From 10b3ce781bbad6a8636a8cc442065c93595bf63a Mon Sep 17 00:00:00 2001
From: Yu Watanabe <watanabe.yu+github@gmail.com>
Date: Dec 08 2022 20:29:56 +0000
Subject: core/device: update comment


(cherry picked from commit 54a4d71509c0f3401aa576346754a0781795214a)

---

diff --git a/src/core/device.c b/src/core/device.c
index 224fc90..c79fd08 100644
--- a/src/core/device.c
+++ b/src/core/device.c
@@ -267,7 +267,7 @@ static int device_coldplug(Unit *u) {
          * 1. MANAGER_IS_RUNNING() == false
          * 2. enumerate devices: manager_enumerate() -> device_enumerate()
          *    Device.enumerated_found is set.
-         * 3. deserialize devices: manager_deserialize() -> device_deserialize()
+         * 3. deserialize devices: manager_deserialize() -> device_deserialize_item()
          *    Device.deserialize_state and Device.deserialized_found are set.
          * 4. coldplug devices: manager_coldplug() -> device_coldplug()
          *    deserialized properties are copied to the main properties.
@@ -282,23 +282,28 @@ static int device_coldplug(Unit *u) {
          *
          * - On switch-root, the udev database may be cleared, except for devices with sticky bit, i.e.
          *   OPTIONS="db_persist". Hence, almost no devices are enumerated in the step 2. However, in
-         *   general, we have several serialized devices. So, DEVICE_FOUND_UDEV bit in the deserialized_found
-         *   must be ignored, as udev rules in initrd and the main system are often different. If the
-         *   deserialized state is DEVICE_PLUGGED, we need to downgrade it to DEVICE_TENTATIVE. Unlike the
-         *   other starting mode, MANAGER_IS_SWITCHING_ROOT() is true when device_coldplug() and
-         *   device_catchup() are called.  Hence, let's conditionalize the operations by using the
-         *   flag. After switch-root, systemd-udevd will (re-)process all devices, and the Device.found and
-         *   Device.state will be adjusted.
+         *   general, we have several serialized devices. So, DEVICE_FOUND_UDEV bit in the
+         *   Device.deserialized_found must be ignored, as udev rules in initrd and the main system are often
+         *   different. If the deserialized state is DEVICE_PLUGGED, we need to downgrade it to
+         *   DEVICE_TENTATIVE. Unlike the other starting mode, MANAGER_IS_SWITCHING_ROOT() is true when
+         *   device_coldplug() and device_catchup() are called. Hence, let's conditionalize the operations by
+         *   using the flag. After switch-root, systemd-udevd will (re-)process all devices, and the
+         *   Device.found and Device.state will be adjusted.
          *
-         * - On reload or reexecute, we can trust enumerated_found, deserialized_found, and deserialized_state.
-         *   Of course, deserialized parameters may be outdated, but the unit state can be adjusted later by
-         *   device_catchup() or uevents. */
+         * - On reload or reexecute, we can trust Device.enumerated_found, Device.deserialized_found, and
+         *   Device.deserialized_state. Of course, deserialized parameters may be outdated, but the unit
+         *   state can be adjusted later by device_catchup() or uevents. */
 
         if (MANAGER_IS_SWITCHING_ROOT(m) &&
             !FLAGS_SET(d->enumerated_found, DEVICE_FOUND_UDEV)) {
-                found &= ~DEVICE_FOUND_UDEV; /* ignore DEVICE_FOUND_UDEV bit */
+
+                /* The device has not been enumerated. On switching-root, such situation is natural. See the
+                 * above comment. To prevent problematic state transition active → dead → active, let's
+                 * drop the DEVICE_FOUND_UDEV flag and downgrade state to DEVICE_TENTATIVE(activating). See
+                 * issue #12953 and #23208. */
+                found &= ~DEVICE_FOUND_UDEV;
                 if (state == DEVICE_PLUGGED)
-                        state = DEVICE_TENTATIVE; /* downgrade state */
+                        state = DEVICE_TENTATIVE;
         }
 
         if (d->found == found && d->state == state)