Am 01.03.2012 20:45, schrieb Kai Meyer:
On 03/01/2012 08:03 AM, Kevin Wolf wrote:
Am 29.02.2012 22:52, schrieb Kai Meyer:
Is it possible to extend qemu to support a new image type? I have an
image type that is ready for consumption and I'm looking for the
integration point between qemu and the new image format.
Which image format do you want to get integrated?
Have a look at block/qcow2.c to get an idea of what a qemu block
driver
looks like. At the bottom of the file there is a struct that contains
function pointers to all exported functions, so this is usually a good
place to start exploring a driver.
Kevin
Great, this is exactly what we're after. I work for StorageCraft,
and we would like to figure out some way to allow qemu to directly
consume our image-based backups. It would provide us with user-space
mounting (via libguestfs) as well as booting VMs directly from
Backup images. We already have a proprietary image access library
that provides block-wise access to our image files. I have been able
to scratch together a proof of concept already, which I am really
pleased with.
I see only two roadblocks for which I don't have immediate answers for.
1) Licensing
Is it possible to license our contributions in such a way that we do
not need to open the source code of our image access library?
This is not possible if you want to link your image access library
statically.
QEMU uses GPL v2. You can use a patched QEMU internally,
but as soon as you want to give it to customers (or get it integrated
in the official source tree), you must publish all code which is needed
under an open license.
If your image access library is a shared library (linked at runtime),
the situation is more difficult. The intention of the GPL is still
that you have to publish your code (this is also what the FSF says),
but there are different opinions for GPL v2. See
http://en.wikipedia.org/wiki/GNU_General_Public_License for
more information.
I personally don't like the idea of QEMU supporting closed source
shared libraries.
2) External dependency on our image access library.
We do not want to force qemu to require our image access library to
be present to build. Would it be better to do a conditional build
(./configure --with-spf) or a run-time check for our image access
library?
You'll need the conditional build for those people who don't want
support
for your image type.
Regards,
Stefan Weil