linux-vybrid_public/fs/ocfs2/dlm/dlmmaster.c

/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * dlmmod.c
 *
 * standalone DLM module
 *
 * Copyright (C) 2004 Oracle.  All rights reserved.
 *
 * 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 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 *
 */


#include <linux/module.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/utsname.h>
#include <linux/init.h>
#include <linux/sysctl.h>
#include <linux/random.h>
#include <linux/blkdev.h>
#include <linux/socket.h>
#include <linux/inet.h>
#include <linux/spinlock.h>
#include <linux/delay.h>


#include "cluster/heartbeat.h"
#include "cluster/nodemanager.h"
#include "cluster/tcp.h"

#include "dlmapi.h"
#include "dlmcommon.h"
#include "dlmdebug.h"
#include "dlmdomain.h"

#define MLOG_MASK_PREFIX (ML_DLM|ML_DLM_MASTER)
#include "cluster/masklog.h"

enum dlm_mle_type {
	DLM_MLE_BLOCK,
	DLM_MLE_MASTER,
	DLM_MLE_MIGRATION
};

struct dlm_lock_name
{
	u8 len;
	u8 name[DLM_LOCKID_NAME_MAX];
};

struct dlm_master_list_entry
{
	struct list_head list;
	struct list_head hb_events;
	struct dlm_ctxt *dlm;
	spinlock_t spinlock;
	wait_queue_head_t wq;
	atomic_t woken;
	struct kref mle_refs;
	unsigned long maybe_map[BITS_TO_LONGS(O2NM_MAX_NODES)];
	unsigned long vote_map[BITS_TO_LONGS(O2NM_MAX_NODES)];
	unsigned long response_map[BITS_TO_LONGS(O2NM_MAX_NODES)];
	unsigned long node_map[BITS_TO_LONGS(O2NM_MAX_NODES)];
	u8 master;
	u8 new_master;
	enum dlm_mle_type type;
	struct o2hb_callback_func mle_hb_up;
	struct o2hb_callback_func mle_hb_down;
	union {
		struct dlm_lock_resource *res;
		struct dlm_lock_name name;
	} u;
};

static void dlm_mle_node_down(struct dlm_ctxt *dlm,
			      struct dlm_master_list_entry *mle,
			      struct o2nm_node *node,
			      int idx);
static void dlm_mle_node_up(struct dlm_ctxt *dlm,
			    struct dlm_master_list_entry *mle,
			    struct o2nm_node *node,
			    int idx);

static void dlm_assert_master_worker(struct dlm_work_item *item, void *data);
static int dlm_do_assert_master(struct dlm_ctxt *dlm, const char *lockname,
				unsigned int namelen, void *nodemap,
				u32 flags);

static inline int dlm_mle_equal(struct dlm_ctxt *dlm,
				struct dlm_master_list_entry *mle,
				const char *name,
				unsigned int namelen)
{
	struct dlm_lock_resource *res;

	if (dlm != mle->dlm)
		return 0;

	if (mle->type == DLM_MLE_BLOCK ||
	    mle->type == DLM_MLE_MIGRATION) {
		if (namelen != mle->u.name.len ||
    	    	    memcmp(name, mle->u.name.name, namelen)!=0)
			return 0;
	} else {
		res = mle->u.res;
		if (namelen != res->lockname.len ||
		    memcmp(res->lockname.name, name, namelen) != 0)
			return 0;
	}
	return 1;
}

#if 0
/* Code here is included but defined out as it aids debugging */

void dlm_print_one_mle(struct dlm_master_list_entry *mle)
{
	int i = 0, refs;
	char *type;
	char attached;
	u8 master;
	unsigned int namelen;
	const char *name;
	struct kref *k;

	k = &mle->mle_refs;
	if (mle->type == DLM_MLE_BLOCK)
		type = "BLK";
	else if (mle->type == DLM_MLE_MASTER)
		type = "MAS";
	else
		type = "MIG";
	refs = atomic_read(&k->refcount);
	master = mle->master;
	attached = (list_empty(&mle->hb_events) ? 'N' : 'Y');

	if (mle->type != DLM_MLE_MASTER) {
		namelen = mle->u.name.len;
		name = mle->u.name.name;
	} else {
		namelen = mle->u.res->lockname.len;
		name = mle->u.res->lockname.name;
	}

	mlog(ML_NOTICE, "  #%3d: %3s  %3d  %3u   %3u %c    (%d)%.*s\n",
		  i, type, refs, master, mle->new_master, attached,
		  namelen, namelen, name);
}

static void dlm_dump_mles(struct dlm_ctxt *dlm)
{
	struct dlm_master_list_entry *mle;
	struct list_head *iter;
	
	mlog(ML_NOTICE, "dumping all mles for domain %s:\n", dlm->name);
	mlog(ML_NOTICE, "  ####: type refs owner new events? lockname nodemap votemap respmap maybemap\n");
	spin_lock(&dlm->master_lock);
	list_for_each(iter, &dlm->master_list) {
		mle = list_entry(iter, struct dlm_master_list_entry, list);
		dlm_print_one_mle(mle);
	}
	spin_unlock(&dlm->master_lock);
}

int dlm_dump_all_mles(const char __user *data, unsigned int len)
{
	struct list_head *iter;
	struct dlm_ctxt *dlm;

	spin_lock(&dlm_domain_lock);
	list_for_each(iter, &dlm_domains) {
		dlm = list_entry (iter, struct dlm_ctxt, list);
		mlog(ML_NOTICE, "found dlm: %p, name=%s\n", dlm, dlm->name);
		dlm_dump_mles(dlm);
	}
	spin_unlock(&dlm_domain_lock);
	return len;
}
EXPORT_SYMBOL_GPL(dlm_dump_all_mles);

#endif  /*  0  */


static kmem_cache_t *dlm_mle_cache = NULL;


static void dlm_mle_release(struct kref *kref);
static void dlm_init_mle(struct dlm_master_list_entry *mle,
			enum dlm_mle_type type,
			struct dlm_ctxt *dlm,
			struct dlm_lock_resource *res,
			const char *name,
			unsigned int namelen);
static void dlm_put_mle(struct dlm_master_list_entry *mle);
static void __dlm_put_mle(struct dlm_master_list_entry *mle);
static int dlm_find_mle(struct dlm_ctxt *dlm,
			struct dlm_master_list_entry **mle,
			char *name, unsigned int namelen);

static int dlm_do_master_request(struct dlm_master_list_entry *mle, int to);


static int dlm_wait_for_lock_mastery(struct dlm_ctxt *dlm,
				     struct dlm_lock_resource *res,
				     struct dlm_master_list_entry *mle,
				     int *blocked);
static int dlm_restart_lock_mastery(struct dlm_ctxt *dlm,
				    struct dlm_lock_resource *res,
				    struct dlm_master_list_entry *mle,
				    int blocked);
static int dlm_add_migration_mle(struct dlm_ctxt *dlm,
				 struct dlm_lock_resource *res,
				 struct dlm_master_list_entry *mle,
				 struct dlm_master_list_entry **oldmle,
				 const char *name, unsigned int namelen,
				 u8 new_master, u8 master);

static u8 dlm_pick_migration_target(struct dlm_ctxt *dlm,
				    struct dlm_lock_resource *res);
static void dlm_remove_nonlocal_locks(struct dlm_ctxt *dlm,
				      struct dlm_lock_resource *res);
static int dlm_mark_lockres_migrating(struct dlm_ctxt *dlm,
				       struct dlm_lock_resource *res,
				       u8 target);


int dlm_is_host_down(int errno)
{
	switch (errno) {
		case -EBADF:
		case -ECONNREFUSED:
		case -ENOTCONN:
		case -ECONNRESET:
		case -EPIPE:
		case -EHOSTDOWN:
		case -EHOSTUNREACH:
		case -ETIMEDOUT:
		case -ECONNABORTED:
		case -ENETDOWN:
		case -ENETUNREACH:
		case -ENETRESET:
		case -ESHUTDOWN:
		case -ENOPROTOOPT:
		case -EINVAL:   /* if returned from our tcp code,
				   this means there is no socket */
			return 1;
	}
	return 0;
}


/*
 * MASTER LIST FUNCTIONS
 */


/*
 * regarding master list entries and heartbeat callbacks:
 *
 * in order to avoid sleeping and allocation that occurs in
 * heartbeat, master list entries are simply attached to the
 * dlm's established heartbeat callbacks.  the mle is attached
 * when it is created, and since the dlm->spinlock is held at
 * that time, any heartbeat event will be properly discovered
 * by the mle.  the mle needs to be detached from the
 * dlm->mle_hb_events list as soon as heartbeat events are no
 * longer useful to the mle, and before the mle is freed.
 *
 * as a general rule, heartbeat events are no longer needed by
 * the mle once an "answer" regarding the lock master has been
 * received.
 */
static inline void __dlm_mle_attach_hb_events(struct dlm_ctxt *dlm,
					      struct dlm_master_list_entry *mle)
{
	assert_spin_locked(&dlm->spinlock);

	list_add_tail(&mle->hb_events, &dlm->mle_hb_events);
}


static inline void __dlm_mle_detach_hb_events(struct dlm_ctxt *dlm,
					      struct dlm_master_list_entry *mle)
{
	if (!list_empty(&mle->hb_events))
		list_del_init(&mle->hb_events);
}


static inline void dlm_mle_detach_hb_events(struct dlm_ctxt *dlm,
					    struct dlm_master_list_entry *mle)
{
	spin_lock(&dlm->spinlock);
	__dlm_mle_detach_hb_events(dlm, mle);
	spin_unlock(&dlm->spinlock);
}

/* remove from list and free */
static void __dlm_put_mle(struct dlm_master_list_entry *mle)
{
	struct dlm_ctxt *dlm;
	dlm = mle->dlm;

	assert_spin_locked(&dlm->spinlock);
	assert_spin_locked(&dlm->master_lock);
	BUG_ON(!atomic_read(&mle->mle_refs.refcount));

	kref_put(&mle->mle_refs, dlm_mle_release);
}


/* must not have any spinlocks coming in */
static void dlm_put_mle(struct dlm_master_list_entry *mle)
{
	struct dlm_ctxt *dlm;
	dlm = mle->dlm;

	spin_lock(&dlm->spinlock);
	spin_lock(&dlm->master_lock);
	__dlm_put_mle(mle);
	spin_unlock(&dlm->master_lock);
	spin_unlock(&dlm->spinlock);
}

static inline void dlm_get_mle(struct dlm_master_list_entry *mle)
{
	kref_get(&mle->mle_refs);
}

static void dlm_init_mle(struct dlm_master_list_entry *mle,
			enum dlm_mle_type type,
			struct dlm_ctxt *dlm,
			struct dlm_lock_resource *res,
			const char *name,
			unsigned int namelen)
{
	assert_spin_locked(&dlm->spinlock);

	mle->dlm = dlm;
	mle->type = type;
	INIT_LIST_HEAD(&mle->list);
	INIT_LIST_HEAD(&mle->hb_events);
	memset(mle->maybe_map, 0, sizeof(mle->maybe_map));
	spin_lock_init(&mle->spinlock);
	init_waitqueue_head(&mle->wq);
	atomic_set(&mle->woken, 0);
	kref_init(&mle->mle_refs);
	memset(mle->response_map, 0, sizeof(mle->response_map));
	mle->master = O2NM_MAX_NODES;
	mle->new_master = O2NM_MAX_NODES;

	if (mle->type == DLM_MLE_MASTER) {
		BUG_ON(!res);
		mle->u.res = res;
	} else if (mle->type == DLM_MLE_BLOCK) {
		BUG_ON(!name);
		memcpy(mle->u.name.name, name, namelen);
		mle->u.name.len = namelen;
	} else /* DLM_MLE_MIGRATION */ {
		BUG_ON(!name);
		memcpy(mle->u.name.name, name, namelen);
		mle->u.name.len = namelen;
	}

