On Thu, Feb 04, 2021 at 11:32:41AM +0100, Jan Beulich wrote: > On 04.02.2021 11:21, Roger Pau Monné wrote: > > On Thu, Feb 04, 2021 at 11:13:43AM +0100, Jan Beulich wrote: > >> On 04.02.2021 10:59, Roger Pau Monné wrote: > >>> On Thu, Feb 04, 2021 at 10:46:58AM +0100, Jan Beulich wrote: > >>>> On 04.02.2021 10:38, Roger Pau Monne wrote: > >>>>> --- a/tools/configure.ac > >>>>> +++ b/tools/configure.ac > >>>>> @@ -74,6 +74,7 @@ m4_include([../m4/ax_compare_version.m4]) > >>>>> m4_include([../m4/paths.m4]) > >>>>> m4_include([../m4/systemd.m4]) > >>>>> m4_include([../m4/golang.m4]) > >>>>> +m4_include([../m4/header.m4]) > >>>>> > >>>>> AX_XEN_EXPAND_CONFIG() > >>>>> > >>>>> @@ -517,4 +518,6 @@ AC_ARG_ENABLE([pvshim], > >>>>> ]) > >>>>> AC_SUBST(pvshim) > >>>>> > >>>>> +AX_FIND_HEADER([INCLUDE_ENDIAN_H], [endian.h sys/endian.h]) > >>>> > >>>> Instead of a new macro, can't you use AC_CHECK_HEADERS()? > >>> > >>> AC_CHECK_HEADERS doesn't do what we want here: it will instead produce > >>> a HAVE_header-file define for each header on the list that's present, > >>> and the action-if-found doesn't get passed the path of the found > >>> header according to the documentation. > >>> > >>> Here I want the variable to be set to the include path of the first > >>> header on the list that's present on the system. > >> > >> I was thinking of > >> > >> #if defined(HAVE_SYS_ENDIAN_H) > >> # include <sys/endian.h> > >> #elif defined(HAVE_ENDIAN_H) > >> # include <endian.h> > >> #else > >> # error ... > >> #endif > > > > I think having to replicate this logic in all places that include > > endian.h is cumbersome. > > Right - I would further encapsulate this in a local header.
IMO encapsulating in configure achieves the same purpose. > >>>> I'm also not certain about the order of checks - what if both > >>>> exist? > >>> > >>> With my macro the first one will be picked. > >> > >> And which one is to be the first one? IOW how likely is it that > >> on a system having both the first one is what we're after vs > >> the second one? > > > > Not sure, but the same will happen with your proposal above: in your > > chunk sys/endian.h will be picked over endian.h. > > Oh, sure - the two points are entirely orthogonal. And I'm > also not certain at all whether checking sys/ first is > better, equal, or worse. I simply don't know what the > conventions are. I'm not sure either. For the specific case of endian.h I would expect only one to be present, and I think we should first check for top level (ie: endian.h) before checking for subfolders (ie: sys/), as top level should have precedence. I really don't have a strong opinion either way, so if there's an argument to do it the other way around that would also be fine. > As a result I wonder whether we shouldn't > check that the header provides what we need. Right, that would be a step forward I think. I'm not opposed to it, but I also don't have plans to implement myself. Just checking the path seem to be fine for the purpose here. It could be expanded to also use AC_CHECK_DECLS to check for specific declarations once the header path is found. Thanks, Roger.
