// SPDX-License-Identifier: GPL-2.0-only
#include <linux/errno.h>
#include <linux/numa.h>
#include <linux/slab.h>
#include <linux/rculist.h>
#include <linux/threads.h>
#include <linux/preempt.h>
#include <linux/irqflags.h>
#include <linux/vmalloc.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/device-mapper.h>

#include "dm-core.h"
#include "dm-stats.h"

#define DM_MSG_PREFIX "stats"

static int dm_stat_need_rcu_barrier;

/*
 * Using 64-bit values to avoid overflow (which is a
 * problem that block/genhd.c's IO accounting has).
 */
struct dm_stat_percpu {
        unsigned long long sectors[2];
        unsigned long long ios[2];
        unsigned long long merges[2];
        unsigned long long ticks[2];
        unsigned long long io_ticks[2];
        unsigned long long io_ticks_total;
        unsigned long long time_in_queue;
        unsigned long long *histogram;
};

struct dm_stat_shared {
        atomic_t in_flight[2];
        unsigned long long stamp;
        struct dm_stat_percpu tmp;
};

struct dm_stat {
        struct list_head list_entry;
        int id;
        unsigned int stat_flags;
        size_t n_entries;
        sector_t start;
        sector_t end;
        sector_t step;
        unsigned int n_histogram_entries;
        unsigned long long *histogram_boundaries;
        const char *program_id;
        const char *aux_data;
        struct rcu_head rcu_head;
        size_t shared_alloc_size;
        size_t percpu_alloc_size;
        size_t histogram_alloc_size;
        struct dm_stat_percpu *stat_percpu[NR_CPUS];
        struct dm_stat_shared stat_shared[] __counted_by(n_entries);
};

#define STAT_PRECISE_TIMESTAMPS         1

struct dm_stats_last_position {
        sector_t last_sector;
        unsigned int last_rw;
};

#define DM_STAT_MAX_ENTRIES             8388608
#define DM_STAT_MAX_HISTOGRAM_ENTRIES   134217728

/*
 * A typo on the command line could possibly make the kernel run out of memory
 * and crash. To prevent the crash we account all used memory. We fail if we
 * exhaust 1/4 of all memory or 1/2 of vmalloc space.
 */
#define DM_STATS_MEMORY_FACTOR          4
#define DM_STATS_VMALLOC_FACTOR         2

static DEFINE_SPINLOCK(shared_memory_lock);

static unsigned long shared_memory_amount;

static bool __check_shared_memory(size_t alloc_size)
{
        size_t a;

        a = shared_memory_amount + alloc_size;
        if (a < shared_memory_amount)
                return false;
        if (a >> PAGE_SHIFT > totalram_pages() / DM_STATS_MEMORY_FACTOR)
                return false;
#ifdef CONFIG_MMU
        if (a > (VMALLOC_END - VMALLOC_START) / DM_STATS_VMALLOC_FACTOR)
                return false;
#endif
        return true;
}

static bool check_shared_memory(size_t alloc_size)
{
        bool ret;

        spin_lock_irq(&shared_memory_lock);

        ret = __check_shared_memory(alloc_size);

        spin_unlock_irq(&shared_memory_lock);

        return ret;
}

static bool claim_shared_memory(size_t alloc_size)
{
        spin_lock_irq(&shared_memory_lock);

        if (!__check_shared_memory(alloc_size)) {
                spin_unlock_irq(&shared_memory_lock);
                return false;
        }

        shared_memory_amount += alloc_size;

        spin_unlock_irq(&shared_memory_lock);

        return true;
}

static void free_shared_memory(size_t alloc_size)
{
        unsigned long flags;

        spin_lock_irqsave(&shared_memory_lock, flags);

        if (WARN_ON_ONCE(shared_memory_amount < alloc_size)) {
                spin_unlock_irqrestore(&shared_memory_lock, flags);
                DMCRIT("Memory usage accounting bug.");
                return;
        }

        shared_memory_amount -= alloc_size;

        spin_unlock_irqrestore(&shared_memory_lock, flags);
}

static void *dm_kvzalloc(size_t alloc_size, int node)
{
        void *p;

        if (!claim_shared_memory(alloc_size))
                return NULL;

        p = kvzalloc_node(alloc_size, GFP_KERNEL | __GFP_NOMEMALLOC, node);
        if (p)
                return p;

        free_shared_memory(alloc_size);

        return NULL;
}

static void dm_kvfree(void *ptr, size_t alloc_size)
{
        if (!ptr)
                return;

        free_shared_memory(alloc_size);

        kvfree(ptr);
}

static void dm_stat_free(struct rcu_head *head)
{
        int cpu;
        struct dm_stat *s = container_of(head, struct dm_stat, rcu_head);

        kfree(s->histogram_boundaries);
        kfree(s->program_id);
        kfree(s->aux_data);
        for_each_possible_cpu(cpu) {
                dm_kvfree(s->stat_percpu[cpu][0].histogram, s->histogram_alloc_size);
                dm_kvfree(s->stat_percpu[cpu], s->percpu_alloc_size);
        }
        dm_kvfree(s->stat_shared[0].tmp.histogram, s->histogram_alloc_size);
        dm_kvfree(s, s->shared_alloc_size);
}

