echo.c

#include <sys/param.h>
#include <sys/module.h>
#include <sys/kernel.h>
#include <sys/systm.h>

#include <sys/conf.h>
#include <sys/uio.h>
#include <sys/malloc.h>

#define BUFFER_SIZE 256

/* Forward declarations. */
static d_open_t		echo_open;
static d_close_t	echo_close;
static d_read_t		echo_read;
static d_write_t	echo_write;

static struct cdevsw echo_cdevsw = {
	.d_version =		D_VERSION,
	.d_open	=		echo_open,
	.d_close =		echo_close,
	.d_read =		echo_read,
	.d_write =		echo_write,
	.d_name =		"echo"
};

typedef struct echo {
	char buffer[BUFFER_SIZE];
	int length;
} echo_t;

static echo_t *echo_message;
static struct cdev *echo_dev;

static int
echo_open(struct cdev *dev, int oflags, int devtype, struct thread *td)
{
	uprintf("Opening echo device.\n");
	return(0);
}

static int
echo_close(struct cdev *dev, int fflags, int devtype, struct thread *td)
{
	uprintf("Closing echo device.\n");
	return(0);
}

static int
echo_write(struct cdev *dev, struct uio *uio, int ioflag)
{
	int error = 0;
	error = copyin(uio->uio_iov->iov_base, echo_message->buffer,
			MIN(uio->uio_iov->iov_len, BUFFER_SIZE - 1));
	if (error != 0) {
		uprintf("Write failed.\n");
		return (error);
	}

	*(echo_message->buffer +
			MIN(uio->uio_iov->iov_len, BUFFER_SIZE - 1)) = 0;

	echo_message->length = MIN(uio->uio_iov->iov_len, BUFFER_SIZE - 1);

	return(error);
}

static int
echo_read(struct cdev *dev, struct uio *uio, int ioflag)
{
	int error = 0;
	int amount;

	amount = MIN(uio->uio_resid,
			(echo_message->length - uio->uio_offset > 0) ?
			 echo_message->length - uio->uio_offset : 0);
	error = uiomove(echo_message->buffer + uio->uio_offset, amount, uio);
	if (error != 0)
		uprintf("Read failed.\n");

	return (error);
}


static int
echo_modevent(module_t mod __unused, int event, void *arg __unused)
{
	int error = 0;

	switch (event) {
	case MOD_LOAD:
		echo_message = malloc(sizeof(echo_t), M_TEMP, M_WAITOK);
		echo_dev = make_dev(&echo_cdevsw, 0, UID_ROOT, GID_WHEEL,
				0600, "echo");
		uprintf("Echo driver loaded.\n");
		break;
	case MOD_UNLOAD:
		destroy_dev(echo_dev);
		free(echo_message, M_TEMP);
		uprintf("Echo driver unloaded.\n");
		break;
	default:
		error = EOPNOTSUPP;
		break;
	}

	return (error);
}

DEV_MODULE(echo, echo_modevent, NULL);