From bf059e4050bd4f49e3665172360c8ede5e102157 Mon Sep 17 00:00:00 2001
From: Marek Marczykowski <marmarek@invisiblethingslab.com>
Date: Sun, 27 Jan 2013 00:02:30 +0100
Subject: [PATCH] dom0/udev: allow only one xenstore-write at the time

This apparently causes deadlocks when many xenstore-write (one for each block
device) called at the same time.
---
 misc/block_add_change | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/misc/block_add_change b/misc/block_add_change
index b366f9d..7b65a2d 100755
--- a/misc/block_add_change
+++ b/misc/block_add_change
@@ -43,6 +43,17 @@ fi
 if [ -d /sys/$DEVPATH/loop ]; then
     DESC=$(cat /sys/$DEVPATH/loop/backing_file)
 fi
+
+# Get lock only in dom0 - there are so many block devices so it causes xenstore
+# deadlocks sometimes.
+if [ -f /etc/qubes-release ]; then
+    # Skip xenstore-write if cannot obtain lock. This can mean very early system startup
+    # stage without /run mounted (or populated). Devices will be rediscovered later
+    # by qubes-core startup script.
+    exec 9>>/var/run/qubes/block-xenstore.lock || exit 0
+    flock 9
+fi
+
 xenstore-write "$XS_KEY/desc" "$DESC" "$XS_KEY/size" "$SIZE" "$XS_KEY/mode" "$MODE"
 echo QUBES_EXPOSED=1