static int dm_stat_in_flight(struct dm_stat_shared *shared)
{
        return atomic_read(&shared->in_flight[READ]) +
               atomic_read(&shared->in_flight[WRITE]);
}

int dm_stats_init(struct dm_stats *stats)
{
        int cpu;
        struct dm_stats_last_position *last;

        mutex_init(&stats->mutex);
        INIT_LIST_HEAD(&stats->list);
        stats->precise_timestamps = false;
        stats->last = alloc_percpu(struct dm_stats_last_position);
        if (!stats->last)
                return -ENOMEM;

        for_each_possible_cpu(cpu) {
                last = per_cpu_ptr(stats->last, cpu);
                last->last_sector = (sector_t)ULLONG_MAX;
                last->last_rw = UINT_MAX;
        }

        return 0;
}

void dm_stats_cleanup(struct dm_stats *stats)
{
        size_t ni;
        struct dm_stat *s;
        struct dm_stat_shared *shared;

        while (!list_empty(&stats->list)) {
                s = container_of(stats->list.next, struct dm_stat, list_entry);
                list_del(&s->list_entry);
                for (ni = 0; ni < s->n_entries; ni++) {
                        shared = &s->stat_shared[ni];
                        if (WARN_ON(dm_stat_in_flight(shared))) {
                                DMCRIT("leaked in-flight counter at index %lu "
                                       "(start %llu, end %llu, step %llu): reads %d, writes %d",
                                       (unsigned long)ni,
                                       (unsigned long long)s->start,
                                       (unsigned long long)s->end,
                                       (unsigned long long)s->step,
                                       atomic_read(&shared->in_flight[READ]),
                                       atomic_read(&shared->in_flight[WRITE]));
                        }
                        cond_resched();
                }
                dm_stat_free(&s->rcu_head);
        }
        free_percpu(stats->last);
        mutex_destroy(&stats->mutex);
}

static void dm_stats_recalc_precise_timestamps(struct dm_stats *stats)
{
        struct list_head *l;
        struct dm_stat *tmp_s;
        bool precise_timestamps = false;

        list_for_each(l, &stats->list) {
                tmp_s = container_of(l, struct dm_stat, list_entry);
                if (tmp_s->stat_flags & STAT_PRECISE_TIMESTAMPS) {
                        precise_timestamps = true;
                        break;
                }
        }
        stats->precise_timestamps = precise_timestamps;
}

static int dm_stats_create(struct dm_stats *stats, sector_t start, sector_t end,
                           sector_t step, unsigned int stat_flags,
                           unsigned int n_histogram_entries,
                           unsigned long long *histogram_boundaries,
                           const char *program_id, const char *aux_data,
                           void (*suspend_callback)(struct mapped_device *),
                           void (*resume_callback)(struct mapped_device *),
                           struct mapped_device *md)
{
        struct list_head *l;
        struct dm_stat *s, *tmp_s;
        sector_t n_entries;
        size_t ni;
        size_t shared_alloc_size;
        size_t percpu_alloc_size;
        size_t histogram_alloc_size;
        struct dm_stat_percpu *p;
        int cpu;
        int ret_id;
        int r;

        if (end < start || !step)
                return -EINVAL;

        n_entries = end - start;
        if (dm_sector_div64(n_entries, step))
                n_entries++;

        if (n_entries != (size_t)n_entries || !(size_t)(n_entries + 1))
                return -EOVERFLOW;

        if (n_entries > DM_STAT_MAX_ENTRIES)
                return -EOVERFLOW;

        shared_alloc_size = struct_size(s, stat_shared, n_entries);
        if ((shared_alloc_size - sizeof(struct dm_stat)) / sizeof(struct dm_stat_shared) != n_entries)
                return -EOVERFLOW;

        percpu_alloc_size = (size_t)n_entries * sizeof(struct dm_stat_percpu);
        if (percpu_alloc_size / sizeof(struct dm_stat_percpu) != n_entries)
                return -EOVERFLOW;

        histogram_alloc_size = (n_histogram_entries + 1) * (size_t)n_entries * sizeof(unsigned long long);
        if (histogram_alloc_size / (n_histogram_entries + 1) != (size_t)n_entries * sizeof(unsigned long long))
                return -EOVERFLOW;

        if ((n_histogram_entries + 1) * (size_t)n_entries > DM_STAT_MAX_HISTOGRAM_ENTRIES)
                return -EOVERFLOW;

        if (!check_shared_memory(shared_alloc_size + histogram_alloc_size +
                                 num_possible_cpus() * (percpu_alloc_size + histogram_alloc_size)))
                return -ENOMEM;

        s = dm_kvzalloc(shared_alloc_size, NUMA_NO_NODE);
        if (!s)
                return -ENOMEM;

        s->stat_flags = stat_flags;
        s->n_entries = n_entries;
        s->start = start;
        s->end = end;
        s->step = step;
        s->shared_alloc_size = shared_alloc_size;
        s->percpu_alloc_size = percpu_alloc_size;
        s->histogram_alloc_size = histogram_alloc_size;

