text: #ifndef _SPINLOCK_H
  #define _SPINLOCK_H
  // 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.
  };
  
  #endif