	/* copy off the node_map and register hb callbacks on our copy */
	memcpy(mle->node_map, dlm->domain_map, sizeof(mle->node_map));
	memcpy(mle->vote_map, dlm->domain_map, sizeof(mle->vote_map));
	clear_bit(dlm->node_num, mle->vote_map);
	clear_bit(dlm->node_num, mle->node_map);

	/* attach the mle to the domain node up/down events */
	__dlm_mle_attach_hb_events(dlm, mle);
}


/* returns 1 if found, 0 if not */
static int dlm_find_mle(struct dlm_ctxt *dlm,
			struct dlm_master_list_entry **mle,
			char *name, unsigned int namelen)
{
	struct dlm_master_list_entry *tmpmle;
	struct list_head *iter;

	assert_spin_locked(&dlm->master_lock);

	list_for_each(iter, &dlm->master_list) {
		tmpmle = list_entry(iter, struct dlm_master_list_entry, list);
		if (!dlm_mle_equal(dlm, tmpmle, name, namelen))
			continue;
		dlm_get_mle(tmpmle);
		*mle = tmpmle;
		return 1;
	}
	return 0;
}

void dlm_hb_event_notify_attached(struct dlm_ctxt *dlm, int idx, int node_up)
{
	struct dlm_master_list_entry *mle;
	struct list_head *iter;

	assert_spin_locked(&dlm->spinlock);
	
	list_for_each(iter, &dlm->mle_hb_events) {
		mle = list_entry(iter, struct dlm_master_list_entry, 
				 hb_events);
		if (node_up)
			dlm_mle_node_up(dlm, mle, NULL, idx);
		else
			dlm_mle_node_down(dlm, mle, NULL, idx);
	}
}

static void dlm_mle_node_down(struct dlm_ctxt *dlm,
			      struct dlm_master_list_entry *mle,
			      struct o2nm_node *node, int idx)
{
	spin_lock(&mle->spinlock);

	if (!test_bit(idx, mle->node_map))
		mlog(0, "node %u already removed from nodemap!\n", idx);
	else
		clear_bit(idx, mle->node_map);

	spin_unlock(&mle->spinlock);
}

static void dlm_mle_node_up(struct dlm_ctxt *dlm,
			    struct dlm_master_list_entry *mle,
			    struct o2nm_node *node, int idx)
{
	spin_lock(&mle->spinlock);

	if (test_bit(idx, mle->node_map))
		mlog(0, "node %u already in node map!\n", idx);
	else
		set_bit(idx, mle->node_map);

	spin_unlock(&mle->spinlock);
}


int dlm_init_mle_cache(void)
{
	dlm_mle_cache = kmem_cache_create("dlm_mle_cache",
					  sizeof(struct dlm_master_list_entry),
					  0, SLAB_HWCACHE_ALIGN,
					  NULL, NULL);
	if (dlm_mle_cache == NULL)
		return -ENOMEM;
	return 0;
}

void dlm_destroy_mle_cache(void)
{
	if (dlm_mle_cache)
		kmem_cache_destroy(dlm_mle_cache);
}

static void dlm_mle_release(struct kref *kref)
{
	struct dlm_master_list_entry *mle;
	struct dlm_ctxt *dlm;

	mlog_entry_void();

	mle = container_of(kref, struct dlm_master_list_entry, mle_refs);
	dlm = mle->dlm;

	if (mle->type != DLM_MLE_MASTER) {
		mlog(0, "calling mle_release for %.*s, type %d\n",
		     mle->u.name.len, mle->u.name.name, mle->type);
	} else {
		mlog(0, "calling mle_release for %.*s, type %d\n",
		     mle->u.res->lockname.len,
		     mle->u.res->lockname.name, mle->type);
	}
	assert_spin_locked(&dlm->spinlock);
	assert_spin_locked(&dlm->master_lock);

	/* remove from list if not already */
	if (!list_empty(&mle->list))
		list_del_init(&mle->list);

	/* detach the mle from the domain node up/down events */
	__dlm_mle_detach_hb_events(dlm, mle);

	/* NOTE: kfree under spinlock here.
	 * if this is bad, we can move this to a freelist. */
	kmem_cache_free(dlm_mle_cache, mle);
}


/*
 * LOCK RESOURCE FUNCTIONS
 */

static void dlm_set_lockres_owner(struct dlm_ctxt *dlm,
				  struct dlm_lock_resource *res,
				  u8 owner)
{
	assert_spin_locked(&res->spinlock);

	mlog_entry("%.*s, %u\n", res->lockname.len, res->lockname.name, owner);

	if (owner == dlm->node_num)
		atomic_inc(&dlm->local_resources);
	else if (owner == DLM_LOCK_RES_OWNER_UNKNOWN)
		atomic_inc(&dlm->unknown_resources);
	else
		atomic_inc(&dlm->remote_resources);

	res->owner = owner;
}

void dlm_change_lockres_owner(struct dlm_ctxt *dlm,
			      struct dlm_lock_resource *res, u8 owner)
{
	assert_spin_locked(&res->spinlock);

	if (owner == res->owner)
		return;

	if (res->owner == dlm->node_num)
		atomic_dec(&dlm->local_resources);
	else if (res->owner == DLM_LOCK_RES_OWNER_UNKNOWN)
		atomic_dec(&dlm->unknown_resources);
	else
		atomic_dec(&dlm->remote_resources);

	dlm_set_lockres_owner(dlm, res, owner);
}


static void dlm_lockres_release(struct kref *kref)
{
	struct dlm_lock_resource *res;

	res = container_of(kref, struct dlm_lock_resource, refs);

	/* This should not happen -- all lockres' have a name
	 * associated with them at init time. */
	BUG_ON(!res->lockname.name);

	mlog(0, "destroying lockres %.*s\n", res->lockname.len,
	     res->lockname.name);

	/* By the time we're ready to blow this guy away, we shouldn't
	 * be on any lists. */
	BUG_ON(!list_empty(&res->list));
	BUG_ON(!list_empty(&res->granted));
	BUG_ON(!list_empty(&res->converting));
	BUG_ON(!list_empty(&res->blocked));
	BUG_ON(!list_empty(&res->dirty));
	BUG_ON(!list_empty(&res->recovering));
	BUG_ON(!list_empty(&res->purge));

	kfree(res->lockname.name);

	kfree(res);
}

void dlm_lockres_get(struct dlm_lock_resource *res)
{
	kref_get(&res->refs);
}

void dlm_lockres_put(struct dlm_lock_resource *res)
{
	kref_put(&res->refs, dlm_lockres_release);
}

static void dlm_init_lockres(struct dlm_ctxt *dlm,
			     struct dlm_lock_resource *res,
			     const char *name, unsigned int namelen)
{
	char *qname;

	/* If we memset here, we lose our reference to the kmalloc'd
	 * res->lockname.name, so be sure to init every field
	 * correctly! */

	qname = (char *) res->lockname.name;
	memcpy(qname, name, namelen);

	res->lockname.len = namelen;
	res->lockname.hash = full_name_hash(name, namelen);

	init_waitqueue_head(&res->wq);
	spin_lock_init(&res->spinlock);
	INIT_LIST_HEAD(&res->list);
	INIT_LIST_HEAD(&res->granted);
	INIT_LIST_HEAD(&res->converting);
	INIT_LIST_HEAD(&res->blocked);
	INIT_LIST_HEAD(&res->dirty);
	INIT_LIST_HEAD(&res->recovering);
	INIT_LIST_HEAD(&res->purge);
	atomic_set(&res->asts_reserved, 0);
	res->migration_pending = 0;

	kref_init(&res->refs);

	/* just for consistency */
	spin_lock(&res->spinlock);
	dlm_set_lockres_owner(dlm, res, DLM_LOCK_RES_OWNER_UNKNOWN);
	spin_unlock(&res->spinlock);

	res->state = DLM_LOCK_RES_IN_PROGRESS;

	res->last_used = 0;

	memset(res->lvb, 0, DLM_LVB_LEN);
}

struct dlm_lock_resource *dlm_new_lockres(struct dlm_ctxt *dlm,
				   const char *name,
				   unsigned int namelen)
{
	struct dlm_lock_resource *res;

	res = kmalloc(sizeof(struct dlm_lock_resource), GFP_KERNEL);
	if (!res)
		return NULL;

	res->lockname.name = kmalloc(namelen, GFP_KERNEL);
	if (!res->lockname.name) {
		kfree(res);
		return NULL;
	}

	dlm_init_lockres(dlm, res, name, namelen);
	return res;
}

/*
 * lookup a lock resource by name.
 * may already exist in the hashtable.
 * lockid is null terminated
 *
 * if not, allocate enough for the lockres and for
 * the temporary structure used in doing the mastering.
 *
 * also, do a lookup in the dlm->master_list to see
 * if another node has begun mastering the same lock.
 * if so, there should be a block entry in there
 * for this name, and we should *not* attempt to master
 * the lock here.   need to wait around for that node
 * to assert_master (or die).
 *
 */
struct dlm_lock_resource * dlm_get_lock_resource(struct dlm_ctxt *dlm,
					  const char *lockid,
					  int flags)
{
	struct dlm_lock_resource *tmpres=NULL, *res=NULL;
	struct dlm_master_list_entry *mle = NULL;
	struct dlm_master_list_entry *alloc_mle = NULL;
	int blocked = 0;
	int ret, nodenum;
	struct dlm_node_iter iter;
	unsigned int namelen;
	int tries = 0;

