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

[Marc-André Lureau]

Hi

On Mon, Dec 10, 2018 at 5:28 PM Markus Armbruster <address@hidden> wrote:
>
> Marc-André Lureau <address@hidden> writes:
>
> > Hi
> >
> > On Mon, Dec 10, 2018 at 1:52 PM Markus Armbruster <address@hidden> wrote:
> >>
> >> 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?
> >>
> >
> > It's the discussion about #if in headers (and enums in particular)
> > that started this. We want to make sure all compilation units share
> > the same data structure/ABI. I proposed to include osdep.h in qapi
> > headers, but that was rejected.
> > The warning is a different approach. I agree it could apply to all
> > headers. Do you think I should update all headers as well?
>
> That would replace the rule 'all .c files must include "qemu/osdep.h"
> first' by 'all .h files must check "qemu/osdep.h" has been included
> already', which is not an improvement.

That would be an improvement since headers may also be impacted by osdep.h

Alternatively, why not use -include ?

>
> All we have right now to help with enforcing our osdep.h rule is
> scripts/clean-includes.  We run it periodically to fix rule breakers.
> It's manual, because we have a few .c files in the tree where the rule
> doesn't apply, and the script doesn't know about them.  Fixable, I
> guess.  Most recent run:
>
>     Subject: [PATCH] Clean up includes
>     Message-Id: <address@hidden>
>     https://lists.nongnu.org/archive/html/qemu-devel/2018-12/msg00605.html
>
> The obvious improvement would be flagging rule breakers before they get
> committed.
>
> checkpatch.pl could flag patches adding .c files that don't include
> "qemu/osdep.h" first.  The "first" part might be a bit annoying to code.
> The "adding files" part already exists: checkpatch.pl warns when you add
> a file without updating MAINTAINERS.
>
> checkpatch.pl could also flag patches removing #include "qemu/osdep.h".
>
> Other projects use a syntax-check make target to check sources.  If we
> decide we like that better than checkpatch.pl for some checks, we can do
> that.



-- 
Marc-André Lureau