mm-only debug patch...

[mmotm.git] / fs / ocfs2 / cluster / heartbeat.c

/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * Copyright (C) 2004, 2005 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/kernel.h>
#include <linux/sched.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/delay.h>
#include <linux/file.h>
#include <linux/kthread.h>
#include <linux/configfs.h>
#include <linux/random.h>
#include <linux/crc32.h>
#include <linux/time.h>
#include <linux/debugfs.h>

#include "heartbeat.h"
#include "tcp.h"
#include "nodemanager.h"
#include "quorum.h"

#include "masklog.h"


/*
 * The first heartbeat pass had one global thread that would serialize all hb
 * callback calls.  This global serializing sem should only be removed once
 * we've made sure that all callees can deal with being called concurrently
 * from multiple hb region threads.
 */
static DECLARE_RWSEM(o2hb_callback_sem);

/*
 * multiple hb threads are watching multiple regions.  A node is live
 * whenever any of the threads sees activity from the node in its region.
 */
static DEFINE_SPINLOCK(o2hb_live_lock);
static struct list_head o2hb_live_slots[O2NM_MAX_NODES];
static unsigned long o2hb_live_node_bitmap[BITS_TO_LONGS(O2NM_MAX_NODES)];
static LIST_HEAD(o2hb_node_events);
static DECLARE_WAIT_QUEUE_HEAD(o2hb_steady_queue);

#define O2HB_DEBUG_DIR                  "o2hb"
#define O2HB_DEBUG_LIVENODES            "livenodes"
static struct dentry *o2hb_debug_dir;
static struct dentry *o2hb_debug_livenodes;

static LIST_HEAD(o2hb_all_regions);

static struct o2hb_callback {
        struct list_head list;
} o2hb_callbacks[O2HB_NUM_CB];

static struct o2hb_callback *hbcall_from_type(enum o2hb_callback_type type);

#define O2HB_DEFAULT_BLOCK_BITS       9

unsigned int o2hb_dead_threshold = O2HB_DEFAULT_DEAD_THRESHOLD;

/* Only sets a new threshold if there are no active regions. 
 *
 * No locking or otherwise interesting code is required for reading
 * o2hb_dead_threshold as it can't change once regions are active and
 * it's not interesting to anyone until then anyway. */
static void o2hb_dead_threshold_set(unsigned int threshold)
{
        if (threshold > O2HB_MIN_DEAD_THRESHOLD) {
                spin_lock(&o2hb_live_lock);
                if (list_empty(&o2hb_all_regions))
                        o2hb_dead_threshold = threshold;
                spin_unlock(&o2hb_live_lock);
        }
}

struct o2hb_node_event {
        struct list_head        hn_item;
        enum o2hb_callback_type hn_event_type;
        struct o2nm_node        *hn_node;
        int                     hn_node_num;
};

struct o2hb_disk_slot {
        struct o2hb_disk_heartbeat_block *ds_raw_block;
        u8                      ds_node_num;
        u64                     ds_last_time;
        u64                     ds_last_generation;
        u16                     ds_equal_samples;
        u16                     ds_changed_samples;
        struct list_head        ds_live_item;
};

/* each thread owns a region.. when we're asked to tear down the region
 * we ask the thread to stop, who cleans up the region */
struct o2hb_region {
        struct config_item      hr_item;

        struct list_head        hr_all_item;
        unsigned                hr_unclean_stop:1;

        /* protected by the hr_callback_sem */
        struct task_struct      *hr_task;

        unsigned int            hr_blocks;
        unsigned long long      hr_start_block;

        unsigned int            hr_block_bits;
        unsigned int            hr_block_bytes;

        unsigned int            hr_slots_per_page;
        unsigned int            hr_num_pages;

        struct page             **hr_slot_data;
        struct block_device     *hr_bdev;
        struct o2hb_disk_slot   *hr_slots;

        /* let the person setting up hb wait for it to return until it
         * has reached a 'steady' state.  This will be fixed when we have
         * a more complete api that doesn't lead to this sort of fragility. */
        atomic_t                hr_steady_iterations;

        char                    hr_dev_name[BDEVNAME_SIZE];

        unsigned int            hr_timeout_ms;

        /* randomized as the region goes up and down so that a node
         * recognizes a node going up and down in one iteration */
        u64                     hr_generation;

        struct delayed_work     hr_write_timeout_work;
        unsigned long           hr_last_timeout_start;

        /* Used during o2hb_check_slot to hold a copy of the block
         * being checked because we temporarily have to zero out the
         * crc field. */
        struct o2hb_disk_heartbeat_block *hr_tmp_block;
};

struct o2hb_bio_wait_ctxt {
        atomic_t          wc_num_reqs;
        struct completion wc_io_complete;
        int               wc_error;
};

static void o2hb_write_timeout(struct work_struct *work)
{
        struct o2hb_region *reg =
                container_of(work, struct o2hb_region,
                             hr_write_timeout_work.work);

        mlog(ML_ERROR, "Heartbeat write timeout to device %s after %u "
             "milliseconds\n", reg->hr_dev_name,
             jiffies_to_msecs(jiffies - reg->hr_last_timeout_start)); 
        o2quo_disk_timeout();
}

static void o2hb_arm_write_timeout(struct o2hb_region *reg)
{
        mlog(0, "Queue write timeout for %u ms\n", O2HB_MAX_WRITE_TIMEOUT_MS);

        cancel_delayed_work(&reg->hr_write_timeout_work);
        reg->hr_last_timeout_start = jiffies;
        schedule_delayed_work(&reg->hr_write_timeout_work,
                              msecs_to_jiffies(O2HB_MAX_WRITE_TIMEOUT_MS));
}

static void o2hb_disarm_write_timeout(struct o2hb_region *reg)
{
        cancel_delayed_work(&reg->hr_write_timeout_work);
        flush_scheduled_work();
}

static inline void o2hb_bio_wait_init(struct o2hb_bio_wait_ctxt *wc)
{
        atomic_set(&wc->wc_num_reqs, 1);
        init_completion(&wc->wc_io_complete);
        wc->wc_error = 0;
}

/* Used in error paths too */
static inline void o2hb_bio_wait_dec(struct o2hb_bio_wait_ctxt *wc,
                                     unsigned int num)
{
        /* sadly atomic_sub_and_test() isn't available on all platforms.  The
         * good news is that the fast path only completes one at a time */
        while(num--) {
                if (atomic_dec_and_test(&wc->wc_num_reqs)) {
                        BUG_ON(num > 0);
                        complete(&wc->wc_io_complete);
                }
        }
}

static void o2hb_wait_on_io(struct o2hb_region *reg,
                            struct o2hb_bio_wait_ctxt *wc)
{
        struct address_space *mapping = reg->hr_bdev->bd_inode->i_mapping;

        blk_run_address_space(mapping);
        o2hb_bio_wait_dec(wc, 1);

        wait_for_completion(&wc->wc_io_complete);
}

static void o2hb_bio_end_io(struct bio *bio,
                           int error)
{
        struct o2hb_bio_wait_ctxt *wc = bio->bi_private;

        if (error) {
                mlog(ML_ERROR, "IO Error %d\n", error);
                wc->wc_error = error;
        }

        o2hb_bio_wait_dec(wc, 1);
        bio_put(bio);
}

/* Setup a Bio to cover I/O against num_slots slots starting at
 * start_slot. */
static struct bio *o2hb_setup_one_bio(struct o2hb_region *reg,
                                      struct o2hb_bio_wait_ctxt *wc,
                                      unsigned int *current_slot,
                                      unsigned int max_slots)
{
        int len, current_page;
        unsigned int vec_len, vec_start;
        unsigned int bits = reg->hr_block_bits;
        unsigned int spp = reg->hr_slots_per_page;
        unsigned int cs = *current_slot;
        struct bio *bio;
        struct page *page;

