[Qemu-devel] [PATCH 0/2] Introducing qcow2 extensions + keep backing file format

[Uri Lublin <uril@redhat.com>]

Qcow2 extensions are build of magic (id) len (in bytes) and data.
They reside between the end of the header and the filename.

We can keep the backing file format in a such a qcow2 extension, to
1. Provide a way to know the backing file format without probing
   it (setting the format at creation time).
2. Enable using qcow2 format over host block devices.
   (only if the user specifically asks for it, by providing the format
   at creation time).

I've added bdrv_create2 and drv->bdrv_create2 (implemented only
by block-qcow2 currently) to pass the backing-format to create.

Based on a work done by Shahar Frank.

Also fixes a security flaw found by Daniel P. Berrange on [1]
which summarizes: "Autoprobing: just say no."

[1] http://lists.gnu.org/archive/html/qemu-devel/2008-12/msg01083.html

Changes from V4:
   old commented code deleted.
   fix temporary snapshot (e.g. -snapshot) support.

Signed-off-by: Uri Lublin <uril@redhat.com>