md-cluster.c

/*
 * Copyright (C) 2015, SUSE
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 */


#include <linux/module.h>
#include <linux/dlm.h>
#include <linux/sched.h>
#include "md.h"
#include "bitmap.h"
#include "md-cluster.h"

#define LVB_SIZE	64

struct dlm_lock_resource {
	dlm_lockspace_t *ls;
	struct dlm_lksb lksb;
	char *name; /* lock name. */
	uint32_t flags; /* flags to pass to dlm_lock() */
	struct completion completion; /* completion for synchronized locking */
	void (*bast)(void *arg, int mode); /* blocking AST function pointer*/
	struct mddev *mddev; /* pointing back to mddev. */
};

struct suspend_info {
	int slot;
	sector_t lo;
	sector_t hi;
	struct list_head list;
};

struct resync_info {
	__le64 lo;
	__le64 hi;
};

struct md_cluster_info {
	/* dlm lock space and resources for clustered raid. */
	dlm_lockspace_t *lockspace;
	int slot_number;
	struct completion completion;
	struct dlm_lock_resource *sb_lock;
	struct mutex sb_mutex;
	struct dlm_lock_resource *bitmap_lockres;
	struct list_head suspend_list;
	spinlock_t suspend_lock;
	struct md_thread *recovery_thread;
	unsigned long recovery_map;
	/* communication loc resources */
	struct dlm_lock_resource *ack_lockres;
	struct dlm_lock_resource *message_lockres;
	struct dlm_lock_resource *token_lockres;
	struct md_thread *recv_thread;
};

enum msg_type {
	METADATA_UPDATED = 0,
	RESYNCING,
};

struct cluster_msg {
	int type;
	int slot;
	sector_t low;
	sector_t high;
};

static void sync_ast(void *arg)
{
	struct dlm_lock_resource *res;

	res = (struct dlm_lock_resource *) arg;
	complete(&res->completion);
}

static int dlm_lock_sync(struct dlm_lock_resource *res, int mode)
{
	int ret = 0;

	init_completion(&res->completion);
	ret = dlm_lock(res->ls, mode, &res->lksb,
			res->flags, res->name, strlen(res->name),
			0, sync_ast, res, res->bast);
	if (ret)
		return ret;
	wait_for_completion(&res->completion);
	return res->lksb.sb_status;
}

static int dlm_unlock_sync(struct dlm_lock_resource *res)
{
	return dlm_lock_sync(res, DLM_LOCK_NL);
}

static struct dlm_lock_resource *lockres_init(struct mddev *mddev,
		char *name, void (*bastfn)(void *arg, int mode), int with_lvb)
{
	struct dlm_lock_resource *res = NULL;
	int ret, namelen;
	struct md_cluster_info *cinfo = mddev->cluster_info;

	res = kzalloc(sizeof(struct dlm_lock_resource), GFP_KERNEL);
	if (!res)
		return NULL;
	res->ls = cinfo->lockspace;
	res->mddev = mddev;
	namelen = strlen(name);
	res->name = kzalloc(namelen + 1, GFP_KERNEL);
	if (!res->name) {
		pr_err("md-cluster: Unable to allocate resource name for resource %s\n", name);
		goto out_err;
	}
	strlcpy(res->name, name, namelen + 1);
	if (with_lvb) {
		res->lksb.sb_lvbptr = kzalloc(LVB_SIZE, GFP_KERNEL);
		if (!res->lksb.sb_lvbptr) {
			pr_err("md-cluster: Unable to allocate LVB for resource %s\n", name);
			goto out_err;
		}
		res->flags = DLM_LKF_VALBLK;
	}

	if (bastfn)
		res->bast = bastfn;

	res->flags |= DLM_LKF_EXPEDITE;

	ret = dlm_lock_sync(res, DLM_LOCK_NL);
	if (ret) {
		pr_err("md-cluster: Unable to lock NL on new lock resource %s\n", name);
		goto out_err;
	}
	res->flags &= ~DLM_LKF_EXPEDITE;
	res->flags |= DLM_LKF_CONVERT;

	return res;
out_err:
	kfree(res->lksb.sb_lvbptr);
	kfree(res->name);
	kfree(res);
	return NULL;
}

static void lockres_free(struct dlm_lock_resource *res)
{
	if (!res)
		return;