        /* Testing has shown this allocation to take long enough under
         * GFP_KERNEL that the local node can get fenced. It would be
         * nicest if we could pre-allocate these bios and avoid this
         * all together. */
        bio = bio_alloc(GFP_ATOMIC, 16);
        if (!bio) {
                mlog(ML_ERROR, "Could not alloc slots BIO!\n");
                bio = ERR_PTR(-ENOMEM);
                goto bail;
        }

        /* Must put everything in 512 byte sectors for the bio... */
        bio->bi_sector = (reg->hr_start_block + cs) << (bits - 9);
        bio->bi_bdev = reg->hr_bdev;
        bio->bi_private = wc;
        bio->bi_end_io = o2hb_bio_end_io;

        vec_start = (cs << bits) % PAGE_CACHE_SIZE;
        while(cs < max_slots) {
                current_page = cs / spp;
                page = reg->hr_slot_data[current_page];

                vec_len = min(PAGE_CACHE_SIZE - vec_start,
                              (max_slots-cs) * (PAGE_CACHE_SIZE/spp) );

                mlog(ML_HB_BIO, "page %d, vec_len = %u, vec_start = %u\n",
                     current_page, vec_len, vec_start);

                len = bio_add_page(bio, page, vec_len, vec_start);
                if (len != vec_len) break;

                cs += vec_len / (PAGE_CACHE_SIZE/spp);
                vec_start = 0;
        }

bail:
        *current_slot = cs;
        return bio;
}

static int o2hb_read_slots(struct o2hb_region *reg,
                           unsigned int max_slots)
{
        unsigned int current_slot=0;
        int status;
        struct o2hb_bio_wait_ctxt wc;
        struct bio *bio;

        o2hb_bio_wait_init(&wc);

        while(current_slot < max_slots) {
                bio = o2hb_setup_one_bio(reg, &wc, &current_slot, max_slots);
                if (IS_ERR(bio)) {
                        status = PTR_ERR(bio);
                        mlog_errno(status);
                        goto bail_and_wait;
                }

                atomic_inc(&wc.wc_num_reqs);
                submit_bio(READ, bio);
        }

        status = 0;

bail_and_wait:
        o2hb_wait_on_io(reg, &wc);
        if (wc.wc_error && !status)
                status = wc.wc_error;

        return status;
}

static int o2hb_issue_node_write(struct o2hb_region *reg,
                                 struct o2hb_bio_wait_ctxt *write_wc)
{
        int status;
        unsigned int slot;
        struct bio *bio;

        o2hb_bio_wait_init(write_wc);

        slot = o2nm_this_node();

        bio = o2hb_setup_one_bio(reg, write_wc, &slot, slot+1);
        if (IS_ERR(bio)) {
                status = PTR_ERR(bio);
                mlog_errno(status);
                goto bail;
        }

        atomic_inc(&write_wc->wc_num_reqs);
        submit_bio(WRITE, bio);

        status = 0;
bail:
        return status;
}

static u32 o2hb_compute_block_crc_le(struct o2hb_region *reg,
                                     struct o2hb_disk_heartbeat_block *hb_block)
{
        __le32 old_cksum;
        u32 ret;

        /* We want to compute the block crc with a 0 value in the
         * hb_cksum field. Save it off here and replace after the
         * crc. */
        old_cksum = hb_block->hb_cksum;
        hb_block->hb_cksum = 0;

        ret = crc32_le(0, (unsigned char *) hb_block, reg->hr_block_bytes);

        hb_block->hb_cksum = old_cksum;

        return ret;
}

static void o2hb_dump_slot(struct o2hb_disk_heartbeat_block *hb_block)
{
        mlog(ML_ERROR, "Dump slot information: seq = 0x%llx, node = %u, "
             "cksum = 0x%x, generation 0x%llx\n",
             (long long)le64_to_cpu(hb_block->hb_seq),
             hb_block->hb_node, le32_to_cpu(hb_block->hb_cksum),
             (long long)le64_to_cpu(hb_block->hb_generation));
}

static int o2hb_verify_crc(struct o2hb_region *reg,
                           struct o2hb_disk_heartbeat_block *hb_block)
{
        u32 read, computed;

        read = le32_to_cpu(hb_block->hb_cksum);
        computed = o2hb_compute_block_crc_le(reg, hb_block);

        return read == computed;
}

/* We want to make sure that nobody is heartbeating on top of us --
 * this will help detect an invalid configuration. */
static int o2hb_check_last_timestamp(struct o2hb_region *reg)
{
        int node_num, ret;
        struct o2hb_disk_slot *slot;
        struct o2hb_disk_heartbeat_block *hb_block;

        node_num = o2nm_this_node();

        ret = 1;
        slot = &reg->hr_slots[node_num];
        /* Don't check on our 1st timestamp */
        if (slot->ds_last_time) {
                hb_block = slot->ds_raw_block;

                if (le64_to_cpu(hb_block->hb_seq) != slot->ds_last_time)
                        ret = 0;
        }

        return ret;
}

static inline void o2hb_prepare_block(struct o2hb_region *reg,
                                      u64 generation)
{
        int node_num;
        u64 cputime;
        struct o2hb_disk_slot *slot;
        struct o2hb_disk_heartbeat_block *hb_block;

        node_num = o2nm_this_node();
        slot = &reg->hr_slots[node_num];

        hb_block = (struct o2hb_disk_heartbeat_block *)slot->ds_raw_block;
        memset(hb_block, 0, reg->hr_block_bytes);
        /* TODO: time stuff */
        cputime = CURRENT_TIME.tv_sec;
        if (!cputime)
                cputime = 1;

        hb_block->hb_seq = cpu_to_le64(cputime);
        hb_block->hb_node = node_num;
        hb_block->hb_generation = cpu_to_le64(generation);
        hb_block->hb_dead_ms = cpu_to_le32(o2hb_dead_threshold * O2HB_REGION_TIMEOUT_MS);

        /* This step must always happen last! */
        hb_block->hb_cksum = cpu_to_le32(o2hb_compute_block_crc_le(reg,
                                                                   hb_block));

        mlog(ML_HB_BIO, "our node generation = 0x%llx, cksum = 0x%x\n",
             (long long)generation,
             le32_to_cpu(hb_block->hb_cksum));
}

static void o2hb_fire_callbacks(struct o2hb_callback *hbcall,
                                struct o2nm_node *node,
                                int idx)
{
        struct list_head *iter;
        struct o2hb_callback_func *f;

        list_for_each(iter, &hbcall->list) {
                f = list_entry(iter, struct o2hb_callback_func, hc_item);
                mlog(ML_HEARTBEAT, "calling funcs %p\n", f);
                (f->hc_func)(node, idx, f->hc_data);
        }
}

/* Will run the list in order until we process the passed event */
static void o2hb_run_event_list(struct o2hb_node_event *queued_event)
{
        int empty;
        struct o2hb_callback *hbcall;
        struct o2hb_node_event *event;

        spin_lock(&o2hb_live_lock);
        empty = list_empty(&queued_event->hn_item);
        spin_unlock(&o2hb_live_lock);
        if (empty)
                return;

        /* Holding callback sem assures we don't alter the callback
         * lists when doing this, and serializes ourselves with other
         * processes wanting callbacks. */
        down_write(&o2hb_callback_sem);

        spin_lock(&o2hb_live_lock);
        while (!list_empty(&o2hb_node_events)
               && !list_empty(&queued_event->hn_item)) {
                event = list_entry(o2hb_node_events.next,
                                   struct o2hb_node_event,
                                   hn_item);
                list_del_init(&event->hn_item);
                spin_unlock(&o2hb_live_lock);

                mlog(ML_HEARTBEAT, "Node %s event for %d\n",
                     event->hn_event_type == O2HB_NODE_UP_CB ? "UP" : "DOWN",
                     event->hn_node_num);

                hbcall = hbcall_from_type(event->hn_event_type);

