Re: [Qemu-devel] [PATCH 2/2] Added target to build libvdisk

[Saggi Mizrahi]

On Tue 23 Aug 2011 07:21:56 PM IDT, Anthony Liguori wrote:
> On 08/23/2011 11:18 AM, Daniel P. Berrange wrote:
> > On Tue, Aug 23, 2011 at 11:14:20AM -0500, Anthony Liguori wrote:
> > > On 08/23/2011 11:12 AM, Daniel P. Berrange wrote:
> > > > $(block-obj-y) pulls in 'aio.o' which is built from aio.c which
> > > > is licensed "GPLv2 only". So even those many files are BSD
> > > > licenses, the combined work will be GPLv2-only. Unfortunately ending
> > > > up with a libqemublock.so which is GPLv2-only is as good as useless
> > > > for libs/apps since it is incompatible with both LGPLv2(+) and GPLv3.
> > > >
> > > > Now in this case aio.c is labelled as Copyright IBM / Anthony,
> > > > so IBM could likely resolve this licensing to be more widely
> > > > compatible. This could^H^Hwould become a non-trivial task if we
> > > > need to look at many files& then also any patches accepted to
> > > > those files from 3rd parties over the years :-(
> > >
> > > If there was a block driver library, I would expect it to be GPL, not 
> > > LGPL.
> >
> > This would prevent us from using it in libvirt, unless we wrote a
> > helper program which we spawned anytime we wanted to use some
> > functionality library :-(
>
> libvirtd is GPL, no?
>
> But QEMU is GPL. Libraries derived from QEMU will also be GPL.
>
> Regards,
>
> Anthony Liguori
>
> > Regards,
> > Daniel

OK, I admit it was a pretty naive solution. But I always try to do the 
simplest solution first.
The license issues can be solved later. (Having it as GPL later 
changing to LGPL if we can).

As for the API I can create start a specialized API for the lib that 
uses the internal API.
I can hide BlockDriverState and export it as an fd.
int vdisk_open(path, format, flags)
size_t vdisk_pread(fd, buf, size, offset)
size_t vdisk_pwrite(fd, buff, size, offset)
int vdisk_close(fd)

int vdisk_get_size(fd)

That way no internal structures are exported and we use a minimal set 
of functions that are very unlikely to change.
There is no support for snapshots, metadata etc. But these APIs can be 
added later.

And of-course we can always define the lib as experimental until the 
API stabilizes.