install: when a template unit is instantiated via a /usr symlink, consider it enabled

If a unit foobar@.service stored below /usr is instantiated via a
symlink foobar@quux.service also below /usr, then we should consider the
instance statically enabled, while the template itself should continue
to be considered enabled/disabled/static depending on its [Install]
section.

In order to implement this we'll now look for enablement symlinks in all
unit search paths, not just in the config and runtime dirs.

Fixes: #5136

2 files changed, 107 insertions, 35 deletions

diff --git a/src/shared/install.c b/src/shared/install.c
index 975a789ebe..b938507587 100644
--- a/src/shared/install.c
+++ b/src/shared/install.c
@@ -208,7 +208,7 @@ static int path_is_control(const LookupPaths *p, const char *path) {
                path_equal_ptr(parent, p->runtime_control);
 }
 
-static int path_is_config(const LookupPaths *p, const char *path) {
+static int path_is_config(const LookupPaths *p, const char *path, bool check_parent) {
         _cleanup_free_ char *parent = NULL;
 
         assert(p);
@@ -217,15 +217,19 @@ static int path_is_config(const LookupPaths *p, const char *path) {
         /* Note that we do *not* have generic checks for /etc or /run in place, since with
          * them we couldn't discern configuration from transient or generated units */
 
-        parent = dirname_malloc(path);
-        if (!parent)
-                return -ENOMEM;
+        if (check_parent) {
+                parent = dirname_malloc(path);
+                if (!parent)
+                        return -ENOMEM;
 
-        return path_equal_ptr(parent, p->persistent_config) ||
-               path_equal_ptr(parent, p->runtime_config);
+                path = parent;
+        }
+
+        return path_equal_ptr(path, p->persistent_config) ||
+               path_equal_ptr(path, p->runtime_config);
 }
 
-static int path_is_runtime(const LookupPaths *p, const char *path) {
+static int path_is_runtime(const LookupPaths *p, const char *path, bool check_parent) {
         _cleanup_free_ char *parent = NULL;
         const char *rpath;
 
@@ -239,16 +243,20 @@ static int path_is_runtime(const LookupPaths *p, const char *path) {
         if (rpath && path_startswith(rpath, "/run"))
                 return true;
 
-        parent = dirname_malloc(path);
-        if (!parent)
-                return -ENOMEM;
+        if (check_parent) {
+                parent = dirname_malloc(path);
+                if (!parent)
+                        return -ENOMEM;
 
-        return path_equal_ptr(parent, p->runtime_config) ||
-               path_equal_ptr(parent, p->generator) ||
-               path_equal_ptr(parent, p->generator_early) ||
-               path_equal_ptr(parent, p->generator_late) ||
-               path_equal_ptr(parent, p->transient) ||
-               path_equal_ptr(parent, p->runtime_control);
+                path = parent;
+        }
+
+        return path_equal_ptr(path, p->runtime_config) ||
+               path_equal_ptr(path, p->generator) ||
+               path_equal_ptr(path, p->generator_early) ||
+               path_equal_ptr(path, p->generator_late) ||
+               path_equal_ptr(path, p->transient) ||
+               path_equal_ptr(path, p->runtime_control);
 }
 
 static int path_is_vendor(const LookupPaths *p, const char *path) {
@@ -826,7 +834,9 @@ static int find_symlinks_in_scope(
                 const char *name,
                 UnitFileState *state) {
 
-        bool same_name_link_runtime = false, same_name_link = false;
+        bool same_name_link_runtime = false, same_name_link_config = false;
+        bool enabled_in_runtime = false, enabled_at_all = false;
+        char **p;
         int r;
 
         assert(scope >= 0);
@@ -834,27 +844,66 @@ static int find_symlinks_in_scope(
         assert(paths);
         assert(name);
 
-        /* First look in the persistent config path */
-        r = find_symlinks(paths->root_dir, name, paths->persistent_config, paths, &same_name_link);
-        if (r < 0)
-                return r;
-        if (r > 0) {
-                *state = UNIT_FILE_ENABLED;
-                return r;
+        STRV_FOREACH(p, paths->search_path)  {
+                bool same_name_link = false;
+
+                r = find_symlinks(paths->root_dir, name, *p, paths, &same_name_link);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        /* We found symlinks in this dir? Yay! Let's see where precisely it is enabled. */
+
+                        r = path_is_config(paths, *p, false);
+                        if (r < 0)
+                                return r;
+                        if (r > 0) {
+                                /* This is the best outcome, let's return it immediately. */
+                                *state = UNIT_FILE_ENABLED;
+                                return 1;
+                        }
+
+                        r = path_is_runtime(paths, *p, false);
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                enabled_in_runtime = true;
+                        else
+                                enabled_at_all = true;
+
+                } else if (same_name_link) {
+
+                        r = path_is_config(paths, *p, false);
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                same_name_link_config = true;
+                        else {
+                                r = path_is_runtime(paths, *p, false);
+                                if (r < 0)
+                                        return r;
+                                if (r > 0)
+                                        same_name_link_runtime = true;
+                        }
+                }
         }
 
