[libvirt-users] [libvirt] Creating a storage volume for raw format file

[Paul Carlton]

On 04/05/16 14:30, Cole Robinson wrote:
> On 05/04/2016 09:25 AM, Paul Carlton wrote:
>>
>> On 04/05/16 14:07, Cole Robinson wrote:
>>> On 05/04/2016 06:54 AM, Paul Carlton wrote:
>>>> Hi
>>>>
>>>> I'm trying to create a volume in an existing storage pool using python by
>>>> calling createXML() on the pool object.
>>>> If the file that is the subject of the new volume exists you get and error,
>>>> also if it doesn't exist
>>>>
>>>> I worked out that specifying
>>>>
>>>> <source>
>>>>     <path>path to copy of file</path>
>>>> </source>
>>>>
>>>>    works, seemingly by copying the 'source' file to the intended location of
>>>> the
>>>> volume file
>>>>
>>>> However I am concerned about the overhead of copying the file, is there a way
>>>> to tell it to move the file (i.e. rename)
>>> Unfortunately there isn't any simple API to 'rename' a storage volume
>>>
>>> - Cole
>>>
>> Actually I don't want to rename a storage pool, in my inept attempt a brevity
>> I failed to explain myself clearly.
>>
>> I want to create a raw format file in a directory that is referenced by
>> directory storage pool and register it as a storage volume
>>
>> If I place the file in the directory then try to create a storage volume to
>> reference it the operation fails due to the file already existing.
>> however if I try to create the storage pool then copy the file to the
>> directory it fails to create the storage pool because the file does not exist.
>> I figured out that if I create the file in another directory then create the
>> storage volume as follows...
>>
> Not sure if I fully follow, but if you manually create the file in the
> directory, outside of libvirt's APIs, just do a pool.refresh() and libvirt
> will notice the new volume and it will show up in listVolumes. createXML is
> only for telling libvirt to create an entirely new disk image (likely by
> invoking qemu-img), not to teach it about an existing image... that's what
> pool.refresh() is essentially for
>
> - Cole
>
>>      def create_volume(self, vol_name, src_path):
>>          def create_vol_xml(name, src):
>>              xml = """<volume type='file'>
>>                        <name>{name}</name>
>>                        <allocation unit='bytes'>{allocation}</allocation>
>>                        <capacity unit='bytes'>{capacity}</capacity>
>>                        <source>
>>                          <path>{src_path}</path>
>>                        </source>
>>                        <target>
>>                          <permissions>
>>                            <mode>{mode}</mode>
>>                            <owner>{uid}</owner>
>>                            <group>{gid}</group>
>>                          </permissions>
>>                        </target>
>>                       </volume>"""
>>              stat = os.stat(src)
>>              qmeu_info = images.qemu_img_info(src)
>>              return xml.format(**{'name': name,
>>                                   'capacity': qmeu_info.virtual_size,
>>                                   'allocation': qmeu_info.disk_size,
>>                                   'src_path': src,
>>                                   'format': qmeu_info.file_format,
>>                                   'mode': oct(stat.st_mode)[-3:],
>>                                   'uid': stat.st_uid,
>>                                   'gid': stat.st_gid})
>>
>>          vol_xml = create_vol_xml(vol_name, src_path)
>>          self._vols[vol_name] = self._pool.createXML(vol_xml, 0)
>>
>> Where 'src_path' is the path to a file in another directory it seems to copy
>> src_path to my storage pool directory as 'vol_name' and
>> creates a storage volume that references it.
>>
>> This is fine except, my concern is what if the file is very large the copy
>> operation could take a long time and we'd use twice the
>> disk space we should do.
>>
>> Since I could not find any documentation on the <source> elements for a
>> directory pool's volume xml I was wondering if there
>> was a setting that would make it move/rename src_file to the vol_name file in
>> my pool directory rather than copy it?
>>
>>
Cole,

Thanks, that is what I will use!

-- 
Paul Carlton
Software Engineer
Cloud Services
Hewlett Packard
BUK03:T242
Longdown Avenue
Stoke Gifford
Bristol BS34 8QZ

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Email:    mailto:paul.carlton2 at hpe.com
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