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  shoule solve the question?   thanks!