[Qemu-devel] [Bug 1103868] Re: drive_mirror crashes on full disk copy of a resized disk with a backing file

[Vish Ishaya]

Reformatted patch and submitted upstream:

http://lists.gnu.org/archive/html/qemu-devel/2013-01/msg04585.html

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https://bugs.launchpad.net/bugs/1103868

Title:
  drive_mirror crashes on full disk copy of a resized disk with a
  backing file

Status in QEMU:
  In Progress

Bug description:
  This bug was discovered using libvirt on ubuntu with a build of qemu
  1.3 but it is trivailly reproducible with the curent git version.

  Repro steps:

  qemu-img create -f qcow2 base 32M
  qemu-img create -f qcow2 -o backing_file=base disk
  qemu-img resize /home/vishvananda/disk 64M
  qemu-system-x86_64 -drive file=disk,id=vda -vnc :1 -monitor stdio
  QEMU 1.3.0 monitor - type 'help' for more information
  (qemu) drive_mirror -f vda test
  Formatting 'test', fmt=qcow2 size=67108864 encryption=off cluster_size=65536 
lazy_refcounts=off 
  qemu-system-x86_64: /build/buildd/qemu-1.3.0+dfsg/block/mirror.c:129: 
mirror_run: Assertion `n > 0' failed.
  Aborted

  Note that the command works just fine if the front image is not
  resized:

  qemu-img create -f qcow2 base 32M
  qemu-img create -f qcow2 -o backing_file=base disk
  qemu-system-x86_64 -drive file=disk,id=vda -vnc :1 -monitor stdio

  or if the backing file is resized as well:

  qemu-img create -f qcow2 base 32M
  qemu-img create -f qcow2 -o backing_file=base disk
  qemu-img resize /home/vishvananda/disk 64M
  qemu-img resize /home/vishvananda/base 64M
  qemu-system-x86_64 -drive file=disk,id=vda -vnc :1 -monitor stdio

  or if we don't use -f when creating the mirror:

  QEMU 1.3.0 monitor - type 'help' for more information
  (qemu) drive_mirror vda test
  Formatting 'test', fmt=qcow2 size=33554432 backing_file='base' 
backing_fmt='qcow2' encryption=off cluster_size=65536 lazy_refcounts=off 

  although in this final case the mirror is created the same size as the
  backing file which seems wrong:

  qemu-img info test
  image: test
  file format: qcow2
  virtual size: 32M (33554432 bytes)
  disk size: 196K
  cluster_size: 65536
  backing file: base
  backing file format: qcow2

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