	init_completion(&res->completion);
	dlm_unlock(res->ls, res->lksb.sb_lkid, 0, &res->lksb, res);
	wait_for_completion(&res->completion);

	kfree(res->name);
	kfree(res->lksb.sb_lvbptr);
	kfree(res);
}

static char *pretty_uuid(char *dest, char *src)
{
	int i, len = 0;

	for (i = 0; i < 16; i++) {
		if (i == 4 || i == 6 || i == 8 || i == 10)
			len += sprintf(dest + len, "-");
		len += sprintf(dest + len, "%02x", (__u8)src[i]);
	}
	return dest;
}

static void add_resync_info(struct mddev *mddev, struct dlm_lock_resource *lockres,
		sector_t lo, sector_t hi)
{
	struct resync_info *ri;

	ri = (struct resync_info *)lockres->lksb.sb_lvbptr;
	ri->lo = cpu_to_le64(lo);
	ri->hi = cpu_to_le64(hi);
}

static struct suspend_info *read_resync_info(struct mddev *mddev, struct dlm_lock_resource *lockres)
{
	struct resync_info ri;
	struct suspend_info *s = NULL;
	sector_t hi = 0;

	dlm_lock_sync(lockres, DLM_LOCK_CR);
	memcpy(&ri, lockres->lksb.sb_lvbptr, sizeof(struct resync_info));
	hi = le64_to_cpu(ri.hi);
	if (ri.hi > 0) {
		s = kzalloc(sizeof(struct suspend_info), GFP_KERNEL);
		if (!s)
			goto out;
		s->hi = hi;
		s->lo = le64_to_cpu(ri.lo);
	}
	dlm_unlock_sync(lockres);
out:
	return s;
}

void recover_bitmaps(struct md_thread *thread)
{
	struct mddev *mddev = thread->mddev;
	struct md_cluster_info *cinfo = mddev->cluster_info;
	struct dlm_lock_resource *bm_lockres;
	char str[64];
	int slot, ret;
	struct suspend_info *s, *tmp;
	sector_t lo, hi;

	while (cinfo->recovery_map) {
		slot = fls64((u64)cinfo->recovery_map) - 1;

		/* Clear suspend_area associated with the bitmap */
		spin_lock_irq(&cinfo->suspend_lock);
		list_for_each_entry_safe(s, tmp, &cinfo->suspend_list, list)
			if (slot == s->slot) {
				list_del(&s->list);
				kfree(s);
			}
		spin_unlock_irq(&cinfo->suspend_lock);

		snprintf(str, 64, "bitmap%04d", slot);
		bm_lockres = lockres_init(mddev, str, NULL, 1);
		if (!bm_lockres) {
			pr_err("md-cluster: Cannot initialize bitmaps\n");
			goto clear_bit;
		}

		ret = dlm_lock_sync(bm_lockres, DLM_LOCK_PW);
		if (ret) {
			pr_err("md-cluster: Could not DLM lock %s: %d\n",
					str, ret);
			goto clear_bit;
		}
		ret = bitmap_copy_from_slot(mddev, slot, &lo, &hi);
		if (ret) {
			pr_err("md-cluster: Could not copy data from bitmap %d\n", slot);
			goto dlm_unlock;
		}
		if (hi > 0) {
			/* TODO:Wait for current resync to get over */
			set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
			if (lo < mddev->recovery_cp)
				mddev->recovery_cp = lo;
			md_check_recovery(mddev);
		}
dlm_unlock:
		dlm_unlock_sync(bm_lockres);
clear_bit:
		clear_bit(slot, &cinfo->recovery_map);
	}
}

static void recover_prep(void *arg)
{
}

static void recover_slot(void *arg, struct dlm_slot *slot)
{
	struct mddev *mddev = arg;
	struct md_cluster_info *cinfo = mddev->cluster_info;

	pr_info("md-cluster: %s Node %d/%d down. My slot: %d. Initiating recovery.\n",
			mddev->bitmap_info.cluster_name,
			slot->nodeid, slot->slot,
			cinfo->slot_number);
	set_bit(slot->slot - 1, &cinfo->recovery_map);
	if (!cinfo->recovery_thread) {
		cinfo->recovery_thread = md_register_thread(recover_bitmaps,
				mddev, "recover");
		if (!cinfo->recovery_thread) {
			pr_warn("md-cluster: Could not create recovery thread\n");
			return;
		}
	}
	md_wakeup_thread(cinfo->recovery_thread);
}