        s->n_histogram_entries = n_histogram_entries;
        s->histogram_boundaries = kmemdup(histogram_boundaries,
                                          s->n_histogram_entries * sizeof(unsigned long long), GFP_KERNEL);
        if (!s->histogram_boundaries) {
                r = -ENOMEM;
                goto out;
        }

        s->program_id = kstrdup(program_id, GFP_KERNEL);
        if (!s->program_id) {
                r = -ENOMEM;
                goto out;
        }
        s->aux_data = kstrdup(aux_data, GFP_KERNEL);
        if (!s->aux_data) {
                r = -ENOMEM;
                goto out;
        }

        for (ni = 0; ni < n_entries; ni++) {
                atomic_set(&s->stat_shared[ni].in_flight[READ], 0);
                atomic_set(&s->stat_shared[ni].in_flight[WRITE], 0);
                cond_resched();
        }

        if (s->n_histogram_entries) {
                unsigned long long *hi;

                hi = dm_kvzalloc(s->histogram_alloc_size, NUMA_NO_NODE);
                if (!hi) {
                        r = -ENOMEM;
                        goto out;
                }
                for (ni = 0; ni < n_entries; ni++) {
                        s->stat_shared[ni].tmp.histogram = hi;
                        hi += s->n_histogram_entries + 1;
                        cond_resched();
                }
        }

        for_each_possible_cpu(cpu) {
                p = dm_kvzalloc(percpu_alloc_size, cpu_to_node(cpu));
                if (!p) {
                        r = -ENOMEM;
                        goto out;
                }
                s->stat_percpu[cpu] = p;
                if (s->n_histogram_entries) {
                        unsigned long long *hi;

                        hi = dm_kvzalloc(s->histogram_alloc_size, cpu_to_node(cpu));
                        if (!hi) {
                                r = -ENOMEM;
                                goto out;
                        }
                        for (ni = 0; ni < n_entries; ni++) {
                                p[ni].histogram = hi;
                                hi += s->n_histogram_entries + 1;
                                cond_resched();
                        }
                }
        }

        /*
         * Suspend/resume to make sure there is no i/o in flight,
         * so that newly created statistics will be exact.
         *
         * (note: we couldn't suspend earlier because we must not
         * allocate memory while suspended)
         */
        suspend_callback(md);

        mutex_lock(&stats->mutex);
        s->id = 0;
        list_for_each(l, &stats->list) {
                tmp_s = container_of(l, struct dm_stat, list_entry);
                if (WARN_ON(tmp_s->id < s->id)) {
                        r = -EINVAL;
                        goto out_unlock_resume;
                }
                if (tmp_s->id > s->id)
                        break;
                if (unlikely(s->id == INT_MAX)) {
                        r = -ENFILE;
                        goto out_unlock_resume;
                }
                s->id++;
        }
        ret_id = s->id;
        list_add_tail_rcu(&s->list_entry, l);

        dm_stats_recalc_precise_timestamps(stats);

        if (!static_key_enabled(&stats_enabled.key))
                static_branch_enable(&stats_enabled);

        mutex_unlock(&stats->mutex);

        resume_callback(md);

        return ret_id;

out_unlock_resume:
        mutex_unlock(&stats->mutex);
        resume_callback(md);
out:
        dm_stat_free(&s->rcu_head);
        return r;
}

static struct dm_stat *__dm_stats_find(struct dm_stats *stats, int id)
{
        struct dm_stat *s;

        list_for_each_entry(s, &stats->list, list_entry) {
                if (s->id > id)
                        break;
                if (s->id == id)
                        return s;
        }

        return NULL;
}

static int dm_stats_delete(struct dm_stats *stats, int id)
{
        struct dm_stat *s;
        int cpu;

        mutex_lock(&stats->mutex);

        s = __dm_stats_find(stats, id);
        if (!s) {
                mutex_unlock(&stats->mutex);
                return -ENOENT;
        }

        list_del_rcu(&s->list_entry);

        dm_stats_recalc_precise_timestamps(stats);

        mutex_unlock(&stats->mutex);

        /*
         * vfree can't be called from RCU callback
         */
        for_each_possible_cpu(cpu)
                if (is_vmalloc_addr(s->stat_percpu) ||
                    is_vmalloc_addr(s->stat_percpu[cpu][0].histogram))
                        goto do_sync_free;
        if (is_vmalloc_addr(s) ||
            is_vmalloc_addr(s->stat_shared[0].tmp.histogram)) {
do_sync_free:
                synchronize_rcu_expedited();
                dm_stat_free(&s->rcu_head);
        } else {
                WRITE_ONCE(dm_stat_need_rcu_barrier, 1);
                call_rcu(&s->rcu_head, dm_stat_free);
        }
        return 0;
}

static int dm_stats_list(struct dm_stats *stats, const char *program,
                         char *result, unsigned int maxlen)
{
        struct dm_stat *s;
        sector_t len;
        unsigned int sz = 0;

