--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/uprogs/spinlock.h	Sun Jan 06 19:27:03 2019 +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.
+};
+