#ifndef __LINUX_UACCESS_H__
  #define __LINUX_UACCESS_H__
  
  #include <linux/preempt.h>
  #include <asm/uaccess.h>
  
  /*
   * These routines enable/disable the pagefault handler in that
   * it will not take any locks and go straight to the fixup table.
   *
   * They have great resemblance to the preempt_disable/enable calls
   * and in fact they are identical; this is because currently there is
   * no other way to make the pagefault handlers do this. So we do
   * disable preemption but we don't necessarily care about that.
   */
  static inline void pagefault_disable(void)
  {
  	preempt_count_inc();
  	/*
  	 * make sure to have issued the store before a pagefault
  	 * can hit.
  	 */
  	barrier();
  }
  
  static inline void pagefault_enable(void)
  {
  #ifndef CONFIG_PREEMPT
  	/*
  	 * make sure to issue those last loads/stores before enabling
  	 * the pagefault handler again.
  	 */
  	barrier();
  	preempt_count_dec();
  #else
  	preempt_enable();
  #endif
  }
  
  #ifndef ARCH_HAS_NOCACHE_UACCESS
  
  static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
  				const void __user *from, unsigned long n)
  {
  	return __copy_from_user_inatomic(to, from, n);
  }
  
  static inline unsigned long __copy_from_user_nocache(void *to,
  				const void __user *from, unsigned long n)
  {
  	return __copy_from_user(to, from, n);
  }
  
  #endif		/* ARCH_HAS_NOCACHE_UACCESS */
  
  /**
   * probe_kernel_address(): safely attempt to read from a location
   * @addr: address to read from - its type is type typeof(retval)*
   * @retval: read into this variable
   *
   * Safely read from address @addr into variable @revtal.  If a kernel fault
   * happens, handle that and return -EFAULT.
   * We ensure that the __get_user() is executed in atomic context so that
   * do_page_fault() doesn't attempt to take mmap_sem.  This makes
   * probe_kernel_address() suitable for use within regions where the caller
   * already holds mmap_sem, or other locks which nest inside mmap_sem.
   * This must be a macro because __get_user() needs to know the types of the
   * args.
   *
   * We don't include enough header files to be able to do the set_fs().  We
   * require that the probe_kernel_address() caller will do that.
   */
  #define probe_kernel_address(addr, retval)		\
  	({						\
  		long ret;				\
  		mm_segment_t old_fs = get_fs();		\
  							\
  		set_fs(KERNEL_DS);			\
  		pagefault_disable();			\
  		ret = __copy_from_user_inatomic(&(retval), (__force typeof(retval) __user *)(addr), sizeof(retval));		\
  		pagefault_enable();			\
  		set_fs(old_fs);				\
  		ret;					\
  	})
  
  /*
   * probe_kernel_read(): safely attempt to read from a location
   * @dst: pointer to the buffer that shall take the data
   * @src: address to read from
   * @size: size of the data chunk
   *
   * Safely read from address @src to the buffer at @dst.  If a kernel fault
   * happens, handle that and return -EFAULT.
   */
  extern long probe_kernel_read(void *dst, const void *src, size_t size);
  extern long __probe_kernel_read(void *dst, const void *src, size_t size);
  
  /*
   * probe_kernel_write(): safely attempt to write to a location
   * @dst: address to write to
   * @src: pointer to the data that shall be written
   * @size: size of the data chunk
   *
   * Safely write to address @dst from the buffer at @src.  If a kernel fault
   * happens, handle that and return -EFAULT.
   */
  extern long notrace probe_kernel_write(void *dst, const void *src, size_t size);
  extern long notrace __probe_kernel_write(void *dst, const void *src, size_t size);
  
  #endif		/* __LINUX_UACCESS_H__ */