Re: [Qemu-devel] Design of the blobstore

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Sep 15, 2011 at 06:22:15AM -0400, Stefan Berger wrote:
> 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

Ah, I get it. I was confused thinking this
queries a single store.
Instead this returns info about *all* blobstores.
query-blobstores would be a better name then.
Otherwise I think it's fine.


Also, should we rename blobstore to 'nvram' or
something else that tells the user what this does?


> 
> >
> >>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.