Re: [Qemu-devel] [PATCH 1/2] configure: add libsystemd check

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Thu, Jan 05, 2017 at 05:45:50PM +0000, Daniel P. Berrange wrote:
> On Thu, Jan 05, 2017 at 05:31:06PM +0000, Stefan Hajnoczi wrote:
> > libsystemd provides APIs for daemons that wish to integrate socket
> > activation and other systemd-related functionality.  This will be used
> > as an optional dependency by qemu-guest-agent.
> > 
> > In the future it could also be used for systemd logging or sd_notify(3)
> > service startup notification.
> > 
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > ---
> >  configure | 34 ++++++++++++++++++++++++++++++++++
> >  1 file changed, 34 insertions(+)
> > 
> > diff --git a/configure b/configure
> > index 218df87..c353ff7 100755
> > --- a/configure
> > +++ b/configure
> > @@ -321,6 +321,7 @@ numa=""
> >  tcmalloc="no"
> >  jemalloc="no"
> >  replication="yes"
> > +systemd=""
> >  
> >  # parse CC options first
> >  for opt do
> > @@ -1168,6 +1169,10 @@ for opt do
> >    ;;
> >    --enable-replication) replication="yes"
> >    ;;
> > +  --disable-systemd) systemd="no"
> > +  ;;
> > +  --enable-systemd) systemd="yes"
> > +  ;;
> >    *)
> >        echo "ERROR: unknown option $opt"
> >        echo "Try '$0 --help' for more information"
> > @@ -1401,6 +1406,7 @@ disabled with --disable-FEATURE, default is enabled if available:
> >    tcmalloc        tcmalloc support
> >    jemalloc        jemalloc support
> >    replication     replication support
> > +  systemd         systemd support
> >  
> >  NOTE: The object files are built at the place where configure is launched
> >  EOF
> > @@ -4720,6 +4726,27 @@ if compile_prog "" "" ; then
> >      have_af_vsock=yes
> >  fi
> >  
> > +##########################################
> > +# check for libsystemd
> > +if test "$systemd" != "no" ; then
> > +  cat > $TMPC << EOF
> > +#include <systemd/sd-daemon.h>
> > +int main(void) { (void)sd_listen_fds(1); return 0; }
> > +EOF
> > +  systemd_cflags=$($pkg_config --cflags libsystemd 2>/dev/null)
> > +  systemd_libs=$($pkg_config --libs libsystemd 2>/dev/null)
> > +  if $pkg_config libsystemd >/dev/null 2>&1 && \
> > +     compile_prog "$systemd_cflags" "$systemd_libs" ; then
> 
> Any reason why you're going to the trouble of compiling a
> program here ? The key benefit of pkg-config is that you
> don't need to do things like that to test for existance
> of the library - just trust the result of pkg-config check.
> 
> FWIW, it is easy to support socket activation without even
> using libsystemd. The systemd activation "protocol" is
> trivial - it merely sets "LISTEN_FDS" env variable to the
> number of FDs it has been passed down, and they are numbered
> from stderr fileno + 1.

After looking into it I found that LISTEN_FDS is considered stable and
"reimplementable independently":
https://www.freedesktop.org/wiki/Software/systemd/InterfacePortabilityAndStabilityChart/

I'll resend this patch without the libsystemd dependency.

I guess that will make packagers happy who wish to provide packages that
work both with and without systemd installed.

Stefan

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