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[Qemu-devel] [Bug 1790617] Re: Version of disk image format not exhibite

From: Daniel Berrange
Subject: [Qemu-devel] [Bug 1790617] Re: Version of disk image format not exhibited using the 'qemu-img info' command
Date: Tue, 04 Sep 2018 10:54:15 -0000

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

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':

             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.

** Changed in: qemu
       Status: New => Invalid

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  Version of disk image format not exhibited using the 'qemu-img info'

Status in QEMU:

Bug description:
  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 
  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 
  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
  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.'.

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