how to use the function copyout()

Norbert Koch NKoch at
Mon Jul 25 15:01:39 GMT 2005

> > So if I get it right, it's impossible in FreeBSD to gain access to
> > 64KB of user's program memory with ioctl?
> >
> > My situation is this - I have a device driver for Linux. My task is
> > port it as it is (1:1) into FreeBSD.
> >
> > In the Linux driver Ioctl is realized with the macroses _put_user
> > _get_user all over it. As I understand in FreeBSD their analogues are
> > functions described in store(9), copy(9) and fetch(9).
> >
> > So the problem is that in my user program an array short unsigned int
> > Data[32768] is defined. I need to gain access to the array(to each
> > element of it) from device driver with Ioctl handler.
> >
> > Is it possible to do? If yes, then how it can be done?
> A better alternative that doesn't involve copying huge amounts of data
> from userlevel to kernel space and vice versa is probably to pass just
> the address of the area with an ioctl() and then map the appropriate
> pages from the address space of the user process to an area where the
> kernel can access the data directly?

I think that could work (only an idea, not tested):

struct Region
  void * p;
  size_t s;

#define IOBIG _IOWR ('b', 123, struct Region)


  char data[1000];
  struct Region r;

  r.p = data;
  r.s = sizeof data;
  int error = ioctl (fd, IOBIG, &r);

  int my_ioctl(..., caddr_t data, ...)
    char data[1000];
    return copyout(data, ((struct Region *) data)->p, ((struct Region *)

Have a try and tell us if it works.


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