static void recover_done(void *arg, struct dlm_slot *slots,
		int num_slots, int our_slot,
		uint32_t generation)
{
	struct mddev *mddev = arg;
	struct md_cluster_info *cinfo = mddev->cluster_info;

	cinfo->slot_number = our_slot;
	complete(&cinfo->completion);
}

static const struct dlm_lockspace_ops md_ls_ops = {
	.recover_prep = recover_prep,
	.recover_slot = recover_slot,
	.recover_done = recover_done,
};

/*
 * The BAST function for the ack lock resource
 * This function wakes up the receive thread in
 * order to receive and process the message.
 */
static void ack_bast(void *arg, int mode)
{
	struct dlm_lock_resource *res = (struct dlm_lock_resource *)arg;
	struct md_cluster_info *cinfo = res->mddev->cluster_info;

	if (mode == DLM_LOCK_EX)
		md_wakeup_thread(cinfo->recv_thread);
}

static void __remove_suspend_info(struct md_cluster_info *cinfo, int slot)
{
	struct suspend_info *s, *tmp;

	list_for_each_entry_safe(s, tmp, &cinfo->suspend_list, list)
		if (slot == s->slot) {
			pr_info("%s:%d Deleting suspend_info: %d\n",
					__func__, __LINE__, slot);
			list_del(&s->list);
			kfree(s);
			break;
		}
}

static void remove_suspend_info(struct md_cluster_info *cinfo, int slot)
{
	spin_lock_irq(&cinfo->suspend_lock);
	__remove_suspend_info(cinfo, slot);
	spin_unlock_irq(&cinfo->suspend_lock);
}


static void process_suspend_info(struct md_cluster_info *cinfo,
		int slot, sector_t lo, sector_t hi)
{
	struct suspend_info *s;

	if (!hi) {
		remove_suspend_info(cinfo, slot);
		return;
	}
	s = kzalloc(sizeof(struct suspend_info), GFP_KERNEL);
	if (!s)
		return;
	s->slot = slot;
	s->lo = lo;
	s->hi = hi;
	spin_lock_irq(&cinfo->suspend_lock);
	/* Remove existing entry (if exists) before adding */
	__remove_suspend_info(cinfo, slot);
	list_add(&s->list, &cinfo->suspend_list);
	spin_unlock_irq(&cinfo->suspend_lock);
}

static void process_recvd_msg(struct mddev *mddev, struct cluster_msg *msg)
{
	switch (msg->type) {
	case METADATA_UPDATED:
		pr_info("%s: %d Received message: METADATA_UPDATE from %d\n",
			__func__, __LINE__, msg->slot);
		md_reload_sb(mddev);
		break;
	case RESYNCING:
		pr_info("%s: %d Received message: RESYNCING from %d\n",
			__func__, __LINE__, msg->slot);
		process_suspend_info(mddev->cluster_info, msg->slot,
				msg->low, msg->high);
		break;
	};
}

/*
 * thread for receiving message
 */
static void recv_daemon(struct md_thread *thread)
{
	struct md_cluster_info *cinfo = thread->mddev->cluster_info;
	struct dlm_lock_resource *ack_lockres = cinfo->ack_lockres;
	struct dlm_lock_resource *message_lockres = cinfo->message_lockres;
	struct cluster_msg msg;

	/*get CR on Message*/
	if (dlm_lock_sync(message_lockres, DLM_LOCK_CR)) {
		pr_err("md/raid1:failed to get CR on MESSAGE\n");
		return;
	}

	/* read lvb and wake up thread to process this message_lockres */
	memcpy(&msg, message_lockres->lksb.sb_lvbptr, sizeof(struct cluster_msg));
	process_recvd_msg(thread->mddev, &msg);

	/*release CR on ack_lockres*/
	dlm_unlock_sync(ack_lockres);
	/*up-convert to EX on message_lockres*/
	dlm_lock_sync(message_lockres, DLM_LOCK_EX);
	/*get CR on ack_lockres again*/
	dlm_lock_sync(ack_lockres, DLM_LOCK_CR);
	/*release CR on message_lockres*/
	dlm_unlock_sync(message_lockres);
}

