text: #ifndef __ASM_GENERIC_UACCESS_H
  #define __ASM_GENERIC_UACCESS_H
  
  /*
   * User space memory access functions, these should work
   * on a ny machine that has kernel and user data in the same
   * address space, e.g. all NOMMU machines.
   */
  #include <linux/sched.h>
  #include <linux/string.h>
  
  #include <asm/segment.h>
  
  #define MAKE_MM_SEG(s)	((mm_segment_t) { (s) })
  
  #ifndef KERNEL_DS
  #define KERNEL_DS	MAKE_MM_SEG(~0UL)
  #endif
  
  #ifndef USER_DS
  #define USER_DS		MAKE_MM_SEG(TASK_SIZE - 1)
  #endif
  
  #ifndef get_fs
  #define get_ds()	(KERNEL_DS)
  #define get_fs()	(current_thread_info()->addr_limit)
  
  static inline void set_fs(mm_segment_t fs)
  {
  	current_thread_info()->addr_limit = fs;
  }
  #endif
  
  #ifndef segment_eq
  #define segment_eq(a, b) ((a).seg == (b).seg)
  #endif
  
  #define VERIFY_READ	0
  #define VERIFY_WRITE	1
  
  #define access_ok(type, addr, size) __access_ok((unsigned long)(addr),(size))
  
  /*
   * The architecture should really override this if possible, at least
   * doing a check on the get_fs()
   */
  #ifndef __access_ok
  static inline int __access_ok(unsigned long addr, unsigned long size)
  {
  	return 1;
  }
  #endif
  
  /*
   * The exception table consists of pairs of addresses: the first is the
   * address of an instruction that is allowed to fault, and the second is
   * the address at which the program should continue.  No registers are
   * modified, so it is entirely up to the continuation code to figure out
   * what to do.
   *
   * All the routines below use bits of fixup code that are out of line
   * with the main instruction path.  This means when everything is well,
   * we don't even have to jump over them.  Further, they do not intrude
   * on our cache or tlb entries.
   */
  
  struct exception_table_entry
  {
  	unsigned long insn, fixup;
  };
  
  /* Returns 0 if exception not found and fixup otherwise.  */
  extern unsigned long search_exception_table(unsigned long);
  
  /*
   * architectures with an MMU should override these two
   */
  #ifndef __copy_from_user
  static inline __must_check long __copy_from_user(void *to,
  		const void __user * from, unsigned long n)
  {
  	if (__builtin_constant_p(n)) {
  		switch(n) {
  		case 1:
  			*(u8 *)to = *(u8 __force *)from;
  			return 0;
  		case 2:
  			*(u16 *)to = *(u16 __force *)from;
  			return 0;
  		case 4:
  			*(u32 *)to = *(u32 __force *)from;
  			return 0;
  #ifdef CONFIG_64BIT
  		case 8:
  			*(u64 *)to = *(u64 __force *)from;
  			return 0;
  #endif
  		default:
  			break;
  		}
  	}
  
  	memcpy(to, (const void __force *)from, n);
  	return 0;
  }
  #endif
  
  #ifndef __copy_to_user
  static inline __must_check long __copy_to_user(void __user *to,
  		const void *from, unsigned long n)
  {
  	if (__builtin_constant_p(n)) {
  		switch(n) {
  		case 1:
  			*(u8 __force *)to = *(u8 *)from;
  			return 0;
  		case 2:
  			*(u16 __force *)to = *(u16 *)from;
  			return 0;
  		case 4:
  			*(u32 __force *)to = *(u32 *)from;
  			return 0;
  #ifdef CONFIG_64BIT
  		case 8:
  			*(u64 __force *)to = *(u64 *)from;
  			return 0;
  #endif
  		default:
  			break;
  		}
  	}
  
  	memcpy((void __force *)to, from, n);
  	return 0;
  }
  #endif
  
  /*
   * These are the main single-value transfer routines.  They automatically
   * use the right size if we just have the right pointer type.
   * This version just falls back to copy_{from,to}_user, which should
   * provide a fast-path for small values.
   */
  #define __put_user(x, ptr) \
  ({								\
  	__typeof__(*(ptr)) __x = (x);				\
  	int __pu_err = -EFAULT;					\
          __chk_user_ptr(ptr);                                    \
  	switch (sizeof (*(ptr))) {				\
  	case 1:							\
  	case 2:							\
  	case 4:							\
  	case 8:							\
  		__pu_err = __put_user_fn(sizeof (*(ptr)),	\
  					 ptr, &__x);		\
  		break;						\
  	default:						\
  		__put_user_bad();				\
  		break;						\
  	 }							\
  	__pu_err;						\
  })
  
  #define put_user(x, ptr)					\
  ({								\
  	might_sleep();						\
  	access_ok(VERIFY_WRITE, ptr, sizeof(*ptr)) ?		\
  		__put_user(x, ptr) :				\
  		-EFAULT;					\
  })
  
  #ifndef __put_user_fn
  
  static inline int __put_user_fn(size_t size, void __user *ptr, void *x)
  {
  	size = __copy_to_user(ptr, x, size);
  	return size ? -EFAULT : size;
  }
  
  #define __put_user_fn(sz, u, k)	__put_user_fn(sz, u, k)
  
