dm: add flakey target

dm-flakey

=========

This target is the same as the linear target except that it returns I/O

errors periodically.  It's been found useful in simulating failing

devices for testing purposes.

Starting from the time the table is loaded, the device is available for

<up interval> seconds, then returns errors for <down interval> seconds,

and then this cycle repeats.

Parameters: <dev path> <offset> <up interval> <down interval>

    <dev path>: Full pathname to the underlying block-device, or a

                "major:minor" device-number.

    <offset>: Starting sector within the device.

    <up interval>: Number of seconds device is available.

    <down interval>: Number of seconds device returns errors.

	---help---

	Generate udev events for DM events.

config DM_FLAKEY

       tristate "Flakey target (EXPERIMENTAL)"

       depends on BLK_DEV_DM && EXPERIMENTAL

       ---help---

         A target that intermittently fails I/O for debugging purposes.

endif # MD

obj-$(CONFIG_BLK_DEV_DM)	+= dm-mod.o

obj-$(CONFIG_DM_CRYPT)		+= dm-crypt.o

obj-$(CONFIG_DM_DELAY)		+= dm-delay.o

obj-$(CONFIG_DM_FLAKEY)		+= dm-flakey.o

obj-$(CONFIG_DM_MULTIPATH)	+= dm-multipath.o dm-round-robin.o

obj-$(CONFIG_DM_MULTIPATH_QL)	+= dm-queue-length.o

obj-$(CONFIG_DM_MULTIPATH_ST)	+= dm-service-time.o

/*

 * Copyright (C) 2003 Sistina Software (UK) Limited.

 * Copyright (C) 2004, 2010 Red Hat, Inc. All rights reserved.

 *

 * This file is released under the GPL.

 */

#include <linux/device-mapper.h>

#include <linux/module.h>

#include <linux/init.h>

#include <linux/blkdev.h>

#include <linux/bio.h>

#include <linux/slab.h>

#define DM_MSG_PREFIX "flakey"

/*

 * Flakey: Used for testing only, simulates intermittent,

 * catastrophic device failure.

 */

struct flakey_c {

	struct dm_dev *dev;

	unsigned long 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_c *fc;

	unsigned long long tmp;

	if (argc != 4) {

		ti->error = "dm-flakey: Invalid argument count";

		return -EINVAL;

	}

	fc = kmalloc(sizeof(*fc), GFP_KERNEL);

	if (!fc) {

		ti->error = "dm-flakey: Cannot allocate linear context";

		return -ENOMEM;

	}

	fc->start_time = jiffies;

	if (sscanf(argv[1], "%llu", &tmp) != 1) {

		ti->error = "dm-flakey: Invalid device sector";

		goto bad;

	}

	fc->start = tmp;

	if (sscanf(argv[2], "%u", &fc->up_interval) != 1) {

		ti->error = "dm-flakey: Invalid up interval";

		goto bad;

	}

	if (sscanf(argv[3], "%u", &fc->down_interval) != 1) {

		ti->error = "dm-flakey: Invalid down interval";

		goto bad;

	}

	if (!(fc->up_interval + fc->down_interval)) {

		ti->error = "dm-flakey: Total (up + down) interval is zero";

		goto bad;

	}

	if (fc->up_interval + fc->down_interval < fc->up_interval) {

		ti->error = "dm-flakey: Interval overflow";

		goto bad;

	}

	if (dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &fc->dev)) {

		ti->error = "dm-flakey: Device lookup failed";

		goto bad;

	}

	ti->num_flush_requests = 1;

	ti->private = fc;

	return 0;

bad:

	kfree(fc);

	return -EINVAL;

}

static void flakey_dtr(struct dm_target *ti)

{

	struct flakey_c *fc = ti->private;

	dm_put_device(ti, fc->dev);

	kfree(fc);

}

static sector_t flakey_map_sector(struct dm_target *ti, sector_t bi_sector)

{

	struct flakey_c *fc = ti->private;

	return fc->start + (bi_sector - ti->begin);

}

static void flakey_map_bio(struct dm_target *ti, struct bio *bio)

{

	struct flakey_c *fc = ti->private;

	bio->bi_bdev = fc->dev->bdev;

	if (bio_sectors(bio))

		bio->bi_sector = flakey_map_sector(ti, bio->bi_sector);

}

static int flakey_map(struct dm_target *ti, struct bio *bio,

		      union map_info *map_context)

{

	struct flakey_c *fc = ti->private;

	unsigned elapsed;

	/* Are we alive ? */

	elapsed = (jiffies - fc->start_time) / HZ;

	if (elapsed % (fc->up_interval + fc->down_interval) >= fc->up_interval)

		return -EIO;

	flakey_map_bio(ti, bio);

	return DM_MAPIO_REMAPPED;

}

static int flakey_status(struct dm_target *ti, status_type_t type,

			 char *result, unsigned int maxlen)

{

	struct flakey_c *fc = ti->private;

	switch (type) {

	case STATUSTYPE_INFO:

		result[0] = '\0';

		break;

	case STATUSTYPE_TABLE:

		snprintf(result, maxlen, "%s %llu %u %u", fc->dev->name,

			 (unsigned long long)fc->start, fc->up_interval,

			 fc->down_interval);

		break;

	}

	return 0;

}

static int flakey_ioctl(struct dm_target *ti, unsigned int cmd, unsigned long arg)

{

	struct flakey_c *fc = ti->private;

	return __blkdev_driver_ioctl(fc->dev->bdev, fc->dev->mode, cmd, arg);

}

static int flakey_merge(struct dm_target *ti, struct bvec_merge_data *bvm,

			struct bio_vec *biovec, int max_size)

{

	struct flakey_c *fc = ti->private;

	struct request_queue *q = bdev_get_queue(fc->dev->bdev);

	if (!q->merge_bvec_fn)

		return max_size;

	bvm->bi_bdev = fc->dev->bdev;

	bvm->bi_sector = flakey_map_sector(ti, bvm->bi_sector);

	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));

}

static int flakey_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn, void *data)

{

	struct flakey_c *fc = ti->private;

	return fn(ti, fc->dev, fc->start, ti->len, data);

}

static struct target_type flakey_target = {

	.name   = "flakey",

	.version = {1, 1, 0},

	.module = THIS_MODULE,

	.ctr    = flakey_ctr,

	.dtr    = flakey_dtr,

	.map    = flakey_map,

	.status = flakey_status,

	.ioctl	= flakey_ioctl,

	.merge	= flakey_merge,

	.iterate_devices = flakey_iterate_devices,

};

static int __init dm_flakey_init(void)

{

	int r = dm_register_target(&flakey_target);

	if (r < 0)

		DMERR("register failed %d", r);

	return r;

}

static void __exit dm_flakey_exit(void)

{

	dm_unregister_target(&flakey_target);

}

/* 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");