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Re: [Qemu-devel] Design of the blobstore

From: Stefan Berger
Subject: Re: [Qemu-devel] Design of the blobstore
Date: Wed, 14 Sep 2011 17:12:48 -0400
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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 \


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.


WRT 'format and run in one go' I strongly disagree with it.
It's just too easy to shoot oneself in the foot.

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