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!