/*
 * Copyright (c) 2019 Tom Marshall <tdm.code@gmail.com>
 *
 * 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., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA. 
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/device-mapper.h>
#include <linux/workqueue.h>
#include <linux/mutex.h>

#include <linux/lz4.h>

#include <linux/dm-compress.h>

struct pbat {
    struct list_head            list;
    u32                         zone;
    struct mutex                reflock;
    unsigned int                ref;

    struct mutex                lock;
    struct cbd_params*          params;
    bool                        full;
    u32                         last_alloc;
    struct page**               pagev;
    u8*                         buf;
};

static bool
pbat_ctr(struct pbat* pbat,
         struct cbd_params* params)
{
    u32 nr_pages = pbat_len(params);

    memset(pbat, 0, sizeof(struct pbat));
    INIT_LIST_HEAD(&pbat->list);
    pbat->zone = ZONE_NONE;
    mutex_init(&pbat->reflock);
    pbat->ref = 0;
    mutex_init(&pbat->lock);
    pbat->params = params;
    pbat->full = false;
    pbat->last_alloc = 0;
    pbat->pagev = kzalloc(nr_pages * sizeof(struct page*), GFP_KERNEL);
    if (!pbat->pagev) {
        return false;
    }
    if (!cbd_alloc_pagev(pbat->pagev, nr_pages)) {
        return false;
    }
    pbat->buf = vmap(pbat->pagev, nr_pages, VM_MAP, PAGE_KERNEL);
    if (!pbat->buf) {
        return false;
    }

    return true;
}

static void
pbat_dtr(struct pbat* pbat)
{
    u32 nr_pages = pbat_len(pbat->params);
    u32 n;

    for (n = 0; n < nr_pages; ++n) {
        lock_page(pbat->pagev[n]);
    }
    vunmap(pbat->buf);
    pbat->buf = NULL;
    cbd_free_pagev(pbat->pagev, nr_pages);
    kfree(pbat->pagev);
    pbat->pagev = NULL;
}

static bool
pbat_error(struct pbat* pbat)
{
    return PageError(pbat->pagev[0]);
}

static int
pbat_flush(struct pbat* pbat)
{
    int ret = 0;
    u32 nr_pages = pbat_len(pbat->params);
    u32 n;
    u64 pblk;

    mutex_lock(&pbat->lock);
    if (!PageDirty(pbat->pagev[0])) {
        goto unlock;
    }
    if (pbat_error(pbat)) {
        ret = -EIO;
        goto unlock;
    }
    pblk = pbat_off(pbat->params, pbat->zone);
    pblk_write(pbat->params->priv, pblk, nr_pages, pbat->pagev);
    mutex_unlock(&pbat->lock);

    return ret;

unlock:
    for (n = 0; n < nr_pages; ++n) {
        unlock_page(pbat->pagev[n]);
    }
    mutex_unlock(&pbat->lock);

    return ret;
}

static int
pbat_read(struct pbat* pbat)
{
    int ret = 0;
    u32 nr_pages = pbat_len(pbat->params);
    u64 pblk;

    /* XXX: can't happen because pbatcache will not use a page with an error */
    if (PageError(pbat->pagev[0])) {
        return -EIO;
    }
    pblk = pbat_off(pbat->params, pbat->zone);
    ret = pblk_read_wait(pbat->params->priv, pblk, nr_pages, pbat->pagev);

    return ret;
}

static int
pbat_reset(struct pbat* pbat, u32 zone)
{
    int ret = 0;
    u32 nr_pages = pbat_len(pbat->params);
    u32 n;

    for (n = 0; n < nr_pages; ++n) {
        lock_page(pbat->pagev[n]);
    }
    if (pbat->zone != zone) {
        pbat->zone = zone;
        pbat->full = false;
        pbat->last_alloc = 0;
        ret = pbat_read(pbat);
    }

    if (ret) {
        for (n = 0; n < nr_pages; ++n) {
            unlock_page(pbat->pagev[n]);
        }
        pbat->zone = ZONE_NONE;
    }

    return ret;
}

u32
pbat_zone(struct pbat* pbat)
{
    return pbat->zone;
}

u64
pbat_alloc(struct pbat* pbat)
{
    u32 pblk_count = pbat_len(pbat->params) * PBLK_SIZE_BITS;
    u32 idx;
    u64 pblk;

    mutex_lock(&pbat->lock);
    if (pbat->full) {
        pblk = PBLK_NONE;
        goto out;
    }
    idx = cbd_bitmap_alloc(pbat->buf, pblk_count, pbat->last_alloc);
    if (idx == pblk_count) {
        pbat->full = true;
        pblk = PBLK_NONE;
        goto out;
    }
    pbat->last_alloc = idx;
    pblk = idx + zone_data_off(pbat->params, pbat->zone);
    SetPageDirty(pbat->pagev[0]);

