core: when loading .wants and .requires, follow the same logic as .d …

…conf dropins

Essentially, instead of sequentially adding deps based on all symlinks
encountered in .wants and .requires dirs for each name and each unit file load
path, iteratate over the load paths and unit names gathering symlinks,
then order them based on priority, filter our masked entries, and then
iterate over the final list, adding dependencies.

This patch doesn't change the logic too much, except of course the added
ability to mask entires in .wants and .requires. Adding additional filtering on
the symlinks is left for later patches.

Fixes systemd#1169.
Fixes systemd#4830.

Example log errors:
Feb 04 22:13:28 systemd[1462]: foo.service: Wants dependency on empty_file.service is masked by /home/zbyszek/.config/systemd/user/foo.service.wants/empty_file.service, ignoring
Feb 04 22:13:28 systemd[1462]: foo.service: Wants dependency on masked.service is masked by /home/zbyszek/.config/systemd/user/foo.service.wants/masked.service, ignoring

src/basic/conf-files.c

@@ -43,7 +43,6 @@ static int files_add(Hashmap *h, const char *root, const char *path, const char
         int r;
 
         assert(path);
-        assert(suffix);
 
         dirpath = prefix_roota(root, path);
 
@@ -94,7 +93,6 @@ static int conf_files_list_strv_internal(char ***strv, const char *suffix, const
         int r;
 
         assert(strv);
-        assert(suffix);
 
         /* This alters the dirs string array */
         if (!path_strv_resolve_uniq(dirs, root))
@@ -126,7 +124,6 @@ int conf_files_list_strv(char ***strv, const char *suffix, const char *root, con
         _cleanup_strv_free_ char **copy = NULL;
 
         assert(strv);
-        assert(suffix);
 
         copy = strv_copy((char**) dirs);
         if (!copy)

src/basic/dirent-util.c

@@ -70,5 +70,8 @@ bool dirent_is_file_with_suffix(const struct dirent *de, const char *suffix) {
         if (de->d_name[0] == '.')
                 return false;
 
+        if (!suffix)
+                return true;
+
         return endswith(de->d_name, suffix);
 }

src/core/load-dropin.c

@@ -22,48 +22,77 @@
 #include "load-dropin.h"
 #include "load-fragment.h"
 #include "log.h"
+#include "stat-util.h"
 #include "strv.h"
 #include "unit-name.h"
 #include "unit.h"
 
-static int add_dependency_consumer(
-                UnitDependency dependency,
-                const char *entry,
-                const char* filepath,
-                void *arg) {
-        Unit *u = arg;
+static int process_deps(Unit *u, UnitDependency dependency, const char *dir_suffix) {
+        _cleanup_strv_free_ char **paths = NULL;
+        char **p;
         int r;
 
-        assert(u);
-
-        r = unit_add_dependency_by_name(u, dependency, entry, filepath, true);
+        r = unit_file_find_dropin_paths(u->manager->lookup_paths.search_path,
+                                        u->manager->unit_path_cache,
+                                        dir_suffix,
+                                        NULL,
+                                        u->names,
+                                        &paths);
         if (r < 0)
-                log_error_errno(r, "Cannot add dependency %s to %s, ignoring: %m", entry, u->id);
+                return r;
+
+        STRV_FOREACH(p, paths) {
+                const char *entry;
+
+                entry = basename(*p);
+
+                if (null_or_empty_path(*p) > 0) {
+                        /* an error usually means an invalid symlink, which is not a mask */
+                        log_unit_debug(u, "%s dependency on %s is masked by %s, ignoring",
+                                       unit_dependency_to_string(dependency), entry, *p);
+                        continue;
+                }
+
+                r = is_symlink(*p);
+                if (r < 0) {
+                        log_unit_warning_errno(u, r, "%s dropin %s unreadable, ignoring: %m",
+                                               unit_dependency_to_string(dependency), *p);
+                        continue;
+                }
+                if (r == 0) {
+                        log_unit_warning(u, "%s dependency dropin %s is not a symlink, ignoring",
+                                         unit_dependency_to_string(dependency), *p);
+                        continue;
+                }
+
+                /* TODO: add more checks on the symlink name and target here */
+
+                r = unit_add_dependency_by_name(u, dependency, entry, *p, true);
+                if (r < 0)
+                        log_unit_error_errno(u, r, "cannot add %s dependency on %s, ignoring: %m",
+                                             unit_dependency_to_string(dependency), entry);
+        }
 
         return 0;
 }
 
 int unit_load_dropin(Unit *u) {
         _cleanup_strv_free_ char **l = NULL;
-        Iterator i;
-        char *t, **f;
+        char **f;
         int r;
 
         assert(u);
 
