Re: [Qemu-devel] Design of the blobstore

[Stefan Berger]

On 09/15/2011 02:57 AM, Michael S. Tsirkin wrote:
> On Wed, Sep 14, 2011 at 05:12:48PM -0400, Stefan Berger wrote:
> > 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"}]}
> I'll let some QMP experts to comment.
>
> We don't strictly need the id here, right?
> It is passed to the command.
>
> BTW is it [] or {}? It's the total size, right? Should it be
> {"return": {"size": 84480}}
> ?
The id serves to distinguish one blobstore from the other. We'll have 
any number of blobstores. Since we get rid of the -blobstore option they 
will only be identifiable via the ID of the drive they are using. If 
that's not good, please let me know. The example I had shown yesterday 
were using the name of the blobstore,  rather than the drive ID, to 
connect the device to the blobstore.

before:

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

now:

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



   Stefan

> > 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.