                /* We should *never* have gotten on to the list with a
                 * bad type... This isn't something that we should try
                 * to recover from. */
                BUG_ON(IS_ERR(hbcall));

                o2hb_fire_callbacks(hbcall, event->hn_node, event->hn_node_num);

                spin_lock(&o2hb_live_lock);
        }
        spin_unlock(&o2hb_live_lock);

        up_write(&o2hb_callback_sem);
}

static void o2hb_queue_node_event(struct o2hb_node_event *event,
                                  enum o2hb_callback_type type,
                                  struct o2nm_node *node,
                                  int node_num)
{
        assert_spin_locked(&o2hb_live_lock);

        event->hn_event_type = type;
        event->hn_node = node;
        event->hn_node_num = node_num;

        mlog(ML_HEARTBEAT, "Queue node %s event for node %d\n",
             type == O2HB_NODE_UP_CB ? "UP" : "DOWN", node_num);

        list_add_tail(&event->hn_item, &o2hb_node_events);
}

static void o2hb_shutdown_slot(struct o2hb_disk_slot *slot)
{
        struct o2hb_node_event event =
                { .hn_item = LIST_HEAD_INIT(event.hn_item), };
        struct o2nm_node *node;

        node = o2nm_get_node_by_num(slot->ds_node_num);
        if (!node)
                return;

        spin_lock(&o2hb_live_lock);
        if (!list_empty(&slot->ds_live_item)) {
                mlog(ML_HEARTBEAT, "Shutdown, node %d leaves region\n",
                     slot->ds_node_num);

                list_del_init(&slot->ds_live_item);

                if (list_empty(&o2hb_live_slots[slot->ds_node_num])) {
                        clear_bit(slot->ds_node_num, o2hb_live_node_bitmap);

                        o2hb_queue_node_event(&event, O2HB_NODE_DOWN_CB, node,
                                              slot->ds_node_num);
                }
        }
        spin_unlock(&o2hb_live_lock);

        o2hb_run_event_list(&event);

        o2nm_node_put(node);
}

static int o2hb_check_slot(struct o2hb_region *reg,
                           struct o2hb_disk_slot *slot)
{
        int changed = 0, gen_changed = 0;
        struct o2hb_node_event event =
                { .hn_item = LIST_HEAD_INIT(event.hn_item), };
        struct o2nm_node *node;
        struct o2hb_disk_heartbeat_block *hb_block = reg->hr_tmp_block;
        u64 cputime;
        unsigned int dead_ms = o2hb_dead_threshold * O2HB_REGION_TIMEOUT_MS;
        unsigned int slot_dead_ms;

        memcpy(hb_block, slot->ds_raw_block, reg->hr_block_bytes);

        /* Is this correct? Do we assume that the node doesn't exist
         * if we're not configured for him? */
        node = o2nm_get_node_by_num(slot->ds_node_num);
        if (!node)
                return 0;

        if (!o2hb_verify_crc(reg, hb_block)) {
                /* all paths from here will drop o2hb_live_lock for
                 * us. */
                spin_lock(&o2hb_live_lock);

                /* Don't print an error on the console in this case -
                 * a freshly formatted heartbeat area will not have a
                 * crc set on it. */
                if (list_empty(&slot->ds_live_item))
                        goto out;

                /* The node is live but pushed out a bad crc. We
                 * consider it a transient miss but don't populate any
                 * other values as they may be junk. */
                mlog(ML_ERROR, "Node %d has written a bad crc to %s\n",
                     slot->ds_node_num, reg->hr_dev_name);
                o2hb_dump_slot(hb_block);

                slot->ds_equal_samples++;
                goto fire_callbacks;
        }

        /* we don't care if these wrap.. the state transitions below
         * clear at the right places */
        cputime = le64_to_cpu(hb_block->hb_seq);
        if (slot->ds_last_time != cputime)
                slot->ds_changed_samples++;
        else
                slot->ds_equal_samples++;
        slot->ds_last_time = cputime;

        /* The node changed heartbeat generations. We assume this to
         * mean it dropped off but came back before we timed out. We
         * want to consider it down for the time being but don't want
         * to lose any changed_samples state we might build up to
         * considering it live again. */
        if (slot->ds_last_generation != le64_to_cpu(hb_block->hb_generation)) {
                gen_changed = 1;
                slot->ds_equal_samples = 0;
                mlog(ML_HEARTBEAT, "Node %d changed generation (0x%llx "
                     "to 0x%llx)\n", slot->ds_node_num,
                     (long long)slot->ds_last_generation,
                     (long long)le64_to_cpu(hb_block->hb_generation));
        }

        slot->ds_last_generation = le64_to_cpu(hb_block->hb_generation);

        mlog(ML_HEARTBEAT, "Slot %d gen 0x%llx cksum 0x%x "
             "seq %llu last %llu changed %u equal %u\n",
             slot->ds_node_num, (long long)slot->ds_last_generation,
             le32_to_cpu(hb_block->hb_cksum),
             (unsigned long long)le64_to_cpu(hb_block->hb_seq), 
             (unsigned long long)slot->ds_last_time, slot->ds_changed_samples,
             slot->ds_equal_samples);

        spin_lock(&o2hb_live_lock);

fire_callbacks:
        /* dead nodes only come to life after some number of
         * changes at any time during their dead time */
        if (list_empty(&slot->ds_live_item) &&
            slot->ds_changed_samples >= O2HB_LIVE_THRESHOLD) {
                mlog(ML_HEARTBEAT, "Node %d (id 0x%llx) joined my region\n",
                     slot->ds_node_num, (long long)slot->ds_last_generation);

                /* first on the list generates a callback */
                if (list_empty(&o2hb_live_slots[slot->ds_node_num])) {
                        set_bit(slot->ds_node_num, o2hb_live_node_bitmap);

                        o2hb_queue_node_event(&event, O2HB_NODE_UP_CB, node,
                                              slot->ds_node_num);

                        changed = 1;
                }

                list_add_tail(&slot->ds_live_item,
                              &o2hb_live_slots[slot->ds_node_num]);

                slot->ds_equal_samples = 0;

                /* We want to be sure that all nodes agree on the
                 * number of milliseconds before a node will be
                 * considered dead. The self-fencing timeout is
                 * computed from this value, and a discrepancy might
                 * result in heartbeat calling a node dead when it
                 * hasn't self-fenced yet. */
                slot_dead_ms = le32_to_cpu(hb_block->hb_dead_ms);
                if (slot_dead_ms && slot_dead_ms != dead_ms) {
                        /* TODO: Perhaps we can fail the region here. */
                        mlog(ML_ERROR, "Node %d on device %s has a dead count "
                             "of %u ms, but our count is %u ms.\n"
                             "Please double check your configuration values "
                             "for 'O2CB_HEARTBEAT_THRESHOLD'\n",
                             slot->ds_node_num, reg->hr_dev_name, slot_dead_ms,
                             dead_ms);
                }
                goto out;
        }

        /* if the list is dead, we're done.. */
        if (list_empty(&slot->ds_live_item))
                goto out;

        /* live nodes only go dead after enough consequtive missed
         * samples..  reset the missed counter whenever we see
         * activity */
        if (slot->ds_equal_samples >= o2hb_dead_threshold || gen_changed) {
                mlog(ML_HEARTBEAT, "Node %d left my region\n",
                     slot->ds_node_num);

                /* last off the live_slot generates a callback */
                list_del_init(&slot->ds_live_item);
                if (list_empty(&o2hb_live_slots[slot->ds_node_num])) {
                        clear_bit(slot->ds_node_num, o2hb_live_node_bitmap);

                        o2hb_queue_node_event(&event, O2HB_NODE_DOWN_CB, node,
                                              slot->ds_node_num);

