Re: [Qemu-devel] Design of the blobstore

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

On 09/14/2011 01:56 PM, Michael S. Tsirkin wrote:
> On Wed, Sep 14, 2011 at 01:49:50PM -0400, Stefan Berger wrote:
>> On 09/14/2011 01:40 PM, Michael S. Tsirkin wrote:
>>> On Wed, Sep 14, 2011 at 01:05:44PM -0400, Stefan Berger wrote:
>>>> qemu ... \
>>>>      -blobstore name=my-blobstore,drive=tpm-bs,showsize \
>>>>      -drive if=none,id=tpm-bs \
>>>>      -tpmdev libtpms,blobstore=my-blobstore,id=tpm0 \
>>>>      -device tpm-tis,tpmdev=tpm0
>>>>
>>>> which would result in QEMU printing to stdout:
>>>>
>>>> Blobstore tpm-store on drive with ID tpm-bs requires 83kb.
>>> So you envision tools parsing this freetext then?
>>> Seems like a step back, we are trying to move to QMP ...
>> I extended it first for the way I typically interact with QEMU. I do
>> not use the monitor much.
> It will work even better if there's a tool to do the job instead of cut
> and pasting stuff, won't it? And for that, we need monitor commands.
>
I am not so sure about the design of the QMP commands and how to break 
things up into individual calls. So does this sequence here and the 
'query-blobstore' output look ok?

{ "execute": "qmp_capabilities" }
{"return": {}}
{ "execute": "query-blobstore" }
{"return": [{"size": 84480, "id": "tpm-bs"}]}


Corresponding command line parameters are:

     -tpmdev libtpms,blobstore=tpm-bs,id=tpm0 \
     -drive if=none,id=tpm-bs,file=$TPMSTATE \

Regards,
     Stefan


>>> So with above, the raw case which we don't expect to be used often
>>> is easy to use, but qcow which we expect to be the main case
>>> is close to imposible, involving manual cut and paste
>>> of image size.
>>>
>>> Formatting images seems a rare enough occasion,
>>> that I think only using monitor command for that
>>> would be a better idea than a ton of new command
>>> line options. On top of that, let's write a
>>> script that run qemu, queries image size,
>>> creates a qcow2 file, run qemu again to format,
>>> all this using QMP.
>> Creates the qcow2 using 'qemu-img' I suppose.
>>
>>     Stefan
> Sure.
>
>>> WRT 'format and run in one go' I strongly disagree with it.
>>> It's just too easy to shoot oneself in the foot.