Re: [libvirt PATCH] meson: Check usability of linux/kvm.h

On Thu, Apr 27, 2023 at 11:50:05AM +0200, Michal Prívozník wrote: > On 4/27/23 11:41, Andrea Bolognani wrote: > > +# headers for which we need to check actual usability. in most > > +# cases, checking for presence is enough (and it's way faster) > > +check_headers = [ > > + 'linux/kvm.h', > > +] > > + > > +foreach name : check_headers > > + if cc.check_header(name) > > + conf.set('WITH_@0(a)'.format(name.underscorify().to_upper()), 1) > > + endif > > +endforeach > > One could argue, that the semantics of has_header() is broken then. What > good is there to check if the host has a header file when compiler > rejects it subsequently? > > But leaving meson aside, shouldn't we just use check_header() for every > header file then? I mean, this fixes this particular instance of the > problem, but can't we hit it again with say ifaddrs.h or any other > header file on the list? We could. The Meson documentation recommends not doing this, as check_header() is (understandably) slower than has_header(). I haven't tried to see how much slower we're actually talking... Maybe for the 20-ish headers that we care about, it wouldn't make a measurable difference? Especially since the results of the check are cached between Meson runs.