scripts: Make use of SYSTEMD_OFFLINE environment variable

More info at:
https://github.com/systemd/systemd/pull/7631 AKA
"systemctl,verbs: Introduce SYSTEMD_OFFLINE environment variable"
f38951a628
and in the docs added.

Closes: #1157
Approved by: jlebon

src/libpriv/rpmostree-bwrap.c

@@ -340,6 +340,14 @@ rpmostree_bwrap_set_child_setup (RpmOstreeBwrap *bwrap,
   bwrap->child_setup_data = data;
 }
 
+
+/* Set an environment variable in the child process */
+void
+rpmostree_bwrap_setenv (RpmOstreeBwrap *bwrap, const char *name, const char *value)
+{
+  g_subprocess_launcher_setenv (bwrap->launcher, name, value, TRUE);
+}
+
 /* Execute @bwrap - must have been configured. After executing this method, the
  * @bwrap instance cannot be run again.
  */

src/libpriv/rpmostree-bwrap.h

@@ -46,6 +46,8 @@ RpmOstreeBwrap *rpmostree_bwrap_new (int rootfs,
 void rpmostree_bwrap_append_bwrap_argv (RpmOstreeBwrap *bwrap, ...) G_GNUC_NULL_TERMINATED;
 void rpmostree_bwrap_append_child_argv (RpmOstreeBwrap *bwrap, ...) G_GNUC_NULL_TERMINATED;
 
+void rpmostree_bwrap_setenv (RpmOstreeBwrap *bwrap, const char *name, const char *value);
+
 void rpmostree_bwrap_set_child_setup (RpmOstreeBwrap *bwrap,
                                       GSpawnChildSetupFunc func,
                                       gpointer             data);

src/libpriv/rpmostree-core.c

@@ -3427,6 +3427,10 @@ rpmostree_context_assemble (RpmOstreeContext      *self,
        * start` in its %post which both violates Fedora policy and also will not
        * work with the rpm-ostree model.
        * See also https://github.com/projectatomic/rpm-ostree/issues/550
+       *
+       * See also the SYSTEMD_OFFLINE bits in rpmostree-scripts.c; at some
+       * point in the far future when we don't support CentOS7 we can drop
+       * our wrapper script.  If we remember.
        */
       if (renameat (tmprootfs_dfd, "usr/bin/systemctl",
                     tmprootfs_dfd, "usr/bin/systemctl.rpmostreesave") < 0)

src/libpriv/rpmostree-scripts.c

@@ -278,6 +278,11 @@ run_script_in_bwrap_container (int rootfs_fd,
   if (!bwrap)
     goto out;
 
+  /* https://github.com/systemd/systemd/pull/7631 AKA
+   * "systemctl,verbs: Introduce SYSTEMD_OFFLINE environment variable"
+   * https://github.com/systemd/systemd/commit/f38951a62837a00a0b1ff42d007e9396b347742d
+   */
+  rpmostree_bwrap_setenv (bwrap, "SYSTEMD_OFFLINE", "1");
 
   struct ChildSetupData data = { .stdin_fd = stdin_fd,
                                  .stdout_fd = -1,

tests/vmcheck/test-layering-scripts.sh

@@ -217,6 +217,11 @@ if vm_rpmostree install etc-mutate; then
   assert_not_reached "successfully installed etc-mutate?"
 fi
 
+# SYSTEMD_OFFLINE
+vm_build_rpm test-systemd-offline post 'test "${SYSTEMD_OFFLINE}" = 1'
+vm_rpmostree install test-systemd-offline
+vm_rpmostree uninstall test-systemd-offline
+
 # Ensure this is reset; at least in the Vagrant box with
 # fedora-atomic:fedora/26/x86_64/atomic-host
 # Version: 26.131 (2017-09-19 22:29:04)