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

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, May 26, 2013 at 03:49:53PM -0500, Anthony Liguori wrote:
> Paolo Bonzini <pbonzini@redhat.com> 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.

> 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.

> 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