	BUG_ON(!lockid);

	namelen = strlen(lockid);

	mlog(0, "get lockres %s (len %d)\n", lockid, namelen);

lookup:
	spin_lock(&dlm->spinlock);
	tmpres = __dlm_lookup_lockres(dlm, lockid, namelen);
	if (tmpres) {
		spin_unlock(&dlm->spinlock);
		mlog(0, "found in hash!\n");
		if (res)
			dlm_lockres_put(res);
		res = tmpres;
		goto leave;
	}

	if (!res) {
		spin_unlock(&dlm->spinlock);
		mlog(0, "allocating a new resource\n");
		/* nothing found and we need to allocate one. */
		alloc_mle = (struct dlm_master_list_entry *)
			kmem_cache_alloc(dlm_mle_cache, GFP_KERNEL);
		if (!alloc_mle)
			goto leave;
		res = dlm_new_lockres(dlm, lockid, namelen);
		if (!res)
			goto leave;
		goto lookup;
	}

	mlog(0, "no lockres found, allocated our own: %p\n", res);

	if (flags & LKM_LOCAL) {
		/* caller knows it's safe to assume it's not mastered elsewhere
		 * DONE!  return right away */
		spin_lock(&res->spinlock);
		dlm_change_lockres_owner(dlm, res, dlm->node_num);
		__dlm_insert_lockres(dlm, res);
		spin_unlock(&res->spinlock);
		spin_unlock(&dlm->spinlock);
		/* lockres still marked IN_PROGRESS */
		goto wake_waiters;
	}

	/* check master list to see if another node has started mastering it */
	spin_lock(&dlm->master_lock);

	/* if we found a block, wait for lock to be mastered by another node */
	blocked = dlm_find_mle(dlm, &mle, (char *)lockid, namelen);
	if (blocked) {
		if (mle->type == DLM_MLE_MASTER) {
			mlog(ML_ERROR, "master entry for nonexistent lock!\n");
			BUG();
		} else if (mle->type == DLM_MLE_MIGRATION) {
			/* migration is in progress! */
			/* the good news is that we now know the
			 * "current" master (mle->master). */

			spin_unlock(&dlm->master_lock);
			assert_spin_locked(&dlm->spinlock);

			/* set the lockres owner and hash it */
			spin_lock(&res->spinlock);
			dlm_set_lockres_owner(dlm, res, mle->master);
			__dlm_insert_lockres(dlm, res);
			spin_unlock(&res->spinlock);
			spin_unlock(&dlm->spinlock);

			/* master is known, detach */
			dlm_mle_detach_hb_events(dlm, mle);
			dlm_put_mle(mle);
			mle = NULL;
			goto wake_waiters;
		}
	} else {
		/* go ahead and try to master lock on this node */
		mle = alloc_mle;
		/* make sure this does not get freed below */
		alloc_mle = NULL;
		dlm_init_mle(mle, DLM_MLE_MASTER, dlm, res, NULL, 0);
		set_bit(dlm->node_num, mle->maybe_map);
		list_add(&mle->list, &dlm->master_list);
	}

	/* at this point there is either a DLM_MLE_BLOCK or a
	 * DLM_MLE_MASTER on the master list, so it's safe to add the
	 * lockres to the hashtable.  anyone who finds the lock will
	 * still have to wait on the IN_PROGRESS. */

	/* finally add the lockres to its hash bucket */
	__dlm_insert_lockres(dlm, res);
	/* get an extra ref on the mle in case this is a BLOCK
	 * if so, the creator of the BLOCK may try to put the last
	 * ref at this time in the assert master handler, so we
	 * need an extra one to keep from a bad ptr deref. */
	dlm_get_mle(mle);
	spin_unlock(&dlm->master_lock);
	spin_unlock(&dlm->spinlock);

	/* must wait for lock to be mastered elsewhere */
	if (blocked)
		goto wait;

redo_request:
	ret = -EINVAL;
	dlm_node_iter_init(mle->vote_map, &iter);
	while ((nodenum = dlm_node_iter_next(&iter)) >= 0) {
		ret = dlm_do_master_request(mle, nodenum);
		if (ret < 0)
			mlog_errno(ret);
		if (mle->master != O2NM_MAX_NODES) {
			/* found a master ! */
			break;
		}
	}

wait:
	/* keep going until the response map includes all nodes */
	ret = dlm_wait_for_lock_mastery(dlm, res, mle, &blocked);
	if (ret < 0) {
		mlog(0, "%s:%.*s: node map changed, redo the "
		     "master request now, blocked=%d\n",
		     dlm->name, res->lockname.len,
		     res->lockname.name, blocked);
		if (++tries > 20) {
			mlog(ML_ERROR, "%s:%.*s: spinning on "
			     "dlm_wait_for_lock_mastery, blocked=%d\n", 
			     dlm->name, res->lockname.len, 
			     res->lockname.name, blocked);
			dlm_print_one_lock_resource(res);
			/* dlm_print_one_mle(mle); */
			tries = 0;
		}
		goto redo_request;
	}

	mlog(0, "lockres mastered by %u\n", res->owner);
	/* make sure we never continue without this */
	BUG_ON(res->owner == O2NM_MAX_NODES);

	/* master is known, detach if not already detached */
	dlm_mle_detach_hb_events(dlm, mle);
	dlm_put_mle(mle);
	/* put the extra ref */
	dlm_put_mle(mle);

wake_waiters:
	spin_lock(&res->spinlock);
	res->state &= ~DLM_LOCK_RES_IN_PROGRESS;
	spin_unlock(&res->spinlock);
	wake_up(&res->wq);

leave:
	/* need to free the unused mle */
	if (alloc_mle)
		kmem_cache_free(dlm_mle_cache, alloc_mle);

	return res;
}


#define DLM_MASTERY_TIMEOUT_MS   5000

static int dlm_wait_for_lock_mastery(struct dlm_ctxt *dlm,
				     struct dlm_lock_resource *res,
				     struct dlm_master_list_entry *mle,
				     int *blocked)
{
	u8 m;
	int ret, bit;
	int map_changed, voting_done;
	int assert, sleep;

recheck:
	ret = 0;
	assert = 0;

	/* check if another node has already become the owner */
	spin_lock(&res->spinlock);
	if (res->owner != DLM_LOCK_RES_OWNER_UNKNOWN) {
		spin_unlock(&res->spinlock);
		goto leave;
	}
	spin_unlock(&res->spinlock);

	spin_lock(&mle->spinlock);
	m = mle->master;
	map_changed = (memcmp(mle->vote_map, mle->node_map,
			      sizeof(mle->vote_map)) != 0);
	voting_done = (memcmp(mle->vote_map, mle->response_map,
			     sizeof(mle->vote_map)) == 0);

	/* restart if we hit any errors */
	if (map_changed) {
		int b;
		mlog(0, "%s: %.*s: node map changed, restarting\n",
		     dlm->name, res->lockname.len, res->lockname.name);
		ret = dlm_restart_lock_mastery(dlm, res, mle, *blocked);
		b = (mle->type == DLM_MLE_BLOCK);
		if ((*blocked && !b) || (!*blocked && b)) {
			mlog(0, "%s:%.*s: status change: old=%d new=%d\n", 
			     dlm->name, res->lockname.len, res->lockname.name,
			     *blocked, b);
			*blocked = b;
		}
		spin_unlock(&mle->spinlock);
		if (ret < 0) {
			mlog_errno(ret);
			goto leave;
		}
		mlog(0, "%s:%.*s: restart lock mastery succeeded, "
		     "rechecking now\n", dlm->name, res->lockname.len,
		     res->lockname.name);
		goto recheck;
	}

	if (m != O2NM_MAX_NODES) {
		/* another node has done an assert!
		 * all done! */
		sleep = 0;
	} else {
		sleep = 1;
		/* have all nodes responded? */
		if (voting_done && !*blocked) {
			bit = find_next_bit(mle->maybe_map, O2NM_MAX_NODES, 0);
			if (dlm->node_num <= bit) {
				/* my node number is lowest.
			 	 * now tell other nodes that I am
				 * mastering this. */
				mle->master = dlm->node_num;
				assert = 1;
				sleep = 0;
			}
			/* if voting is done, but we have not received
			 * an assert master yet, we must sleep */
		}
	}

	spin_unlock(&mle->spinlock);

	/* sleep if we haven't finished voting yet */
	if (sleep) {
		unsigned long timeo = msecs_to_jiffies(DLM_MASTERY_TIMEOUT_MS);

		/*
		if (atomic_read(&mle->mle_refs.refcount) < 2)
			mlog(ML_ERROR, "mle (%p) refs=%d, name=%.*s\n", mle,
			atomic_read(&mle->mle_refs.refcount),
			res->lockname.len, res->lockname.name);
		*/
		atomic_set(&mle->woken, 0);
		(void)wait_event_timeout(mle->wq,
					 (atomic_read(&mle->woken) == 1),
					 timeo);
		if (res->owner == O2NM_MAX_NODES) {
			mlog(0, "waiting again\n");
			goto recheck;
		}
		mlog(0, "done waiting, master is %u\n", res->owner);
		ret = 0;
		goto leave;
	}

	ret = 0;   /* done */
	if (assert) {
		m = dlm->node_num;
		mlog(0, "about to master %.*s here, this=%u\n",
		     res->lockname.len, res->lockname.name, m);
		ret = dlm_do_assert_master(dlm, res->lockname.name,
					   res->lockname.len, mle->vote_map, 0);
		if (ret) {
			/* This is a failure in the network path,
			 * not in the response to the assert_master
			 * (any nonzero response is a BUG on this node).
			 * Most likely a socket just got disconnected
			 * due to node death. */
			mlog_errno(ret);
		}
		/* no longer need to restart lock mastery.
		 * all living nodes have been contacted. */
		ret = 0;
	}

	/* set the lockres owner */
	spin_lock(&res->spinlock);
	dlm_change_lockres_owner(dlm, res, m);
	spin_unlock(&res->spinlock);

leave:
	return ret;
}

struct dlm_bitmap_diff_iter
{
	int curnode;
	unsigned long *orig_bm;
	unsigned long *cur_bm;
	unsigned long diff_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
};

enum dlm_node_state_change
{
	NODE_DOWN = -1,
	NODE_NO_CHANGE = 0,
	NODE_UP
};

static void dlm_bitmap_diff_iter_init(struct dlm_bitmap_diff_iter *iter,
				      unsigned long *orig_bm,
				      unsigned long *cur_bm)
{
	unsigned long p1, p2;
	int i;

	iter->curnode = -1;
	iter->orig_bm = orig_bm;
	iter->cur_bm = cur_bm;

	for (i = 0; i < BITS_TO_LONGS(O2NM_MAX_NODES); i++) {
       		p1 = *(iter->orig_bm + i);
	       	p2 = *(iter->cur_bm + i);
		iter->diff_bm[i] = (p1 & ~p2) | (p2 & ~p1);
	}
}

static int dlm_bitmap_diff_iter_next(struct dlm_bitmap_diff_iter *iter,
				     enum dlm_node_state_change *state)
{
	int bit;

	if (iter->curnode >= O2NM_MAX_NODES)
		return -ENOENT;

	bit = find_next_bit(iter->diff_bm, O2NM_MAX_NODES,
			    iter->curnode+1);
	if (bit >= O2NM_MAX_NODES) {
		iter->curnode = O2NM_MAX_NODES;
		return -ENOENT;
	}

