[Sheepdog] [PATCH 0/5] modify the usage of snapshot and cloning

[MORITA Kazutaka]

Hi,

I think the usage of sheepdog snapshot/cloning was a bit confusing,
and I made it more intuitive for those who are familiar with qemu.

This patchset is for the master branch, and depends on the server
patch I sent one minute ago.

Any feedback is welcome!

Thanks,

Kazutaka Morita

==
Usage before/after applying this patchset:

- create a snapshot of a VM image
[before]
  $ qemu-img snapshot -c name sheepdog:[vdi name]
  (the argument of -c option has been ignored)

[after]
  $ qemu-img snapshot -f sheepdog -c [tag name] [vdi name]

- create a clone image (only from a sheepdog image)
[before]
  $ qemu-img create -f sheepdog -b sheepdog:[base vdiname]:[base tag] [vdiname]

[after]
  $ qemu-img create -f sheepdog -F sheepdog -b [base vdiname] -o tag=[base tag] [vdiname]
  or
  $ qemu-img create -f sheepdog -o backing_fmt=sheepdog,backing_file=[base vdi],tag=[base tag] [vdiname]

- use a snapshot image as a backing image of other formats
(note: this feature isn't well-tested and may have a fundamental problem)
[before]
  $ qemu-img create -f qcow2 -b sheepdog:[base vdiname]:[base tag] [filename]

[after]
  $ qemu-img create -f qcow2 -F sheepdog -b [base vdiname] -o tag=[base tag] [filename]
  or
  $ qemu-img create -f qcow2 -o backing_fmt=sheepdog,backing_file=[base vdi],tag=[base tag] [filename]

- boot using a snapshot image
[before]
  $ qemu-system-x86_64 --drive format=sheepdog,file=[vdiname]:[tag]

[after]
  $ qemu-system-x86_64 --drive format=sheepdog,file=[vdiname],tag=[tag]