add a transient user unit directory

This patch adds a transient user unit directory under
`$XDG_RUNTIME_DIR/systemd/user/` and stores transient user-instance
units (such as those created by `systemd-run --user`) under there
instead of putting them in $XDG_CONFIG_HOME/systemd/user/.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=67331

src/core/unit.c

@@ -3080,7 +3080,11 @@ static int unit_drop_in_dir(Unit *u, UnitSetPropertiesMode mode, bool transient,
         if (u->manager->running_as == SYSTEMD_USER) {
                 int r;
 
-                r = user_config_home(dir);
+                if (mode == UNIT_PERSISTENT && !transient)
+                        r = user_config_home(dir);
+                else
+                        r = user_runtime(dir);
+
                 if (r == 0)
                         return -ENOENT;
                 return r;
@@ -3228,7 +3232,7 @@ int unit_make_transient(Unit *u) {
         if (u->manager->running_as == SYSTEMD_USER) {
                 _cleanup_free_ char *c = NULL;
 
-                r = user_config_home(&c);
+                r = user_runtime(&c);
                 if (r < 0)
                         return r;
                 if (r == 0)

src/shared/install.c

@@ -105,10 +105,14 @@ static int get_config_path(UnitFileScope scope, bool runtime, const char *root_d
 
         case UNIT_FILE_USER:
 
-                if (root_dir || runtime)
+                if (root_dir)
                         return -EINVAL;
 
-                r = user_config_home(&p);
+                if (runtime)
+                        r = user_runtime(&p);
+                else
+                        r = user_config_home(&p);
+
                 if (r <= 0)
                         return r < 0 ? r : -ENOENT;
 
@@ -527,36 +531,33 @@ static int find_symlinks_in_scope(
                 UnitFileState *state) {
 
         int r;
-        _cleanup_free_ char *path2 = NULL;
+        _cleanup_free_ char *path = NULL;
         bool same_name_link_runtime = false, same_name_link = false;
 
         assert(scope >= 0);
         assert(scope < _UNIT_FILE_SCOPE_MAX);
         assert(name);
 
-        if (scope == UNIT_FILE_SYSTEM || scope == UNIT_FILE_GLOBAL) {
-                _cleanup_free_ char *path = NULL;
 
-                /* First look in runtime config path */
-                r = get_config_path(scope, true, root_dir, &path);
-                if (r < 0)
-                        return r;
-
-                r = find_symlinks(name, path, &same_name_link_runtime);
-                if (r < 0)
-                        return r;
-                else if (r > 0) {
-                        *state = UNIT_FILE_ENABLED_RUNTIME;
-                        return r;
-                }
-        }
-
-        /* Then look in the normal config path */
-        r = get_config_path(scope, false, root_dir, &path2);
+        /* First look in runtime config path */
+        r = get_config_path(scope, true, root_dir, &path);
         if (r < 0)
                 return r;
 
-        r = find_symlinks(name, path2, &same_name_link);
+        r = find_symlinks(name, path, &same_name_link_runtime);
+        if (r < 0)
+                return r;
+        else if (r > 0) {
+                *state = UNIT_FILE_ENABLED_RUNTIME;
+                return r;
+        }
+
+        /* Then look in the normal config path */
+        r = get_config_path(scope, false, root_dir, &path);
+        if (r < 0)
+                return r;
+
+        r = find_symlinks(name, path, &same_name_link);
         if (r < 0)
                 return r;
         else if (r > 0) {

src/shared/path-lookup.c

@@ -61,6 +61,23 @@ int user_config_home(char **config_home) {
         return 0;
 }
 
+int user_runtime(char **user_runtime_path) {
+        const char *e;
+        char *r;
+
+        e = getenv("XDG_RUNTIME_DIR");
+        if (e) {
+                r = strappend(e, "/systemd/user");
+                if (!r)
+                        return -ENOMEM;
+
+                *user_runtime_path = r;
+                return 1;
+        }
+
+        return 0;
+}
+
 static char** user_dirs(
                 const char *generator,
                 const char *generator_early,
@@ -69,10 +86,11 @@ static char** user_dirs(
         const char * const config_unit_paths[] = {
                 USER_CONFIG_UNIT_PATH,
                 "/etc/systemd/user",
-                "/run/systemd/user",
                 NULL
         };
 
+        const char * const runtime_unit_path = "/run/systemd/user";
+
         const char * const data_unit_paths[] = {
                 "/usr/local/lib/systemd/user",
                 "/usr/local/share/systemd/user",
@@ -83,7 +101,7 @@ static char** user_dirs(
         };
 
         const char *home, *e;
-        _cleanup_free_ char *config_home = NULL, *data_home = NULL;
+        _cleanup_free_ char *config_home = NULL, *user_runtime_dir = NULL, *data_home = NULL;
         _cleanup_strv_free_ char **config_dirs = NULL, **data_dirs = NULL;
         char **r = NULL;
 
@@ -99,6 +117,9 @@ static char** user_dirs(
         if (user_config_home(&config_home) < 0)
                 goto fail;
 
+        if (user_runtime(&user_runtime_dir) < 0)
+                goto fail;
+
         home = getenv("HOME");
 
         e = getenv("XDG_CONFIG_DIRS");
@@ -141,6 +162,13 @@ static char** user_dirs(
                 if (strv_extend(&r, config_home) < 0)
                         goto fail;
 
+        if (user_runtime_dir)
+                if (strv_extend(&r, user_runtime_dir) < 0)
+                        goto fail;
+
+        if (strv_extend(&r, runtime_unit_path) < 0)
+                goto fail;
+
         if (!strv_isempty(config_dirs))
                 if (strv_extend_strv_concat(&r, config_dirs, "/systemd/user") < 0)
                         goto fail;

src/shared/path-lookup.h

@@ -39,6 +39,7 @@ typedef enum SystemdRunningAs {
 } SystemdRunningAs;
 
 int user_config_home(char **config_home);
+int user_runtime(char **user_runtime_path);
 
 int lookup_paths_init(LookupPaths *p,
                       SystemdRunningAs running_as,