	/* if it was there in the original then this node died */
	if (test_bit(bit, iter->orig_bm))
		*state = NODE_DOWN;
	else
		*state = NODE_UP;

	iter->curnode = bit;
	return bit;
}


static int dlm_restart_lock_mastery(struct dlm_ctxt *dlm,
				    struct dlm_lock_resource *res,
				    struct dlm_master_list_entry *mle,
				    int blocked)
{
	struct dlm_bitmap_diff_iter bdi;
	enum dlm_node_state_change sc;
	int node;
	int ret = 0;

	mlog(0, "something happened such that the "
	     "master process may need to be restarted!\n");

	assert_spin_locked(&mle->spinlock);

	dlm_bitmap_diff_iter_init(&bdi, mle->vote_map, mle->node_map);
	node = dlm_bitmap_diff_iter_next(&bdi, &sc);
	while (node >= 0) {
		if (sc == NODE_UP) {
			/* a node came up.  easy.  might not even need
			 * to talk to it if its node number is higher
			 * or if we are already blocked. */
			mlog(0, "node up! %d\n", node);
			if (blocked)
				goto next;

			if (node > dlm->node_num) {
				mlog(0, "node > this node. skipping.\n");
				goto next;
			}

			/* redo the master request, but only for the new node */
			mlog(0, "sending request to new node\n");
			clear_bit(node, mle->response_map);
			set_bit(node, mle->vote_map);
		} else {
			mlog(ML_ERROR, "node down! %d\n", node);

			/* if the node wasn't involved in mastery skip it,
			 * but clear it out from the maps so that it will
			 * not affect mastery of this lockres */
			clear_bit(node, mle->response_map);
			clear_bit(node, mle->vote_map);
			if (!test_bit(node, mle->maybe_map))
				goto next;

			/* if we're already blocked on lock mastery, and the
			 * dead node wasn't the expected master, or there is
			 * another node in the maybe_map, keep waiting */
			if (blocked) {
				int lowest = find_next_bit(mle->maybe_map,
						       O2NM_MAX_NODES, 0);

				/* act like it was never there */
				clear_bit(node, mle->maybe_map);

			       	if (node != lowest)
					goto next;

				mlog(ML_ERROR, "expected master %u died while "
				     "this node was blocked waiting on it!\n",
				     node);
				lowest = find_next_bit(mle->maybe_map,
						       O2NM_MAX_NODES,
						       lowest+1);
				if (lowest < O2NM_MAX_NODES) {
					mlog(0, "still blocked. waiting "
					     "on %u now\n", lowest);
					goto next;
				}

				/* mle is an MLE_BLOCK, but there is now
				 * nothing left to block on.  we need to return
				 * all the way back out and try again with
				 * an MLE_MASTER. dlm_do_local_recovery_cleanup
				 * has already run, so the mle refcount is ok */
				mlog(0, "no longer blocking. we can "
				     "try to master this here\n");
				mle->type = DLM_MLE_MASTER;
				memset(mle->maybe_map, 0,
				       sizeof(mle->maybe_map));
				memset(mle->response_map, 0,
				       sizeof(mle->maybe_map));
				memcpy(mle->vote_map, mle->node_map,
				       sizeof(mle->node_map));
				mle->u.res = res;
				set_bit(dlm->node_num, mle->maybe_map);

				ret = -EAGAIN;
				goto next;
			}

			clear_bit(node, mle->maybe_map);
			if (node > dlm->node_num)
				goto next;

			mlog(0, "dead node in map!\n");
			/* yuck. go back and re-contact all nodes
			 * in the vote_map, removing this node. */
			memset(mle->response_map, 0,
			       sizeof(mle->response_map));
		}
		ret = -EAGAIN;
next:
		node = dlm_bitmap_diff_iter_next(&bdi, &sc);
	}
	return ret;
}


/*
 * DLM_MASTER_REQUEST_MSG
 *
 * returns: 0 on success,
 *          -errno on a network error
 *
 * on error, the caller should assume the target node is "dead"
 *
 */

static int dlm_do_master_request(struct dlm_master_list_entry *mle, int to)
{
	struct dlm_ctxt *dlm = mle->dlm;
	struct dlm_master_request request;
	int ret, response=0, resend;

	memset(&request, 0, sizeof(request));
	request.node_idx = dlm->node_num;

	BUG_ON(mle->type == DLM_MLE_MIGRATION);

	if (mle->type != DLM_MLE_MASTER) {
		request.namelen = mle->u.name.len;
		memcpy(request.name, mle->u.name.name, request.namelen);
	} else {
		request.namelen = mle->u.res->lockname.len;
		memcpy(request.name, mle->u.res->lockname.name,
			request.namelen);
	}

again:
	ret = o2net_send_message(DLM_MASTER_REQUEST_MSG, dlm->key, &request,
				 sizeof(request), to, &response);
	if (ret < 0)  {
		if (ret == -ESRCH) {
			/* should never happen */
			mlog(ML_ERROR, "TCP stack not ready!\n");
			BUG();
		} else if (ret == -EINVAL) {
			mlog(ML_ERROR, "bad args passed to o2net!\n");
			BUG();
		} else if (ret == -ENOMEM) {
			mlog(ML_ERROR, "out of memory while trying to send "
			     "network message!  retrying\n");
			/* this is totally crude */
			msleep(50);
			goto again;
		} else if (!dlm_is_host_down(ret)) {
			/* not a network error. bad. */
			mlog_errno(ret);
			mlog(ML_ERROR, "unhandled error!");
			BUG();
		}
		/* all other errors should be network errors,
		 * and likely indicate node death */
		mlog(ML_ERROR, "link to %d went down!\n", to);
		goto out;
	}

	ret = 0;
	resend = 0;
	spin_lock(&mle->spinlock);
	switch (response) {
		case DLM_MASTER_RESP_YES:
			set_bit(to, mle->response_map);
			mlog(0, "node %u is the master, response=YES\n", to);
			mle->master = to;
			break;
		case DLM_MASTER_RESP_NO:
			mlog(0, "node %u not master, response=NO\n", to);
			set_bit(to, mle->response_map);
			break;
		case DLM_MASTER_RESP_MAYBE:
			mlog(0, "node %u not master, response=MAYBE\n", to);
			set_bit(to, mle->response_map);
			set_bit(to, mle->maybe_map);
			break;
		case DLM_MASTER_RESP_ERROR:
			mlog(0, "node %u hit an error, resending\n", to);
			resend = 1;
			response = 0;
			break;
		default:
			mlog(ML_ERROR, "bad response! %u\n", response);
			BUG();
	}
	spin_unlock(&mle->spinlock);
	if (resend) {
		/* this is also totally crude */
		msleep(50);
		goto again;
	}

out:
	return ret;
}

/*
 * locks that can be taken here:
 * dlm->spinlock
 * res->spinlock
 * mle->spinlock
 * dlm->master_list
 *
 * if possible, TRIM THIS DOWN!!!
 */
int dlm_master_request_handler(struct o2net_msg *msg, u32 len, void *data)
{
	u8 response = DLM_MASTER_RESP_MAYBE;
	struct dlm_ctxt *dlm = data;
	struct dlm_lock_resource *res;
	struct dlm_master_request *request = (struct dlm_master_request *) msg->buf;
	struct dlm_master_list_entry *mle = NULL, *tmpmle = NULL;
	char *name;
	unsigned int namelen;
	int found, ret;
	int set_maybe;

	if (!dlm_grab(dlm))
		return DLM_MASTER_RESP_NO;

	if (!dlm_domain_fully_joined(dlm)) {
		response = DLM_MASTER_RESP_NO;
		goto send_response;
	}

	name = request->name;
	namelen = request->namelen;

	if (namelen > DLM_LOCKID_NAME_MAX) {
		response = DLM_IVBUFLEN;
		goto send_response;
	}

way_up_top:
	spin_lock(&dlm->spinlock);
	res = __dlm_lookup_lockres(dlm, name, namelen);
	if (res) {
		spin_unlock(&dlm->spinlock);

		/* take care of the easy cases up front */
		spin_lock(&res->spinlock);
		if (res->state & DLM_LOCK_RES_RECOVERING) {
			spin_unlock(&res->spinlock);
			mlog(0, "returning DLM_MASTER_RESP_ERROR since res is "
			     "being recovered\n");
			response = DLM_MASTER_RESP_ERROR;
			if (mle)
				kmem_cache_free(dlm_mle_cache, mle);
			goto send_response;
		}

		if (res->owner == dlm->node_num) {
			u32 flags = DLM_ASSERT_MASTER_MLE_CLEANUP;
			spin_unlock(&res->spinlock);
			// mlog(0, "this node is the master\n");
			response = DLM_MASTER_RESP_YES;
			if (mle)
				kmem_cache_free(dlm_mle_cache, mle);

			/* this node is the owner.
			 * there is some extra work that needs to
			 * happen now.  the requesting node has
			 * caused all nodes up to this one to
			 * create mles.  this node now needs to
			 * go back and clean those up. */
			mlog(0, "%u is the owner of %.*s, cleaning everyone else\n",
			     dlm->node_num, res->lockname.len, res->lockname.name);
			ret = dlm_dispatch_assert_master(dlm, res, 1,
							 request->node_idx,
							 flags);
			if (ret < 0) {
				mlog(ML_ERROR, "failed to dispatch assert "
				     "master work\n");
				response = DLM_MASTER_RESP_ERROR;
			}
			goto send_response;
		} else if (res->owner != DLM_LOCK_RES_OWNER_UNKNOWN) {
			spin_unlock(&res->spinlock);
			// mlog(0, "node %u is the master\n", res->owner);
			response = DLM_MASTER_RESP_NO;
			if (mle)
				kmem_cache_free(dlm_mle_cache, mle);
			goto send_response;
		}

		/* ok, there is no owner.  either this node is
		 * being blocked, or it is actively trying to
		 * master this lock. */
		if (!(res->state & DLM_LOCK_RES_IN_PROGRESS)) {
			mlog(ML_ERROR, "lock with no owner should be "
			     "in-progress!\n");
			BUG();
		}

		// mlog(0, "lockres is in progress...\n");
		spin_lock(&dlm->master_lock);
		found = dlm_find_mle(dlm, &tmpmle, name, namelen);
		if (!found) {
			mlog(ML_ERROR, "no mle found for this lock!\n");
			BUG();
		}
		set_maybe = 1;
		spin_lock(&tmpmle->spinlock);
		if (tmpmle->type == DLM_MLE_BLOCK) {
			// mlog(0, "this node is waiting for "
			// "lockres to be mastered\n");
			response = DLM_MASTER_RESP_NO;
		} else if (tmpmle->type == DLM_MLE_MIGRATION) {
			mlog(0, "node %u is master, but trying to migrate to "
			     "node %u.\n", tmpmle->master, tmpmle->new_master);
			if (tmpmle->master == dlm->node_num) {
				response = DLM_MASTER_RESP_YES;
				mlog(ML_ERROR, "no owner on lockres, but this "
				     "node is trying to migrate it to %u?!\n",
				     tmpmle->new_master);
				BUG();
			} else {
				/* the real master can respond on its own */
				response = DLM_MASTER_RESP_NO;
			}
		} else if (tmpmle->master != DLM_LOCK_RES_OWNER_UNKNOWN) {
			set_maybe = 0;
			if (tmpmle->master == dlm->node_num)
				response = DLM_MASTER_RESP_YES;
			else
				response = DLM_MASTER_RESP_NO;
		} else {
			// mlog(0, "this node is attempting to "
			// "master lockres\n");
			response = DLM_MASTER_RESP_MAYBE;
		}
		if (set_maybe)
			set_bit(request->node_idx, tmpmle->maybe_map);
		spin_unlock(&tmpmle->spinlock);

		spin_unlock(&dlm->master_lock);
		spin_unlock(&res->spinlock);

