[Libguestfs] IRC question: does anyone know if libguestfs supports any sort of COW (copy on write) functionality?

[Richard W.M. Jones]

21:51 < foxx> hello! does anyone know if libguestfs supports any sort
              of COW (copy on write) functionality? for example, if i
              mount an image which is RO, can i make it write any
              changes out to a higher dir (such as how overlayfs/aufs
              works)

The answer is yes.  Create a qcow2 overlay on top of your
image before starting:

  qemu-img create -b original.img -f qcow2 overlay.qcow2
  guestfish -a overlay.qcow2
  [etc]

Changes are written to overlay.qcow2.  The original is not modified.

You can also display differences between the overlay and the original
using 'virt-diff':

http://libguestfs.org/virt-diff.1.html
https://rwmj.wordpress.com/2013/12/19/new-in-virt-tools-virt-diff/#content

Rich.

-- 
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