/* lock_comm()
 * Takes the lock on the TOKEN lock resource so no other
 * node can communicate while the operation is underway.
 */
static int lock_comm(struct md_cluster_info *cinfo)
{
	int error;

	error = dlm_lock_sync(cinfo->token_lockres, DLM_LOCK_EX);
	if (error)
		pr_err("md-cluster(%s:%d): failed to get EX on TOKEN (%d)\n",
				__func__, __LINE__, error);
	return error;
}

static void unlock_comm(struct md_cluster_info *cinfo)
{
	dlm_unlock_sync(cinfo->token_lockres);
}

/* __sendmsg()
 * This function performs the actual sending of the message. This function is
 * usually called after performing the encompassing operation
 * The function:
 * 1. Grabs the message lockresource in EX mode
 * 2. Copies the message to the message LVB
 * 3. Downconverts message lockresource to CR
 * 4. Upconverts ack lock resource from CR to EX. This forces the BAST on other nodes
 *    and the other nodes read the message. The thread will wait here until all other
 *    nodes have released ack lock resource.
 * 5. Downconvert ack lockresource to CR
 */
static int __sendmsg(struct md_cluster_info *cinfo, struct cluster_msg *cmsg)
{
	int error;
	int slot = cinfo->slot_number - 1;

	cmsg->slot = cpu_to_le32(slot);
	/*get EX on Message*/
	error = dlm_lock_sync(cinfo->message_lockres, DLM_LOCK_EX);
	if (error) {
		pr_err("md-cluster: failed to get EX on MESSAGE (%d)\n", error);
		goto failed_message;
	}

	memcpy(cinfo->message_lockres->lksb.sb_lvbptr, (void *)cmsg,
			sizeof(struct cluster_msg));
	/*down-convert EX to CR on Message*/
	error = dlm_lock_sync(cinfo->message_lockres, DLM_LOCK_CR);
	if (error) {
		pr_err("md-cluster: failed to convert EX to CR on MESSAGE(%d)\n",
				error);
		goto failed_message;
	}

	/*up-convert CR to EX on Ack*/
	error = dlm_lock_sync(cinfo->ack_lockres, DLM_LOCK_EX);
	if (error) {
		pr_err("md-cluster: failed to convert CR to EX on ACK(%d)\n",
				error);
		goto failed_ack;
	}

	/*down-convert EX to CR on Ack*/
	error = dlm_lock_sync(cinfo->ack_lockres, DLM_LOCK_CR);
	if (error) {
		pr_err("md-cluster: failed to convert EX to CR on ACK(%d)\n",
				error);
		goto failed_ack;
	}

failed_ack:
	dlm_unlock_sync(cinfo->message_lockres);
failed_message:
	return error;
}

static int sendmsg(struct md_cluster_info *cinfo, struct cluster_msg *cmsg)
{
	int ret;

	lock_comm(cinfo);
	ret = __sendmsg(cinfo, cmsg);
	unlock_comm(cinfo);
	return ret;
}

static int gather_all_resync_info(struct mddev *mddev, int total_slots)
{
	struct md_cluster_info *cinfo = mddev->cluster_info;
	int i, ret = 0;
	struct dlm_lock_resource *bm_lockres;
	struct suspend_info *s;
	char str[64];


	for (i = 0; i < total_slots; i++) {
		memset(str, '\0', 64);
		snprintf(str, 64, "bitmap%04d", i);
		bm_lockres = lockres_init(mddev, str, NULL, 1);
		if (!bm_lockres)
			return -ENOMEM;
		if (i == (cinfo->slot_number - 1))
			continue;

		bm_lockres->flags |= DLM_LKF_NOQUEUE;
		ret = dlm_lock_sync(bm_lockres, DLM_LOCK_PW);
		if (ret == -EAGAIN) {
			memset(bm_lockres->lksb.sb_lvbptr, '\0', LVB_SIZE);
			s = read_resync_info(mddev, bm_lockres);
			if (s) {
				pr_info("%s:%d Resync[%llu..%llu] in progress on %d\n",
						__func__, __LINE__,
						(unsigned long long) s->lo,
						(unsigned long long) s->hi, i);
				spin_lock_irq(&cinfo->suspend_lock);
				s->slot = i;
				list_add(&s->list, &cinfo->suspend_list);
				spin_unlock_irq(&cinfo->suspend_lock);
			}
			ret = 0;
			lockres_free(bm_lockres);
			continue;
		}
		if (ret)
			goto out;
		/* TODO: Read the disk bitmap sb and check if it needs recovery */
		dlm_unlock_sync(bm_lockres);
		lockres_free(bm_lockres);
	}
out:
	return ret;
}