		/* keep the mle attached to heartbeat events */
		dlm_put_mle(tmpmle);
		if (mle)
			kmem_cache_free(dlm_mle_cache, mle);
		goto send_response;
	}

	/*
	 * lockres doesn't exist on this node
	 * if there is an MLE_BLOCK, return NO
	 * if there is an MLE_MASTER, return MAYBE
	 * otherwise, add an MLE_BLOCK, return NO
	 */
	spin_lock(&dlm->master_lock);
	found = dlm_find_mle(dlm, &tmpmle, name, namelen);
	if (!found) {
		/* this lockid has never been seen on this node yet */
		// mlog(0, "no mle found\n");
		if (!mle) {
			spin_unlock(&dlm->master_lock);
			spin_unlock(&dlm->spinlock);

			mle = (struct dlm_master_list_entry *)
				kmem_cache_alloc(dlm_mle_cache, GFP_KERNEL);
			if (!mle) {
				// bad bad bad... this sucks.
				response = DLM_MASTER_RESP_ERROR;
				goto send_response;
			}
			spin_lock(&dlm->spinlock);
			dlm_init_mle(mle, DLM_MLE_BLOCK, dlm, NULL,
					 name, namelen);
			spin_unlock(&dlm->spinlock);
			goto way_up_top;
		}

		// mlog(0, "this is second time thru, already allocated, "
		// "add the block.\n");
		set_bit(request->node_idx, mle->maybe_map);
		list_add(&mle->list, &dlm->master_list);
		response = DLM_MASTER_RESP_NO;
	} else {
		// mlog(0, "mle was found\n");
		set_maybe = 1;
		spin_lock(&tmpmle->spinlock);
		if (tmpmle->type == DLM_MLE_BLOCK)
			response = DLM_MASTER_RESP_NO;
		else if (tmpmle->type == DLM_MLE_MIGRATION) {
			mlog(0, "migration mle was found (%u->%u)\n",
			     tmpmle->master, tmpmle->new_master);
			if (tmpmle->master == dlm->node_num) {
				mlog(ML_ERROR, "no lockres, but migration mle "
				     "says that this node is master!\n");
				BUG();
			}
			/* real master can respond on its own */
			response = DLM_MASTER_RESP_NO;
		} else {
			if (tmpmle->master == dlm->node_num) {
				response = DLM_MASTER_RESP_YES;
				set_maybe = 0;
			} else
				response = DLM_MASTER_RESP_MAYBE;
		}
		if (set_maybe)
			set_bit(request->node_idx, tmpmle->maybe_map);
		spin_unlock(&tmpmle->spinlock);
	}
	spin_unlock(&dlm->master_lock);
	spin_unlock(&dlm->spinlock);

	if (found) {
		/* keep the mle attached to heartbeat events */
		dlm_put_mle(tmpmle);
	}
send_response:
	dlm_put(dlm);
	return response;
}

/*
 * DLM_ASSERT_MASTER_MSG
 */


/*
 * NOTE: this can be used for debugging
 * can periodically run all locks owned by this node
 * and re-assert across the cluster...
 */
static int dlm_do_assert_master(struct dlm_ctxt *dlm, const char *lockname,
				unsigned int namelen, void *nodemap,
				u32 flags)
{
	struct dlm_assert_master assert;
	int to, tmpret;
	struct dlm_node_iter iter;
	int ret = 0;

	BUG_ON(namelen > O2NM_MAX_NAME_LEN);

	/* note that if this nodemap is empty, it returns 0 */
	dlm_node_iter_init(nodemap, &iter);
	while ((to = dlm_node_iter_next(&iter)) >= 0) {
		int r = 0;
		mlog(0, "sending assert master to %d (%.*s)\n", to,
		     namelen, lockname);
		memset(&assert, 0, sizeof(assert));
		assert.node_idx = dlm->node_num;
		assert.namelen = namelen;
		memcpy(assert.name, lockname, namelen);
		assert.flags = cpu_to_be32(flags);

		tmpret = o2net_send_message(DLM_ASSERT_MASTER_MSG, dlm->key,
					    &assert, sizeof(assert), to, &r);
		if (tmpret < 0) {
			mlog(ML_ERROR, "assert_master returned %d!\n", tmpret);
			if (!dlm_is_host_down(tmpret)) {
				mlog(ML_ERROR, "unhandled error!\n");
				BUG();
			}
			/* a node died.  finish out the rest of the nodes. */
			mlog(ML_ERROR, "link to %d went down!\n", to);
			/* any nonzero status return will do */
			ret = tmpret;
		} else if (r < 0) {
			/* ok, something horribly messed.  kill thyself. */
			mlog(ML_ERROR,"during assert master of %.*s to %u, "
			     "got %d.\n", namelen, lockname, to, r);
			dlm_dump_lock_resources(dlm);
			BUG();
		}
	}

	return ret;
}

/*
 * locks that can be taken here:
 * dlm->spinlock
 * res->spinlock
 * mle->spinlock
 * dlm->master_list
 *
 * if possible, TRIM THIS DOWN!!!
 */
int dlm_assert_master_handler(struct o2net_msg *msg, u32 len, void *data)
{
	struct dlm_ctxt *dlm = data;
	struct dlm_master_list_entry *mle = NULL;
	struct dlm_assert_master *assert = (struct dlm_assert_master *)msg->buf;
	struct dlm_lock_resource *res = NULL;
	char *name;
	unsigned int namelen;
	u32 flags;

	if (!dlm_grab(dlm))
		return 0;

	name = assert->name;
	namelen = assert->namelen;
	flags = be32_to_cpu(assert->flags);

	if (namelen > DLM_LOCKID_NAME_MAX) {
		mlog(ML_ERROR, "Invalid name length!");
		goto done;
	}

	spin_lock(&dlm->spinlock);

	if (flags)
		mlog(0, "assert_master with flags: %u\n", flags);

	/* find the MLE */
	spin_lock(&dlm->master_lock);
	if (!dlm_find_mle(dlm, &mle, name, namelen)) {
		/* not an error, could be master just re-asserting */
		mlog(0, "just got an assert_master from %u, but no "
		     "MLE for it! (%.*s)\n", assert->node_idx,
		     namelen, name);
	} else {
		int bit = find_next_bit (mle->maybe_map, O2NM_MAX_NODES, 0);
		if (bit >= O2NM_MAX_NODES) {
			/* not necessarily an error, though less likely.
			 * could be master just re-asserting. */
			mlog(ML_ERROR, "no bits set in the maybe_map, but %u "
			     "is asserting! (%.*s)\n", assert->node_idx,
			     namelen, name);
		} else if (bit != assert->node_idx) {
			if (flags & DLM_ASSERT_MASTER_MLE_CLEANUP) {
				mlog(0, "master %u was found, %u should "
				     "back off\n", assert->node_idx, bit);
			} else {
				/* with the fix for bug 569, a higher node
				 * number winning the mastery will respond
				 * YES to mastery requests, but this node
				 * had no way of knowing.  let it pass. */
				mlog(ML_ERROR, "%u is the lowest node, "
				     "%u is asserting. (%.*s)  %u must "
				     "have begun after %u won.\n", bit,
				     assert->node_idx, namelen, name, bit,
				     assert->node_idx);
			}
		}
	}
	spin_unlock(&dlm->master_lock);

	/* ok everything checks out with the MLE
	 * now check to see if there is a lockres */
	res = __dlm_lookup_lockres(dlm, name, namelen);
	if (res) {
		spin_lock(&res->spinlock);
		if (res->state & DLM_LOCK_RES_RECOVERING)  {
			mlog(ML_ERROR, "%u asserting but %.*s is "
			     "RECOVERING!\n", assert->node_idx, namelen, name);
			goto kill;
		}
		if (!mle) {
			if (res->owner != assert->node_idx) {
				mlog(ML_ERROR, "assert_master from "
					  "%u, but current owner is "
					  "%u! (%.*s)\n",
				       assert->node_idx, res->owner,
				       namelen, name);
				goto kill;
			}
		} else if (mle->type != DLM_MLE_MIGRATION) {
			if (res->owner != DLM_LOCK_RES_OWNER_UNKNOWN) {
				/* owner is just re-asserting */
				if (res->owner == assert->node_idx) {
					mlog(0, "owner %u re-asserting on "
					     "lock %.*s\n", assert->node_idx,
					     namelen, name);
					goto ok;
				}
				mlog(ML_ERROR, "got assert_master from "
				     "node %u, but %u is the owner! "
				     "(%.*s)\n", assert->node_idx,
				     res->owner, namelen, name);
				goto kill;
			}
			if (!(res->state & DLM_LOCK_RES_IN_PROGRESS)) {
				mlog(ML_ERROR, "got assert from %u, but lock "
				     "with no owner should be "
				     "in-progress! (%.*s)\n",
				     assert->node_idx,
				     namelen, name);
				goto kill;
			}
		} else /* mle->type == DLM_MLE_MIGRATION */ {
			/* should only be getting an assert from new master */
			if (assert->node_idx != mle->new_master) {
				mlog(ML_ERROR, "got assert from %u, but "
				     "new master is %u, and old master "
				     "was %u (%.*s)\n",
				     assert->node_idx, mle->new_master,
				     mle->master, namelen, name);
				goto kill;
			}

		}
ok:
		spin_unlock(&res->spinlock);
	}
	spin_unlock(&dlm->spinlock);

