udev-node: use symlink_atomic_full_label() to create devlink

If the filename of a device symlink is too long, then the temporary
filename may become invalid, and we fail to create symlink.

The function `tempfn_random()` used in symlink_atomic_full() generates
a safe temporary filename.

Note that, thanks to the PR systemd#23043, now only one worker can handle
the same symlink simultaneously. Hence, the device ID based temporary
filename is not necessary.

src/udev/udev-node.c

@@ -14,6 +14,7 @@
 #include "format-util.h"
 #include "fs-util.h"
 #include "hexdecoct.h"
+#include "label.h"
 #include "mkdir-label.h"
 #include "parse-util.h"
 #include "path-util.h"
@@ -69,8 +70,6 @@ int udev_node_cleanup(void) {
 }
 
 static int node_symlink(sd_device *dev, const char *devnode, const char *slink) {
-        _cleanup_free_ char *target = NULL;
-        const char *id, *slink_tmp;
         struct stat st;
         int r;
 
@@ -91,34 +90,16 @@ static int node_symlink(sd_device *dev, const char *devnode, const char *slink)
         } else if (errno != ENOENT)
                 return log_device_debug_errno(dev, errno, "Failed to lstat() '%s': %m", slink);
 
-        /* use relative link */
-        r = path_make_relative_parent(slink, devnode, &target);
-        if (r < 0)
-                return log_device_debug_errno(dev, r, "Failed to get relative path from '%s' to '%s': %m", slink, devnode);
-
-        r = device_get_device_id(dev, &id);
+        r = mkdir_parents_label(slink, 0755);
         if (r < 0)
-                return log_device_debug_errno(dev, r, "Failed to get device id: %m");
-
-        slink_tmp = strjoina(slink, ".tmp-", id);
-        (void) unlink(slink_tmp);
+                return log_device_debug_errno(dev, r, "Failed to create parent directory of '%s': %m", slink);
 
-        r = mkdir_parents_label(slink_tmp, 0755);
-        if (r < 0)
-                return log_device_debug_errno(dev, r, "Failed to create parent directory of '%s': %m", slink_tmp);
-
-        mac_selinux_create_file_prepare(slink_tmp, S_IFLNK);
-        r = RET_NERRNO(symlink(target, slink_tmp));
-        mac_selinux_create_file_clear();
+        /* use relative link */
+        r = symlink_atomic_full_label(devnode, slink, /* make_relative = */ true);
         if (r < 0)
-                return log_device_debug_errno(dev, r, "Failed to create symlink '%s' to '%s': %m", slink_tmp, target);
-
-        if (rename(slink_tmp, slink) < 0) {
-                r = log_device_debug_errno(dev, errno, "Failed to rename '%s' to '%s': %m", slink_tmp, slink);
-                (void) unlink(slink_tmp);
-                return r;
-        }
+                return log_device_debug_errno(dev, r, "Failed to create symlink '%s' to '%s': %m", slink, devnode);
 
+        log_device_debug(dev, "Successfully created symlink '%s' to '%s'", slink, devnode);
         return 0;
 }