[Qemu-devel] [Bug 1662050] Re: qemu-img convert a overlay qcow2 image into a entire image

[wayen]

@Eric Blake, I used virt-sparsify to sparsify the qcow2 overlay image.
As you said, the actual disk usage is minimized and the apparent file
size is unchanged.It is very valuable for me, because it means that my
disk can hold more files.

But we need to be careful when transfer the sparse qcow2 overlays.
Because some tools do not support sparse file and will convert it into a
common file,for example, scp. And I doubt what will happen when transfer
sparse files between different file systems.

So I want to use qemu-img to convert the sparse qcow2 overlay into
common file. If this was feasible, the holes in the sparse overlay will
be removed and the above problems will disappear.

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https://bugs.launchpad.net/bugs/1662050

Title:
  qemu-img convert a overlay qcow2 image into a entire image

Status in QEMU:
  Incomplete

Bug description:
  I have a base image file "base.qcow2" and a delta qcow2 image file
  "delta.qcow2" whose backing file is "base.qcow2".

  Now I use qemu-img to convert "delta.qcow2" and will get a new image
  file "new.qcow2" which is entire and equivalent to combination of
  "base.qcow2" and "delta.qcow2".

  In fact,I don't want to get a complete image.I just want to convert
  delta qcow2 image file "A" to a New delta overlay qcow2 image "B"
  which is equivalent to "A". So the "new.qcow2" is not what i want. I
  have to admit that this is not bug. Could you please take this as a
  new feature and enable qemu-img to convert qcow2 overlay itself?

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