	// mlog(0, "woo!  got an assert_master from node %u!\n",
	// 	     assert->node_idx);
	if (mle) {
		int extra_ref;
		
		spin_lock(&mle->spinlock);
		extra_ref = !!(mle->type == DLM_MLE_BLOCK
			       || mle->type == DLM_MLE_MIGRATION);
		mle->master = assert->node_idx;
		atomic_set(&mle->woken, 1);
		wake_up(&mle->wq);
		spin_unlock(&mle->spinlock);

		if (mle->type == DLM_MLE_MIGRATION && res) {
			mlog(0, "finishing off migration of lockres %.*s, "
			     "from %u to %u\n",
			       res->lockname.len, res->lockname.name,
			       dlm->node_num, mle->new_master);
			spin_lock(&res->spinlock);
			res->state &= ~DLM_LOCK_RES_MIGRATING;
			dlm_change_lockres_owner(dlm, res, mle->new_master);
			BUG_ON(res->state & DLM_LOCK_RES_DIRTY);
			spin_unlock(&res->spinlock);
		}
		/* master is known, detach if not already detached */
		dlm_mle_detach_hb_events(dlm, mle);
		dlm_put_mle(mle);
		
		if (extra_ref) {
			/* the assert master message now balances the extra
		 	 * ref given by the master / migration request message.
		 	 * if this is the last put, it will be removed
		 	 * from the list. */
			dlm_put_mle(mle);
		}
	}

done:
	if (res)
		dlm_lockres_put(res);
	dlm_put(dlm);
	return 0;

kill:
	/* kill the caller! */
	spin_unlock(&res->spinlock);
	spin_unlock(&dlm->spinlock);
	dlm_lockres_put(res);
	mlog(ML_ERROR, "Bad message received from another node.  Dumping state "
	     "and killing the other node now!  This node is OK and can continue.\n");
	dlm_dump_lock_resources(dlm);
	dlm_put(dlm);
	return -EINVAL;
}

int dlm_dispatch_assert_master(struct dlm_ctxt *dlm,
			       struct dlm_lock_resource *res,
			       int ignore_higher, u8 request_from, u32 flags)
{
	struct dlm_work_item *item;
	item = kcalloc(1, sizeof(*item), GFP_KERNEL);
	if (!item)
		return -ENOMEM;


	/* queue up work for dlm_assert_master_worker */
	dlm_grab(dlm);  /* get an extra ref for the work item */
	dlm_init_work_item(dlm, item, dlm_assert_master_worker, NULL);
	item->u.am.lockres = res; /* already have a ref */
	/* can optionally ignore node numbers higher than this node */
	item->u.am.ignore_higher = ignore_higher;
	item->u.am.request_from = request_from;
	item->u.am.flags = flags;

	spin_lock(&dlm->work_lock);
	list_add_tail(&item->list, &dlm->work_list);
	spin_unlock(&dlm->work_lock);

	schedule_work(&dlm->dispatched_work);
	return 0;
}

static void dlm_assert_master_worker(struct dlm_work_item *item, void *data)
{
	struct dlm_ctxt *dlm = data;
	int ret = 0;
	struct dlm_lock_resource *res;
	unsigned long nodemap[BITS_TO_LONGS(O2NM_MAX_NODES)];
	int ignore_higher;
	int bit;
	u8 request_from;
	u32 flags;

	dlm = item->dlm;
	res = item->u.am.lockres;
	ignore_higher = item->u.am.ignore_higher;
	request_from = item->u.am.request_from;
	flags = item->u.am.flags;

	spin_lock(&dlm->spinlock);
	memcpy(nodemap, dlm->domain_map, sizeof(nodemap));
	spin_unlock(&dlm->spinlock);

	clear_bit(dlm->node_num, nodemap);
	if (ignore_higher) {
		/* if is this just to clear up mles for nodes below
		 * this node, do not send the message to the original
		 * caller or any node number higher than this */
		clear_bit(request_from, nodemap);
		bit = dlm->node_num;
		while (1) {
			bit = find_next_bit(nodemap, O2NM_MAX_NODES,
					    bit+1);
		       	if (bit >= O2NM_MAX_NODES)
				break;
			clear_bit(bit, nodemap);
		}
	}

	/* this call now finishes out the nodemap
	 * even if one or more nodes die */
	mlog(0, "worker about to master %.*s here, this=%u\n",
		     res->lockname.len, res->lockname.name, dlm->node_num);
	ret = dlm_do_assert_master(dlm, res->lockname.name,
				   res->lockname.len,
				   nodemap, flags);
	if (ret < 0) {
		/* no need to restart, we are done */
		mlog_errno(ret);
	}

	dlm_lockres_put(res);

	mlog(0, "finished with dlm_assert_master_worker\n");
}


/*
 * DLM_MIGRATE_LOCKRES
 */


int dlm_migrate_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res,
			u8 target)
{
	struct dlm_master_list_entry *mle = NULL;
	struct dlm_master_list_entry *oldmle = NULL;
 	struct dlm_migratable_lockres *mres = NULL;
	int ret = -EINVAL;
	const char *name;
	unsigned int namelen;
	int mle_added = 0;
	struct list_head *queue, *iter;
	int i;
	struct dlm_lock *lock;
	int empty = 1;

	if (!dlm_grab(dlm))
		return -EINVAL;

	name = res->lockname.name;
	namelen = res->lockname.len;

	mlog(0, "migrating %.*s to %u\n", namelen, name, target);

	/*
	 * ensure this lockres is a proper candidate for migration
	 */
	spin_lock(&res->spinlock);
	if (res->owner == DLM_LOCK_RES_OWNER_UNKNOWN) {
		mlog(0, "cannot migrate lockres with unknown owner!\n");
		spin_unlock(&res->spinlock);
		goto leave;
	}
	if (res->owner != dlm->node_num) {
		mlog(0, "cannot migrate lockres this node doesn't own!\n");
		spin_unlock(&res->spinlock);
		goto leave;
	}
	mlog(0, "checking queues...\n");
	queue = &res->granted;
	for (i=0; i<3; i++) {
		list_for_each(iter, queue) {
			lock = list_entry (iter, struct dlm_lock, list);
			empty = 0;
			if (lock->ml.node == dlm->node_num) {
				mlog(0, "found a lock owned by this node "
				     "still on the %s queue!  will not "
				     "migrate this lockres\n",
				     i==0 ? "granted" :
				     (i==1 ? "converting" : "blocked"));
				spin_unlock(&res->spinlock);
				ret = -ENOTEMPTY;
				goto leave;
			}
		}
		queue++;
	}
	mlog(0, "all locks on this lockres are nonlocal.  continuing\n");
	spin_unlock(&res->spinlock);

	/* no work to do */
	if (empty) {
		mlog(0, "no locks were found on this lockres! done!\n");
		ret = 0;
		goto leave;
	}

	/*
	 * preallocate up front
	 * if this fails, abort
	 */

	ret = -ENOMEM;
	mres = (struct dlm_migratable_lockres *) __get_free_page(GFP_KERNEL);
	if (!mres) {
		mlog_errno(ret);
		goto leave;
	}

	mle = (struct dlm_master_list_entry *) kmem_cache_alloc(dlm_mle_cache,
								GFP_KERNEL);
	if (!mle) {
		mlog_errno(ret);
		goto leave;
	}
	ret = 0;

	/*
	 * find a node to migrate the lockres to
	 */

	mlog(0, "picking a migration node\n");
	spin_lock(&dlm->spinlock);
	/* pick a new node */
	if (!test_bit(target, dlm->domain_map) ||
	    target >= O2NM_MAX_NODES) {
		target = dlm_pick_migration_target(dlm, res);
	}
	mlog(0, "node %u chosen for migration\n", target);

	if (target >= O2NM_MAX_NODES ||
	    !test_bit(target, dlm->domain_map)) {
		/* target chosen is not alive */
		ret = -EINVAL;
	}

	if (ret) {
		spin_unlock(&dlm->spinlock);
		goto fail;
	}

	mlog(0, "continuing with target = %u\n", target);

	/*
	 * clear any existing master requests and
	 * add the migration mle to the list
	 */
	spin_lock(&dlm->master_lock);
	ret = dlm_add_migration_mle(dlm, res, mle, &oldmle, name,
				    namelen, target, dlm->node_num);
	spin_unlock(&dlm->master_lock);
	spin_unlock(&dlm->spinlock);

	if (ret == -EEXIST) {
		mlog(0, "another process is already migrating it\n");
		goto fail;
	}
	mle_added = 1;

	/*
	 * set the MIGRATING flag and flush asts
	 * if we fail after this we need to re-dirty the lockres
	 */
	if (dlm_mark_lockres_migrating(dlm, res, target) < 0) {
		mlog(ML_ERROR, "tried to migrate %.*s to %u, but "
		     "the target went down.\n", res->lockname.len,
		     res->lockname.name, target);
		spin_lock(&res->spinlock);
		res->state &= ~DLM_LOCK_RES_MIGRATING;
		spin_unlock(&res->spinlock);
		ret = -EINVAL;
	}

fail:
	if (oldmle) {
		/* master is known, detach if not already detached */
		dlm_mle_detach_hb_events(dlm, oldmle);
		dlm_put_mle(oldmle);
	}

	if (ret < 0) {
		if (mle_added) {
			dlm_mle_detach_hb_events(dlm, mle);
			dlm_put_mle(mle);
		} else if (mle) {
			kmem_cache_free(dlm_mle_cache, mle);
		}
		goto leave;
	}

	/*
	 * at this point, we have a migration target, an mle
	 * in the master list, and the MIGRATING flag set on
	 * the lockres
	 */


	/* get an extra reference on the mle.
	 * otherwise the assert_master from the new
	 * master will destroy this.
	 * also, make sure that all callers of dlm_get_mle
	 * take both dlm->spinlock and dlm->master_lock */
	spin_lock(&dlm->spinlock);
	spin_lock(&dlm->master_lock);
	dlm_get_mle(mle);
	spin_unlock(&dlm->master_lock);
	spin_unlock(&dlm->spinlock);

	/* notify new node and send all lock state */
	/* call send_one_lockres with migration flag.
	 * this serves as notice to the target node that a
	 * migration is starting. */
	ret = dlm_send_one_lockres(dlm, res, mres, target,
				   DLM_MRES_MIGRATION);

	if (ret < 0) {
		mlog(0, "migration to node %u failed with %d\n",
		     target, ret);
		/* migration failed, detach and clean up mle */
		dlm_mle_detach_hb_events(dlm, mle);
		dlm_put_mle(mle);
		dlm_put_mle(mle);
		goto leave;
	}

	/* at this point, the target sends a message to all nodes,
	 * (using dlm_do_migrate_request).  this node is skipped since
	 * we had to put an mle in the list to begin the process.  this
	 * node now waits for target to do an assert master.  this node
	 * will be the last one notified, ensuring that the migration
	 * is complete everywhere.  if the target dies while this is
	 * going on, some nodes could potentially see the target as the
	 * master, so it is important that my recovery finds the migration
	 * mle and sets the master to UNKNONWN. */


	/* wait for new node to assert master */
	while (1) {
		ret = wait_event_interruptible_timeout(mle->wq,
					(atomic_read(&mle->woken) == 1),
					msecs_to_jiffies(5000));

		if (ret >= 0) {
		       	if (atomic_read(&mle->woken) == 1 ||
			    res->owner == target)
				break;

			mlog(0, "timed out during migration\n");
		}
		if (ret == -ERESTARTSYS) {
			/* migration failed, detach and clean up mle */
			dlm_mle_detach_hb_events(dlm, mle);
			dlm_put_mle(mle);
			dlm_put_mle(mle);
			goto leave;
		}
		/* TODO: if node died: stop, clean up, return error */
	}

