Work around some crazy race condition in devicemapper device creation

pkgs/os-specific/linux/lvm2/assume-uevent-generated.patch

@@ -0,0 +1,39 @@
+Work around LVM/cryptsetup errors like:
+
+  semid 32768: semop failed for cookie 0xd4d41f4: incorrect semaphore state
+  Failed to set a proper state for notification semaphore identified by cookie value 223166964 (0xd4d41f4) to initialize waiting for incoming notifications.
+
+and (when running "cryptsetup --debug"):
+
+  Uevent not generated! Calling udev_complete internally to avoid process lock-up.
+
+Here for some reason libdm *thinks* that the uevent hasn't been
+emitted, so it calls udev_complete.  But the uevent actually *has*
+been emitted, so udev calls ‘dmsetup udevcomplete’ as well, leading to
+a race.
+
+This is probably a reoccurence of the problem described here:
+
+  http://www.redhat.com/archives/dm-devel/2011-August/msg00075.html
+  http://www.redhat.com/archives/linux-lvm/2011-September/msg00023.html
+
+which was fixed in the kernel, so it's not clear why it's surfacing
+again.  Maybe netlink_broadcast_filtered() has started returning some
+other bogus error code.
+  
+diff -ru -x '*~' LVM2.2.02.98/libdm/ioctl/libdm-iface.c LVM2.2.02.98-new/libdm/ioctl/libdm-iface.c
+--- LVM2.2.02.98/libdm/ioctl/libdm-iface.c	2012-10-15 10:24:58.000000000 -0400
++++ LVM2.2.02.98-new/libdm/ioctl/libdm-iface.c	2012-10-15 14:19:06.774363736 -0400
+@@ -1754,9 +1754,12 @@
+ 
+ 	if (ioctl_with_uevent && dm_udev_get_sync_support() &&
+ 	    !_check_uevent_generated(dmi)) {
++		log_debug("warning: Uevent might not be generated!");
++#if 0
+ 		log_debug("Uevent not generated! Calling udev_complete "
+ 			  "internally to avoid process lock-up.");
+ 		_udev_complete(dmt);
++#endif
+ 	}
+ 
+ 	if (!_dm_ioctl_unmangle_names(dmt->type, dmi))

pkgs/os-specific/linux/lvm2/default.nix

@@ -12,6 +12,8 @@ stdenv.mkDerivation {
     sha256 = "0r6q6z8ip6q5qgkzng0saljassp4912k6i21ra10vq7pzrc0l0vi";
   };
 
+  patches = [ ./assume-uevent-generated.patch ];
+
   configureFlags =
     "--disable-readline --enable-udev_rules --enable-udev_sync --enable-pkgconfig --enable-applib";