                        changed = 1;
                }

                /* We don't clear this because the node is still
                 * actually writing new blocks. */
                if (!gen_changed)
                        slot->ds_changed_samples = 0;
                goto out;
        }
        if (slot->ds_changed_samples) {
                slot->ds_changed_samples = 0;
                slot->ds_equal_samples = 0;
        }
out:
        spin_unlock(&o2hb_live_lock);

        o2hb_run_event_list(&event);

        o2nm_node_put(node);
        return changed;
}

/* This could be faster if we just implmented a find_last_bit, but I
 * don't think the circumstances warrant it. */
static int o2hb_highest_node(unsigned long *nodes,
                             int numbits)
{
        int highest, node;

        highest = numbits;
        node = -1;
        while ((node = find_next_bit(nodes, numbits, node + 1)) != -1) {
                if (node >= numbits)
                        break;

                highest = node;
        }

        return highest;
}

static int o2hb_do_disk_heartbeat(struct o2hb_region *reg)
{
        int i, ret, highest_node, change = 0;
        unsigned long configured_nodes[BITS_TO_LONGS(O2NM_MAX_NODES)];
        struct o2hb_bio_wait_ctxt write_wc;

        ret = o2nm_configured_node_map(configured_nodes,
                                       sizeof(configured_nodes));
        if (ret) {
                mlog_errno(ret);
                return ret;
        }

        highest_node = o2hb_highest_node(configured_nodes, O2NM_MAX_NODES);
        if (highest_node >= O2NM_MAX_NODES) {
                mlog(ML_NOTICE, "ocfs2_heartbeat: no configured nodes found!\n");
                return -EINVAL;
        }

        /* No sense in reading the slots of nodes that don't exist
         * yet. Of course, if the node definitions have holes in them
         * then we're reading an empty slot anyway... Consider this
         * best-effort. */
        ret = o2hb_read_slots(reg, highest_node + 1);
        if (ret < 0) {
                mlog_errno(ret);
                return ret;
        }

        /* With an up to date view of the slots, we can check that no
         * other node has been improperly configured to heartbeat in
         * our slot. */
        if (!o2hb_check_last_timestamp(reg))
                mlog(ML_ERROR, "Device \"%s\": another node is heartbeating "
                     "in our slot!\n", reg->hr_dev_name);

        /* fill in the proper info for our next heartbeat */
        o2hb_prepare_block(reg, reg->hr_generation);

        /* And fire off the write. Note that we don't wait on this I/O
         * until later. */
        ret = o2hb_issue_node_write(reg, &write_wc);
        if (ret < 0) {
                mlog_errno(ret);
                return ret;
        }

        i = -1;
        while((i = find_next_bit(configured_nodes, O2NM_MAX_NODES, i + 1)) < O2NM_MAX_NODES) {

                change |= o2hb_check_slot(reg, &reg->hr_slots[i]);
        }

        /*
         * We have to be sure we've advertised ourselves on disk
         * before we can go to steady state.  This ensures that
         * people we find in our steady state have seen us.
         */
        o2hb_wait_on_io(reg, &write_wc);
        if (write_wc.wc_error) {
                /* Do not re-arm the write timeout on I/O error - we
                 * can't be sure that the new block ever made it to
                 * disk */
                mlog(ML_ERROR, "Write error %d on device \"%s\"\n",
                     write_wc.wc_error, reg->hr_dev_name);
                return write_wc.wc_error;
        }

        o2hb_arm_write_timeout(reg);

        /* let the person who launched us know when things are steady */
        if (!change && (atomic_read(&reg->hr_steady_iterations) != 0)) {
                if (atomic_dec_and_test(&reg->hr_steady_iterations))
                        wake_up(&o2hb_steady_queue);
        }

        return 0;
}

/* Subtract b from a, storing the result in a. a *must* have a larger
 * value than b. */
static void o2hb_tv_subtract(struct timeval *a,
                             struct timeval *b)
{
        /* just return 0 when a is after b */
        if (a->tv_sec < b->tv_sec ||
            (a->tv_sec == b->tv_sec && a->tv_usec < b->tv_usec)) {
                a->tv_sec = 0;
                a->tv_usec = 0;
                return;
        }

        a->tv_sec -= b->tv_sec;
        a->tv_usec -= b->tv_usec;
        while ( a->tv_usec < 0 ) {
                a->tv_sec--;
                a->tv_usec += 1000000;
        }
}

static unsigned int o2hb_elapsed_msecs(struct timeval *start,
                                       struct timeval *end)
{
        struct timeval res = *end;

        o2hb_tv_subtract(&res, start);

        return res.tv_sec * 1000 + res.tv_usec / 1000;
}

/*
 * we ride the region ref that the region dir holds.  before the region
 * dir is removed and drops it ref it will wait to tear down this
 * thread.
 */
static int o2hb_thread(void *data)
{
        int i, ret;
        struct o2hb_region *reg = data;
        struct o2hb_bio_wait_ctxt write_wc;
        struct timeval before_hb, after_hb;
        unsigned int elapsed_msec;

        mlog(ML_HEARTBEAT|ML_KTHREAD, "hb thread running\n");

        set_user_nice(current, -20);

        while (!kthread_should_stop() && !reg->hr_unclean_stop) {
                /* We track the time spent inside
                 * o2hb_do_disk_heartbeat so that we avoid more than
                 * hr_timeout_ms between disk writes. On busy systems
                 * this should result in a heartbeat which is less
                 * likely to time itself out. */
                do_gettimeofday(&before_hb);

                i = 0;
                do {
                        ret = o2hb_do_disk_heartbeat(reg);
                } while (ret && ++i < 2);

                do_gettimeofday(&after_hb);
                elapsed_msec = o2hb_elapsed_msecs(&before_hb, &after_hb);

                mlog(0, "start = %lu.%lu, end = %lu.%lu, msec = %u\n",
                     before_hb.tv_sec, (unsigned long) before_hb.tv_usec,
                     after_hb.tv_sec, (unsigned long) after_hb.tv_usec,
                     elapsed_msec);

                if (elapsed_msec < reg->hr_timeout_ms) {
                        /* the kthread api has blocked signals for us so no
                         * need to record the return value. */
                        msleep_interruptible(reg->hr_timeout_ms - elapsed_msec);
                }
        }

        o2hb_disarm_write_timeout(reg);

        /* unclean stop is only used in very bad situation */
        for(i = 0; !reg->hr_unclean_stop && i < reg->hr_blocks; i++)
                o2hb_shutdown_slot(&reg->hr_slots[i]);

        /* Explicit down notification - avoid forcing the other nodes
         * to timeout on this region when we could just as easily
         * write a clear generation - thus indicating to them that
         * this node has left this region.
         *
         * XXX: Should we skip this on unclean_stop? */
        o2hb_prepare_block(reg, 0);
        ret = o2hb_issue_node_write(reg, &write_wc);
        if (ret == 0) {
                o2hb_wait_on_io(reg, &write_wc);
        } else {
                mlog_errno(ret);
        }

        mlog(ML_HEARTBEAT|ML_KTHREAD, "hb thread exiting\n");

        return 0;
}

#ifdef CONFIG_DEBUG_FS
static int o2hb_debug_open(struct inode *inode, struct file *file)
{
        unsigned long map[BITS_TO_LONGS(O2NM_MAX_NODES)];
        char *buf = NULL;
        int i = -1;
        int out = 0;

        buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
        if (!buf)
                goto bail;

        o2hb_fill_node_map(map, sizeof(map));

        while ((i = find_next_bit(map, O2NM_MAX_NODES, i + 1)) < O2NM_MAX_NODES)
                out += snprintf(buf + out, PAGE_SIZE - out, "%d ", i);
        out += snprintf(buf + out, PAGE_SIZE - out, "\n");

        i_size_write(inode, out);

        file->private_data = buf;

        return 0;
bail:
        return -ENOMEM;
}

static int o2hb_debug_release(struct inode *inode, struct file *file)
{
        kfree(file->private_data);
        return 0;
}

static ssize_t o2hb_debug_read(struct file *file, char __user *buf,
                                 size_t nbytes, loff_t *ppos)
{
        return simple_read_from_buffer(buf, nbytes, ppos, file->private_data,
                                       i_size_read(file->f_mapping->host));
}
#else
static int o2hb_debug_open(struct inode *inode, struct file *file)
{
        return 0;
}
static int o2hb_debug_release(struct inode *inode, struct file *file)
{
        return 0;
}
static ssize_t o2hb_debug_read(struct file *file, char __user *buf,
                               size_t nbytes, loff_t *ppos)
{
        return 0;
}
#endif  /* CONFIG_DEBUG_FS */

static const struct file_operations o2hb_debug_fops = {
        .open =         o2hb_debug_open,
        .release =      o2hb_debug_release,
        .read =         o2hb_debug_read,
        .llseek =       generic_file_llseek,
};

void o2hb_exit(void)
{
        if (o2hb_debug_livenodes)
                debugfs_remove(o2hb_debug_livenodes);
        if (o2hb_debug_dir)
                debugfs_remove(o2hb_debug_dir);
}

int o2hb_init(void)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(o2hb_callbacks); i++)
                INIT_LIST_HEAD(&o2hb_callbacks[i].list);

        for (i = 0; i < ARRAY_SIZE(o2hb_live_slots); i++)
                INIT_LIST_HEAD(&o2hb_live_slots[i]);