        /*
         * Output format:
         *   <region_id>: <start_sector>+<length> <step> <program_id> <aux_data>
         */

        mutex_lock(&stats->mutex);
        list_for_each_entry(s, &stats->list, list_entry) {
                if (!program || !strcmp(program, s->program_id)) {
                        len = s->end - s->start;
                        DMEMIT("%d: %llu+%llu %llu %s %s", s->id,
                                (unsigned long long)s->start,
                                (unsigned long long)len,
                                (unsigned long long)s->step,
                                s->program_id,
                                s->aux_data);
                        if (s->stat_flags & STAT_PRECISE_TIMESTAMPS)
                                DMEMIT(" precise_timestamps");
                        if (s->n_histogram_entries) {
                                unsigned int i;

                                DMEMIT(" histogram:");
                                for (i = 0; i < s->n_histogram_entries; i++) {
                                        if (i)
                                                DMEMIT(",");
                                        DMEMIT("%llu", s->histogram_boundaries[i]);
                                }
                        }
                        DMEMIT("\n");
                }
                cond_resched();
        }
        mutex_unlock(&stats->mutex);

        return 1;
}

static void dm_stat_round(struct dm_stat *s, struct dm_stat_shared *shared,
                          struct dm_stat_percpu *p)
{
        /*
         * This is racy, but so is part_round_stats_single.
         */
        unsigned long long now, difference;
        unsigned int in_flight_read, in_flight_write;

        if (likely(!(s->stat_flags & STAT_PRECISE_TIMESTAMPS)))
                now = jiffies;
        else
                now = ktime_to_ns(ktime_get());

        difference = now - shared->stamp;
        if (!difference)
                return;

        in_flight_read = (unsigned int)atomic_read(&shared->in_flight[READ]);
        in_flight_write = (unsigned int)atomic_read(&shared->in_flight[WRITE]);
        if (in_flight_read)
                p->io_ticks[READ] += difference;
        if (in_flight_write)
                p->io_ticks[WRITE] += difference;
        if (in_flight_read + in_flight_write) {
                p->io_ticks_total += difference;
                p->time_in_queue += (in_flight_read + in_flight_write) * difference;
        }
        shared->stamp = now;
}

static void dm_stat_for_entry(struct dm_stat *s, size_t entry,
                              int idx, sector_t len,
                              struct dm_stats_aux *stats_aux, bool end,
                              unsigned long duration_jiffies)
{
        struct dm_stat_shared *shared = &s->stat_shared[entry];
        struct dm_stat_percpu *p;

        /*
         * For strict correctness we should use local_irq_save/restore
         * instead of preempt_disable/enable.
         *
         * preempt_disable/enable is racy if the driver finishes bios
         * from non-interrupt context as well as from interrupt context
         * or from more different interrupts.
         *
         * On 64-bit architectures the race only results in not counting some
         * events, so it is acceptable.  On 32-bit architectures the race could
         * cause the counter going off by 2^32, so we need to do proper locking
         * there.
         *
         * part_stat_lock()/part_stat_unlock() have this race too.
         */
#if BITS_PER_LONG == 32
        unsigned long flags;

        local_irq_save(flags);
#else
        preempt_disable();
#endif
        p = &s->stat_percpu[smp_processor_id()][entry];

        if (!end) {
                dm_stat_round(s, shared, p);
                atomic_inc(&shared->in_flight[idx]);
        } else {
                unsigned long long duration;

                dm_stat_round(s, shared, p);
                atomic_dec(&shared->in_flight[idx]);
                p->sectors[idx] += len;
                p->ios[idx] += 1;
                p->merges[idx] += stats_aux->merged;
                if (!(s->stat_flags & STAT_PRECISE_TIMESTAMPS)) {
                        p->ticks[idx] += duration_jiffies;
                        duration = jiffies_to_msecs(duration_jiffies);
                } else {
                        p->ticks[idx] += stats_aux->duration_ns;
                        duration = stats_aux->duration_ns;
                }
                if (s->n_histogram_entries) {
                        unsigned int lo = 0, hi = s->n_histogram_entries + 1;

                        while (lo + 1 < hi) {
                                unsigned int mid = (lo + hi) / 2;

                                if (s->histogram_boundaries[mid - 1] > duration)
                                        hi = mid;
                                else
                                        lo = mid;
                        }
                        p->histogram[lo]++;
                }
        }

