RE: how to use the function copyout()

From: Norbert Koch (NKoch_at_demig.de)
Date: 07/25/05

  • Next message: Matthew N. Dodd: "RE: how to use the function copyout()" 
    To: "Giorgos Keramidas" <keramida@freebsd.org>, "Felix-KM" <Felix-KM@yandex.ru>
Date: Mon, 25 Jul 2005 16:58:55 +0200

    >
    > > 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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  • Next message: Matthew N. Dodd: "RE: how to use the function copyout()"

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