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To: hackers@freebsd.org
Subject: Device driver help needed...
Date: Sat, 01 Feb 1997 18:36:59 -0500
From: "Brian J. McGovern" <mcgovern@spoon.beta.com>
Sender: owner-hackers@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk

Ok. I'm sure that now I've terribly bastardized the uio structure, but at
least the damn thing compiles :) Let see if I can get some comment
on my interpretation of the uio stucture:

struct uio
  {
    struct iovec *uio_iov;   /* Pointer to IO Vector (possible array?) */
    int uio_iovcnt;          /* Number of IO vectors (?) */
    off_t uio_offset;        /* Offset in to device */
    int   uio_resid;	     /* Length of read request (?) */
    enum uio_seg uio_segflg; /* I assume a segment of some kind, but I
    				can only find reference to UIO_SYSSPACE */
    enum uio_rw uio_rw;	     /* UIO_READ or UIO_WRITE (type of operation(?)) */
    struct proc *uio_procp;  /* No idea, but I've seen it set to curproc */
  };

Ok, guys. Beat me up, and let me know whats incorrect.


With that in mind, I've bent my device driver to look like this:

------ foo.c ---------------------------------------
#define KERNEL
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/reboot.h>
#include <sys/ioctl.h>
#include <sys/tty.h>
#include <sys/proc.h>
#include <sys/conf.h>
#include <sys/file.h>
#include <sys/uio.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/syslog.h>
#ifdef DEVFS
#include <sys/devfsext.h>
#endif
#include <machine/clock.h>
#include <i386/isa/isa.h>
#include <i386/isa/isa_device.h>

static char message[] = "The quick brown fox jumps over a lazy dog\n";

#define CDEV_MAJOR 20

static d_read_t fooread;

static struct cdevsw foo_cdevsw =
  {
    nxopen, nxclose, fooread, nxwrite,
    nxioctl, nxstop, nxreset, nxdevtotty,
    nxselect, nxmmap, NULL, "foo", NULL, -1
  };
    
fooinit()
  {
  }

static int fooread(dev,myuio, flag)
  dev_t dev;
  struct uio *myuio;
  int flag;
  {
    unsigned char *buffer_pointer;
    int toread;
    if ((myuio->uio_iovcnt != 1) || (MINOR(dev) != 0))
      return ENODEV;
    while(myuio->uio_resid)
      {
        buffer_pointer = (message + (myuio->uio_offset % sizeof(message)));
        toread = ((long unsigned int)(message + sizeof(message)) - (long unsigned int)buffer_pointer);
        uiomove(buffer_pointer, toread, myuio);
	myuio->uio_offset + toread;
	myuio->uio_resid = myuio->uio_resid - toread;
      }
  }
#define CDEV_MAJOR 20

-------------------------------------------------

Now, I'm sure there are bugs in there. Hell, I didn't know what I was doing
half the time :) But, now its time to start debugging, which means I need
to get it in to the kernel. Someone mentioned using SYSINIT to get it working
as a pseudo-device driver. The file above is located in
/usr/src/sys/i386/addons/foo.c. Anyone care to give me a set of steps (and
code changes) to get it in the kernel? Thanks.
	-Brian