        INIT_LIST_HEAD(&o2hb_node_events);

        memset(o2hb_live_node_bitmap, 0, sizeof(o2hb_live_node_bitmap));

        o2hb_debug_dir = debugfs_create_dir(O2HB_DEBUG_DIR, NULL);
        if (!o2hb_debug_dir) {
                mlog_errno(-ENOMEM);
                return -ENOMEM;
        }

        o2hb_debug_livenodes = debugfs_create_file(O2HB_DEBUG_LIVENODES,
                                                   S_IFREG|S_IRUSR,
                                                   o2hb_debug_dir, NULL,
                                                   &o2hb_debug_fops);
        if (!o2hb_debug_livenodes) {
                mlog_errno(-ENOMEM);
                debugfs_remove(o2hb_debug_dir);
                return -ENOMEM;
        }

        return 0;
}

/* if we're already in a callback then we're already serialized by the sem */
static void o2hb_fill_node_map_from_callback(unsigned long *map,
                                             unsigned bytes)
{
        BUG_ON(bytes < (BITS_TO_LONGS(O2NM_MAX_NODES) * sizeof(unsigned long)));

        memcpy(map, &o2hb_live_node_bitmap, bytes);
}

/*
 * get a map of all nodes that are heartbeating in any regions
 */
void o2hb_fill_node_map(unsigned long *map, unsigned bytes)
{
        /* callers want to serialize this map and callbacks so that they
         * can trust that they don't miss nodes coming to the party */
        down_read(&o2hb_callback_sem);
        spin_lock(&o2hb_live_lock);
        o2hb_fill_node_map_from_callback(map, bytes);
        spin_unlock(&o2hb_live_lock);
        up_read(&o2hb_callback_sem);
}
EXPORT_SYMBOL_GPL(o2hb_fill_node_map);

/*
 * heartbeat configfs bits.  The heartbeat set is a default set under
 * the cluster set in nodemanager.c.
 */

static struct o2hb_region *to_o2hb_region(struct config_item *item)
{
        return item ? container_of(item, struct o2hb_region, hr_item) : NULL;
}

/* drop_item only drops its ref after killing the thread, nothing should
 * be using the region anymore.  this has to clean up any state that
 * attributes might have built up. */
static void o2hb_region_release(struct config_item *item)
{
        int i;
        struct page *page;
        struct o2hb_region *reg = to_o2hb_region(item);

        if (reg->hr_tmp_block)
                kfree(reg->hr_tmp_block);

        if (reg->hr_slot_data) {
                for (i = 0; i < reg->hr_num_pages; i++) {
                        page = reg->hr_slot_data[i];
                        if (page)
                                __free_page(page);
                }
                kfree(reg->hr_slot_data);
        }

        if (reg->hr_bdev)
                blkdev_put(reg->hr_bdev, FMODE_READ|FMODE_WRITE);

        if (reg->hr_slots)
                kfree(reg->hr_slots);

        spin_lock(&o2hb_live_lock);
        list_del(&reg->hr_all_item);
        spin_unlock(&o2hb_live_lock);

        kfree(reg);
}

static int o2hb_read_block_input(struct o2hb_region *reg,
                                 const char *page,
                                 size_t count,
                                 unsigned long *ret_bytes,
                                 unsigned int *ret_bits)
{
        unsigned long bytes;
        char *p = (char *)page;

        bytes = simple_strtoul(p, &p, 0);
        if (!p || (*p && (*p != '\n')))
                return -EINVAL;

        /* Heartbeat and fs min / max block sizes are the same. */
        if (bytes > 4096 || bytes < 512)
                return -ERANGE;
        if (hweight16(bytes) != 1)
                return -EINVAL;

        if (ret_bytes)
                *ret_bytes = bytes;
        if (ret_bits)
                *ret_bits = ffs(bytes) - 1;

        return 0;
}

static ssize_t o2hb_region_block_bytes_read(struct o2hb_region *reg,
                                            char *page)
{
        return sprintf(page, "%u\n", reg->hr_block_bytes);
}

static ssize_t o2hb_region_block_bytes_write(struct o2hb_region *reg,
                                             const char *page,
                                             size_t count)
{
        int status;
        unsigned long block_bytes;
        unsigned int block_bits;

        if (reg->hr_bdev)
                return -EINVAL;

        status = o2hb_read_block_input(reg, page, count,
                                       &block_bytes, &block_bits);
        if (status)
                return status;

        reg->hr_block_bytes = (unsigned int)block_bytes;
        reg->hr_block_bits = block_bits;

        return count;
}

static ssize_t o2hb_region_start_block_read(struct o2hb_region *reg,
                                            char *page)
{
        return sprintf(page, "%llu\n", reg->hr_start_block);
}

static ssize_t o2hb_region_start_block_write(struct o2hb_region *reg,
                                             const char *page,
                                             size_t count)
{
        unsigned long long tmp;
        char *p = (char *)page;

        if (reg->hr_bdev)
                return -EINVAL;

        tmp = simple_strtoull(p, &p, 0);
        if (!p || (*p && (*p != '\n')))
                return -EINVAL;

        reg->hr_start_block = tmp;

        return count;
}

static ssize_t o2hb_region_blocks_read(struct o2hb_region *reg,
                                       char *page)
{
        return sprintf(page, "%d\n", reg->hr_blocks);
}

static ssize_t o2hb_region_blocks_write(struct o2hb_region *reg,
                                        const char *page,
                                        size_t count)
{
        unsigned long tmp;
        char *p = (char *)page;

        if (reg->hr_bdev)
                return -EINVAL;

        tmp = simple_strtoul(p, &p, 0);
        if (!p || (*p && (*p != '\n')))
                return -EINVAL;

        if (tmp > O2NM_MAX_NODES || tmp == 0)
                return -ERANGE;

        reg->hr_blocks = (unsigned int)tmp;

        return count;
}

static ssize_t o2hb_region_dev_read(struct o2hb_region *reg,
                                    char *page)
{
        unsigned int ret = 0;

        if (reg->hr_bdev)
                ret = sprintf(page, "%s\n", reg->hr_dev_name);

        return ret;
}

static void o2hb_init_region_params(struct o2hb_region *reg)
{
        reg->hr_slots_per_page = PAGE_CACHE_SIZE >> reg->hr_block_bits;
        reg->hr_timeout_ms = O2HB_REGION_TIMEOUT_MS;

        mlog(ML_HEARTBEAT, "hr_start_block = %llu, hr_blocks = %u\n",
             reg->hr_start_block, reg->hr_blocks);
        mlog(ML_HEARTBEAT, "hr_block_bytes = %u, hr_block_bits = %u\n",
             reg->hr_block_bytes, reg->hr_block_bits);
        mlog(ML_HEARTBEAT, "hr_timeout_ms = %u\n", reg->hr_timeout_ms);
        mlog(ML_HEARTBEAT, "dead threshold = %u\n", o2hb_dead_threshold);
}

