[Qemu-block] dirty bitmap restore procedure

[Michael Ablassmeier]

hi there,

im currently playing with incremental backups using the dirty-bitmap
feature (2.7.91 (v2.8.0-rc1-dirty)

My steps as follows (without making use of qemu agent or such):

 1) create base image for live system
   qemu-img create -f qcow2 disk1.imgc 5G
 2) boot, create filesystem, mount, touch /mnt/FULL, sync
 3) create snapshot via QMP:
  blockdev-snapshot-sync device=ide0-hd0 snapshot-file=snapshot-full.img
 4) backup original disk via cp
  cp disk1.img full-backup_1.img
 5) commit back:
  block-commit device=ide0-hd0

At this point for my understanding i should have
created a sufficient full backup.

Now im adding a dirty bitmap to the very same disk:

 1) create bitmap
    block-dirty-bitmap-add node=ide0-hd0 name=INC
 2) copy some files to the filesystem, sync
 3) issue backup to inc file from very same bitmap, wait for job to finish:
    drive-backup device=ide0-hd0 target=inc-backup.1.img sync=incremental 
bitmap=INC

the inc-backup.1.img now contains my changed data blocks as
far as i can see.

after this i shutdown the virtual machine and remove my
original disk. Now i wonder how to restore the system
to its last state. Currently im using something along those
lines:

 1) create new disk with backing device for full backup:
    qemu-img create -f qcow2 -b backup-full.img disk1.img 5G
 2) rebase disk to the inc backup:
    qemu-img rebase backup-full.img -b inc-backup.1.img

if booting the system i can now see my fileystem which contains
all changes done prior to the snapshot and the full backup,
but i dont see any changes applied from the INC backup, i tried
commiting etc but it just does not work. Im sure i miss something
here, can anyone give me a pointer?

thanks,
    - michael