path-lookup: make SYSTEMD_UNIT_PATH more flexible

It can now contain more than one directory, and can be used
to only prepend, not totally override, the normal load path.

3 files changed, 58 insertions, 51 deletions

diff --git a/man/systemd.unit.xml b/man/systemd.unit.xml
index 86a8cbb330..dd3a4a7cd5 100644
--- a/man/systemd.unit.xml
+++ b/man/systemd.unit.xml
@@ -275,8 +275,10 @@
                 (<option>--user</option>) and the variable
                 <varname>$SYSTEMD_UNIT_PATH</varname> is set, this
                 contents of this variable overrides the unit load
-                path.
-                </para>
+                path. If <varname>$SYSTEMD_UNIT_PATH</varname> ends
+                with an empty component (<literal>:</literal>), the
+                usual unit load path will be appended to the contents
+                of the variable.</para>
 
                 <table>
                   <title>
diff --git a/src/core/unit.c b/src/core/unit.c
index 0e4ebfde9b..b68796a941 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -2165,11 +2165,8 @@ int unit_add_two_dependencies_by_name_inverse(Unit *u, UnitDependency d, UnitDep
 }
 
 int set_unit_path(const char *p) {
-        _cleanup_free_ char *c = NULL;
-
         /* This is mostly for debug purposes */
-        c = path_make_absolute_cwd(p);
-        if (setenv("SYSTEMD_UNIT_PATH", c, 0) < 0)
+        if (setenv("SYSTEMD_UNIT_PATH", p, 0) < 0)
                 return -errno;
 
         return 0;
diff --git a/src/shared/path-lookup.c b/src/shared/path-lookup.c
index 46cfc12d7d..7a715b7133 100644
--- a/src/shared/path-lookup.c
+++ b/src/shared/path-lookup.c
@@ -187,6 +187,7 @@ int lookup_paths_init(
                 const char *generator_late) {
 
         const char *e;
+        bool append = false; /* Add items from SYSTEMD_UNIT_PATH before normal directories */
 
         assert(p);
 
@@ -194,69 +195,76 @@ int lookup_paths_init(
          * vars */
         e = getenv("SYSTEMD_UNIT_PATH");
         if (e) {
+                if (endswith(e, ":")) {
+                        e = strndupa(e, strlen(e) - 1);
+                        append = true;
+                }
+
+                /* FIXME: empty components in other places should be
+                 * rejected. */
+
                 p->unit_path = path_split_and_make_absolute(e);
                 if (!p->unit_path)
                         return -ENOMEM;
         } else
                 p->unit_path = NULL;
 
-        if (strv_isempty(p->unit_path)) {
-                /* Nothing is set, so let's figure something out. */
-                strv_free(p->unit_path);
+        if (!p->unit_path || append) {
+                /* Let's figure something out. */
+
+                char **unit_path;
+                int r;
 
                 /* For the user units we include share/ in the search
-                 * path in order to comply with the XDG basedir
-                 * spec. For the system stuff we avoid such
-                 * nonsense. OTOH we include /lib in the search path
-                 * for the system stuff but avoid it for user
-                 * stuff. */
+                 * path in order to comply with the XDG basedir spec.
+                 * For the system stuff we avoid such nonsense. OTOH
+                 * we include /lib in the search path for the system
+                 * stuff but avoid it for user stuff. */
 
                 if (running_as == SYSTEMD_USER) {
-
                         if (personal)
-                                p->unit_path = user_dirs(generator, generator_early, generator_late);
+                                unit_path = user_dirs(generator, generator_early, generator_late);
                         else
-                                p->unit_path = strv_new(
-                                                /* If you modify this you also want to modify
-                                                 * systemduserunitpath= in systemd.pc.in, and
-                                                 * the arrays in user_dirs() above! */
-                                                STRV_IFNOTNULL(generator_early),
-                                                USER_CONFIG_UNIT_PATH,
-                                                "/etc/systemd/user",
-                                                "/run/systemd/user",
-                                                STRV_IFNOTNULL(generator),
-                                                "/usr/local/lib/systemd/user",
-                                                "/usr/local/share/systemd/user",
-                                                USER_DATA_UNIT_PATH,
-                                                "/usr/lib/systemd/user",
-                                                "/usr/share/systemd/user",
-                                                STRV_IFNOTNULL(generator_late),
-                                                NULL);
-
-                        if (!p->unit_path)
-                                return -ENOMEM;
-
-                } else {
-                        p->unit_path = strv_new(
+                                unit_path = strv_new(
                                         /* If you modify this you also want to modify
-                                         * systemdsystemunitpath= in systemd.pc.in! */
+                                         * systemduserunitpath= in systemd.pc.in, and
+                                         * the arrays in user_dirs() above! */
                                         STRV_IFNOTNULL(generator_early),
-                                        SYSTEM_CONFIG_UNIT_PATH,
-                                        "/etc/systemd/system",
-                                        "/run/systemd/system",
+                                        USER_CONFIG_UNIT_PATH,
+                                        "/etc/systemd/user",
+                                        "/run/systemd/user",
                                         STRV_IFNOTNULL(generator),
-                                        "/usr/local/lib/systemd/system",
-                                        SYSTEM_DATA_UNIT_PATH,
-                                        "/usr/lib/systemd/system",
-#ifdef HAVE_SPLIT_USR
-                                        "/lib/systemd/system",
-#endif
+                                        "/usr/local/lib/systemd/user",
+                                        "/usr/local/share/systemd/user",
+                                        USER_DATA_UNIT_PATH,
+                                        "/usr/lib/systemd/user",
+                                        "/usr/share/systemd/user",
                                         STRV_IFNOTNULL(generator_late),
                                         NULL);
+                } else
+                        unit_path = strv_new(
+                                /* If you modify this you also want to modify
+                                 * systemdsystemunitpath= in systemd.pc.in! */
+                                STRV_IFNOTNULL(generator_early),
+                                SYSTEM_CONFIG_UNIT_PATH,
+                                "/etc/systemd/system",
+                                "/run/systemd/system",
+                                STRV_IFNOTNULL(generator),
+                                "/usr/local/lib/systemd/system",
+                                SYSTEM_DATA_UNIT_PATH,
+                                "/usr/lib/systemd/system",
+#ifdef HAVE_SPLIT_USR
+                                "/lib/systemd/system",
+#endif
+                                STRV_IFNOTNULL(generator_late),
+                                NULL);
 
-                        if (!p->unit_path)
-                                return -ENOMEM;
-                }
+                if (!unit_path)
+                        return -ENOMEM;
+
+                r = strv_extend_strv(&p->unit_path, unit_path);
+                if (r < 0)
+                        return r;
         }
 
         if (!path_strv_resolve_uniq(p->unit_path, root_dir))