  #endif
  
  extern int __put_user_bad(void) __attribute__((noreturn));
  
  #define __get_user(x, ptr)					\
  ({								\
  	int __gu_err = -EFAULT;					\
  	__chk_user_ptr(ptr);					\
  	switch (sizeof(*(ptr))) {				\
  	case 1: {						\
  		unsigned char __x;				\
  		__gu_err = __get_user_fn(sizeof (*(ptr)),	\
  					 ptr, &__x);		\
  		(x) = *(__force __typeof__(*(ptr)) *) &__x;	\
  		break;						\
  	};							\
  	case 2: {						\
  		unsigned short __x;				\
  		__gu_err = __get_user_fn(sizeof (*(ptr)),	\
  					 ptr, &__x);		\
  		(x) = *(__force __typeof__(*(ptr)) *) &__x;	\
  		break;						\
  	};							\
  	case 4: {						\
  		unsigned int __x;				\
  		__gu_err = __get_user_fn(sizeof (*(ptr)),	\
  					 ptr, &__x);		\
  		(x) = *(__force __typeof__(*(ptr)) *) &__x;	\
  		break;						\
  	};							\
  	case 8: {						\
  		unsigned long long __x;				\
  		__gu_err = __get_user_fn(sizeof (*(ptr)),	\
  					 ptr, &__x);		\
  		(x) = *(__force __typeof__(*(ptr)) *) &__x;	\
  		break;						\
  	};							\
  	default:						\
  		__get_user_bad();				\
  		break;						\
  	}							\
  	__gu_err;						\
  })
  
  #define get_user(x, ptr)					\
  ({								\
  	might_sleep();						\
  	access_ok(VERIFY_READ, ptr, sizeof(*ptr)) ?		\
  		__get_user(x, ptr) :				\
  		((x) = (__typeof__(*(ptr)))0,-EFAULT);		\
  })
  
  #ifndef __get_user_fn
  static inline int __get_user_fn(size_t size, const void __user *ptr, void *x)
  {
  	size_t n = __copy_from_user(x, ptr, size);
  	if (unlikely(n)) {
  		memset(x + (size - n), 0, n);
  		return -EFAULT;
  	}
  	return 0;
  }
  
  #define __get_user_fn(sz, u, k)	__get_user_fn(sz, u, k)
  
  #endif
  
  extern int __get_user_bad(void) __attribute__((noreturn));
  
  #ifndef __copy_from_user_inatomic
  #define __copy_from_user_inatomic __copy_from_user
  #endif
  
  #ifndef __copy_to_user_inatomic
  #define __copy_to_user_inatomic __copy_to_user
  #endif
  
  static inline long copy_from_user(void *to,
  		const void __user * from, unsigned long n)
  {
  	unsigned long res = n;
  	might_sleep();
  	if (likely(access_ok(VERIFY_READ, from, n)))
  		res = __copy_from_user(to, from, n);
  	if (unlikely(res))
  		memset(to + (n - res), 0, res);
  	return res;
  }
  
  static inline long copy_to_user(void __user *to,
  		const void *from, unsigned long n)
  {
  	might_sleep();
  	if (access_ok(VERIFY_WRITE, to, n))
  		return __copy_to_user(to, from, n);
  	else
  		return n;
  }
  
  /*
   * Copy a null terminated string from userspace.
   */
  #ifndef __strncpy_from_user
  static inline long
  __strncpy_from_user(char *dst, const char __user *src, long count)
  {
  	char *tmp;
  	strncpy(dst, (const char __force *)src, count);
  	for (tmp = dst; *tmp && count > 0; tmp++, count--)
  		;
  	return (tmp - dst);
  }
  #endif
  
  static inline long
  strncpy_from_user(char *dst, const char __user *src, long count)
  {
  	if (!access_ok(VERIFY_READ, src, 1))
  		return -EFAULT;
  	return __strncpy_from_user(dst, src, count);
  }
  
  /*
   * Return the size of a string (including the ending 0)
   *
   * Return 0 on exception, a value greater than N if too long
   */
  #ifndef __strnlen_user
  #define __strnlen_user(s, n) (strnlen((s), (n)) + 1)
  #endif
  
  /*
   * Unlike strnlen, strnlen_user includes the nul terminator in
   * its returned count. Callers should check for a returned value
   * greater than N as an indication the string is too long.
   */
  static inline long strnlen_user(const char __user *src, long n)
  {
  	if (!access_ok(VERIFY_READ, src, 1))
  		return 0;
  	return __strnlen_user(src, n);
  }
  
  static inline long strlen_user(const char __user *src)
  {
  	return strnlen_user(src, 32767);
  }
  
  /*
   * Zero Userspace
   */
  #ifndef __clear_user
  static inline __must_check unsigned long
  __clear_user(void __user *to, unsigned long n)
  {
  	memset((void __force *)to, 0, n);
  	return 0;
  }
  #endif
  
  static inline __must_check unsigned long
  clear_user(void __user *to, unsigned long n)
  {
  	might_sleep();
  	if (!access_ok(VERIFY_WRITE, to, n))
  		return n;
  
  	return __clear_user(to, n);
  }
  
  #endif /* __ASM_GENERIC_UACCESS_H */
  