diff --git a/sys/boot/zfs/zfstest.c b/sys/boot/zfs/zfstest.c
new file mode 100644
index 000000000000..303ef5f08efe
--- /dev/null
+++ b/sys/boot/zfs/zfstest.c
@@ -0,0 +1,120 @@
+/*-
+ * Copyright (c) 2010 Doug Rabson
+ * 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 AUTHOR 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 AUTHOR 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.
+ */
+/* $FreeBSD$ */
+/*
+ * Compile with 'cc -I. -I../../cddl/boot/zfs zfstest.c -o zfstest'
+ */
+
+#include <sys/param.h>
+#include <sys/queue.h>
+#include <fcntl.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <errno.h>
+
+#define NBBY 8
+
+void
+pager_output(const char *line)
+{
+	printf("%s", line);
+}
+
+#include "zfsimpl.c"
+
+static int
+vdev_read(vdev_t *vdev, void *priv, off_t off, void *buf, size_t bytes)
+{
+	int fd = *(int *) priv;
+
+	if (pread(fd, buf, bytes, off) != bytes)
+		return -1;
+	return 0;
+}
+
+static int
+zfs_read(spa_t *spa, dnode_phys_t *dn, void *buf, size_t size, off_t off)
+{
+	const znode_phys_t *zp = (const znode_phys_t *) dn->dn_bonus;
+	size_t n;
+	int rc;
+
+	n = size;
+	if (off + n > zp->zp_size)
+		n = zp->zp_size - off;
+	
+	rc = dnode_read(spa, dn, off, buf, n);
+	if (rc)
+		return (rc);
+
+	return (n);
+}
+
+int
+main(int argc, char** argv)
+{
+	int i, n, off;
+	int fd[99];
+	spa_t *spa;
+	dnode_phys_t dn;
+	char buf[512];
+
+	zfs_init();
+	if (argc == 1) {
+		static char *av[] = {
+			"zfstest", "/dev/da0p2", "/dev/da1p2", "/dev/da2p2",
+			NULL,
+		};
+		argc = 4;
+		argv = av;
+	}
+	for (i = 1; i < argc; i++) {
+		fd[i] = open(argv[i], O_RDONLY);
+		if (fd[i] < 0)
+			continue;
+		if (vdev_probe(vdev_read, &fd[i], NULL) != 0)
+			close(fd[i]);
+	}
+	spa_all_status();
+
+	spa = STAILQ_FIRST(&zfs_pools);
+	if (!spa || zfs_mount_pool(spa))
+		exit(1);
+
+	if (zfs_lookup(spa, "zfs.c", &dn))
+		exit(1);
+
+	off = 0;
+	do {
+		n = zfs_read(spa, &dn, buf, 512, off);
+		write(1, buf, n);
+		off += n;
+	} while (n == 512);
+}