New machine independant /dev/null and /dev/zero driver. This device is

severely stripped down compared with its predecessor, and is measurably
a _lot_ faster.

Many thanks to Jeroen van Gelderen for lots of good ideas.

There is still a problem with this; it is written as a mudule, and as
such is theoretically unloadable. However, there is no refcounting done
as I would prefer to do that a'la device_busy(9), rather than some
"home-rolled" scheme. The point is pretty moot, as /dev/null is
effectively compulsory.

Reviewed by:	dfr

1 files changed, 137 insertions, 0 deletions

diff --git a/sys/dev/null/null.c b/sys/dev/null/null.c
new file mode 100644
index 0000000..bbc610e
--- /dev/null
+++ b/sys/dev/null/null.c
@@ -0,0 +1,137 @@
+/*-
+ * Copyright (c) 2000 Mark R. V. Murray & Jeroen C. van Gelderen
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer
+ *    in this position and unchanged.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/conf.h>
+#include <sys/uio.h>
+#include <sys/kernel.h>
+#include <sys/malloc.h>
+#include <sys/module.h>
+#include <sys/bus.h>
+#include <machine/bus.h>
+#include <machine/resource.h>
+#include <sys/rman.h>
+
+/* For use with destroy_dev(9). */
+static dev_t null_dev;
+static dev_t zero_dev;
+
+static d_read_t nullwrite;
+static d_read_t zeroread;
+
+#define CDEV_MAJOR	2
+#define NULL_MINOR	2
+#define ZERO_MINOR	12
+
+static struct cdevsw null_cdevsw = {
+	/* open */	(d_open_t *)nullop,
+	/* close */	(d_close_t *)nullop,
+	/* read */	(d_read_t *)nullop,
+	/* write */	nullwrite,
+	/* ioctl */	noioctl,
+	/* poll */	nopoll,
+	/* mmap */	nommap,
+	/* strategy */	nostrategy,
+	/* name */	"null",
+	/* maj */	CDEV_MAJOR,
+	/* dump */	nodump,
+	/* psize */	nopsize,
+	/* flags */	0,
+	/* bmaj */	-1
+};
+
+static struct cdevsw zero_cdevsw = {
+	/* open */	(d_open_t *)nullop,
+	/* close */	(d_close_t *)nullop,
+	/* read */	zeroread,
+	/* write */	nullwrite,
+	/* ioctl */	noioctl,
+	/* poll */	nopoll,
+	/* mmap */	nommap,
+	/* strategy */	nostrategy,
+	/* name */	"zero",
+	/* maj */	CDEV_MAJOR,
+	/* dump */	nodump,
+	/* psize */	nopsize,
+	/* flags */	D_MMAP_ANON,
+	/* bmaj */	-1
+};
+
+static void *zbuf;
+
+static int
+nullwrite(dev_t dev, struct uio *uio, int flag)
+{
+	uio->uio_resid = 0;
+	return 0;
+}
+
+static int
+zeroread(dev_t dev, struct uio *uio, int flag)
+{
+	u_int c;
+	int error = 0;
+
+	while (uio->uio_resid > 0 && error == 0) {
+		c = min(uio->uio_resid, PAGE_SIZE);
+		error = uiomove(zbuf, c, uio);
+	}
+	return error;
+}
+
+static int
+null_modevent(module_t mod, int type, void *data)
+{
+	switch(type) {
+	case MOD_LOAD:
+		if (bootverbose)
+			printf("nulldev: <null device, zero device>\n");
+		zbuf = (void *)malloc(PAGE_SIZE, M_TEMP, M_WAITOK);
+		bzero(zbuf, PAGE_SIZE);
+		zero_dev = make_dev(&zero_cdevsw, ZERO_MINOR, UID_ROOT,
+			GID_WHEEL, 0666, "zero");
+		null_dev = make_dev(&null_cdevsw, NULL_MINOR, UID_ROOT,
+			GID_WHEEL, 0666, "null");
+		return 0;
+
+	case MOD_UNLOAD:
+		destroy_dev(null_dev);
+		destroy_dev(zero_dev);
+		free(zbuf, M_TEMP);
+		return 0;
+
+	case MOD_SHUTDOWN:
+		return 0;
+
+	default:
+		return EOPNOTSUPP;
+	}
+}
+
+DEV_MODULE(nulldev, null_modevent, NULL);