out:
    mutex_unlock(&pbat->lock);
    return pblk;
}

int
pbat_free(struct pbat* pbat, u64 pblk)
{
    u32 pblk_count = pbat_len(pbat->params) * PBLK_SIZE_BITS;
    u32 zone;
    u32 idx;

    zone = zone_for_pblk(pbat->params, pblk);
    BUG_ON(zone != pbat->zone);
    if (pblk < zone_data_off(pbat->params, zone)) {
        printk(KERN_ERR "%s: pblk in metadata\n", __func__);
        return -EINVAL;
    }
    idx = pblk - zone_data_off(pbat->params, zone);
    BUG_ON(idx >= pblk_count);
    mutex_lock(&pbat->lock);
    cbd_bitmap_free(pbat->buf, idx);
    pbat->full = false;
    SetPageDirty(pbat->pagev[0]);
    mutex_unlock(&pbat->lock);

    return 0;
}

struct pbatcache {
    struct mutex                lock;
    struct cbd_params*          params;
    struct list_head            cache_head;
    unsigned int                cache_len;
    struct pbat*                cache;
};

size_t
pbatcache_size(void)
{
    return sizeof(struct pbatcache);
}

bool
pbatcache_ctr(struct pbatcache* pc,
        struct cbd_params* params, u32 cache_pages)
{
    struct pbat* cache;
    u32 cache_len;
    u32 n;

    memset(pc, 0, sizeof(struct pbatcache));
    mutex_init(&pc->lock);
    pc->params = params;

    /* pbatcache gets 1/32 of cache_pages */
    cache_len = (cache_pages * 1 / 32) / pbat_len(params);
    if (!cache_len) {
        printk(KERN_ERR "%s: Cache too small\n", __func__);
        return false;
    }
    printk(KERN_INFO "%s: cache_len=%u\n", __func__, cache_len);
    cache = kzalloc(cache_len * sizeof(struct pbat), GFP_KERNEL);
    if (!cache) {
        return false;
    }
    INIT_LIST_HEAD(&pc->cache_head);
    pc->cache_len = cache_len;
    pc->cache = cache;
    for (n = 0; n < cache_len; ++n) {
        if (!pbat_ctr(&cache[n], pc->params)) {
            return false;
        }
        list_add_tail(&cache[n].list, &pc->cache_head);
    }

    return true;
}

void
pbatcache_dtr(struct pbatcache* pc)
{
    unsigned int n;
    struct pbat* pbat;

    for (n = 0; n < pc->cache_len; ++n) {
        pbat = &pc->cache[n];
        if (!pbat) {
            continue;
        }
        pbat_dtr(pbat);
        if (pbat->ref) {
            printk(KERN_ERR "%s: pbat ref leak: n=%u ref=%u\n", __func__, n, pbat->ref);
        }
    }
    kfree(pc->cache);
    pc->cache = NULL;
    pc->cache_len = 0;
    INIT_LIST_HEAD(&pc->cache_head);
    pc->params = NULL;
}

struct pbat*
pbatcache_get(struct pbatcache* pc, u32 zone)
{
    struct pbat* pbat;

    mutex_lock(&pc->lock);
    list_for_each_entry(pbat, &pc->cache_head, list) {
        mutex_lock(&pbat->reflock);
        if (pbat->zone == zone) {
            list_move(&pbat->list, &pc->cache_head);
            if (pbat->ref == 0) {
                goto found;
            }
            mutex_unlock(&pc->lock);
            ++pbat->ref;
            mutex_unlock(&pbat->reflock);
            return pbat;
        }
        if (pbat->zone == ZONE_NONE) {
            list_move(&pbat->list, &pc->cache_head);
            goto found;
        }
        mutex_unlock(&pbat->reflock);
    }
    list_for_each_entry_reverse(pbat, &pc->cache_head, list) {
        mutex_lock(&pbat->reflock);
        if (pbat->ref == 0 && !pbat_error(pbat)) {
            list_move(&pbat->list, &pc->cache_head);
            goto found;
        }
        mutex_unlock(&pbat->reflock);
    }
    printk(KERN_ERR "%s: failed to find free entry\n", __func__);
    mutex_unlock(&pc->lock);
    return NULL;

found:
    mutex_unlock(&pc->lock);
    if (pbat_reset(pbat, zone) != 0) {
        mutex_unlock(&pbat->reflock);
        return NULL;
    }
    pbat->ref = 1;
    mutex_unlock(&pbat->reflock);

    return pbat;
}

int
pbatcache_put(struct pbatcache* pc, struct pbat* pbat)
{
    int ret = 0;

    if (!pbat) {
        return 0;
    }
    mutex_lock(&pbat->reflock);
    if (--pbat->ref == 0) {
        ret = pbat_flush(pbat);
        if (ret) {
            printk(KERN_ERR "%s: pbat_flush failed\n", __func__);
        }
    }
    mutex_unlock(&pbat->reflock);

    return ret;
}