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Version of disk image format not exhibited using the 'qemu-img info' command
OS: Fedora (64 bits) – Linux –. Last available component: qemu-img.x86_64 2:2.11.2-2.fc28
Description: version of disk image format not exhibited using the 'qemu-img info' command.
Command 'qemu-img info qcow2 [image-file-name.img]' produces this stderr message:
qemu-img: Expecting one image file name
Try 'qemu-img --help' for more information
How to reproduce in terminal:
1. Create a VM using Raw disk image format
2. Run either commands 'qemu-img info -f raw [image-file-name.img]', 'qemu-img info [image-file-name.img]'.
3. Run either commands 'qemu-img info -f qcow2 [image-file-name.qcow2]', 'qemu-img info [image-file-name.qcow2]'.
Actual result: output model resulting from step .2 exhibits following informations:
image: image-file-name.img
file format: raw
virtual size: _G (_ bytes)
disk size: _G
Output model resulting from step .3 exhibits following informations:
image: image-file-name.qcow2
file format: qcow2
virtual size: _G (_ bytes)
disk size: _G
cluster_size: _
Snapshot list:
ID TAG VM SIZE DATE VM CLOCK
1 snapshot1 _G 2018-07-31 18:27:49 00:03:45.890
Format specific information:
compat: 1.1
lazy refcounts: true
refcount bits: 16
corrupt: false
Actual result: raw and qcow2 formats respective versions –which are likely to be mentioned as "version"– to be exhibited.
Additional information: in documentation lastly updated 2018-08-23 at https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/virtualization_deployment_and_administration_guide/index it is stated in chapters:
14.10 – 'images in raw format can be resized in both directions, whereas qcow2 version 2 or qcow2 version 3 images can be grown';
14.12 – 'the qcow2 version supplied with Red Hat Enterprise Linux 7 is 1.1', 'To know which version you are using, run qemu-img info qcow2 [imagefilename.img] command.'.
There's no concept of versions for "raw" images as there's no metadata at all - its just raw disk content.
For the qcow2 format, the version 2 vs version 3 distinction is not something that is intended to be exposed externally. A version 3 format file is still handled by the qcow2 format driver, and there is no qcow3 driver.
At an end user level you can specify a compatibility level "0.10" vs "1.1" which indicates what QEMU version your image shuld be compatible with - from 'man qemu-img':
"compat"
Determines the qcow2 version to use. "compat=0.10" uses the traditional image format
that can be read by any QEMU since 0.10. "compat=1.1" enables image format extensions
that only QEMU 1.1 and newer understand (this is the default). Amongst others, this
includes zero clusters, which allow efficient copy-on-read for sparse images.
Internally, compat=1.1, will cause qemu to use qcow2 version 3, but that's not something users should be concerned with.
Docs that talk about version 2 vs version 3 should be fixed as that's not something user should be exposed to. They should just talk about the compat level.
So many useful information that would be worth to be part of the documentation associated to the above mentioned link.
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