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. > >> 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. If we think that's the right precedence I can adjust AX_FIND_HEADER to be: AX_FIND_HEADER([INCLUDE_ENDIAN_H], [sys/endian.h endian.h]) Which will achieve the same as your proposed snipped. I can also add a comment to the macro that the first match will be the one that gets set. Thanks, Roger.
