Re: [Qemu-devel] RFC v3: blockdev_add & friends, brief rationale, QMP docs

[Stefan Hajnoczi <stefanha@gmail.com>]

On Wed, Jun 16, 2010 at 6:27 PM, Markus Armbruster <armbru@redhat.com> wrote:
> blockdev_add
> ------------
>
> Add host block device.
>
> Arguments:
>
> - "id": the host block device's ID, must be unique (json-string)
> - "format": image format (json-string, optional)
>    - Possible values: "raw", "qcow2", ...

What is the default when unset?  (I expect we'll auto-detect the
format but this should be documented.)

> - "protocol": image access protocol (json-string, optional)
>    - Possible values: "auto", "file", "nbd", ...

The semantics of "auto" are not documented here.

> Notes:
>
> (1) If argument "protocol" is missing, all other optional arguments must
>    be missing as well.  This defines a block device with no media
>    inserted.

Perhaps this is what "auto" means?

> (2) It's possible to list supported disk formats and protocols by
>    running QEMU with arguments "-blockdev_add \?".

Is there an query-block-driver command or something in QMP to
enumerate supported formats and protocols?  Not sure how useful this
would be to the management stack - blockdev_add will probably return
an error if an attempt is made to open an unsupported file.

> blockdev_del
> ------------
>
> Remove a host block device.
>
> Arguments:
>
> - "id": the host block device's ID (json-string)
>
> Example:
>
> -> { "execute": "blockdev_del", "arguments": { "id": "blk1" } }
> <- { "return": {} }

What about an attached guest device?  Will this fail if the virtio-blk
PCI device is still present?  For SCSI I imagine we can usually just
remove the host block device.  For IDE there isn't hotplug support
AFAIK, what happens?

Stefan