core: rework device state logic

This change introduces a new state "tentative" for device units. Device
units are considered "plugged" when udev announced them, "dead" when
they are not available in the kernel, and "tentative" when they are
referenced in /proc/self/mountinfo or /proc/swaps but not (yet)
announced via udev.

This should fix a race when device nodes (like loop devices) are created
and immediately mounted. Previously, systemd might end up seeing the
mount unit before the device, and would thus pull down the mount because
its BindTo dependency on the device would not be fulfilled.

1 files changed, 12 insertions, 2 deletions

diff --git a/src/core/device.h b/src/core/device.h
index 906508530d..9f46e08953 100644
--- a/src/core/device.h
+++ b/src/core/device.h
@@ -28,20 +28,28 @@ typedef struct Device Device;
  * simplifies the state engine greatly */
 typedef enum DeviceState {
         DEVICE_DEAD,
-        DEVICE_PLUGGED,
+        DEVICE_TENTATIVE, /* mounted or swapped, but not (yet) announced by udev */
+        DEVICE_PLUGGED,   /* announced by udev */
         _DEVICE_STATE_MAX,
         _DEVICE_STATE_INVALID = -1
 } DeviceState;
 
+typedef enum DeviceFound {
+        DEVICE_NOT_FOUND = 0,
+        DEVICE_FOUND_UDEV = 1,
+        DEVICE_FOUND_MOUNT = 2,
+        DEVICE_FOUND_SWAP = 4,
+} DeviceFound;
+
 struct Device {
         Unit meta;
 
         char *sysfs;
+        DeviceFound found;
 
         /* In order to be able to distinguish dependencies on
         different device nodes we might end up creating multiple
         devices for the same sysfs path. We chain them up here. */
-
         LIST_FIELDS(struct Device, same_sysfs);
 
         DeviceState state;
@@ -51,3 +59,5 @@ extern const UnitVTable device_vtable;
 
 const char* device_state_to_string(DeviceState i) _const_;
 DeviceState device_state_from_string(const char *s) _pure_;
+
+int device_found_node(Manager *m, const char *node, bool add, DeviceFound found, bool now);