From: Joe Thornber <dm-devel@redhat.com>

Flakey.
---

Index: linux-2.6.16-rc1/drivers/md/Kconfig
===================================================================
--- linux-2.6.16-rc1.orig/drivers/md/Kconfig
+++ linux-2.6.16-rc1/drivers/md/Kconfig
@@ -254,5 +254,11 @@ config DM_RWSPLIT
 
 	  If unsure, say N.
 
+config DM_FLAKEY
+       tristate "Flakey target (EXPERIMENTAL)"
+       depends on BLK_DEV_DM && EXPERIMENTAL
+       ---help---
+         A debug only target that intermittently fails io.
+
 endmenu
 
Index: linux-2.6.16-rc1/drivers/md/Makefile
===================================================================
--- linux-2.6.16-rc1.orig/drivers/md/Makefile
+++ linux-2.6.16-rc1/drivers/md/Makefile
@@ -32,6 +32,7 @@ obj-$(CONFIG_MD_FAULTY)		+= faulty.o
 obj-$(CONFIG_BLK_DEV_MD)	+= md-mod.o
 obj-$(CONFIG_BLK_DEV_DM)	+= dm-mod.o
 obj-$(CONFIG_DM_CRYPT)		+= dm-crypt.o
+obj-$(CONFIG_DM_FLAKEY)		+= dm-flakey.o
 obj-$(CONFIG_DM_LOOP)		+= dm-loop.o
 obj-$(CONFIG_DM_MULTIPATH)	+= dm-multipath.o dm-round-robin.o
 obj-$(CONFIG_DM_MULTIPATH_EMC)	+= dm-emc.o
Index: linux-2.6.16-rc1/drivers/md/dm-flakey.c
===================================================================
--- /dev/null
+++ linux-2.6.16-rc1/drivers/md/dm-flakey.c
@@ -0,0 +1,158 @@
+/*
+ * Copyright (C) 2003 Sistina Software (UK) Limited.
+ * Copyright (C) 2004 Red Hat, Inc. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm.h"
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+
+typedef typeof(jiffies) jiffy_t;
+
+/*
+ * Flakey: Used for testing only, simulates intermittent,
+ * catastrophic device failure.
+ */
+struct flakey {
+	struct dm_dev *dev;
+	jiffy_t start_time;
+	sector_t start;
+	unsigned up_interval;
+	unsigned down_interval;
+};
+
+/*
+ * Construct a flakey mapping: <dev_path> <offset> <up interval> <down interval>
+ */
+static int flakey_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+	struct flakey *f;
+
+	if (argc != 4) {
+		ti->error = "dm-flakey: Invalid argument count";
+		return -EINVAL;
+	}
+
+	f = kmalloc(sizeof(*f), GFP_KERNEL);
+	if (!f) {
+		ti->error = "dm-flakey: Cannot allocate linear context";
+		return -ENOMEM;
+	}
+	f->start_time = jiffies;
+
+	if (sscanf(argv[1], SECTOR_FORMAT, &f->start) != 1) {
+		ti->error = "dm-flakey: Invalid device sector";
+		goto bad;
+	}
+
+	if (sscanf(argv[2], "%u", &f->up_interval) != 1) {
+		ti->error = "dm-flakey: Invalid up interval";
+		goto bad;
+	}
+
+	if (sscanf(argv[3], "%u", &f->down_interval) != 1) {
+		ti->error = "dm-flakey: Invalid down interval";
+		goto bad;
+	}
+
+	if (dm_get_device(ti, argv[0], f->start, ti->len,
+			  dm_table_get_mode(ti->table), &f->dev)) {
+		ti->error = "dm-flakey: Device lookup failed";
+		goto bad;
+	}
+
+	ti->private = f;
+	return 0;
+
+ bad:
+	kfree(f);
+	return -EINVAL;
+}
+
+static void flakey_dtr(struct dm_target *ti)
+{
+	struct flakey *f = (struct flakey *) ti->private;
+
+	dm_put_device(ti, f->dev);
+	kfree(f);
+}
+
+static int flakey_map(struct dm_target *ti, struct bio *bio,
+		      union map_info *map_context)
+{
+	struct flakey *f = (struct flakey *) ti->private;
+	unsigned elapsed;
+
+	/* are we alive ? */
+	elapsed = (jiffies - f->start_time) / HZ;
+	elapsed %= (f->up_interval + f->down_interval);
+	if (elapsed >= f->up_interval)
+		return -EIO;
+
+	else {
+		bio->bi_bdev = f->dev->bdev;
+		bio->bi_sector = f->start + (bio->bi_sector - ti->begin);
+	}
+
+	return 1;
+}
+
+static int flakey_status(struct dm_target *ti, status_type_t type,
+			 char *result, unsigned int maxlen)
+{
+	struct flakey *f = (struct flakey *) ti->private;
+
+	switch (type) {
+	case STATUSTYPE_INFO:
+		result[0] = '\0';
+		break;
+
+	case STATUSTYPE_TABLE:
+		snprintf(result, maxlen, "%s " SECTOR_FORMAT, f->dev->name,
+			 f->start);
+		break;
+	}
+	return 0;
+}
+
+static struct target_type flakey_target = {
+	.name   = "flakey",
+	.version= {1, 0, 1},
+	.module = THIS_MODULE,
+	.ctr    = flakey_ctr,
+	.dtr    = flakey_dtr,
+	.map    = flakey_map,
+	.status = flakey_status,
+};
+
+int __init dm_flakey_init(void)
+{
+	int r = dm_register_target(&flakey_target);
+
+	if (r < 0)
+		DMERR("flakey: register failed %d", r);
+
+	return r;
+}
+
+void __exit dm_flakey_exit(void)
+{
+	int r = dm_unregister_target(&flakey_target);
+
+	if (r < 0)
+		DMERR("flakey: unregister failed %d", r);
+}
+
+/* Module hooks */
+module_init(dm_flakey_init);
+module_exit(dm_flakey_exit);
+
+MODULE_DESCRIPTION(DM_NAME " flakey target");
+MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
+MODULE_LICENSE("GPL");