#if BITS_PER_LONG == 32
        local_irq_restore(flags);
#else
        preempt_enable();
#endif
}

static void __dm_stat_bio(struct dm_stat *s, int bi_rw,
                          sector_t bi_sector, sector_t end_sector,
                          bool end, unsigned long duration_jiffies,
                          struct dm_stats_aux *stats_aux)
{
        sector_t rel_sector, offset, todo, fragment_len;
        size_t entry;

        if (end_sector <= s->start || bi_sector >= s->end)
                return;
        if (unlikely(bi_sector < s->start)) {
                rel_sector = 0;
                todo = end_sector - s->start;
        } else {
                rel_sector = bi_sector - s->start;
                todo = end_sector - bi_sector;
        }
        if (unlikely(end_sector > s->end))
                todo -= (end_sector - s->end);

        offset = dm_sector_div64(rel_sector, s->step);
        entry = rel_sector;
        do {
                if (WARN_ON_ONCE(entry >= s->n_entries)) {
                        DMCRIT("Invalid area access in region id %d", s->id);
                        return;
                }
                fragment_len = todo;
                if (fragment_len > s->step - offset)
                        fragment_len = s->step - offset;
                dm_stat_for_entry(s, entry, bi_rw, fragment_len,
                                  stats_aux, end, duration_jiffies);
                todo -= fragment_len;
                entry++;
                offset = 0;
        } while (unlikely(todo != 0));
}

void dm_stats_account_io(struct dm_stats *stats, unsigned long bi_rw,
                         sector_t bi_sector, unsigned int bi_sectors, bool end,
                         unsigned long start_time,
                         struct dm_stats_aux *stats_aux)
{
        struct dm_stat *s;
        sector_t end_sector;
        struct dm_stats_last_position *last;
        bool got_precise_time;
        unsigned long duration_jiffies = 0;

        if (unlikely(!bi_sectors))
                return;

        end_sector = bi_sector + bi_sectors;

        if (!end) {
                /*
                 * A race condition can at worst result in the merged flag being
                 * misrepresented, so we don't have to disable preemption here.
                 */
                last = raw_cpu_ptr(stats->last);
                stats_aux->merged =
                        bi_sector == READ_ONCE(last->last_sector) &&
                                (bi_rw == WRITE) == (READ_ONCE(last->last_rw) == WRITE);
                WRITE_ONCE(last->last_sector, end_sector);
                WRITE_ONCE(last->last_rw, bi_rw);
        } else
                duration_jiffies = jiffies - start_time;

        rcu_read_lock();

        got_precise_time = false;
        list_for_each_entry_rcu(s, &stats->list, list_entry) {
                if (s->stat_flags & STAT_PRECISE_TIMESTAMPS && !got_precise_time) {
                        /* start (!end) duration_ns is set by DM core's alloc_io() */
                        if (end)
                                stats_aux->duration_ns = ktime_to_ns(ktime_get()) - stats_aux->duration_ns;
                        got_precise_time = true;
                }
                __dm_stat_bio(s, bi_rw, bi_sector, end_sector, end, duration_jiffies, stats_aux);
        }

        rcu_read_unlock();
}

static void __dm_stat_init_temporary_percpu_totals(struct dm_stat_shared *shared,
                                                   struct dm_stat *s, size_t x)
{
        int cpu;
        struct dm_stat_percpu *p;

        local_irq_disable();
        p = &s->stat_percpu[smp_processor_id()][x];
        dm_stat_round(s, shared, p);
        local_irq_enable();

        shared->tmp.sectors[READ] = 0;
        shared->tmp.sectors[WRITE] = 0;
        shared->tmp.ios[READ] = 0;
        shared->tmp.ios[WRITE] = 0;
        shared->tmp.merges[READ] = 0;
        shared->tmp.merges[WRITE] = 0;
        shared->tmp.ticks[READ] = 0;
        shared->tmp.ticks[WRITE] = 0;
        shared->tmp.io_ticks[READ] = 0;
        shared->tmp.io_ticks[WRITE] = 0;
        shared->tmp.io_ticks_total = 0;
        shared->tmp.time_in_queue = 0;

        if (s->n_histogram_entries)
                memset(shared->tmp.histogram, 0, (s->n_histogram_entries + 1) * sizeof(unsigned long long));

        for_each_possible_cpu(cpu) {
                p = &s->stat_percpu[cpu][x];
                shared->tmp.sectors[READ] += READ_ONCE(p->sectors[READ]);
                shared->tmp.sectors[WRITE] += READ_ONCE(p->sectors[WRITE]);
                shared->tmp.ios[READ] += READ_ONCE(p->ios[READ]);
                shared->tmp.ios[WRITE] += READ_ONCE(p->ios[WRITE]);
                shared->tmp.merges[READ] += READ_ONCE(p->merges[READ]);
                shared->tmp.merges[WRITE] += READ_ONCE(p->merges[WRITE]);
                shared->tmp.ticks[READ] += READ_ONCE(p->ticks[READ]);
                shared->tmp.ticks[WRITE] += READ_ONCE(p->ticks[WRITE]);
                shared->tmp.io_ticks[READ] += READ_ONCE(p->io_ticks[READ]);
                shared->tmp.io_ticks[WRITE] += READ_ONCE(p->io_ticks[WRITE]);
                shared->tmp.io_ticks_total += READ_ONCE(p->io_ticks_total);
                shared->tmp.time_in_queue += READ_ONCE(p->time_in_queue);
                if (s->n_histogram_entries) {
                        unsigned int i;

