MAN sezione 9 - Torna all'indice

Contents

• NAME
• SYNOPSIS
• DESCRIPTION
• RETURN VALUE
• EXAMPLES
• AVAILABILITY
• SEE ALSO
• AUTHOR

NAME

       get_user,  put_user,  copy_from_user,  copy_to_user - copy
       data between kernel space and user space

SYNOPSIS

       #include <asm/uaccess.h>

       err = get_user ( x, addr );
       err = put_user ( x, addr );

       bytes_left = copy_from_user(void*to, const void *from,
                                   unsigned long n );
       bytes_left = copy_to_user(void*to, const void *from,
                                 unsigned long n );

DESCRIPTION

       These macros transfer data between kernel space  and  user
       space.   In  the first example, the kernel variable x gets
       the value of the thing pointed to by addr (in user space).
       For  put_user,  the  value  of  the  variable x is written
       starting at the address addr.  Note well that x is a vari­
       able,  not  a  pointer.   addr  must  be  a properly typed
       pointer, since its type determines number  of  bytes  that
       are copied.

       copy_from_user  copies  n  bytes from address from in user
       space to address to in kernel space.  copy_to_user  copies
       in the opposite direction.

       None  of these need the old verify_area() call, as they do
       all the area verification on their own  using  the  paging
       unit  in the CPU hardware.  Less chance of missing address
       verification that way.  Also, the new address verification
       is much faster than the old scheme was.

RETURN VALUE

       get_user and put_user return 0 for success and -EFAULT for
       bad access.  copy_from_user and  copy_to_user  return  the
       number  of  bytes  they failed to copy (so again zero is a
       successful return).

EXAMPLES

            if (get_user(type, (char *)arg))
            return -EFAULT;
            switch (type) {
            ...

            b.maxwidth = 768;
            b.maxheight = 576;
            b.minwidth = 32;
            b.minheight = 32;
            if(copy_to_user(arg, &b, sizeof(b)))
                return -EFAULT;
            return 0;
            ...

AVAILABILITY

       Linux 2.1.4+

SEE ALSO

       verify_area(9)

AUTHOR

       Manual page by Jim Van Zandt <jrv@vanzandt.mv.com>


Linux DDI                February 5, 1998                       2