[PATCH] cmake: fix sync_file_range detection

[Vladimir Davydov]

On Mon, Oct 08, 2018 at 12:23:58PM +0300, Alexander Turenko wrote:
> On Mon, Oct 08, 2018 at 11:00:12AM +0300, Vladimir Davydov wrote:
> > On Mon, Oct 08, 2018 at 06:04:08AM +0300, Alexander Turenko wrote:
> > > On Sat, Oct 06, 2018 at 05:51:48PM +0300, Vladimir Davydov wrote:
> > > > sync_file_range is declared only if _GNU_SOURCE macro is defined.
> > > > Also, in order to be used in a source file, HAVE_SYNC_FILE_RANGE
> > > > must be present in config.h.cmake.
> > > > 
> > > > Fixes commit caae99e5eaa0 ("Refactor xlog writer").
> > > > ---
> > > > https://github.com/tarantool/tarantool/commits/dv/cmake-fix-gnu-symbol-detection
> > > > 
> > > >  CMakeLists.txt            | 2 ++
> > > >  src/trivia/config.h.cmake | 1 +
> > > >  2 files changed, 3 insertions(+)
> > > > 
> > > > diff --git a/CMakeLists.txt b/CMakeLists.txt
> > > > index bf68d187..b26d2abf 100644
> > > > --- a/CMakeLists.txt
> > > > +++ b/CMakeLists.txt
> > > > @@ -69,6 +69,8 @@ include(cmake/profile.cmake)
> > > >  include(cmake/module.cmake)
> > > >  include(cmake/thread.cmake)
> > > >  
> > > > +list(APPEND CMAKE_REQUIRED_DEFINITIONS -D_GNU_SOURCE)
> > > > +
> > > 
> > > cmake/os.cmake already has `add_definitions("-D_GNU_SOURCE")`, is that
> > > not sufficient?
> > 
> > Looks like not. I checked - sync_page_range isn't used on Linux without
> > this patch.
> 
> It looks similar to the cmake issue [1].
> 
> Maybe it is better to set CMAKE_REQUIRED_DEFINITIONS in sync with
> add_definitions (in os.cmake), what do you think?

I don't think so. We typically set CMAKE_REQUIRED_* before checking for
symbols.

BTW, I should have probably used set() instead of list(APPEND).