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

On Thu, Apr 27, 2023 at 12:00:59PM +0200, Andrea Bolognani wrote: > On Thu, Apr 27, 2023 at 11:50:05AM +0200, Michal Prívozník wrote: > > 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. I tried testing: diff --git a/meson.build b/meson.build index c15003ce02..3ae02ce4df 100644 --- a/meson.build +++ b/meson.build @@ -633,14 +633,14 @@ if host_machine.system() == 'freebsd' endif foreach name : headers - if cc.has_header(name) + if cc.check_header(name) conf.set('WITH_@0(a)'.format(name.underscorify().to_upper()), 1) endif endforeach # check for kernel header required by src/util/virnetdevbridge.c if host_machine.system() == 'linux' - if not cc.has_header('linux/sockios.h') + if not cc.check_header('linux/sockios.h') error('You must install kernel-headers in order to compile libvirt with QEMU or LXC support') endif endif and could not measure any deterministic change in execution time before/after