-        /* Then look in runtime config path */
-        r = find_symlinks(paths->root_dir, name, paths->runtime_config, paths, &same_name_link_runtime);
-        if (r < 0)
-                return r;
-        if (r > 0) {
+        if (enabled_in_runtime) {
                 *state = UNIT_FILE_ENABLED_RUNTIME;
-                return r;
+                return 1;
+        }
+
+        /* Here's a special rule: if the unit we are looking for is an instance, and it symlinked in the search path
+         * outside of runtime and configuration directory, then we consider it statically enabled. Note we do that only
+         * for instance, not for regular names, as those are merely aliases, while instances explicitly instantiate
+         * something, and hence are a much stronger concept. */
+        if (enabled_at_all && unit_name_is_valid(name, UNIT_NAME_INSTANCE)) {
+                *state = UNIT_FILE_STATIC;
+                return 1;
         }
 
         /* Hmm, we didn't find it, but maybe we found the same name
          * link? */
-        if (same_name_link) {
+        if (same_name_link_config) {
                 *state = UNIT_FILE_LINKED;
                 return 1;
         }
@@ -1409,7 +1458,7 @@ static int install_info_traverse(
                         return -ELOOP;
 
                 if (!(flags & SEARCH_FOLLOW_CONFIG_SYMLINKS)) {
-                        r = path_is_config(paths, i->path);
+                        r = path_is_config(paths, i->path, true);
                         if (r < 0)
                                 return r;
                         if (r > 0)
@@ -2040,7 +2089,7 @@ static int path_shall_revert(const LookupPaths *paths, const char *path) {
 
         /* Checks whether the path is one where the drop-in directories shall be removed. */
 
-        r = path_is_config(paths, path);
+        r = path_is_config(paths, path, true);
         if (r != 0)
                 return r;
 
@@ -2148,7 +2197,7 @@ int unit_file_revert(
                                 if (errno != ENOENT)
                                         return -errno;
                         } else if (S_ISREG(st.st_mode) || S_ISLNK(st.st_mode)) {
-                                r = path_is_config(&paths, path);
+                                r = path_is_config(&paths, path, true);
                                 if (r < 0)
                                         return r;
                                 if (r > 0) {
@@ -2494,7 +2543,7 @@ static int unit_file_lookup_state(
         switch (i->type) {
 
         case UNIT_FILE_TYPE_MASKED:
-                r = path_is_runtime(paths, i->path);
+                r = path_is_runtime(paths, i->path, true);
                 if (r < 0)
                         return r;
 
diff --git a/src/test/test-install-root.c b/src/test/test-install-root.c
index d0bc8004f3..575401cb91 100644
--- a/src/test/test-install-root.c
+++ b/src/test/test-install-root.c
@@ -736,6 +736,28 @@ static void test_preset_order(const char *root) {
         assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "prefix-2.service", &state) >= 0 && state == UNIT_FILE_DISABLED);
 }
 
+static void test_static_instance(const char *root) {
+        UnitFileState state;
+        const char *p;
+
+        assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "static-instance@.service", &state) == -ENOENT);
+        assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "static-instance@foo.service", &state) == -ENOENT);
+
+        p = strjoina(root, "/usr/lib/systemd/system/static-instance@.service");
+        assert_se(write_string_file(p,
+                                    "[Install]\n"
+                                    "WantedBy=multi-user.target\n", WRITE_STRING_FILE_CREATE) >= 0);
+
+        assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "static-instance@.service", &state) >= 0 && state == UNIT_FILE_DISABLED);
+        assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "static-instance@foo.service", &state) >= 0 && state == UNIT_FILE_DISABLED);
+
+        p = strjoina(root, "/usr/lib/systemd/system/static-instance@foo.service");
+        assert_se(symlink("static-instance@.service", p) >= 0);
+
+        assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "static-instance@.service", &state) >= 0 && state == UNIT_FILE_DISABLED);
+        assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "static-instance@foo.service", &state) >= 0 && state == UNIT_FILE_STATIC);
+}
+
 int main(int argc, char *argv[]) {
         char root[] = "/tmp/rootXXXXXX";
         const char *p;
@@ -766,6 +788,7 @@ int main(int argc, char *argv[]) {
         test_preset_and_list(root);
         test_preset_order(root);
         test_revert(root);
+        test_static_instance(root);
 
         assert_se(rm_rf(root, REMOVE_ROOT|REMOVE_PHYSICAL) >= 0);