configure: keep the replacement libsystemd opt-in

Building it by default installs our libsystemd.so.0 in $libdir.  Where
the real one is already present, and contrib/debian/build.sh configures
--prefix=/usr --exec-prefix= on a Debian host, ours outranks it in the
loader cache, and every program linking libsystemd loses
sd_journal_stream_fd and the LIBSYSTEMD_209 symbol versions.  The test
sysroot ran into exactly that, dbus-daemon exited 127 on every restart.

Restore the default to no.  sulogin and watchdogd stay on, they only add
binaries.  distcheck asks for the library so it stays covered.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Makefile.am

@@ -65,4 +65,5 @@ release: distcheck
 
 DISTCHECK_CONFIGURE_FLAGS = --prefix=/usr --sysconfdir=/etc --localstatedir=/var \
 			    --enable-testserv-plugin --enable-x11-common-plugin  \
-			    --with-fstab=/etc/fstab --with-bash-completion-dir=no
+			    --with-fstab=/etc/fstab --with-libsystemd            \
+			    --with-bash-completion-dir=no

configure.ac

@@ -191,8 +191,8 @@ AC_ARG_WITH(watchdog,
 	[watchdog=$withval], [with_watchdog=yes watchdog=yes])
 
 AC_ARG_WITH(libsystemd,
-        AS_HELP_STRING([--without-libsystemd], [Skip replacement libsystemd library, default: yes]),
-	[with_libsystemd=$withval], [with_libsystemd=yes])
+        AS_HELP_STRING([--with-libsystemd], [Build replacement libsystemd library, default: no]),
+	[with_libsystemd=$withval], [with_libsystemd=no])
 
 AC_ARG_WITH(hook-scripts-path,
         AS_HELP_STRING([--with-hook-scripts-path=DIR], [Base directory for hook scripts, default $libexecdir/finit/hook]),

doc/ChangeLog.md

@@ -69,12 +69,10 @@ All relevant changes are documented in this file.
   `tmpfiles.d/dbus.conf`, so both can be overridden from `/etc` like any other
   system file.  Those directories are no longer chowned to `messagebus`,
   matching how Finit ships directories for other daemons
-- The bundled `sulogin` and `watchdogd`, and the replacement `libsystemd`,
-  are now built and installed by default, like keventd and the D-Bus
-  support.  `--without-sulogin`, `--without-watchdog`, and
-  `--without-libsystemd` opt out.  Note, Finit starts `watchdogd` by
-  itself when the WDT device node exists, and `libsystemd.so` is
-  installed to `$libdir`, where a system with systemd already has one
+- The bundled `sulogin` and `watchdogd` are now built and installed by
+  default, like keventd and the D-Bus support.  `--without-sulogin` and
+  `--without-watchdog` opt out.  Note, Finit starts `watchdogd` by itself
+  when the WDT device node exists
 - The `tty` block takes `passenv`, which the line-based format has had since
   v4.4 (issue #286) and the block format was missing
 - New `provides` setting for run/task/service/sysv blocks, naming conditions

doc/build.md

@@ -89,10 +89,13 @@ Below are a few of the main switches to configure:
   on `/dev/watchdog`, `--with-watchdog=DEV` selects another device.
   Finit starts it when the device node exists, see [Watchdog](watchdog.md).
 
-* `--without-libsystemd`: Drop the replacement `libsystemd`, built and
-  installed by default, which lets programs that use `sd_notify()` talk
-  to Finit without systemd.  Note, it installs `libsystemd.so` in
-  `$libdir`, where a system with systemd already has one.
+* `--with-libsystemd`: Build the replacement `libsystemd`, which lets
+  programs that use `sd_notify()` talk to Finit without systemd.  Off by
+  default because it installs `libsystemd.so.0` in `$libdir`: on a host
+  that has the real one, ours shadows it in the loader cache and every
+  program linking it, `dbus-daemon` and `udevd` included, loses the
+  symbols it needs.  Safe on a systemd-free system, which is the point
+  of it.
 
 For more configure flags, see <kbd>./configure --help</kbd>