[libvirt] [PATCH libvirt] storage: add preallocation element
Eric Blake
eblake at redhat.com
Thu May 17 22:13:19 UTC 2012
On 05/17/2012 03:35 PM, Marc-André Lureau wrote:
> Allow to specify preallocation mode for QCOW2 images.
> If not specified or not available, it's ignored.
>
> This change only modify the schema, doc, parsing and tests.
> ---
> docs/formatstorage.html.in | 7 +++++++
> docs/schemas/storagevol.rng | 18 ++++++++++++++++++
> src/conf/storage_conf.c | 26 ++++++++++++++++++++++++++
> src/conf/storage_conf.h | 1 +
> src/util/storage_file.c | 4 ++++
> src/util/storage_file.h | 10 ++++++++++
> tests/storagevolxml2xmlin/vol-qcow2.xml | 1 +
> tests/storagevolxml2xmlout/vol-qcow2.xml | 1 +
> 8 files changed, 68 insertions(+)
Meta-question - is pre-allocation something that is persistent with the
existence of the storage volume, or is it something that is one-shot at
the creation of the volume?
If pre-allocation is a persistent property of the volume itself, then I
would expect qemu-img to tell me whether an image is currently
pre-allocated, as well as having knobs to tweak to force an image to
become pre-allocated where it was not previously in that state. The
converse direction, going from pre-allocated to sparse as a form of
compression, might also be possible. If this is the case, then making
pre-allocation part of the XML for describing a storage volume makes sense.
On the other hand, if pre-allocation is only a knob to creation, but
once the image is created it is no longer possible to tell whether it
was created sparse or pre-allocated, nor is it possible to tweak the
image to change between the two states at will, then it makes more sense
to add a flag to the creation methods that specify whether to request
pre-allocation, and to leave it out of the XML.
I need to know the answer to that meta-question before I can review this
part of the patch series.
--
Eric Blake eblake at redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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