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Date:      Mon, 25 Jul 2005 16:58:55 +0200
From:      "Norbert Koch" <NKoch@demig.de>
To:        "Giorgos Keramidas" <keramida@freebsd.org>, "Felix-KM" <Felix-KM@yandex.ru>
Cc:        freebsd-hackers@freebsd.org
Subject:   RE: how to use the function copyout()
Message-ID:  <000001c59129$6099b560$4801a8c0@ws-ew-3.W2KDEMIG>
In-Reply-To: <20050725142745.GA26647@beatrix.daedalusnetworks.priv>
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>
> > 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)


userland:

  char data[1000];
  struct Region r;

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


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


Have a try and tell us if it works.


Norbert

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