shared/unit-file: add a function to validate unit alias symlinks

It turns out most possible symlinks are invalid, because the type has to match,
and template units can only be linked to template units.

I'm not sure if the existing code made the same checks consistently. At least
I don't see the same rules expressed in a single place.

2 files changed, 37 insertions, 0 deletions

diff --git a/src/test/meson.build b/src/test/meson.build
index ddc04dda65..c25ecf62fc 100644
--- a/src/test/meson.build
+++ b/src/test/meson.build
@@ -137,6 +137,10 @@ tests += [
          [],
          'ENABLE_EFI'],
 
+        [['src/test/test-unit-file.c'],
+         [],
+         []],
+
         [['src/test/test-unit-name.c',
           'src/test/test-helper.c'],
          [libcore,
diff --git a/src/test/test-unit-file.c b/src/test/test-unit-file.c
new file mode 100644
index 0000000000..5e281b28d5
--- /dev/null
+++ b/src/test/test-unit-file.c
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include "path-lookup.h"
+#include "strv.h"
+#include "tests.h"
+#include "unit-file.h"
+
+static void test_unit_validate_alias_symlink_and_warn(void) {
+        log_info("/* %s */", __func__);
+
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a.service", "/other/b.service") == 0);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a.service", "/other/b.socket") == -EXDEV);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a.service", "/other/b.foobar") == -EXDEV);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a@.service", "/other/b@.service") == 0);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a@.service", "/other/b@.socket") == -EXDEV);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a@XXX.service", "/other/b@YYY.service") == -EXDEV);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a@XXX.service", "/other/b@YYY.socket") == -EXDEV);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a@.service", "/other/b@YYY.service") == -EXDEV);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a@XXX.service", "/other/b@XXX.service") == 0);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a@XXX.service", "/other/b@.service") == 0);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a@.service", "/other/b.service") == -EXDEV);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a.service", "/other/b@.service") == -EXDEV);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a@.slice", "/other/b.slice") == -EINVAL);
+        assert_se(unit_validate_alias_symlink_and_warn("/path/a.slice", "/other/b.slice") == -EINVAL);
+}
+
+int main(int argc, char **argv) {
+        test_setup_logging(LOG_DEBUG);
+
+        test_unit_validate_alias_symlink_and_warn();
+
+        return 0;
+}