basic/path-util: do not say that /dev and /sys are device paths

"/dev" or "/dev/" is the mount point, not a device path. In particular,
'systemctl status /dev' clearly does not refer to a device, so let's tweak
the code a bit to say that those are not device paths.

(Treating "/../dev" same as "/dev" would be also be reasonable, but that
requires chase(), which requires disk access, which we don't want to do from
this lightweight function.)

(cherry picked from commit 8f1998b)
(cherry picked from commit fc13a26)

src/basic/path-util.c

@@ -1252,9 +1252,16 @@ bool hidden_or_backup_file(const char *filename) {
 bool is_device_path(const char *path) {
 
         /* Returns true for paths that likely refer to a device, either by path in sysfs or to something in
-         * /dev. */
+         * /dev. This accepts any path that starts with /dev/ or /sys/ and has something after that prefix.
+         * It does not actually resolve the path.
+         *
+         * Examples:
+         * /dev/sda, /dev/sda/foo, /sys/class, /dev/.., /sys/.., /./dev/foo → yes.
+         * /../dev/sda, /dev, /sys, /usr/path, /usr/../dev/sda → no.
+         */
 
-        return PATH_STARTSWITH_SET(path, "/dev/", "/sys/");
+        const char *p = PATH_STARTSWITH_SET(ASSERT_PTR(path), "/dev/", "/sys/");
+        return !isempty(p);
 }
 
 bool valid_device_node_path(const char *path) {

src/test/test-path-util.c

@@ -104,18 +104,18 @@ TEST(is_device_path) {
         assert_se(!is_device_path(""));
         assert_se(!is_device_path(".."));
 
-        assert_se( is_device_path("/dev"));
-        assert_se( is_device_path("/./dev"));
-        assert_se( is_device_path("/./dev/."));
+        assert_se(!is_device_path("/dev"));
+        assert_se(!is_device_path("/./dev"));
+        assert_se(!is_device_path("/./dev/."));
         assert_se(!is_device_path("/./dev."));
         assert_se( is_device_path("/./dev/foo"));
         assert_se( is_device_path("/./dev/./foo"));
         assert_se(!is_device_path("/./dev./foo"));
-        assert_se( is_device_path("//dev"));
-        assert_se( is_device_path("///dev"));
-        assert_se( is_device_path("/dev/"));
-        assert_se( is_device_path("///dev/"));
-        assert_se( is_device_path("/./dev/"));
+        assert_se(!is_device_path("//dev"));
+        assert_se(!is_device_path("///dev"));
+        assert_se(!is_device_path("/dev/"));
+        assert_se(!is_device_path("///dev/"));
+        assert_se(!is_device_path("/./dev/"));
         assert_se(!is_device_path("/../dev/"));
         assert_se( is_device_path("/dev/sda"));
         assert_se( is_device_path("/dev/sda5"));
@@ -125,19 +125,19 @@ TEST(is_device_path) {
         assert_se(!is_device_path("/../../dev/sda5"));
         assert_se(!is_device_path("/../../../dev/sda5b3"));
         assert_se(!is_device_path("/.././.././dev/sda5b3/idontexit"));
-        assert_se( is_device_path("/sys"));
-        assert_se( is_device_path("/sys/"));
-        assert_se( is_device_path("/./sys"));
-        assert_se( is_device_path("/./sys/."));
+        assert_se(!is_device_path("/sys"));
+        assert_se(!is_device_path("/sys/"));
+        assert_se(!is_device_path("/./sys"));
+        assert_se(!is_device_path("/./sys/."));
         assert_se(!is_device_path("/./sys."));
         assert_se( is_device_path("/./sys/foo"));
         assert_se( is_device_path("/./sys/./foo"));
         assert_se(!is_device_path("/./sys./foo"));
         assert_se( is_device_path("/sys/what"));
         assert_se( is_device_path("/sys/something/.."));
         assert_se( is_device_path("/sys/something/../"));
-        assert_se( is_device_path("/sys////"));
-        assert_se( is_device_path("/sys////."));
+        assert_se(!is_device_path("/sys////"));
+        assert_se(!is_device_path("/sys////."));
         assert_se( is_device_path("/sys/.."));
         assert_se( is_device_path("/sys/../"));
         assert_se(!is_device_path("/usr/../dev/sda"));