                        for (i = 0; i < s->n_histogram_entries + 1; i++)
                                shared->tmp.histogram[i] += READ_ONCE(p->histogram[i]);
                }
        }
}

static void __dm_stat_clear(struct dm_stat *s, size_t idx_start, size_t idx_end,
                            bool init_tmp_percpu_totals)
{
        size_t x;
        struct dm_stat_shared *shared;
        struct dm_stat_percpu *p;

        for (x = idx_start; x < idx_end; x++) {
                shared = &s->stat_shared[x];
                if (init_tmp_percpu_totals)
                        __dm_stat_init_temporary_percpu_totals(shared, s, x);
                local_irq_disable();
                p = &s->stat_percpu[smp_processor_id()][x];
                p->sectors[READ] -= shared->tmp.sectors[READ];
                p->sectors[WRITE] -= shared->tmp.sectors[WRITE];
                p->ios[READ] -= shared->tmp.ios[READ];
                p->ios[WRITE] -= shared->tmp.ios[WRITE];
                p->merges[READ] -= shared->tmp.merges[READ];
                p->merges[WRITE] -= shared->tmp.merges[WRITE];
                p->ticks[READ] -= shared->tmp.ticks[READ];
                p->ticks[WRITE] -= shared->tmp.ticks[WRITE];
                p->io_ticks[READ] -= shared->tmp.io_ticks[READ];
                p->io_ticks[WRITE] -= shared->tmp.io_ticks[WRITE];
                p->io_ticks_total -= shared->tmp.io_ticks_total;
                p->time_in_queue -= shared->tmp.time_in_queue;
                local_irq_enable();
                if (s->n_histogram_entries) {
                        unsigned int i;

                        for (i = 0; i < s->n_histogram_entries + 1; i++) {
                                local_irq_disable();
                                p = &s->stat_percpu[smp_processor_id()][x];
                                p->histogram[i] -= shared->tmp.histogram[i];
                                local_irq_enable();
                        }
                }
                cond_resched();
        }
}

static int dm_stats_clear(struct dm_stats *stats, int id)
{
        struct dm_stat *s;

        mutex_lock(&stats->mutex);

        s = __dm_stats_find(stats, id);
        if (!s) {
                mutex_unlock(&stats->mutex);
                return -ENOENT;
        }

        __dm_stat_clear(s, 0, s->n_entries, true);

        mutex_unlock(&stats->mutex);

        return 1;
}

/*
 * This is like jiffies_to_msec, but works for 64-bit values.
 */
static unsigned long long dm_jiffies_to_msec64(struct dm_stat *s, unsigned long long j)
{
        unsigned long long result;
        unsigned int mult;

        if (s->stat_flags & STAT_PRECISE_TIMESTAMPS)
                return j;

        result = 0;
        if (j)
                result = jiffies_to_msecs(j & 0x3fffff);
        if (j >= 1 << 22) {
                mult = jiffies_to_msecs(1 << 22);
                result += (unsigned long long)mult * ((j >> 22) & 0x3fffff);
        }
        if (j >= 1ULL << 44)
                result += (unsigned long long)mult * (unsigned long long)(1 << 22) * (j >> 44);

        return result;
}

static int dm_stats_print(struct dm_stats *stats, int id,
                          size_t idx_start, size_t idx_len,
                          bool clear, char *result, unsigned int maxlen)
{
        unsigned int sz = 0;
        struct dm_stat *s;
        size_t x;
        sector_t start, end, step;
        size_t idx_end;
        struct dm_stat_shared *shared;

        /*
         * Output format:
         *   <start_sector>+<length> counters
         */

        mutex_lock(&stats->mutex);

        s = __dm_stats_find(stats, id);
        if (!s) {
                mutex_unlock(&stats->mutex);
                return -ENOENT;
        }

        idx_end = idx_start + idx_len;
        if (idx_end < idx_start ||
            idx_end > s->n_entries)
                idx_end = s->n_entries;

        if (idx_start > idx_end)
                idx_start = idx_end;

        step = s->step;
        start = s->start + (step * idx_start);

        for (x = idx_start; x < idx_end; x++, start = end) {
                shared = &s->stat_shared[x];
                end = start + step;
                if (unlikely(end > s->end))
                        end = s->end;

                __dm_stat_init_temporary_percpu_totals(shared, s, x);

                DMEMIT("%llu+%llu %llu %llu %llu %llu %llu %llu %llu %llu %d %llu %llu %llu %llu",
                       (unsigned long long)start,
                       (unsigned long long)step,
                       shared->tmp.ios[READ],
                       shared->tmp.merges[READ],
                       shared->tmp.sectors[READ],
                       dm_jiffies_to_msec64(s, shared->tmp.ticks[READ]),
                       shared->tmp.ios[WRITE],
                       shared->tmp.merges[WRITE],
                       shared->tmp.sectors[WRITE],
                       dm_jiffies_to_msec64(s, shared->tmp.ticks[WRITE]),
                       dm_stat_in_flight(shared),
                       dm_jiffies_to_msec64(s, shared->tmp.io_ticks_total),
                       dm_jiffies_to_msec64(s, shared->tmp.time_in_queue),
                       dm_jiffies_to_msec64(s, shared->tmp.io_ticks[READ]),
                       dm_jiffies_to_msec64(s, shared->tmp.io_ticks[WRITE]));
                if (s->n_histogram_entries) {
                        unsigned int i;

