On Mon, Jul 28, 2008 at 11:06 PM, Anthony Liguori
<address@hidden> wrote:
Nathaniel McCallum wrote:
Well, the point is to not have a separate configuration file.
I've dug up a few more bits of info. First, the offset option will never work without changing at least qcow2's on disk format.
qemu -drive file=offset:foo.img:offset=32,if=ide
The syntax of -drive erks me here but you get the gist. Then backing files would work fine.
It won't work... See lines 339-366 of block.c.
This is because when you start qemu in snapshot mode, it creates a new qcow2 image and uses it as the main image. However, the offset was meant to apply to the underlying image and there is no field in qcow2 to specify the offset of the backing_file.
Second, when creating a new qcow2 file, the l1_table_offset is 4096. There does not appear to be anything stored between the end of the header and the 4096. So, in theory, you could put anything you want there. No?
There's no guarantee that that space won't be used in future versions of QCOW2 so you can't just cram arbitrary stuff in there.
Yeah, I'm thinking "Could we just add metadata_{offset|size} to the end of QCOW2 and maintain compatibility?"
Nathaniel