static int join(struct mddev *mddev, int nodes)
{
	struct md_cluster_info *cinfo;
	int ret, ops_rv;
	char str[64];

	if (!try_module_get(THIS_MODULE))
		return -ENOENT;

	cinfo = kzalloc(sizeof(struct md_cluster_info), GFP_KERNEL);
	if (!cinfo)
		return -ENOMEM;

	init_completion(&cinfo->completion);

	mutex_init(&cinfo->sb_mutex);
	mddev->cluster_info = cinfo;

	memset(str, 0, 64);
	pretty_uuid(str, mddev->uuid);
	ret = dlm_new_lockspace(str, mddev->bitmap_info.cluster_name,
				DLM_LSFL_FS, LVB_SIZE,
				&md_ls_ops, mddev, &ops_rv, &cinfo->lockspace);
	if (ret)
		goto err;
	wait_for_completion(&cinfo->completion);
	if (nodes <= cinfo->slot_number) {
		pr_err("md-cluster: Slot allotted(%d) greater than available slots(%d)", cinfo->slot_number - 1,
			nodes);
		ret = -ERANGE;
		goto err;
	}
	cinfo->sb_lock = lockres_init(mddev, "cmd-super",
					NULL, 0);
	if (!cinfo->sb_lock) {
		ret = -ENOMEM;
		goto err;
	}
	/* Initiate the communication resources */
	ret = -ENOMEM;
	cinfo->recv_thread = md_register_thread(recv_daemon, mddev, "cluster_recv");
	if (!cinfo->recv_thread) {
		pr_err("md-cluster: cannot allocate memory for recv_thread!\n");
		goto err;
	}
	cinfo->message_lockres = lockres_init(mddev, "message", NULL, 1);
	if (!cinfo->message_lockres)
		goto err;
	cinfo->token_lockres = lockres_init(mddev, "token", NULL, 0);
	if (!cinfo->token_lockres)
		goto err;
	cinfo->ack_lockres = lockres_init(mddev, "ack", ack_bast, 0);
	if (!cinfo->ack_lockres)
		goto err;
	/* get sync CR lock on ACK. */
	if (dlm_lock_sync(cinfo->ack_lockres, DLM_LOCK_CR))
		pr_err("md-cluster: failed to get a sync CR lock on ACK!(%d)\n",
				ret);

	pr_info("md-cluster: Joined cluster %s slot %d\n", str, cinfo->slot_number);
	snprintf(str, 64, "bitmap%04d", cinfo->slot_number - 1);
	cinfo->bitmap_lockres = lockres_init(mddev, str, NULL, 1);
	if (!cinfo->bitmap_lockres)
		goto err;
	if (dlm_lock_sync(cinfo->bitmap_lockres, DLM_LOCK_PW)) {
		pr_err("Failed to get bitmap lock\n");
		ret = -EINVAL;
		goto err;
	}

	INIT_LIST_HEAD(&cinfo->suspend_list);
	spin_lock_init(&cinfo->suspend_lock);

	ret = gather_all_resync_info(mddev, nodes);
	if (ret)
		goto err;

	return 0;
err:
	lockres_free(cinfo->message_lockres);
	lockres_free(cinfo->token_lockres);
	lockres_free(cinfo->ack_lockres);
	lockres_free(cinfo->bitmap_lockres);
	lockres_free(cinfo->sb_lock);
	if (cinfo->lockspace)
		dlm_release_lockspace(cinfo->lockspace, 2);
	mddev->cluster_info = NULL;
	kfree(cinfo);
	module_put(THIS_MODULE);
	return ret;
}

static int leave(struct mddev *mddev)
{
	struct md_cluster_info *cinfo = mddev->cluster_info;

	if (!cinfo)
		return 0;
	md_unregister_thread(&cinfo->recovery_thread);
	md_unregister_thread(&cinfo->recv_thread);
	lockres_free(cinfo->message_lockres);
	lockres_free(cinfo->token_lockres);
	lockres_free(cinfo->ack_lockres);
	lockres_free(cinfo->sb_lock);
	lockres_free(cinfo->bitmap_lockres);
	dlm_release_lockspace(cinfo->lockspace, 2);
	return 0;
}

