Re: [Qemu-devel] [PATCH v2 00/11] qemu: use virtio linux headers in portable code

[Michael S. Tsirkin]

On Sun, May 26, 2013 at 07:55:25PM -0500, Anthony Liguori wrote:
> "Michael S. Tsirkin" <address@hidden> writes:
> 
> > On Sun, May 26, 2013 at 03:49:53PM -0500, Anthony Liguori wrote:
> >> Paolo Bonzini <address@hidden> writes:
> >> 
> >> > Il 26/05/2013 22:02, Michael S. Tsirkin ha scritto:
> >> >> > My fault.  I should have looked at linux/types.h (actually 
> >> >> > asm-generic/).
> >> >> 
> >> >> Not really, __uX appear in the headers that were posted.
> >> 
> >> Which is a problem because this is a reserved namespace in C99.
> >> 
> >> >> What I'm saying is - a chance of a conflict is very remote,
> >> >> if it happens it's a build failure so easy to debug.
> >> >
> >> > I'm sure that others will complain, :) but you can go ahead.
> >> 
> >> I think we should clean up the virtio headers in the kernel first.
> >> Seems like a good thing to do given the standardization effort too.
> >> There are lots of headers in uapi that use the C99 int types
> >
> > I found 4:
> > $ grep -l uint include/uapi/linux/*h
> > include/uapi/linux/dm-log-userspace.h
> > include/uapi/linux/fuse.h
> > include/uapi/linux/jffs2.h
> > include/uapi/linux/pps.h
> > include/uapi/linux/rds.h
> > include/uapi/linux/sctp.h
> >
> > That's not really lots.
> >
> >> so there
> >> doesn't seem to be a reason they couldn't be used in virtio.  fuse.h
> >> even has a:
> >> 
> >>     #ifdef __KERNEL__
> >>     #include <linux/types.h>
> >>     #else
> >>     #include <stdint.h>
> >>     #endif
> >> 
> >> Which seems like a reasonable thing to do.
> >
> > In kernel, we really want to use things like endian-ness
> > checks (and, we really should have them in userspace too!).
> > So we want __le32 and other kernel goodies
> > like that. stdint.h won't cut it.
> 
> With the spec being standardized, I think having a stand alone set of
> headers is a good thing.

Sure, that's possible. We'll have to find some way to
preserve the endian-ness annotations, I think.
And then import them into kernel/qemu with some script, converting
to kernel/qemu style and annotations?

>  Licensing is problematic here too.
> 
> If virtio headers depend on other Linux headers, then it really doesn't
> matter if they are BSD licensed if you need a GPL header (like
> linux/if_ether.h).
> 
> Now, we can certainly debate the copyrightability of these defines and
> what have you but if the headers are meant to be 1) consumed outside the
> kernel 2) licensed under a different license than the general kernel
> then depending on kernel goodies is the wrong strategy.

Well specifically if_ether.h says GPLv2+ so it's OK for QEMU.
Do you mean for some other non GPL app?

> >> The only other kernel dependency is linux/if_ether.h to define
> >> ETH_ALEN.  But it seems completely reasonable to define a
> >> VIRTIO_NET_MAC_ALEN or something like that.
> >
> > Ugh. Not really reasonable IMO. We also use ETH_P_IP in code,
> > would like to get rid of redefining that too.
> > But we can have our own linux/if_ether.h for non-linux hosts,
> > just with a
> > couple of macros like that, it's not a big deal.
> 
> See above.
> 
> Regards,
> 
> Anthony Liguori
> 
> >
> >> This would make the virtio headers completely stand alone and includable
> >> in userspace (without violating C99).
> >> 
> >> Perhaps it's even worth moving the headers from uapi/linux to
> >> uapi/virtio.  Rusty, what do you think?
> >> 
> >> Regards,
> >> 
> >> Anhtony Liguori
> >> 
> >> >
> >> > Paolo