[PATCH 3/4] kvm tools: Add a brlock

[Sasha Levin <levinsasha928@gmail.com>]

brlock is a lock which is very cheap for reads, but very expensive
for writes.
This lock will be used when updates are very rare and reads are
common.
This lock is currently implemented by stopping the guest while
performing the updates. We assume that the only threads which
read from the locked data are VCPU threads, and the only writer
isn't a VCPU thread.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
---
 tools/kvm/include/kvm/brlock.h |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)
 create mode 100644 tools/kvm/include/kvm/brlock.h

diff --git a/tools/kvm/include/kvm/brlock.h b/tools/kvm/include/kvm/brlock.h
new file mode 100644
index 0000000..f192071
--- /dev/null
+++ b/tools/kvm/include/kvm/brlock.h
@@ -0,0 +1,12 @@
+#ifndef KVM__BRLOCK_H
+#define KVM__BRLOCK_H
+
+#include "kvm/kvm.h"
+#include "kvm/barrier.h"
+
+#define br_read_lock()		mb()
+#define br_read_unlock()	mb()
+
+#define br_write_lock()		kvm__pause()
+#define br_write_unlock()	kvm__continue()
+#endif
-- 
1.7.5.rc3