashi
>
>
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