	/* all done, set the owner, clear the flag */
	spin_lock(&res->spinlock);
	dlm_set_lockres_owner(dlm, res, target);
	res->state &= ~DLM_LOCK_RES_MIGRATING;
	dlm_remove_nonlocal_locks(dlm, res);
	spin_unlock(&res->spinlock);
	wake_up(&res->wq);

	/* master is known, detach if not already detached */
	dlm_mle_detach_hb_events(dlm, mle);
	dlm_put_mle(mle);
	ret = 0;

	dlm_lockres_calc_usage(dlm, res);

leave:
	/* re-dirty the lockres if we failed */
	if (ret < 0)
		dlm_kick_thread(dlm, res);

	/* TODO: cleanup */
	if (mres)
		free_page((unsigned long)mres);

	dlm_put(dlm);

	mlog(0, "returning %d\n", ret);
	return ret;
}
EXPORT_SYMBOL_GPL(dlm_migrate_lockres);

int dlm_lock_basts_flushed(struct dlm_ctxt *dlm, struct dlm_lock *lock)
{
	int ret;
	spin_lock(&dlm->ast_lock);
	spin_lock(&lock->spinlock);
	ret = (list_empty(&lock->bast_list) && !lock->bast_pending);
	spin_unlock(&lock->spinlock);
	spin_unlock(&dlm->ast_lock);
	return ret;
}

static int dlm_migration_can_proceed(struct dlm_ctxt *dlm,
				     struct dlm_lock_resource *res,
				     u8 mig_target)
{
	int can_proceed;
	spin_lock(&res->spinlock);
	can_proceed = !!(res->state & DLM_LOCK_RES_MIGRATING);
	spin_unlock(&res->spinlock);

	/* target has died, so make the caller break out of the 
	 * wait_event, but caller must recheck the domain_map */
	spin_lock(&dlm->spinlock);
	if (!test_bit(mig_target, dlm->domain_map))
		can_proceed = 1;
	spin_unlock(&dlm->spinlock);
	return can_proceed;
}

int dlm_lockres_is_dirty(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
{
	int ret;
	spin_lock(&res->spinlock);
	ret = !!(res->state & DLM_LOCK_RES_DIRTY);
	spin_unlock(&res->spinlock);
	return ret;
}


static int dlm_mark_lockres_migrating(struct dlm_ctxt *dlm,
				       struct dlm_lock_resource *res,
				       u8 target)
{
	int ret = 0;

	mlog(0, "dlm_mark_lockres_migrating: %.*s, from %u to %u\n",
	       res->lockname.len, res->lockname.name, dlm->node_num,
	       target);
	/* need to set MIGRATING flag on lockres.  this is done by
	 * ensuring that all asts have been flushed for this lockres. */
	spin_lock(&res->spinlock);
	BUG_ON(res->migration_pending);
	res->migration_pending = 1;
	/* strategy is to reserve an extra ast then release
	 * it below, letting the release do all of the work */
	__dlm_lockres_reserve_ast(res);
	spin_unlock(&res->spinlock);

	/* now flush all the pending asts.. hang out for a bit */
	dlm_kick_thread(dlm, res);
	wait_event(dlm->ast_wq, !dlm_lockres_is_dirty(dlm, res));
	dlm_lockres_release_ast(dlm, res);

	mlog(0, "about to wait on migration_wq, dirty=%s\n",
	       res->state & DLM_LOCK_RES_DIRTY ? "yes" : "no");
	/* if the extra ref we just put was the final one, this
	 * will pass thru immediately.  otherwise, we need to wait
	 * for the last ast to finish. */
again:
	ret = wait_event_interruptible_timeout(dlm->migration_wq,
		   dlm_migration_can_proceed(dlm, res, target),
		   msecs_to_jiffies(1000));
	if (ret < 0) {
		mlog(0, "woken again: migrating? %s, dead? %s\n",
		       res->state & DLM_LOCK_RES_MIGRATING ? "yes":"no",
		       test_bit(target, dlm->domain_map) ? "no":"yes");
	} else {
		mlog(0, "all is well: migrating? %s, dead? %s\n",
		       res->state & DLM_LOCK_RES_MIGRATING ? "yes":"no",
		       test_bit(target, dlm->domain_map) ? "no":"yes");
	}
	if (!dlm_migration_can_proceed(dlm, res, target)) {
		mlog(0, "trying again...\n");
		goto again;
	}

	/* did the target go down or die? */
	spin_lock(&dlm->spinlock);
	if (!test_bit(target, dlm->domain_map)) {
		mlog(ML_ERROR, "aha. migration target %u just went down\n",
		     target);
		ret = -EHOSTDOWN;
	}
	spin_unlock(&dlm->spinlock);

	/*
	 * at this point:
	 *
	 *   o the DLM_LOCK_RES_MIGRATING flag is set
	 *   o there are no pending asts on this lockres
	 *   o all processes trying to reserve an ast on this
	 *     lockres must wait for the MIGRATING flag to clear
	 */
	return ret;
}

/* last step in the migration process.
 * original master calls this to free all of the dlm_lock
 * structures that used to be for other nodes. */
static void dlm_remove_nonlocal_locks(struct dlm_ctxt *dlm,
				      struct dlm_lock_resource *res)
{
	struct list_head *iter, *iter2;
	struct list_head *queue = &res->granted;
	int i;
	struct dlm_lock *lock;

	assert_spin_locked(&res->spinlock);

	BUG_ON(res->owner == dlm->node_num);

	for (i=0; i<3; i++) {
		list_for_each_safe(iter, iter2, queue) {
			lock = list_entry (iter, struct dlm_lock, list);
			if (lock->ml.node != dlm->node_num) {
				mlog(0, "putting lock for node %u\n",
				     lock->ml.node);
				/* be extra careful */
				BUG_ON(!list_empty(&lock->ast_list));
				BUG_ON(!list_empty(&lock->bast_list));
				BUG_ON(lock->ast_pending);
				BUG_ON(lock->bast_pending);
				list_del_init(&lock->list);
				dlm_lock_put(lock);
			}
		}
		queue++;
	}
}

/* for now this is not too intelligent.  we will
 * need stats to make this do the right thing.
 * this just finds the first lock on one of the
 * queues and uses that node as the target. */
static u8 dlm_pick_migration_target(struct dlm_ctxt *dlm,
				    struct dlm_lock_resource *res)
{
	int i;
	struct list_head *queue = &res->granted;
	struct list_head *iter;
	struct dlm_lock *lock;
	int nodenum;

	assert_spin_locked(&dlm->spinlock);

	spin_lock(&res->spinlock);
	for (i=0; i<3; i++) {
		list_for_each(iter, queue) {
			/* up to the caller to make sure this node
			 * is alive */
			lock = list_entry (iter, struct dlm_lock, list);
			if (lock->ml.node != dlm->node_num) {
				spin_unlock(&res->spinlock);
				return lock->ml.node;
			}
		}
		queue++;
	}
	spin_unlock(&res->spinlock);
	mlog(0, "have not found a suitable target yet! checking domain map\n");

	/* ok now we're getting desperate.  pick anyone alive. */
	nodenum = -1;
	while (1) {
		nodenum = find_next_bit(dlm->domain_map,
					O2NM_MAX_NODES, nodenum+1);
		mlog(0, "found %d in domain map\n", nodenum);
		if (nodenum >= O2NM_MAX_NODES)
			break;
		if (nodenum != dlm->node_num) {
			mlog(0, "picking %d\n", nodenum);
			return nodenum;
		}
	}

	mlog(0, "giving up.  no master to migrate to\n");
	return DLM_LOCK_RES_OWNER_UNKNOWN;
}



/* this is called by the new master once all lockres
 * data has been received */
static int dlm_do_migrate_request(struct dlm_ctxt *dlm,
				  struct dlm_lock_resource *res,
				  u8 master, u8 new_master,
				  struct dlm_node_iter *iter)
{
	struct dlm_migrate_request migrate;
	int ret, status = 0;
	int nodenum;

	memset(&migrate, 0, sizeof(migrate));
	migrate.namelen = res->lockname.len;
	memcpy(migrate.name, res->lockname.name, migrate.namelen);
	migrate.new_master = new_master;
	migrate.master = master;

	ret = 0;

	/* send message to all nodes, except the master and myself */
	while ((nodenum = dlm_node_iter_next(iter)) >= 0) {
		if (nodenum == master ||
		    nodenum == new_master)
			continue;

		ret = o2net_send_message(DLM_MIGRATE_REQUEST_MSG, dlm->key,
					 &migrate, sizeof(migrate), nodenum,
					 &status);
		if (ret < 0)
			mlog_errno(ret);
		else if (status < 0) {
			mlog(0, "migrate request (node %u) returned %d!\n",
			     nodenum, status);
			ret = status;
		}
	}

	if (ret < 0)
		mlog_errno(ret);

	mlog(0, "returning ret=%d\n", ret);
	return ret;
}


/* if there is an existing mle for this lockres, we now know who the master is.
 * (the one who sent us *this* message) we can clear it up right away.
 * since the process that put the mle on the list still has a reference to it,
 * we can unhash it now, set the master and wake the process.  as a result,
 * we will have no mle in the list to start with.  now we can add an mle for
 * the migration and this should be the only one found for those scanning the
 * list.  */
int dlm_migrate_request_handler(struct o2net_msg *msg, u32 len, void *data)
{
	struct dlm_ctxt *dlm = data;
	struct dlm_lock_resource *res = NULL;
	struct dlm_migrate_request *migrate = (struct dlm_migrate_request *) msg->buf;
	struct dlm_master_list_entry *mle = NULL, *oldmle = NULL;
	const char *name;
	unsigned int namelen;
	int ret = 0;

	if (!dlm_grab(dlm))
		return -EINVAL;

	name = migrate->name;
	namelen = migrate->namelen;

	/* preallocate.. if this fails, abort */
	mle = (struct dlm_master_list_entry *) kmem_cache_alloc(dlm_mle_cache,
							 GFP_KERNEL);

	if (!mle) {
		ret = -ENOMEM;
		goto leave;
	}

	/* check for pre-existing lock */
	spin_lock(&dlm->spinlock);
	res = __dlm_lookup_lockres(dlm, name, namelen);
	spin_lock(&dlm->master_lock);

	if (res) {
		spin_lock(&res->spinlock);
		if (res->state & DLM_LOCK_RES_RECOVERING) {
			/* if all is working ok, this can only mean that we got
		 	* a migrate request from a node that we now see as
		 	* dead.  what can we do here?  drop it to the floor? */
			spin_unlock(&res->spinlock);
			mlog(ML_ERROR, "Got a migrate request, but the "
			     "lockres is marked as recovering!");
			kmem_cache_free(dlm_mle_cache, mle);
			ret = -EINVAL; /* need a better solution */
			goto unlock;
		}
		res->state |= DLM_LOCK_RES_MIGRATING;
		spin_unlock(&res->spinlock);
	}

