/*
 * 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 {
    u32                         zone;
    struct mutex                reflock;
    unsigned int                ref;

    struct mutex                lock;
    enum cache_state            state;
    struct cbd_params*          params;
    struct page*                pages;
    u8*                         buf;
};

bool
pbat_ctr(struct pbat* pbat,
         struct cbd_params* params)
{
    memset(pbat, 0, sizeof(struct pbat));
    pbat->zone = ZONE_NONE;
    mutex_init(&pbat->reflock);
    pbat->ref = 0;
    mutex_init(&pbat->lock);
    pbat->state = CACHE_STATE_UNCACHED;
    pbat->params = params;
    pbat->pages = cbd_alloc_pages(pbat_len(params));
    if (!pbat->pages) {
        printk(KERN_ERR "%s: Failed to alloc pbat_buf\n", __func__);
        return false;
    }
    pbat->buf = page_address(pbat->pages);

    return true;
}

void
pbat_dtr(struct pbat* pbat)
{
    pbat->buf = NULL;
    cbd_free_pages(pbat->pages, pbat_len(pbat->params));
    pbat->pages = NULL;
}

static void
pbat_flush_endio(struct bio* bio)
{
    struct pbat* pbat = bio->bi_private;
    int ret;
    unsigned int n;

    for (n = 0; n < bio->bi_max_vecs; ++n) {
        cbd_free_page(bio->bi_io_vec[0].bv_page);
    }
    ret = pblk_endio(bio);
    if (ret) {
        printk(KERN_ERR "%s: I/O failed\n", __func__);
        pbat->state = CACHE_STATE_ERROR;
    }
}

int
pbat_flush(struct pbat* pbat)
{
    int ret = 0;
    u32 count = pbat_len(pbat->params);
    struct page* iopagev[count];
    u64 pblk;
    u32 n;
    u8* iobuf;

    mutex_lock(&pbat->lock);
    if (pbat->state != CACHE_STATE_DIRTY) {
        if (pbat->state == CACHE_STATE_ERROR) {
            ret = -EIO;
        }
        goto out;
    }
    pblk = pbat_off(pbat->params, pbat->zone);
    if (!cbd_alloc_pagev(iopagev, count)) {
        printk(KERN_ERR "%s: out of memory\n", __func__);
        ret = -ENOMEM;
        goto out;
    }
    for (n = 0; n < count; ++n) {
        iobuf = page_address(iopagev[n]);
        memcpy(iobuf, pbat->buf + n * PBLK_SIZE, PBLK_SIZE);
    }
    pblk_write(pbat->params, pblk, count, iopagev, pbat_flush_endio, pbat);
    pbat->state = CACHE_STATE_CLEAN;

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

int
pbat_read(struct pbat* pbat)
{
    int ret = 0;
    u32 count = pbat_len(pbat->params);
    struct page* pagev[count];
    u64 pblk;
    u32 n;

    mutex_lock(&pbat->lock);
    if (pbat->state != CACHE_STATE_UNCACHED) {
        goto out;
    }
    pblk = pbat_off(pbat->params, pbat->zone);
    for (n = 0; n < count; ++n) {
        pagev[n] = virt_to_page(pbat->buf + n * PBLK_SIZE);
    }
    ret = pblk_read_wait(pbat->params, pblk, count, pagev);
    if (ret) {
        goto out;
    }
    pbat->state = CACHE_STATE_CLEAN;

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

void
pbat_reset(struct pbat* pbat, u32 zone)
{
    if (pbat->zone != zone) {
        pbat->zone = zone;
        pbat->state = CACHE_STATE_UNCACHED;
    }
}

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);
    BUG_ON(pbat->state == CACHE_STATE_UNCACHED);
    idx = cbd_bitmap_alloc(pbat->buf, pblk_count);
    if (idx == pblk_count) {
        pblk = PBLK_NONE;
        goto out;
    }
    pblk = idx + zone_data_off(pbat->params, pbat->zone);
    pbat->state = CACHE_STATE_DIRTY;

