--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/spinlock.h	Fri May 26 23:11:05 2017 +0900
@@ -0,0 +1,11 @@
+// Mutual exclusion lock.
+struct spinlock {
+    uint        locked;     // Is the lock held?
+
+    // For debugging:
+    char        *name;      // Name of lock.
+    struct cpu  *cpu;       // The cpu holding the lock.
+    uint        pcs[10];    // The call stack (an array of program counters)
+    // that locked the lock.
+};
+