                        for (i = 0; i < s->n_histogram_entries + 1; i++)
                                DMEMIT("%s%llu", !i ? " " : ":", shared->tmp.histogram[i]);
                }
                DMEMIT("\n");

                if (unlikely(sz + 1 >= maxlen))
                        goto buffer_overflow;

                cond_resched();
        }

        if (clear)
                __dm_stat_clear(s, idx_start, idx_end, false);

buffer_overflow:
        mutex_unlock(&stats->mutex);

        return 1;
}

static int dm_stats_set_aux(struct dm_stats *stats, int id, const char *aux_data)
{
        struct dm_stat *s;
        const char *new_aux_data;

        mutex_lock(&stats->mutex);

        s = __dm_stats_find(stats, id);
        if (!s) {
                mutex_unlock(&stats->mutex);
                return -ENOENT;
        }

        new_aux_data = kstrdup(aux_data, GFP_KERNEL);
        if (!new_aux_data) {
                mutex_unlock(&stats->mutex);
                return -ENOMEM;
        }

        kfree(s->aux_data);
        s->aux_data = new_aux_data;

        mutex_unlock(&stats->mutex);

        return 0;
}

static int parse_histogram(const char *h, unsigned int *n_histogram_entries,
                           unsigned long long **histogram_boundaries)
{
        const char *q;
        unsigned int n;
        unsigned long long last;

        *n_histogram_entries = 1;
        for (q = h; *q; q++)
                if (*q == ',')
                        (*n_histogram_entries)++;

        *histogram_boundaries = kmalloc_objs(unsigned long long,
                                             *n_histogram_entries);
        if (!*histogram_boundaries)
                return -ENOMEM;

        n = 0;
        last = 0;
        while (1) {
                unsigned long long hi;
                int s;
                char ch;

                s = sscanf(h, "%llu%c", &hi, &ch);
                if (!s || (s == 2 && ch != ','))
                        return -EINVAL;
                if (hi <= last)
                        return -EINVAL;
                last = hi;
                (*histogram_boundaries)[n] = hi;
                if (s == 1)
                        return 0;
                h = strchr(h, ',') + 1;
                n++;
        }
}

static int message_stats_create(struct mapped_device *md,
                                unsigned int argc, char **argv,
                                char *result, unsigned int maxlen)
{
        int r;
        int id;
        char dummy;
        unsigned long long start, end, len, step;
        unsigned int divisor;
        const char *program_id, *aux_data;
        unsigned int stat_flags = 0;
        unsigned int n_histogram_entries = 0;
        unsigned long long *histogram_boundaries = NULL;
        struct dm_arg_set as, as_backup;
        const char *a;
        unsigned int feature_args;

        /*
         * Input format:
         *   <range> <step> [<extra_parameters> <parameters>] [<program_id> [<aux_data>]]
         */

        if (argc < 3)
                goto ret_einval;

        as.argc = argc;
        as.argv = argv;
        dm_consume_args(&as, 1);

        a = dm_shift_arg(&as);
        if (!strcmp(a, "-")) {
                start = 0;
                len = dm_get_size(md);
                if (!len)
                        len = 1;
        } else if (sscanf(a, "%llu+%llu%c", &start, &len, &dummy) != 2 ||
                   start != (sector_t)start || len != (sector_t)len)
                goto ret_einval;

        end = start + len;
        if (start >= end)
                goto ret_einval;

        a = dm_shift_arg(&as);
        if (sscanf(a, "/%u%c", &divisor, &dummy) == 1) {
                if (!divisor)
                        return -EINVAL;
                step = end - start;
                if (do_div(step, divisor))
                        step++;
                if (!step)
                        step = 1;
        } else if (sscanf(a, "%llu%c", &step, &dummy) != 1 ||
                   step != (sector_t)step || !step)
                goto ret_einval;

        as_backup = as;
        a = dm_shift_arg(&as);
        if (a && sscanf(a, "%u%c", &feature_args, &dummy) == 1) {
                while (feature_args--) {
                        a = dm_shift_arg(&as);
                        if (!a)
                                goto ret_einval;
                        if (!strcasecmp(a, "precise_timestamps"))
                                stat_flags |= STAT_PRECISE_TIMESTAMPS;
                        else if (!strncasecmp(a, "histogram:", 10)) {
                                if (n_histogram_entries)
                                        goto ret_einval;
                                r = parse_histogram(a + 10, &n_histogram_entries, &histogram_boundaries);
                                if (r)
                                        goto ret;
                        } else
                                goto ret_einval;
                }
        } else {
                as = as_backup;
        }

        program_id = "-";
        aux_data = "-";

        a = dm_shift_arg(&as);
        if (a)
                program_id = a;

        a = dm_shift_arg(&as);
        if (a)
                aux_data = a;

        if (as.argc)
                goto ret_einval;