static int o2hb_map_slot_data(struct o2hb_region *reg)
{
        int i, j;
        unsigned int last_slot;
        unsigned int spp = reg->hr_slots_per_page;
        struct page *page;
        char *raw;
        struct o2hb_disk_slot *slot;

        reg->hr_tmp_block = kmalloc(reg->hr_block_bytes, GFP_KERNEL);
        if (reg->hr_tmp_block == NULL) {
                mlog_errno(-ENOMEM);
                return -ENOMEM;
        }

        reg->hr_slots = kcalloc(reg->hr_blocks,
                                sizeof(struct o2hb_disk_slot), GFP_KERNEL);
        if (reg->hr_slots == NULL) {
                mlog_errno(-ENOMEM);
                return -ENOMEM;
        }

        for(i = 0; i < reg->hr_blocks; i++) {
                slot = &reg->hr_slots[i];
                slot->ds_node_num = i;
                INIT_LIST_HEAD(&slot->ds_live_item);
                slot->ds_raw_block = NULL;
        }

        reg->hr_num_pages = (reg->hr_blocks + spp - 1) / spp;
        mlog(ML_HEARTBEAT, "Going to require %u pages to cover %u blocks "
                           "at %u blocks per page\n",
             reg->hr_num_pages, reg->hr_blocks, spp);

        reg->hr_slot_data = kcalloc(reg->hr_num_pages, sizeof(struct page *),
                                    GFP_KERNEL);
        if (!reg->hr_slot_data) {
                mlog_errno(-ENOMEM);
                return -ENOMEM;
        }

        for(i = 0; i < reg->hr_num_pages; i++) {
                page = alloc_page(GFP_KERNEL);
                if (!page) {
                        mlog_errno(-ENOMEM);
                        return -ENOMEM;
                }

                reg->hr_slot_data[i] = page;

                last_slot = i * spp;
                raw = page_address(page);
                for (j = 0;
                     (j < spp) && ((j + last_slot) < reg->hr_blocks);
                     j++) {
                        BUG_ON((j + last_slot) >= reg->hr_blocks);

                        slot = &reg->hr_slots[j + last_slot];
                        slot->ds_raw_block =
                                (struct o2hb_disk_heartbeat_block *) raw;

                        raw += reg->hr_block_bytes;
                }
        }

        return 0;
}

/* Read in all the slots available and populate the tracking
 * structures so that we can start with a baseline idea of what's
 * there. */
static int o2hb_populate_slot_data(struct o2hb_region *reg)
{
        int ret, i;
        struct o2hb_disk_slot *slot;
        struct o2hb_disk_heartbeat_block *hb_block;

        mlog_entry_void();

        ret = o2hb_read_slots(reg, reg->hr_blocks);
        if (ret) {
                mlog_errno(ret);
                goto out;
        }

        /* We only want to get an idea of the values initially in each
         * slot, so we do no verification - o2hb_check_slot will
         * actually determine if each configured slot is valid and
         * whether any values have changed. */
        for(i = 0; i < reg->hr_blocks; i++) {
                slot = &reg->hr_slots[i];
                hb_block = (struct o2hb_disk_heartbeat_block *) slot->ds_raw_block;

                /* Only fill the values that o2hb_check_slot uses to
                 * determine changing slots */
                slot->ds_last_time = le64_to_cpu(hb_block->hb_seq);
                slot->ds_last_generation = le64_to_cpu(hb_block->hb_generation);
        }

out:
        mlog_exit(ret);
        return ret;
}

/* this is acting as commit; we set up all of hr_bdev and hr_task or nothing */
static ssize_t o2hb_region_dev_write(struct o2hb_region *reg,
                                     const char *page,
                                     size_t count)
{
        struct task_struct *hb_task;
        long fd;
        int sectsize;
        char *p = (char *)page;
        struct file *filp = NULL;
        struct inode *inode = NULL;
        ssize_t ret = -EINVAL;

        if (reg->hr_bdev)
                goto out;

        /* We can't heartbeat without having had our node number
         * configured yet. */
        if (o2nm_this_node() == O2NM_MAX_NODES)
                goto out;

        fd = simple_strtol(p, &p, 0);
        if (!p || (*p && (*p != '\n')))
                goto out;

        if (fd < 0 || fd >= INT_MAX)
                goto out;

        filp = fget(fd);
        if (filp == NULL)
                goto out;

        if (reg->hr_blocks == 0 || reg->hr_start_block == 0 ||
            reg->hr_block_bytes == 0)
                goto out;

        inode = igrab(filp->f_mapping->host);
        if (inode == NULL)
                goto out;

        if (!S_ISBLK(inode->i_mode))
                goto out;

        reg->hr_bdev = I_BDEV(filp->f_mapping->host);
        ret = blkdev_get(reg->hr_bdev, FMODE_WRITE | FMODE_READ);
        if (ret) {
                reg->hr_bdev = NULL;
                goto out;
        }
        inode = NULL;

        bdevname(reg->hr_bdev, reg->hr_dev_name);

        sectsize = bdev_logical_block_size(reg->hr_bdev);
        if (sectsize != reg->hr_block_bytes) {
                mlog(ML_ERROR,
                     "blocksize %u incorrect for device, expected %d",
                     reg->hr_block_bytes, sectsize);
                ret = -EINVAL;
                goto out;
        }

        o2hb_init_region_params(reg);

        /* Generation of zero is invalid */
        do {
                get_random_bytes(&reg->hr_generation,
                                 sizeof(reg->hr_generation));
        } while (reg->hr_generation == 0);

        ret = o2hb_map_slot_data(reg);
        if (ret) {
                mlog_errno(ret);
                goto out;
        }

        ret = o2hb_populate_slot_data(reg);
        if (ret) {
                mlog_errno(ret);
                goto out;
        }

        INIT_DELAYED_WORK(&reg->hr_write_timeout_work, o2hb_write_timeout);

        /*
         * A node is considered live after it has beat LIVE_THRESHOLD
         * times.  We're not steady until we've given them a chance
         * _after_ our first read.
         */
        atomic_set(&reg->hr_steady_iterations, O2HB_LIVE_THRESHOLD + 1);

        hb_task = kthread_run(o2hb_thread, reg, "o2hb-%s",
                              reg->hr_item.ci_name);
        if (IS_ERR(hb_task)) {
                ret = PTR_ERR(hb_task);
                mlog_errno(ret);
                goto out;
        }

        spin_lock(&o2hb_live_lock);
        reg->hr_task = hb_task;
        spin_unlock(&o2hb_live_lock);

        ret = wait_event_interruptible(o2hb_steady_queue,
                                atomic_read(&reg->hr_steady_iterations) == 0);
        if (ret) {
                /* We got interrupted (hello ptrace!).  Clean up */
                spin_lock(&o2hb_live_lock);
                hb_task = reg->hr_task;
                reg->hr_task = NULL;
                spin_unlock(&o2hb_live_lock);

                if (hb_task)
                        kthread_stop(hb_task);
                goto out;
        }

