[sheepdog] Live snapshot not working via libvirt. Possible regression?

[Hitoshi Mitake]

On Fri, Sep 11, 2015 at 4:43 PM, Vasiliy Tolstov <v.tolstov at selfip.ru> wrote:
> 2015-09-10 18:20 GMT+03:00 Jason Noble <noblej at yahoo.com>:
>> While both protocols support internal snapshots of the disk qemu is not
>>     able to use it as it requires some place to store the memory image. The
>>     check if the disk is backed by a qcow2 image needs to be executed
>>     always.
>>
>> I reverted the above commit, built libvirt and tried again and got the
>> following error:
>>
>> "error: Operation not supported: live snapshot creation is supported only
>> with external checkpoints"
>>
>> Before digging any further into this issue, I wanted to ask on the mailing
>> list if this behavior seems incorrect to others. If this behavior _is_
>> expected then I think the wiki page linked in the opening of this email
>> should be updated to reflect that.
>>
>> The versions of qemu, libvirt and sheepdog I'm using are listed below.
>
>
> As i'm understand commit messae, when we create vdi with 20 Gb size
> and want to to create full snapshot (with disk and memory), qemu needs
> additional space to store memory. But all disk size from vdi already
> populated to running domain and simply qemu does not have free space
> to store memory.
> Hitoshi, when the sheepdog announce this feature hot qemu store memory
> inside sheepdog ? Does qemu create  additional volume for memory or
> something else ?
>

sheepdog can store vm state in its store, like other objects (ordinal
objects, inode objects, ledger objects). A flag for the objects is
defined like this:
#define VMSTATE_BIT (UINT64_C(1) << 62)

Seems that the problem seems just to be degrade of QEMU. Could you try
the live snapshot with older QEMU and detect the commit which caused
this degrade, Vasiliy and Jason?

Thanks,
Hitoshi

> --
> Vasiliy Tolstov,
> e-mail: v.tolstov at selfip.ru
> --
> sheepdog mailing list
> sheepdog at lists.wpkg.org
> https://lists.wpkg.org/mailman/listinfo/sheepdog