/* slot_number(): Returns the MD slot number to use
 * DLM starts the slot numbers from 1, wheras cluster-md
 * wants the number to be from zero, so we deduct one
 */
static int slot_number(struct mddev *mddev)
{
	struct md_cluster_info *cinfo = mddev->cluster_info;

	return cinfo->slot_number - 1;
}

static void resync_info_update(struct mddev *mddev, sector_t lo, sector_t hi)
{
	struct md_cluster_info *cinfo = mddev->cluster_info;

	add_resync_info(mddev, cinfo->bitmap_lockres, lo, hi);
	/* Re-acquire the lock to refresh LVB */
	dlm_lock_sync(cinfo->bitmap_lockres, DLM_LOCK_PW);
}

static int metadata_update_start(struct mddev *mddev)
{
	return lock_comm(mddev->cluster_info);
}

static int metadata_update_finish(struct mddev *mddev)
{
	struct md_cluster_info *cinfo = mddev->cluster_info;
	struct cluster_msg cmsg;
	int ret;

	memset(&cmsg, 0, sizeof(cmsg));
	cmsg.type = cpu_to_le32(METADATA_UPDATED);
	ret = __sendmsg(cinfo, &cmsg);
	unlock_comm(cinfo);
	return ret;
}

static int metadata_update_cancel(struct mddev *mddev)
{
	struct md_cluster_info *cinfo = mddev->cluster_info;

	return dlm_unlock_sync(cinfo->token_lockres);
}

static int resync_send(struct mddev *mddev, enum msg_type type,
		sector_t lo, sector_t hi)
{
	struct md_cluster_info *cinfo = mddev->cluster_info;
	struct cluster_msg cmsg;
	int slot = cinfo->slot_number - 1;

	pr_info("%s:%d lo: %llu hi: %llu\n", __func__, __LINE__,
			(unsigned long long)lo,
			(unsigned long long)hi);
	resync_info_update(mddev, lo, hi);
	cmsg.type = cpu_to_le32(type);
	cmsg.slot = cpu_to_le32(slot);
	cmsg.low = cpu_to_le64(lo);
	cmsg.high = cpu_to_le64(hi);
	return sendmsg(cinfo, &cmsg);
}

static int resync_start(struct mddev *mddev, sector_t lo, sector_t hi)
{
	pr_info("%s:%d\n", __func__, __LINE__);
	return resync_send(mddev, RESYNCING, lo, hi);
}

static void resync_finish(struct mddev *mddev)
{
	pr_info("%s:%d\n", __func__, __LINE__);
	resync_send(mddev, RESYNCING, 0, 0);
}

static int area_resyncing(struct mddev *mddev, sector_t lo, sector_t hi)
{
	struct md_cluster_info *cinfo = mddev->cluster_info;
	int ret = 0;
	struct suspend_info *s;

	spin_lock_irq(&cinfo->suspend_lock);
	if (list_empty(&cinfo->suspend_list))
		goto out;
	list_for_each_entry(s, &cinfo->suspend_list, list)
		if (hi > s->lo && lo < s->hi) {
			ret = 1;
			break;
		}
out:
	spin_unlock_irq(&cinfo->suspend_lock);
	return ret;
}

static struct md_cluster_operations cluster_ops = {
	.join   = join,
	.leave  = leave,
	.slot_number = slot_number,
	.resync_info_update = resync_info_update,
	.resync_start = resync_start,
	.resync_finish = resync_finish,
	.metadata_update_start = metadata_update_start,
	.metadata_update_finish = metadata_update_finish,
	.metadata_update_cancel = metadata_update_cancel,
	.area_resyncing = area_resyncing,
};

static int __init cluster_init(void)
{
	pr_warn("md-cluster: EXPERIMENTAL. Use with caution\n");
	pr_info("Registering Cluster MD functions\n");
	register_md_cluster_operations(&cluster_ops, THIS_MODULE);
	return 0;
}

static void cluster_exit(void)
{
	unregister_md_cluster_operations();
}

module_init(cluster_init);
module_exit(cluster_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Clustering support for MD");