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List:       freebsd-hackers
Subject:    request for help: netcat kernel module for FreeBSD
From:       Eitan Adler <lists () eitanadler ! com>
Date:       2014-04-25 5:42:14
Message-ID: CAF6rxgkREDE3ictVzhJseY7zsPgtRtyxweyBOTdgUuHBRictTQ () mail ! gmail ! com
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Hi all,

In an effort to teach myself how to write a kernel module I decided to
port the netcat kernel module to FreeBSD.

For those that havn't heard of it, the original is here:
https://github.com/usrbinnc/netcat-cpi-kernel-module.
You will need the original to compile this as well (for the data files)

N.B. This is not intended to commit.


When I load this module the system just freezes.   If I put a return
(0); right before make_dev_p it works.

Can anyone help me figure out what else I did wrong.  (read() code is
untested atm)


#include <sys/param.h>
#include <sys/module.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/conf.h>   /* cdevsw struct */
#include <sys/types.h>
#include <sys/uio.h>

#include "tracks/trk1.h"
#include "tracks/trk2.h"
#include "tracks/trk3.h"
#include "tracks/trk4.h"
#include "tracks/trk5.h"
#include "tracks/trk6.h"

/* Function prototypes */
static d_open_t      netcat_open;
static d_close_t     netcat_close;
static d_read_t      netcat_read;
static d_write_t     netcat_write;

static struct cdevsw netcat_cdevsw = {
	.d_version = D_VERSION,
	.d_open = netcat_open,
	.d_close = netcat_close,
	.d_read = netcat_read,
	.d_write = netcat_write,
	.d_name = "netcat",
};

static char *tracks[] = {netcat_cpi_trk1,
                         netcat_cpi_trk2,
                         netcat_cpi_trk3,
                         netcat_cpi_trk4,
                         netcat_cpi_trk5,
                         netcat_cpi_trk6};

static char *tracknames[] = {"Interrupt 0x7f",
			 "The Internet is an Apt Motherfucker",
			 "Interrupt 0x0d",
			 "netcat",
			 "Interrupt 0xbb",
			 "Approximating the Circumference of the Earth"};

static unsigned long tracklens[] = {NETCAT_CPI_TRK1_LEN,
				    NETCAT_CPI_TRK2_LEN,
				    NETCAT_CPI_TRK3_LEN,
				    NETCAT_CPI_TRK4_LEN,
				    NETCAT_CPI_TRK5_LEN,
				    NETCAT_CPI_TRK6_LEN};

static struct {
	char	*msg;
	int	current_track;
	size_t	bytes;
} netcatdata;

static struct cdev *netcat_dev;

static int netcat_loader(struct module *module, int event, void *arg) {
	int e = 0;

	switch (event) {
		case MOD_LOAD:
			uprintf("netcat - Cycles Per Instruction - Kernel Module Edition - 2014\n");
			uprintf("netcat is Brandon Lucia, Andrew Olmstead, and David Balatero\n");
			uprintf("On the web at http://netcat.co\n");
			uprintf("'ogg123 - < /dev/netcat' to play.\n");
			e = make_dev_p(MAKEDEV_CHECKNAME | MAKEDEV_WAITOK,
				&netcat_dev,
				&netcat_cdevsw,
				0,
				UID_ROOT,
				GID_WHEEL,
				0444,
				"netcat");
			if (e != 0)
				break;

			break;
		case MOD_UNLOAD:
			destroy_dev(netcat_dev);
			break;

		default:
			e = EOPNOTSUPP;
			break;
	}

	return (e);
}

static int netcat_open(struct cdev *dev __unused, int oflags __unused,
int devtype __unused, struct thread *td __unused)
{
	int error = 0;

	netcatdata.current_track = 0;
	netcatdata.msg = tracks[netcatdata.current_track];        /* track 1 */
	netcatdata.bytes = 0;
	uprintf("Now playing %s\n", tracknames[netcatdata.current_track]);

	return (error);
}

static int netcat_close(struct cdev *dev __unused, int oflags
__unused, int devtype __unused, struct thread *td __unused)
{
	int error = 0;

	return (error);
}

static int
netcat_read(struct cdev *dev __unused, struct uio *uio, int ioflag __unused)
{
	int error = 0;
	size_t totalbytesleft;

	totalbytesleft = uio->uio_resid;

	while (totalbytesleft > 0) {
		int amt = MIN(uio->uio_resid,
				tracklens[netcatdata.current_track] - netcatdata.bytes);
		error = uiomove(tracks[netcatdata.current_track] + uio->uio_offset, amt, uio);
		netcatdata.bytes += amt;
		if (netcatdata.bytes == tracklens[netcatdata.current_track]) {
			uprintf("Now playing %s\n", tracknames[netcatdata.current_track]);
			netcatdata.bytes = 0;
			netcatdata.current_track = (netcatdata.current_track + 1) % 6;
		}

	}



	error = uiomove(tracks[netcatdata.current_track], 1, uio);

	if (error != 0)
		uprintf("uiomove failed!\n");

	return (error);
}

static int
netcat_write(struct cdev *dev __unused, struct uio *uio, int ioflag __unused)
{
	int error = EOPNOTSUPP;

	return (error);
}


DEV_MODULE(netcat, netcat_loader, NULL);




-- 
Eitan Adler
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