udevd: serialize device chain event sequence

[Kay Sievers <kay.sievers@vrfy.org>]

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Any objections against the serialization of the event sequence of a
chain of devices. Currently udevd delays only events for the same
DEVPATH.

Example of an "add" event sequence:
  /block/sda
  /block/sda/sda1

With this change, we make sure, that the udev process handling /block/sda
has finished its work (waited for all attributes, created the node) before
we fork the udev event for /block/sda/sda1. This way the event for sda1 can
be sure, that the node for the main device is already created (may be
useful for disk labels).

The main motivation to do this is the program execution of the dev.d/
and hotplug.d/ directory. If we don't wait for the parent event to exit,
we can't be sure that the executed scripts are run in the right order.

It will not affect any parallel device handling, only the sequence of the
devices directory chain is serialized. The 10.000 disks plugged in will still
run as parallel events :)

Thanks,
Kay

[-- Attachment #2: udevd-serialize-event-sequence-01.patch --]
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===== udevd.c 1.53 vs edited =====
--- 1.53/udevd.c	2004-11-28 05:56:22 +01:00
+++ edited/udevd.c	2004-12-09 00:04:57 +01:00
@@ -151,16 +151,24 @@
 	}
 }
 
-/* returns already running task with devpath */
+/* returns still running task for the same event sequence */
 static struct hotplug_msg *running_with_devpath(struct hotplug_msg *msg)
 {
 	struct hotplug_msg *loop_msg;
+	int i;
+
 	list_for_each_entry(loop_msg, &running_list, list) {
 		if (loop_msg->devpath == NULL || msg->devpath == NULL)
 			continue;
 
-		if (strcmp(loop_msg->devpath, msg->devpath) == 0)
-			return loop_msg;
+		/* is one DEVPATH a complete part of the other? */
+		for (i = 0; i < DEVPATH_SIZE; i++) {
+			if (loop_msg->devpath[i] == '\0' || msg->devpath[i] == '\0')
+				return loop_msg;
+
+			if (loop_msg->devpath[i] != msg->devpath[i])
+				break;
+		}
 	}
 
 	return NULL;
@@ -181,8 +189,8 @@
 			udev_run(loop_msg);
 			dbg("moved seq %llu to running list", loop_msg->seqnum);
 		} else {
-			dbg("delay seq %llu, cause seq %llu already working on '%s'",
-				loop_msg->seqnum, msg->seqnum, msg->devpath);
+			dbg("delay seq %llu (%s), cause seq %llu (%s) is still running",
+			    loop_msg->seqnum, loop_msg->devpath, msg->seqnum, msg->devpath);
 		}
 	}
 }