        /* Ok, we were woken.  Make sure it wasn't by drop_item() */
        spin_lock(&o2hb_live_lock);
        hb_task = reg->hr_task;
        spin_unlock(&o2hb_live_lock);

        if (hb_task)
                ret = count;
        else
                ret = -EIO;

out:
        if (filp)
                fput(filp);
        if (inode)
                iput(inode);
        if (ret < 0) {
                if (reg->hr_bdev) {
                        blkdev_put(reg->hr_bdev, FMODE_READ|FMODE_WRITE);
                        reg->hr_bdev = NULL;
                }
        }
        return ret;
}

static ssize_t o2hb_region_pid_read(struct o2hb_region *reg,
                                      char *page)
{
        pid_t pid = 0;

        spin_lock(&o2hb_live_lock);
        if (reg->hr_task)
                pid = task_pid_nr(reg->hr_task);
        spin_unlock(&o2hb_live_lock);

        if (!pid)
                return 0;

        return sprintf(page, "%u\n", pid);
}

struct o2hb_region_attribute {
        struct configfs_attribute attr;
        ssize_t (*show)(struct o2hb_region *, char *);
        ssize_t (*store)(struct o2hb_region *, const char *, size_t);
};

static struct o2hb_region_attribute o2hb_region_attr_block_bytes = {
        .attr   = { .ca_owner = THIS_MODULE,
                    .ca_name = "block_bytes",
                    .ca_mode = S_IRUGO | S_IWUSR },
        .show   = o2hb_region_block_bytes_read,
        .store  = o2hb_region_block_bytes_write,
};

static struct o2hb_region_attribute o2hb_region_attr_start_block = {
        .attr   = { .ca_owner = THIS_MODULE,
                    .ca_name = "start_block",
                    .ca_mode = S_IRUGO | S_IWUSR },
        .show   = o2hb_region_start_block_read,
        .store  = o2hb_region_start_block_write,
};

static struct o2hb_region_attribute o2hb_region_attr_blocks = {
        .attr   = { .ca_owner = THIS_MODULE,
                    .ca_name = "blocks",
                    .ca_mode = S_IRUGO | S_IWUSR },
        .show   = o2hb_region_blocks_read,
        .store  = o2hb_region_blocks_write,
};

static struct o2hb_region_attribute o2hb_region_attr_dev = {
        .attr   = { .ca_owner = THIS_MODULE,
                    .ca_name = "dev",
                    .ca_mode = S_IRUGO | S_IWUSR },
        .show   = o2hb_region_dev_read,
        .store  = o2hb_region_dev_write,
};

static struct o2hb_region_attribute o2hb_region_attr_pid = {
       .attr   = { .ca_owner = THIS_MODULE,
                   .ca_name = "pid",
                   .ca_mode = S_IRUGO | S_IRUSR },
       .show   = o2hb_region_pid_read,
};

static struct configfs_attribute *o2hb_region_attrs[] = {
        &o2hb_region_attr_block_bytes.attr,
        &o2hb_region_attr_start_block.attr,
        &o2hb_region_attr_blocks.attr,
        &o2hb_region_attr_dev.attr,
        &o2hb_region_attr_pid.attr,
        NULL,
};

static ssize_t o2hb_region_show(struct config_item *item,
                                struct configfs_attribute *attr,
                                char *page)
{
        struct o2hb_region *reg = to_o2hb_region(item);
        struct o2hb_region_attribute *o2hb_region_attr =
                container_of(attr, struct o2hb_region_attribute, attr);
        ssize_t ret = 0;

        if (o2hb_region_attr->show)
                ret = o2hb_region_attr->show(reg, page);
        return ret;
}

static ssize_t o2hb_region_store(struct config_item *item,
                                 struct configfs_attribute *attr,
                                 const char *page, size_t count)
{
        struct o2hb_region *reg = to_o2hb_region(item);
        struct o2hb_region_attribute *o2hb_region_attr =
                container_of(attr, struct o2hb_region_attribute, attr);
        ssize_t ret = -EINVAL;

        if (o2hb_region_attr->store)
                ret = o2hb_region_attr->store(reg, page, count);
        return ret;
}

static struct configfs_item_operations o2hb_region_item_ops = {
        .release                = o2hb_region_release,
        .show_attribute         = o2hb_region_show,
        .store_attribute        = o2hb_region_store,
};

static struct config_item_type o2hb_region_type = {
        .ct_item_ops    = &o2hb_region_item_ops,
        .ct_attrs       = o2hb_region_attrs,
        .ct_owner       = THIS_MODULE,
};

/* heartbeat set */

struct o2hb_heartbeat_group {
        struct config_group hs_group;
        /* some stuff? */
};

static struct o2hb_heartbeat_group *to_o2hb_heartbeat_group(struct config_group *group)
{
        return group ?
                container_of(group, struct o2hb_heartbeat_group, hs_group)
                : NULL;
}

static struct config_item *o2hb_heartbeat_group_make_item(struct config_group *group,
                                                          const char *name)
{
        struct o2hb_region *reg = NULL;

        reg = kzalloc(sizeof(struct o2hb_region), GFP_KERNEL);
        if (reg == NULL)
                return ERR_PTR(-ENOMEM);

        config_item_init_type_name(&reg->hr_item, name, &o2hb_region_type);

        spin_lock(&o2hb_live_lock);
        list_add_tail(&reg->hr_all_item, &o2hb_all_regions);
        spin_unlock(&o2hb_live_lock);

        return &reg->hr_item;
}

static void o2hb_heartbeat_group_drop_item(struct config_group *group,
                                           struct config_item *item)
{
        struct task_struct *hb_task;
        struct o2hb_region *reg = to_o2hb_region(item);

        /* stop the thread when the user removes the region dir */
        spin_lock(&o2hb_live_lock);
        hb_task = reg->hr_task;
        reg->hr_task = NULL;
        spin_unlock(&o2hb_live_lock);

        if (hb_task)
                kthread_stop(hb_task);

        /*
         * If we're racing a dev_write(), we need to wake them.  They will
         * check reg->hr_task
         */
        if (atomic_read(&reg->hr_steady_iterations) != 0) {
                atomic_set(&reg->hr_steady_iterations, 0);
                wake_up(&o2hb_steady_queue);
        }

        config_item_put(item);
}

struct o2hb_heartbeat_group_attribute {
        struct configfs_attribute attr;
        ssize_t (*show)(struct o2hb_heartbeat_group *, char *);
        ssize_t (*store)(struct o2hb_heartbeat_group *, const char *, size_t);
};

static ssize_t o2hb_heartbeat_group_show(struct config_item *item,
                                         struct configfs_attribute *attr,
                                         char *page)
{
        struct o2hb_heartbeat_group *reg = to_o2hb_heartbeat_group(to_config_group(item));
        struct o2hb_heartbeat_group_attribute *o2hb_heartbeat_group_attr =
                container_of(attr, struct o2hb_heartbeat_group_attribute, attr);
        ssize_t ret = 0;

        if (o2hb_heartbeat_group_attr->show)
                ret = o2hb_heartbeat_group_attr->show(reg, page);
        return ret;
}

static ssize_t o2hb_heartbeat_group_store(struct config_item *item,
                                          struct configfs_attribute *attr,
                                          const char *page, size_t count)
{
        struct o2hb_heartbeat_group *reg = to_o2hb_heartbeat_group(to_config_group(item));
        struct o2hb_heartbeat_group_attribute *o2hb_heartbeat_group_attr =
                container_of(attr, struct o2hb_heartbeat_group_attribute, attr);
        ssize_t ret = -EINVAL;

        if (o2hb_heartbeat_group_attr->store)
                ret = o2hb_heartbeat_group_attr->store(reg, page, count);
        return ret;
}

static ssize_t o2hb_heartbeat_group_threshold_show(struct o2hb_heartbeat_group *group,
                                                     char *page)
{
        return sprintf(page, "%u\n", o2hb_dead_threshold);
}

static ssize_t o2hb_heartbeat_group_threshold_store(struct o2hb_heartbeat_group *group,
                                                    const char *page,
                                                    size_t count)
{
        unsigned long tmp;
        char *p = (char *)page;

        tmp = simple_strtoul(p, &p, 10);
        if (!p || (*p && (*p != '\n')))
                return -EINVAL;