-        /* Load dependencies from supplementary drop-in directories */
-
-        SET_FOREACH(t, u->names, i) {
-                char **p;
+        /* Load dependencies from .wants and .requires directories */
+        r = process_deps(u, UNIT_WANTS, ".wants");
+        if (r < 0)
+                return r;
 
-                STRV_FOREACH(p, u->manager->lookup_paths.search_path) {
-                        unit_file_process_dir(u->manager->unit_path_cache, *p, t, ".wants", UNIT_WANTS,
-                                              add_dependency_consumer, u, NULL);
-                        unit_file_process_dir(u->manager->unit_path_cache, *p, t, ".requires", UNIT_REQUIRES,
-                                              add_dependency_consumer, u, NULL);
-                }
-        }
+        r = process_deps(u, UNIT_REQUIRES, ".requires");
+        if (r < 0)
+                return r;
 
+        /* Load .conf dropins */
         r = unit_find_dropin_paths(u, &l);
         if (r <= 0)
                 return 0;

src/core/load-dropin.h

@@ -25,10 +25,10 @@
 /* Read service data supplementary drop-in directories */
 
 static inline int unit_find_dropin_paths(Unit *u, char ***paths) {
-        return unit_file_find_dropin_paths(u->manager->lookup_paths.search_path,
-                                           u->manager->unit_path_cache,
-                                           u->names,
-                                           paths);
+        return unit_file_find_dropin_conf_paths(u->manager->lookup_paths.search_path,
+                                                u->manager->unit_path_cache,
+                                                u->names,
+                                                paths);
 }
 
 int unit_load_dropin(Unit *u);

src/shared/dropin.c

@@ -164,7 +164,7 @@ static int iterate_dir(
         return 0;
 }
 
-int unit_file_process_dir(
+static int unit_file_process_dir(
                 Set *unit_path_cache,
                 const char *unit_path,
                 const char *name,
@@ -210,6 +210,8 @@ int unit_file_process_dir(
 int unit_file_find_dropin_paths(
                 char **lookup_path,
                 Set *unit_path_cache,
+                const char *dir_suffix,
+                const char *file_suffix,
                 Set *names,
                 char ***paths) {
 
@@ -224,17 +226,28 @@ int unit_file_find_dropin_paths(
                 char **p;
 
                 STRV_FOREACH(p, lookup_path)
-                        unit_file_process_dir(unit_path_cache, *p, t, ".d", _UNIT_DEPENDENCY_INVALID, NULL, NULL, &strv);
+                        unit_file_process_dir(unit_path_cache, *p, t, dir_suffix, _UNIT_DEPENDENCY_INVALID, NULL, NULL, &strv);
         }
 
         if (strv_isempty(strv))
                 return 0;
 
-        r = conf_files_list_strv(&ans, ".conf", NULL, (const char**) strv);
+        r = conf_files_list_strv(&ans, file_suffix, NULL, (const char**) strv);
         if (r < 0)
-                return log_warning_errno(r, "Failed to get list of configuration files: %m");
+                return log_warning_errno(r, "Failed to sort the list of configuration files: %m");
 
         *paths = ans;
         ans = NULL;
         return 1;
 }
+
+int unit_file_find_dropin_conf_paths(
+                char **lookup_path,
+                Set *unit_path_cache,
+                Set *names,
+                char ***paths) {
+
+        return unit_file_find_dropin_paths(lookup_path, unit_path_cache,
+                                           ".d", ".conf",
+                                           names, paths);
+}

src/shared/dropin.h

@@ -44,17 +44,15 @@ typedef int (*dependency_consumer_t)(UnitDependency dependency,
                                      const char* filepath,
                                      void *arg);
 
-int unit_file_process_dir(
-                Set * unit_path_cache,
-                const char *unit_path,
-                const char *name,
-                const char *suffix,
-                UnitDependency dependency,
-                dependency_consumer_t consumer,
-                void *arg,
-                char ***strv);
-
 int unit_file_find_dropin_paths(
+                char **lookup_path,
+                Set *unit_path_cache,
+                const char *dir_suffix,
+                const char *file_suffix,
+                Set *names,
+                char ***paths);
+
+int unit_file_find_dropin_conf_paths(
                 char **lookup_path,
                 Set *unit_path_cache,
                 Set *names,

src/systemctl/systemctl.c

@@ -2601,7 +2601,7 @@ static int unit_find_paths(
                         return log_error_errno(r, "Failed to add unit name: %m");
 
                 if (dropin_paths) {
-                        r = unit_file_find_dropin_paths(lp->search_path, NULL, names, &dropins);
+                        r = unit_file_find_dropin_conf_paths(lp->search_path, NULL, names, &dropins);
                         if (r < 0)
                                 return r;
                 }