        /*
         * If a buffer overflow happens after we created the region,
         * it's too late (the userspace would retry with a larger
         * buffer, but the region id that caused the overflow is already
         * leaked).  So we must detect buffer overflow in advance.
         */
        snprintf(result, maxlen, "%d", INT_MAX);
        if (dm_message_test_buffer_overflow(result, maxlen)) {
                r = 1;
                goto ret;
        }

        id = dm_stats_create(dm_get_stats(md), start, end, step, stat_flags,
                             n_histogram_entries, histogram_boundaries, program_id, aux_data,
                             dm_internal_suspend_fast, dm_internal_resume_fast, md);
        if (id < 0) {
                r = id;
                goto ret;
        }

        snprintf(result, maxlen, "%d", id);

        r = 1;
        goto ret;

ret_einval:
        r = -EINVAL;
ret:
        kfree(histogram_boundaries);
        return r;
}

static int message_stats_delete(struct mapped_device *md,
                                unsigned int argc, char **argv)
{
        int id;
        char dummy;

        if (argc != 2)
                return -EINVAL;

        if (sscanf(argv[1], "%d%c", &id, &dummy) != 1 || id < 0)
                return -EINVAL;

        return dm_stats_delete(dm_get_stats(md), id);
}

static int message_stats_clear(struct mapped_device *md,
                               unsigned int argc, char **argv)
{
        int id;
        char dummy;

        if (argc != 2)
                return -EINVAL;

        if (sscanf(argv[1], "%d%c", &id, &dummy) != 1 || id < 0)
                return -EINVAL;

        return dm_stats_clear(dm_get_stats(md), id);
}

static int message_stats_list(struct mapped_device *md,
                              unsigned int argc, char **argv,
                              char *result, unsigned int maxlen)
{
        int r;
        const char *program = NULL;

        if (argc < 1 || argc > 2)
                return -EINVAL;

        if (argc > 1) {
                program = kstrdup(argv[1], GFP_KERNEL);
                if (!program)
                        return -ENOMEM;
        }

        r = dm_stats_list(dm_get_stats(md), program, result, maxlen);

        kfree(program);

        return r;
}

static int message_stats_print(struct mapped_device *md,
                               unsigned int argc, char **argv, bool clear,
                               char *result, unsigned int maxlen)
{
        int id;
        char dummy;
        unsigned long idx_start = 0, idx_len = ULONG_MAX;

        if (argc != 2 && argc != 4)
                return -EINVAL;

        if (sscanf(argv[1], "%d%c", &id, &dummy) != 1 || id < 0)
                return -EINVAL;

        if (argc > 3) {
                if (strcmp(argv[2], "-") &&
                    sscanf(argv[2], "%lu%c", &idx_start, &dummy) != 1)
                        return -EINVAL;
                if (strcmp(argv[3], "-") &&
                    sscanf(argv[3], "%lu%c", &idx_len, &dummy) != 1)
                        return -EINVAL;
        }

        return dm_stats_print(dm_get_stats(md), id, idx_start, idx_len, clear,
                              result, maxlen);
}

static int message_stats_set_aux(struct mapped_device *md,
                                 unsigned int argc, char **argv)
{
        int id;
        char dummy;

        if (argc != 3)
                return -EINVAL;

        if (sscanf(argv[1], "%d%c", &id, &dummy) != 1 || id < 0)
                return -EINVAL;

        return dm_stats_set_aux(dm_get_stats(md), id, argv[2]);
}

int dm_stats_message(struct mapped_device *md, unsigned int argc, char **argv,
                     char *result, unsigned int maxlen)
{
        int r;

        /* All messages here must start with '@' */
        if (!strcasecmp(argv[0], "@stats_create"))
                r = message_stats_create(md, argc, argv, result, maxlen);
        else if (!strcasecmp(argv[0], "@stats_delete"))
                r = message_stats_delete(md, argc, argv);
        else if (!strcasecmp(argv[0], "@stats_clear"))
                r = message_stats_clear(md, argc, argv);
        else if (!strcasecmp(argv[0], "@stats_list"))
                r = message_stats_list(md, argc, argv, result, maxlen);
        else if (!strcasecmp(argv[0], "@stats_print"))
                r = message_stats_print(md, argc, argv, false, result, maxlen);
        else if (!strcasecmp(argv[0], "@stats_print_clear"))
                r = message_stats_print(md, argc, argv, true, result, maxlen);
        else if (!strcasecmp(argv[0], "@stats_set_aux"))
                r = message_stats_set_aux(md, argc, argv);
        else
                return 2; /* this wasn't a stats message */

        if (r == -EINVAL)
                DMCRIT("Invalid parameters for message %s", argv[0]);

        return r;
}

int __init dm_statistics_init(void)
{
        shared_memory_amount = 0;
        dm_stat_need_rcu_barrier = 0;
        return 0;
}

void dm_statistics_exit(void)
{
        if (dm_stat_need_rcu_barrier)
                rcu_barrier();
        if (WARN_ON(shared_memory_amount))
                DMCRIT("shared_memory_amount leaked: %lu", shared_memory_amount);
}

module_param_named(stats_current_allocated_bytes, shared_memory_amount, ulong, 0444);
MODULE_PARM_DESC(stats_current_allocated_bytes, "Memory currently used by statistics");