libvirt users - Oct 2015 - virsh can't support VM offline blockcommit

Hi  everyone!
     I use the libvirt(version: 1.2.2) and QEMU(version: 2.2.1) to test
qemu snapshot features:

     I tried virsh blockcommit when VM offline,  the virsh blockcommit
failed: the error messase as below:
    *                      error: Requested operation is not valid: domain
is not running*
     when I start the VM,  the virsh blockcommit  work fine!
     my question is :   we need virsh support blockcommit when
VM offline。how do？

    we  test qemu snapshot as follows：
    we need  create  snapshot of the cycle，and  by virsh blockcommit
merge snapshot chain，but whenVM offline， the virsh blockcommit will
fail， someone suggest me：when VM offline，may use qemu-img commit to
submit snapshot turn，but qemu-img can't modify snapshot chain backing
relation，it need
we use qemu-img  rebase amend snapshot‘s backingfile，* the main
question* is when we use qemu-img rebase modify snapshot's
backingfile, if someone start the VM, it  will may lead to VM filesystem
readonly。

   we  should how to  solve the question?   thanks!