        /* this will validate ranges for us. */
        o2hb_dead_threshold_set((unsigned int) tmp);

        return count;
}

static struct o2hb_heartbeat_group_attribute o2hb_heartbeat_group_attr_threshold = {
        .attr   = { .ca_owner = THIS_MODULE,
                    .ca_name = "dead_threshold",
                    .ca_mode = S_IRUGO | S_IWUSR },
        .show   = o2hb_heartbeat_group_threshold_show,
        .store  = o2hb_heartbeat_group_threshold_store,
};

static struct configfs_attribute *o2hb_heartbeat_group_attrs[] = {
        &o2hb_heartbeat_group_attr_threshold.attr,
        NULL,
};

static struct configfs_item_operations o2hb_hearbeat_group_item_ops = {
        .show_attribute         = o2hb_heartbeat_group_show,
        .store_attribute        = o2hb_heartbeat_group_store,
};

static struct configfs_group_operations o2hb_heartbeat_group_group_ops = {
        .make_item      = o2hb_heartbeat_group_make_item,
        .drop_item      = o2hb_heartbeat_group_drop_item,
};

static struct config_item_type o2hb_heartbeat_group_type = {
        .ct_group_ops   = &o2hb_heartbeat_group_group_ops,
        .ct_item_ops    = &o2hb_hearbeat_group_item_ops,
        .ct_attrs       = o2hb_heartbeat_group_attrs,
        .ct_owner       = THIS_MODULE,
};

/* this is just here to avoid touching group in heartbeat.h which the
 * entire damn world #includes */
struct config_group *o2hb_alloc_hb_set(void)
{
        struct o2hb_heartbeat_group *hs = NULL;
        struct config_group *ret = NULL;

        hs = kzalloc(sizeof(struct o2hb_heartbeat_group), GFP_KERNEL);
        if (hs == NULL)
                goto out;

        config_group_init_type_name(&hs->hs_group, "heartbeat",
                                    &o2hb_heartbeat_group_type);

        ret = &hs->hs_group;
out:
        if (ret == NULL)
                kfree(hs);
        return ret;
}

void o2hb_free_hb_set(struct config_group *group)
{
        struct o2hb_heartbeat_group *hs = to_o2hb_heartbeat_group(group);
        kfree(hs);
}

/* hb callback registration and issueing */

static struct o2hb_callback *hbcall_from_type(enum o2hb_callback_type type)
{
        if (type == O2HB_NUM_CB)
                return ERR_PTR(-EINVAL);

        return &o2hb_callbacks[type];
}

void o2hb_setup_callback(struct o2hb_callback_func *hc,
                         enum o2hb_callback_type type,
                         o2hb_cb_func *func,
                         void *data,
                         int priority)
{
        INIT_LIST_HEAD(&hc->hc_item);
        hc->hc_func = func;
        hc->hc_data = data;
        hc->hc_priority = priority;
        hc->hc_type = type;
        hc->hc_magic = O2HB_CB_MAGIC;
}
EXPORT_SYMBOL_GPL(o2hb_setup_callback);

static struct o2hb_region *o2hb_find_region(const char *region_uuid)
{
        struct o2hb_region *p, *reg = NULL;

        assert_spin_locked(&o2hb_live_lock);

        list_for_each_entry(p, &o2hb_all_regions, hr_all_item) {
                if (!strcmp(region_uuid, config_item_name(&p->hr_item))) {
                        reg = p;
                        break;
                }
        }

        return reg;
}

static int o2hb_region_get(const char *region_uuid)
{
        int ret = 0;
        struct o2hb_region *reg;

        spin_lock(&o2hb_live_lock);

        reg = o2hb_find_region(region_uuid);
        if (!reg)
                ret = -ENOENT;
        spin_unlock(&o2hb_live_lock);

        if (ret)
                goto out;

        ret = o2nm_depend_this_node();
        if (ret)
                goto out;

        ret = o2nm_depend_item(&reg->hr_item);
        if (ret)
                o2nm_undepend_this_node();

out:
        return ret;
}

static void o2hb_region_put(const char *region_uuid)
{
        struct o2hb_region *reg;

        spin_lock(&o2hb_live_lock);

        reg = o2hb_find_region(region_uuid);

        spin_unlock(&o2hb_live_lock);

        if (reg) {
                o2nm_undepend_item(&reg->hr_item);
                o2nm_undepend_this_node();
        }
}

int o2hb_register_callback(const char *region_uuid,
                           struct o2hb_callback_func *hc)
{
        struct o2hb_callback_func *tmp;
        struct list_head *iter;
        struct o2hb_callback *hbcall;
        int ret;

        BUG_ON(hc->hc_magic != O2HB_CB_MAGIC);
        BUG_ON(!list_empty(&hc->hc_item));

        hbcall = hbcall_from_type(hc->hc_type);
        if (IS_ERR(hbcall)) {
                ret = PTR_ERR(hbcall);
                goto out;
        }

        if (region_uuid) {
                ret = o2hb_region_get(region_uuid);
                if (ret)
                        goto out;
        }

        down_write(&o2hb_callback_sem);

        list_for_each(iter, &hbcall->list) {
                tmp = list_entry(iter, struct o2hb_callback_func, hc_item);
                if (hc->hc_priority < tmp->hc_priority) {
                        list_add_tail(&hc->hc_item, iter);
                        break;
                }
        }
        if (list_empty(&hc->hc_item))
                list_add_tail(&hc->hc_item, &hbcall->list);

        up_write(&o2hb_callback_sem);
        ret = 0;
out:
        mlog(ML_HEARTBEAT, "returning %d on behalf of %p for funcs %p\n",
             ret, __builtin_return_address(0), hc);
        return ret;
}
EXPORT_SYMBOL_GPL(o2hb_register_callback);

void o2hb_unregister_callback(const char *region_uuid,
                              struct o2hb_callback_func *hc)
{
        BUG_ON(hc->hc_magic != O2HB_CB_MAGIC);

        mlog(ML_HEARTBEAT, "on behalf of %p for funcs %p\n",
             __builtin_return_address(0), hc);

        /* XXX Can this happen _with_ a region reference? */
        if (list_empty(&hc->hc_item))
                return;

        if (region_uuid)
                o2hb_region_put(region_uuid);

        down_write(&o2hb_callback_sem);

        list_del_init(&hc->hc_item);

        up_write(&o2hb_callback_sem);
}
EXPORT_SYMBOL_GPL(o2hb_unregister_callback);

int o2hb_check_node_heartbeating(u8 node_num)
{
        unsigned long testing_map[BITS_TO_LONGS(O2NM_MAX_NODES)];

        o2hb_fill_node_map(testing_map, sizeof(testing_map));
        if (!test_bit(node_num, testing_map)) {
                mlog(ML_HEARTBEAT,
                     "node (%u) does not have heartbeating enabled.\n",
                     node_num);
                return 0;
        }

        return 1;
}
EXPORT_SYMBOL_GPL(o2hb_check_node_heartbeating);

int o2hb_check_node_heartbeating_from_callback(u8 node_num)
{
        unsigned long testing_map[BITS_TO_LONGS(O2NM_MAX_NODES)];

        o2hb_fill_node_map_from_callback(testing_map, sizeof(testing_map));
        if (!test_bit(node_num, testing_map)) {
                mlog(ML_HEARTBEAT,
                     "node (%u) does not have heartbeating enabled.\n",
                     node_num);
                return 0;
        }

        return 1;
}
EXPORT_SYMBOL_GPL(o2hb_check_node_heartbeating_from_callback);

/* Makes sure our local node is configured with a node number, and is
 * heartbeating. */
int o2hb_check_local_node_heartbeating(void)
{
        u8 node_num;

        /* if this node was set then we have networking */
        node_num = o2nm_this_node();
        if (node_num == O2NM_MAX_NODES) {
                mlog(ML_HEARTBEAT, "this node has not been configured.\n");
                return 0;
        }

        return o2hb_check_node_heartbeating(node_num);
}
EXPORT_SYMBOL_GPL(o2hb_check_local_node_heartbeating);

/*
 * this is just a hack until we get the plumbing which flips file systems
 * read only and drops the hb ref instead of killing the node dead.
 */
void o2hb_stop_all_regions(void)
{
        struct o2hb_region *reg;

        mlog(ML_ERROR, "stopping heartbeat on all active regions.\n");

        spin_lock(&o2hb_live_lock);

        list_for_each_entry(reg, &o2hb_all_regions, hr_all_item)
                reg->hr_unclean_stop = 1;

        spin_unlock(&o2hb_live_lock);
}
EXPORT_SYMBOL_GPL(o2hb_stop_all_regions);