Re: [Qemu-devel] [Qemu-block] [PATCH 00/10] qcow2: Implement image locking

["Denis V. Lunev" <den-lists@parallels.com>]

On 12/23/2015 05:57 PM, Vasiliy Tolstov wrote:
> 2015-12-22 19:46 GMT+03:00 Kevin Wolf <kwolf@redhat.com>:
>> Enough innocent images have died because users called 'qemu-img snapshot' while
>> the VM was still running. Educating the users doesn't seem to be a working
>> strategy, so this series adds locking to qcow2 that refuses to access the image
>> read-write from two processes.
>>
>> Eric, this will require a libvirt update to deal with qemu crashes which leave
>> locked images behind. The simplest thinkable way would be to unconditionally
>> override the lock in libvirt whenever the option is present. In that case,
>> libvirt VMs would be protected against concurrent non-libvirt accesses, but not
>> the other way round. If you want more than that, libvirt would have to check
>> somehow if it was its own VM that used the image and left the lock behind. I
>> imagine that can't be too hard either.
>
> This breaks ability to create disk only snapshot while vm is running.
> Or i miss something?
>
you should do this by asking running QEMU not by
qemu-img, which is badly wrong.

Den