	/* ignore status.  only nonzero status would BUG. */
	ret = dlm_add_migration_mle(dlm, res, mle, &oldmle,
				    name, namelen,
				    migrate->new_master,
				    migrate->master);

unlock:
	spin_unlock(&dlm->master_lock);
	spin_unlock(&dlm->spinlock);

	if (oldmle) {
		/* master is known, detach if not already detached */
		dlm_mle_detach_hb_events(dlm, oldmle);
		dlm_put_mle(oldmle);
	}

	if (res)
		dlm_lockres_put(res);
leave:
	dlm_put(dlm);
	return ret;
}

/* must be holding dlm->spinlock and dlm->master_lock
 * when adding a migration mle, we can clear any other mles
 * in the master list because we know with certainty that
 * the master is "master".  so we remove any old mle from
 * the list after setting it's master field, and then add
 * the new migration mle.  this way we can hold with the rule
 * of having only one mle for a given lock name at all times. */
static int dlm_add_migration_mle(struct dlm_ctxt *dlm,
				 struct dlm_lock_resource *res,
				 struct dlm_master_list_entry *mle,
				 struct dlm_master_list_entry **oldmle,
				 const char *name, unsigned int namelen,
				 u8 new_master, u8 master)
{
	int found;
	int ret = 0;

	*oldmle = NULL;

	mlog_entry_void();

	assert_spin_locked(&dlm->spinlock);
	assert_spin_locked(&dlm->master_lock);

	/* caller is responsible for any ref taken here on oldmle */
	found = dlm_find_mle(dlm, oldmle, (char *)name, namelen);
	if (found) {
		struct dlm_master_list_entry *tmp = *oldmle;
		spin_lock(&tmp->spinlock);
		if (tmp->type == DLM_MLE_MIGRATION) {
			if (master == dlm->node_num) {
				/* ah another process raced me to it */
				mlog(0, "tried to migrate %.*s, but some "
				     "process beat me to it\n",
				     namelen, name);
				ret = -EEXIST;
			} else {
				/* bad.  2 NODES are trying to migrate! */
				mlog(ML_ERROR, "migration error  mle: "
				     "master=%u new_master=%u // request: "
				     "master=%u new_master=%u // "
				     "lockres=%.*s\n",
				     tmp->master, tmp->new_master,
				     master, new_master,
				     namelen, name);
				BUG();
			}
		} else {
			/* this is essentially what assert_master does */
			tmp->master = master;
			atomic_set(&tmp->woken, 1);
			wake_up(&tmp->wq);
			/* remove it from the list so that only one
			 * mle will be found */
			list_del_init(&tmp->list);
		}
		spin_unlock(&tmp->spinlock);
	}

	/* now add a migration mle to the tail of the list */
	dlm_init_mle(mle, DLM_MLE_MIGRATION, dlm, res, name, namelen);
	mle->new_master = new_master;
	mle->master = master;
	/* do this for consistency with other mle types */
	set_bit(new_master, mle->maybe_map);
	list_add(&mle->list, &dlm->master_list);

	return ret;
}


void dlm_clean_master_list(struct dlm_ctxt *dlm, u8 dead_node)
{
	struct list_head *iter, *iter2;
	struct dlm_master_list_entry *mle;
	struct dlm_lock_resource *res;

	mlog_entry("dlm=%s, dead node=%u\n", dlm->name, dead_node);
top:
	assert_spin_locked(&dlm->spinlock);

	/* clean the master list */
	spin_lock(&dlm->master_lock);
	list_for_each_safe(iter, iter2, &dlm->master_list) {
		mle = list_entry(iter, struct dlm_master_list_entry, list);

		BUG_ON(mle->type != DLM_MLE_BLOCK &&
		       mle->type != DLM_MLE_MASTER &&
		       mle->type != DLM_MLE_MIGRATION);

		/* MASTER mles are initiated locally.  the waiting
		 * process will notice the node map change
		 * shortly.  let that happen as normal. */
		if (mle->type == DLM_MLE_MASTER)
			continue;


		/* BLOCK mles are initiated by other nodes.
		 * need to clean up if the dead node would have
		 * been the master. */
		if (mle->type == DLM_MLE_BLOCK) {
			int bit;

			spin_lock(&mle->spinlock);
			bit = find_next_bit(mle->maybe_map, O2NM_MAX_NODES, 0);
			if (bit != dead_node) {
				mlog(0, "mle found, but dead node %u would "
				     "not have been master\n", dead_node);
				spin_unlock(&mle->spinlock);
			} else {
				/* must drop the refcount by one since the
				 * assert_master will never arrive.  this
				 * may result in the mle being unlinked and
				 * freed, but there may still be a process
				 * waiting in the dlmlock path which is fine. */
				mlog(ML_ERROR, "node %u was expected master\n",
				     dead_node);
				atomic_set(&mle->woken, 1);
				spin_unlock(&mle->spinlock);
				wake_up(&mle->wq);
				/* final put will take care of list removal */
				__dlm_put_mle(mle);
			}
			continue;
		}

		/* everything else is a MIGRATION mle */

		/* the rule for MIGRATION mles is that the master
		 * becomes UNKNOWN if *either* the original or
		 * the new master dies.  all UNKNOWN lockreses
		 * are sent to whichever node becomes the recovery
		 * master.  the new master is responsible for
		 * determining if there is still a master for
		 * this lockres, or if he needs to take over
		 * mastery.  either way, this node should expect
		 * another message to resolve this. */
		if (mle->master != dead_node &&
		    mle->new_master != dead_node)
			continue;

		/* if we have reached this point, this mle needs to
		 * be removed from the list and freed. */

		/* remove from the list early.  NOTE: unlinking
		 * list_head while in list_for_each_safe */
		spin_lock(&mle->spinlock);
		list_del_init(&mle->list);
		atomic_set(&mle->woken, 1);
		spin_unlock(&mle->spinlock);
		wake_up(&mle->wq);

		mlog(0, "node %u died during migration from "
		     "%u to %u!\n", dead_node,
		     mle->master, mle->new_master);
		/* if there is a lockres associated with this
	 	 * mle, find it and set its owner to UNKNOWN */
		res = __dlm_lookup_lockres(dlm, mle->u.name.name,
					mle->u.name.len);
		if (res) {
			/* unfortunately if we hit this rare case, our
		 	 * lock ordering is messed.  we need to drop
		 	 * the master lock so that we can take the
		  	 * lockres lock, meaning that we will have to
			 * restart from the head of list. */
			spin_unlock(&dlm->master_lock);

			/* move lockres onto recovery list */
			spin_lock(&res->spinlock);
			dlm_set_lockres_owner(dlm, res,
				      	DLM_LOCK_RES_OWNER_UNKNOWN);
			dlm_move_lockres_to_recovery_list(dlm, res);
			spin_unlock(&res->spinlock);
			dlm_lockres_put(res);

			/* dump the mle */
			spin_lock(&dlm->master_lock);
			__dlm_put_mle(mle);
			spin_unlock(&dlm->master_lock);

			/* restart */
			goto top;
		}

		/* this may be the last reference */
		__dlm_put_mle(mle);
	}
	spin_unlock(&dlm->master_lock);
}


int dlm_finish_migration(struct dlm_ctxt *dlm, struct dlm_lock_resource *res,
			 u8 old_master)
{
	struct dlm_node_iter iter;
	int ret = 0;

	spin_lock(&dlm->spinlock);
	dlm_node_iter_init(dlm->domain_map, &iter);
	clear_bit(old_master, iter.node_map);
	clear_bit(dlm->node_num, iter.node_map);
	spin_unlock(&dlm->spinlock);

	mlog(0, "now time to do a migrate request to other nodes\n");
	ret = dlm_do_migrate_request(dlm, res, old_master,
				     dlm->node_num, &iter);
	if (ret < 0) {
		mlog_errno(ret);
		goto leave;
	}

	mlog(0, "doing assert master of %.*s to all except the original node\n",
	     res->lockname.len, res->lockname.name);
	/* this call now finishes out the nodemap
	 * even if one or more nodes die */
	ret = dlm_do_assert_master(dlm, res->lockname.name,
				   res->lockname.len, iter.node_map,
				   DLM_ASSERT_MASTER_FINISH_MIGRATION);
	if (ret < 0) {
		/* no longer need to retry.  all living nodes contacted. */
		mlog_errno(ret);
		ret = 0;
	}

	memset(iter.node_map, 0, sizeof(iter.node_map));
	set_bit(old_master, iter.node_map);
	mlog(0, "doing assert master of %.*s back to %u\n",
	     res->lockname.len, res->lockname.name, old_master);
	ret = dlm_do_assert_master(dlm, res->lockname.name,
				   res->lockname.len, iter.node_map,
				   DLM_ASSERT_MASTER_FINISH_MIGRATION);
	if (ret < 0) {
		mlog(0, "assert master to original master failed "
		     "with %d.\n", ret);
		/* the only nonzero status here would be because of
		 * a dead original node.  we're done. */
		ret = 0;
	}

	/* all done, set the owner, clear the flag */
	spin_lock(&res->spinlock);
	dlm_set_lockres_owner(dlm, res, dlm->node_num);
	res->state &= ~DLM_LOCK_RES_MIGRATING;
	spin_unlock(&res->spinlock);
	/* re-dirty it on the new master */
	dlm_kick_thread(dlm, res);
	wake_up(&res->wq);
leave:
	return ret;
}

/*
 * LOCKRES AST REFCOUNT
 * this is integral to migration
 */

/* for future intent to call an ast, reserve one ahead of time.
 * this should be called only after waiting on the lockres
 * with dlm_wait_on_lockres, and while still holding the
 * spinlock after the call. */
void __dlm_lockres_reserve_ast(struct dlm_lock_resource *res)
{
	assert_spin_locked(&res->spinlock);
	if (res->state & DLM_LOCK_RES_MIGRATING) {
		__dlm_print_one_lock_resource(res);
	}
	BUG_ON(res->state & DLM_LOCK_RES_MIGRATING);

	atomic_inc(&res->asts_reserved);
}

/*
 * used to drop the reserved ast, either because it went unused,
 * or because the ast/bast was actually called.
 *
 * also, if there is a pending migration on this lockres,
 * and this was the last pending ast on the lockres,
 * atomically set the MIGRATING flag before we drop the lock.
 * this is how we ensure that migration can proceed with no
 * asts in progress.  note that it is ok if the state of the
 * queues is such that a lock should be granted in the future
 * or that a bast should be fired, because the new master will
 * shuffle the lists on this lockres as soon as it is migrated.
 */
void dlm_lockres_release_ast(struct dlm_ctxt *dlm,
			     struct dlm_lock_resource *res)
{
	if (!atomic_dec_and_lock(&res->asts_reserved, &res->spinlock))
		return;

	if (!res->migration_pending) {
		spin_unlock(&res->spinlock);
		return;
	}

	BUG_ON(res->state & DLM_LOCK_RES_MIGRATING);
	res->migration_pending = 0;
	res->state |= DLM_LOCK_RES_MIGRATING;
	spin_unlock(&res->spinlock);
	wake_up(&res->wq);
	wake_up(&dlm->migration_wq);
}