Add a very simple and small GEOM class - ZERO.

It creates very huge provider (41PB) /dev/gzero.
On BIO_READ request it zero-fills bio_data and on BIO_WRITE it does nothing.
You can also set kern.geom.zero.clear sysctl to 0 to do nothing even for
BIO_READ.

I'm using it for performance testing where it is very helpful.

MFC after:	3 days

1 files changed, 113 insertions, 0 deletions

diff --git a/sys/geom/zero/g_zero.c b/sys/geom/zero/g_zero.c
new file mode 100644
index 0000000..d458379
--- /dev/null
+++ b/sys/geom/zero/g_zero.c
@@ -0,0 +1,113 @@
+/*-
+ * Copyright (c) 2005 Pawel Jakub Dawidek <pjd@FreeBSD.org>
+ * 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.
+ * 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 AND CONTRIBUTORS ``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 AUTHORS OR CONTRIBUTORS 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/bio.h>
+#include <sys/kernel.h>
+#include <sys/limits.h>
+#include <sys/malloc.h>
+#include <sys/queue.h>
+#include <sys/sysctl.h>
+#include <sys/systm.h>
+
+#include <geom/geom.h>
+
+
+#define	G_ZERO_CLASS_NAME	"ZERO"
+
+SYSCTL_DECL(_kern_geom);
+SYSCTL_NODE(_kern_geom, OID_AUTO, zero, CTLFLAG_RW, 0, "GEOM_ZERO stuff");
+static u_int g_zero_clear = 1;
+SYSCTL_UINT(_kern_geom_zero, OID_AUTO, clear, CTLFLAG_RW, &g_zero_clear, 0,
+    "Zero-fill bio_data.");
+
+static void
+g_zero_start(struct bio *bp)
+{
+	int error = ENXIO;
+
+	switch (bp->bio_cmd) {
+	case BIO_READ:
+		if (g_zero_clear)
+			bzero(bp->bio_data, bp->bio_length);
+		/* FALLTHROUGH */
+	case BIO_DELETE:
+	case BIO_WRITE:
+		bp->bio_completed = bp->bio_length;
+		error = 0;
+		break;
+	case BIO_GETATTR:
+	default:
+		error = EOPNOTSUPP;
+		break;
+	}
+	g_io_deliver(bp, error);
+}
+
+static void
+g_zero_init(struct g_class *mp)
+{
+	struct g_geom *gp;
+	struct g_provider *pp;
+
+	g_topology_assert();
+	gp = g_new_geomf(mp, "gzero");
+	gp->start = g_zero_start;
+	gp->access = g_std_access;
+	pp = g_new_providerf(gp, "%s", gp->name);
+	pp->mediasize = 1152921504606846976LLU;
+	pp->sectorsize = 512;
+	g_error_provider(pp, 0);
+}
+
+static int
+g_zero_destroy_geom(struct gctl_req *req __unused, struct g_class *mp __unused,
+    struct g_geom *gp)
+{
+	struct g_provider *pp;
+
+	g_topology_assert();
+	if (gp == NULL)
+		return (0);
+	pp = LIST_FIRST(&gp->provider);
+	if (pp == NULL)
+		return (0);
+	if (pp->acr > 0 || pp->acw > 0 || pp->ace > 0)
+		return (EBUSY);
+	g_wither_geom(gp, ENXIO);
+	return (EBUSY);
+}
+
+static struct g_class g_zero_class = {
+	.name = G_ZERO_CLASS_NAME,
+	.version = G_VERSION,
+	.init = g_zero_init,
+	.destroy_geom = g_zero_destroy_geom
+};
+
+DECLARE_GEOM_CLASS(g_zero_class, g_zero);