text: #ifndef LINUX_HARDIRQ_H
  #define LINUX_HARDIRQ_H
  
  #include <linux/preempt.h>
  #include <linux/smp_lock.h>
  #include <linux/lockdep.h>
  #include <asm/hardirq.h>
  #include <asm/system.h>
  
  /*
   * We put the hardirq and softirq counter into the preemption
   * counter. The bitmask has the following meaning:
   *
   * - bits 0-7 are the preemption count (max preemption depth: 256)
   * - bits 8-15 are the softirq count (max # of softirqs: 256)
   *
   * The hardirq count can be overridden per architecture, the default is:
   *
   * - bits 16-27 are the hardirq count (max # of hardirqs: 4096)
   * - ( bit 28 is the PREEMPT_ACTIVE flag. )
   *
   * PREEMPT_MASK: 0x000000ff
   * SOFTIRQ_MASK: 0x0000ff00
   * HARDIRQ_MASK: 0x0fff0000
   */
  #define PREEMPT_BITS	8
  #define SOFTIRQ_BITS	8
  
  #ifndef HARDIRQ_BITS
  #define HARDIRQ_BITS	12
  
  #ifndef MAX_HARDIRQS_PER_CPU
  #define MAX_HARDIRQS_PER_CPU NR_IRQS
  #endif
  
  /*
   * The hardirq mask has to be large enough to have space for potentially
   * all IRQ sources in the system nesting on a single CPU.
   */
  #if (1 << HARDIRQ_BITS) < MAX_HARDIRQS_PER_CPU
  # error HARDIRQ_BITS is too low!
  #endif
  #endif
  
  #define PREEMPT_SHIFT	0
  #define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)
  #define HARDIRQ_SHIFT	(SOFTIRQ_SHIFT + SOFTIRQ_BITS)
  
  #define __IRQ_MASK(x)	((1UL << (x))-1)
  
  #define PREEMPT_MASK	(__IRQ_MASK(PREEMPT_BITS) << PREEMPT_SHIFT)
  #define SOFTIRQ_MASK	(__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)
  #define HARDIRQ_MASK	(__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)
  
  #define PREEMPT_OFFSET	(1UL << PREEMPT_SHIFT)
  #define SOFTIRQ_OFFSET	(1UL << SOFTIRQ_SHIFT)
  #define HARDIRQ_OFFSET	(1UL << HARDIRQ_SHIFT)
  
  #if PREEMPT_ACTIVE < (1 << (HARDIRQ_SHIFT + HARDIRQ_BITS))
  #error PREEMPT_ACTIVE is too low!
  #endif
  
  #define hardirq_count()	(preempt_count() & HARDIRQ_MASK)
  #define softirq_count()	(preempt_count() & SOFTIRQ_MASK)
  #define irq_count()	(preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK))
  
  /*
   * Are we doing bottom half or hardware interrupt processing?
   * Are we in a softirq context? Interrupt context?
   */
  #define in_irq()		(hardirq_count())
  #define in_softirq()		(softirq_count())
  #define in_interrupt()		(irq_count())
  
  #if defined(CONFIG_PREEMPT) && !defined(CONFIG_PREEMPT_BKL)
  # define in_atomic()	((preempt_count() & ~PREEMPT_ACTIVE) != kernel_locked())
  #else
  # define in_atomic()	((preempt_count() & ~PREEMPT_ACTIVE) != 0)
  #endif
  
  #ifdef CONFIG_PREEMPT
  # define preemptible()	(preempt_count() == 0 && !irqs_disabled())
  # define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)
  #else
  # define preemptible()	0
  # define IRQ_EXIT_OFFSET HARDIRQ_OFFSET
  #endif
  
  #ifdef CONFIG_SMP
  extern void synchronize_irq(unsigned int irq);
  #else
  # define synchronize_irq(irq)	barrier()
  #endif
  
  struct task_struct;
  
  #ifndef CONFIG_VIRT_CPU_ACCOUNTING
  static inline void account_system_vtime(struct task_struct *tsk)
  {
  }
  #endif
  
  /*
   * It is safe to do non-atomic ops on ->hardirq_context,
   * because NMI handlers may not preempt and the ops are
   * always balanced, so the interrupted value of ->hardirq_context
   * will always be restored.
   */
  #define __irq_enter()					\
  	do {						\
  		account_system_vtime(current);		\
  		add_preempt_count(HARDIRQ_OFFSET);	\
  		trace_hardirq_enter();			\
  	} while (0)
  
  /*
   * Enter irq context (on NO_HZ, update jiffies):
   */
  extern void irq_enter(void);
  
  /*
   * Exit irq context without processing softirqs:
   */
  #define __irq_exit()					\
  	do {						\
  		trace_hardirq_exit();			\
  		account_system_vtime(current);		\
  		sub_preempt_count(HARDIRQ_OFFSET);	\
  	} while (0)
  
  /*
   * Exit irq context and process softirqs if needed:
   */
  extern void irq_exit(void);
  
  #define nmi_enter()		do { lockdep_off(); __irq_enter(); } while (0)
  #define nmi_exit()		do { __irq_exit(); lockdep_on(); } while (0)
  
  #endif /* LINUX_HARDIRQ_H */
  