Re: [Qemu-devel] [PATCH for-4.0 v7 01/27] qapi: make sure osdep.h is included in type headers

[Markus Armbruster]

Marc-André Lureau <address@hidden> writes:

> Now that the schema can be configured, it is crucial that all types
> are configured the same. Make sure config-host.h is included, by
> checking osdep.h inclusion. The build-sys tracks the dependency and
> rebuilds the types if the configuration changed.
>
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  scripts/qapi/types.py | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/scripts/qapi/types.py b/scripts/qapi/types.py
> index fd7808103c..3bb9cb6d47 100644
> --- a/scripts/qapi/types.py
> +++ b/scripts/qapi/types.py
> @@ -201,6 +201,9 @@ class QAPISchemaGenTypeVisitor(QAPISchemaModularCVisitor):
>  ''',
>                                        types=types, visit=visit))
>          self._genh.preamble_add(mcgen('''
> +#ifndef QEMU_OSDEP_H
> +#error Please include osdep.h first!
> +#endif
>  #include "qapi/qapi-builtin-types.h"
>  '''))

I understand why you propose this patch.  The QAPI-generated headers use
#ifdef CONFIG_FOO.  The configuration header "qemu/osdep.h" must be
consistently included before the generated headers, or else you end up
with nasty bugs, such as the same enum having different values in
different .o, or the same struct having a different layout.

But this applies to *all* headers that use #ifdef.  Why check it here,
but not there?  What makes the QAPI-generated headers special?