Re: [Qemu-block] dirty bitmap restore procedure

[Kashyap Chamarthy]

On Tue, Nov 29, 2016 at 11:52:49AM -0500, John Snow wrote:
> 
> On 11/29/2016 09:13 AM, Michael Ablassmeier wrote:
> > hi there,

[...]

> The problem here is that the bitmap you are creating is not synchronized to
> the backup you've just made. What if some writes have happened since you
> created your snapshot?
> 
> You need to create your snapshot and add (or reset) the bitmap using a
> transaction.

Oh, good point, revisiting my old tests, I now recall using QMP
'trasaction' to address the point.

Perhaps you might already be aware, a quick example of transactions w/
QMP.  Assuming you have '-qmp unix:./qmp-sock,server'

----------
 ./qmp-shell -v -p /export/qmp-sock 
Welcome to the QMP low-level shell!
Connected to QEMU 2.5.50

(QEMU) transaction(
TRANS> blockdev-snapshot-sync device=drive-ide0-0-0  
snapshot-file=overlay1.qcow2
TRANS> block-dirty-bitmap-add node=drive-ide0-0-0 name=bitmap0
TRANS> )
{
    "execute": "transaction", 
    "arguments": {
        "actions": [
            {
                "data": {
                    "device": "drive-ide0-0-0", 
                    "snapshot-file": "overlay1.qcow2"
                }, 
                "type": "blockdev-snapshot-sync"
            }, 
            {
                "data": {
                    "node": "drive-ide0-0-0", 
                    "name": "bitmap0"
                }, 
                "type": "block-dirty-bitmap-add"
            }
        ]
    }
}
{
    "return": {}
}
(QEMU) 
----------


[Snip some detailed discussion.] 

-- 
/kashyap