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

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

    BUG_ON(pblk < CBD_HEADER_BLOCKS);
    zone = (pblk - CBD_HEADER_BLOCKS) / zone_len(pbat->params);
    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 >= zone_pblk_count);
    mutex_lock(&pbat->lock);
    BUG_ON(pbat->state == CACHE_STATE_UNCACHED);
    cbd_bitmap_free(pbat->buf, idx);
    pbat->state = CACHE_STATE_DIRTY;
    mutex_unlock(&pbat->lock);

    return 0;
}

struct pbatcache {
    struct mutex                lock;
    struct cbd_params*          params;
    unsigned int                len;
    struct pbat**               cache;
};

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

static bool
pbatcache_realloc(struct pbatcache* pc, unsigned int len)
{
    struct pbat** cache;
    unsigned int n;
    struct pbat* pbat;

    cache = kzalloc(len * sizeof(struct pbat*), GFP_KERNEL);
    if (!cache) {
        return false;
    }
    n = 0;
    if (pc->len) {
        memcpy(cache, pc->cache, pc->len * sizeof(struct pbat*));
        n = pc->len;
        kfree(pc->cache);
    }
    pc->len = len;
    pc->cache = cache;
    while (n < len) {
        pbat = kmalloc(sizeof(struct pbat), GFP_KERNEL);
        if (!pbat) {
            return false;
        }
        cache[n++] = pbat;
        if (!pbat_ctr(pbat, pc->params)) {
            return false;
        }
    }

    return true;
}

bool
pbatcache_ctr(struct pbatcache* pc,
        struct cbd_params* params)
{
    memset(pc, 0, sizeof(struct pbatcache));
    mutex_init(&pc->lock);
    pc->params = params;

    return pbatcache_realloc(pc, 1);
}

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

    for (n = 0; n < pc->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(pbat);
    }
    kfree(pc->cache);
    pc->cache = NULL;
    pc->len = 0;
    pc->params = NULL;
}

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

    mutex_lock(&pc->lock);
    for (n = 0; n < pc->len; ++n) {
        pbat = pc->cache[n];
        mutex_lock(&pbat->reflock);
        if (pbat->zone == zone) {
            if (pbat->ref == 0) {
                goto found;
            }
            ++pbat->ref;
            mutex_unlock(&pbat->reflock);
            goto out;
        }
        mutex_unlock(&pbat->reflock);
    }

    for (n = 0; n < pc->len; ++n) {
        pbat = pc->cache[n];
        mutex_lock(&pbat->reflock);
        if (pbat->zone == ZONE_NONE) {
            goto found;
        }
        mutex_unlock(&pbat->reflock);
    }
    for (n = 0; n < pc->len; ++n) {
        pbat = pc->cache[n];
        mutex_lock(&pbat->reflock);
        if (pbat->ref == 0 && pbat->state != CACHE_STATE_ERROR) {
            goto found;
        }
        mutex_unlock(&pbat->reflock);
    }
    printk(KERN_INFO "%s: all objects in use, realloc...\n", __func__);
    n = pc->len;
    if (!pbatcache_realloc(pc, pc->len * 2)) {
        printk(KERN_ERR "%s: realloc failed\n", __func__);
        pbat = NULL;
        goto out;
    }
    printk(KERN_INFO "%s: realloc done, using n=%u\n", __func__, n);
    pbat = pc->cache[n];
    mutex_lock(&pbat->reflock);

found:
    pbat_reset(pbat, zone);
    pbat->ref = 1;
    mutex_unlock(&pbat->reflock);

out:
    mutex_unlock(&pc->lock);

    return pbat;
}

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

    if (!pbat) {
        return 0;
    }
    mutex_lock(&pc->lock);
    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);
    mutex_unlock(&pc->lock);

    return ret;
}