udevadm trigger: log errors and return first failure

When udevadm trigger is called, the list of devices to trigger is always
generated through enumeration, and devices can come and go, so we should not
treat -ENOENT as a failure. But other types of failure should be logged.
It seems they were logged until baa30fbc2c.

Also, return the first error. (I'm not sure if there are other failure modes
which we want to ignore. If they are, they'll need to be whitelisted like
-ENOENT.).

src/udev/udevadm-trigger.c

@@ -25,7 +25,7 @@ static bool arg_dry_run = false;
 
 static int exec_list(sd_device_enumerator *e, const char *action, Set *settle_set) {
         sd_device *d;
-        int r;
+        int r, ret = 0;
 
         FOREACH_DEVICE_AND_SUBSYSTEM(e, d) {
                 _cleanup_free_ char *filename = NULL;
@@ -45,7 +45,10 @@ static int exec_list(sd_device_enumerator *e, const char *action, Set *settle_se
 
                 r = write_string_file(filename, action, WRITE_STRING_FILE_DISABLE_BUFFER);
                 if (r < 0) {
-                        log_debug_errno(r, "Failed to write '%s' to '%s', ignoring: %m", action, filename);
+                        log_full_errno(r == -ENOENT ? LOG_DEBUG : LOG_ERR, r,
+                                       "Failed to write '%s' to '%s': %m", action, filename);
+                        if (ret == 0 && r != -ENOENT)
+                                ret = r;
                         continue;
                 }
 
@@ -56,7 +59,7 @@ static int exec_list(sd_device_enumerator *e, const char *action, Set *settle_se
                 }
         }
 
-        return 0;
+        return ret;
 }
 
 static int device_monitor_handler(sd_device_monitor *m, sd_device *dev, void *userdata) {