[libvirt] [Bug report] - vm start failed after image snapshot rebase

weiwei li weiweili821 at gmail.com
Mon Nov 10 02:18:02 UTC 2014

Hi ,
I hit a bug with libvirt+ qemu+kvm when doing follow steps:
1.initial status :vm = base+z(z is a snapshot)
2. call snapshotCreateXML( ): vm =  base+z +z'
3. call blockRebase( ): vm = base+z''(z rebase to z')
4 .(after rebasing work done) vm shutdown and then start

an error accord like this:
 unable to set user and group to '0:0' on
No such file or directory
A second start may sucess.
I debugged with gdb and found that the error message was cauesed by
virSecurityDACSetSecurityDiskLabel misuse the disk chain(that is base+z
after rebase), and z' was deleted yet.
why virSecurityDACSetSecurityDiskLabel  used old disk chain after rebasing
I finally find that In qemuProcessHandleBlockJob when rebase complete, disk
chain in vm->def is updated but vm->newDef is not(when vm->newDef is not
null). In shutdown( actrully in qemuProcessStop ), if vm->newDef is not
null , vm->def will be replaced  by vm->newDef, which contains a wrong disk
chain!!! the next start will failed with above message.
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