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[Qemu-block] Creating / formatting volumes with non-file based block bac
From: |
Daniel P. Berrange |
Subject: |
[Qemu-block] Creating / formatting volumes with non-file based block backends |
Date: |
Wed, 11 May 2016 15:28:41 +0100 |
User-agent: |
Mutt/1.6.0 (2016-04-01) |
I'm looking once again at the process of creating volumes for QEMU formatted
with LUKS encryption.
For plain files it is easily possible with
qemu-img create -f luks \
--object secret,id=sec0,file=passphrase.txt \
-o key-secret=sec0 \
demo.luks 10G
where 'demo.luks' is the filename to be created, mapping through to the
block driver API
int (*bdrv_create)(const char *filename, QemuOpts *opts, Error **errp);
This creates a plain file and then formats it with LUKS.
Now if I want to instead create a non-plain file (eg a glusterfs image)
and format it with LUKS, AFAICT, this is not possible since we can't
specify options / driver for the next level below the LUKS block backend,
we've only got a plain filename. I'm wondering if perhaps using the JSON
format for the 'filename' parameter value might work, but it would be
desirable to use the regular nested-opts syntax available everywhere else
in the block layer.
A second problem arises if I have an already existing volume that I wish
to merely format with luks. There's no way to skip the create step for
the block backend below the LUKS driver, as create + format are combined
into the same operation. It feels like there's a potential use case for
a separate 'qemu-img format' command which just takes a pre-existing image
and just formats a new image layout on top of it ?
Essentially I would like to be able to create a LUKS formatted image on
top of any QEMU block driver backend that supports the bdrv_create
operation. I would also like to be able to format LUKS onto any pre-existing
image for which there is a QEMU block driver backend with write support.
Any thoughts on this ? If there's clarity around design / requirements,
I have potential free time for working on this in the 2.7 cycle.
Regards,
Daniel
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