Re: [Xen-devel] [Qemu-devel] [PATCH v2 1/4] xen: Fix build with public headers

[Daniel P. Berrangé <berrange@xxxxxxxxxx>]

On Tue, Jun 18, 2019 at 12:23:38PM +0100, Anthony PERARD wrote:
> Following 37677d7db3 "Clean up a few header guard symbols", QEMU start
> to fail to build:
> 
> In file included from ~/xen/tools/../tools/include/xen/io/blkif.h:31:0,
>                  from ~/xen/tools/qemu-xen-dir/hw/block/xen_blkif.h:5,
>                  from ~/xen/tools/qemu-xen-dir/hw/block/xen-block.c:22:
> ~/xen/tools/../tools/include/xen/io/ring.h:68:0: error: "__CONST_RING_SIZE" 
> redefined [-Werror]
>  #define __CONST_RING_SIZE(_s, _sz) \
> 
> In file included from ~/xen/tools/qemu-xen-dir/hw/block/xen_blkif.h:4:0,
>                  from ~/xen/tools/qemu-xen-dir/hw/block/xen-block.c:22:
> ~/xen/tools/qemu-xen-dir/include/hw/xen/io/ring.h:66:0: note: this is the 
> location of the previous definition
>  #define __CONST_RING_SIZE(_s, _sz) \
> 
> The issue is that some public xen headers have been imported (by
> f65eadb639 "xen: import ring.h from xen") but not all. With the change
> in the guards symbole, the ring.h header start to be imported twice.

Ah, so the include/hw/xen/io/ring.h file in tree is a copy of
/usr/include/xen/io/ring.h from xen-devel.  Previously both
these used "#ifndef __XEN_PUBLIC_IO_RING_H__". After
the header guard cleanup in 37677d7db3, our local copy used a
different header guard from the installed copy & thus we're
not protected from dual inclusion.

IMHO the right solutions here are either

 - Don't copy public Xen headers into our tree
 - Keep our Xen header copies identical to the originals

Importing public headers and then changing them locally is the worst
thing to do. With that in mind I think we should revert the part of
commit 37677d7db3 that touched the imported Xen headers.


Regards,
Daniel
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