/*
 * 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 lbatpage {
    u64                         pblk;
    struct mutex                reflock;
    unsigned int                ref;

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

bool
lbatpage_ctr(struct lbatpage* lp, struct cbd_params* params)
{
    lp->pblk = PBLK_NONE;
    mutex_init(&lp->reflock);
    lp->ref = 0;
    mutex_init(&lp->lock);
    lp->state = CACHE_STATE_UNCACHED;
    lp->params = params;
    lp->page = cbd_alloc_page();
    if (!lp->page) {
        return false;
    }
    lp->buf = page_address(lp->page);
    lp->dirty = false;

    return true;
}

void
lbatpage_dtr(struct lbatpage* lp)
{
    lp->buf = NULL;
    cbd_free_page(lp->page);
    lp->page = NULL;
}

static void
lbatpage_flush_endio(struct bio* bio)
{
    struct lbatpage* lp = bio->bi_private;
    int ret;

    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__);
        lp->state = CACHE_STATE_ERROR;
    }
}

int
lbatpage_flush(struct lbatpage* lp)
{
    int ret = 0;
    struct page* iopagev[1];

    mutex_lock(&lp->lock);
    if (lp->state != CACHE_STATE_DIRTY) {
        if (lp->state == CACHE_STATE_ERROR) {
            ret = -EIO;
        }
        goto out;
    }
    iopagev[0] = cbd_alloc_page();
    if (!iopagev[0]) {
        printk(KERN_ERR "%s: out of memory\n", __func__);
        ret = -ENOMEM;
        goto out;
    }
    memcpy(page_address(iopagev[0]), lp->buf, PAGE_SIZE);
    pblk_write(lp->params, lp->pblk, 1, iopagev, lbatpage_flush_endio, lp);
    lp->state = CACHE_STATE_CLEAN;

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

int
lbatpage_read(struct lbatpage* lp)
{
    int ret = 0;
    struct page* pagev[1];

    mutex_lock(&lp->lock);
    if (lp->state != CACHE_STATE_UNCACHED) {
        goto out;
    }
    pagev[0] = lp->page;
    ret = pblk_read_wait(lp->params, lp->pblk, 1, pagev);
    if (ret) {
        printk(KERN_ERR "%s: failed, pblk=%lu\n", __func__, (unsigned long)lp->pblk);
        goto out;
    }
    lp->state = CACHE_STATE_CLEAN;

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

void
lbatpage_reset(struct lbatpage* lp, u64 pblk)
{
    if (lp->pblk != pblk) {
        lp->pblk = pblk;
        lp->state = CACHE_STATE_UNCACHED;
    }
}

u8*
lbatpage_get_buf(struct lbatpage* lp, bool rw)
{
    mutex_lock(&lp->lock);
    BUG_ON(lp->state == CACHE_STATE_UNCACHED);
    if (rw) {
        lp->state = CACHE_STATE_DIRTY;
    }
    return lp->buf;
}

void
lbatpage_put_buf(struct lbatpage* lp)
{
    BUG_ON(lp->state == CACHE_STATE_UNCACHED);
    mutex_unlock(&lp->lock);
}

struct lbatpagecache {
    struct mutex                lock;
    struct cbd_params*          params;
    unsigned int                len;
    struct lbatpage**           cache;
};

size_t
lbatpagecache_size(void)
{
    return sizeof(struct lbatpagecache);
}

static bool
lbatpagecache_realloc(struct lbatpagecache* lpc, unsigned int len)
{
    struct lbatpage** cache;
    unsigned int n;
    struct lbatpage* lp;

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

    return true;
}

bool
lbatpagecache_ctr(struct lbatpagecache* lpc,
        struct cbd_params* params)
{
    memset(lpc, 0, sizeof(struct lbatpagecache));
    mutex_init(&lpc->lock);
    lpc->params = params;

    return lbatpagecache_realloc(lpc, 1);
}

void
lbatpagecache_dtr(struct lbatpagecache* lpc)
{
    unsigned int n;
    struct lbatpage* lp;

    for (n = 0; n < lpc->len; ++n) {
        lp = lpc->cache[n];
        if (!lp) {
            continue;
        }
        lbatpage_dtr(lp);
        if (lp->ref) {
            printk(KERN_ERR "%s: lbatpage ref leak: n=%u ref=%u\n", __func__, n, lp->ref);
        }
        kfree(lp);
    }
    kfree(lpc->cache);
    lpc->cache = NULL;
    lpc->len = 0;
    lpc->params = NULL;
}

struct lbatpage*
lbatpagecache_get(struct lbatpagecache* lpc, u64 pblk)
{
    unsigned int n;
    struct lbatpage* lp;

    mutex_lock(&lpc->lock);
    for (n = 0; n < lpc->len; ++n) {
        lp = lpc->cache[n];
        mutex_lock(&lp->reflock);
        if (lp->pblk == pblk) {
            if (lp->ref == 0) {
                goto found;
            }
            ++lp->ref;
            mutex_unlock(&lp->reflock);
            goto out;
        }
        mutex_unlock(&lp->reflock);
    }
    for (n = 0; n < lpc->len; ++n) {
        lp = lpc->cache[n];
        mutex_lock(&lp->reflock);
        if (lp->pblk == PBLK_NONE) {
            goto found;
        }
        mutex_unlock(&lp->reflock);
    }
    for (n = 0; n < lpc->len; ++n) {
        lp = lpc->cache[n];
        mutex_lock(&lp->reflock);
        if (lp->ref == 0 && lp->state != CACHE_STATE_ERROR) {
            goto found;
        }
        mutex_unlock(&lp->reflock);
    }
    printk(KERN_INFO "%s: all pages in use, realloc...\n", __func__);
    n = lpc->len;
    if (!lbatpagecache_realloc(lpc, lpc->len * 2)) {
        printk(KERN_ERR "%s: realloc failed\n", __func__);
        lp = NULL;
        goto out;
    }
    printk(KERN_INFO "%s: realloc done, using n=%u\n", __func__, n);
    lp = lpc->cache[n];
    mutex_lock(&lp->reflock);

found:
    lbatpage_reset(lp, pblk);
    lp->ref = 1;
    mutex_unlock(&lp->reflock);

out:
    mutex_unlock(&lpc->lock);

    return lp;
}

int
lbatpagecache_put(struct lbatpagecache* lpc, struct lbatpage* lp)
{
    int ret = 0;

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

    return ret;
}