Re: [Qemu-devel] Add support for new image type

[Kevin Wolf <kwolf@redhat.com>]

(Sorry, missed the rest of this thread as I was expecting to be kept in
the CC list)

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?

As other people already said, there's no way that we would accept this.

However, what do you really gain from keeping your file format secret? I
can't imagine that the information required for a (possibly read-only)
properly licensed block driver contains anything of what makes the core
of your products. I can understand that you want to keep sophisticated
source code closed, but I really can't for file formats.

So if you tried to get permission to publish a specification of your
image format and wrote a minimal qemu block driver from scratch, I
believe this would be best for everyone.

> 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?

A conditional build would be required and I'd consider a run-time check
optional.

Kevin