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

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

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

    return true;
}

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

static bool
lbatpage_error(struct lbatpage* lp)
{
    return PageError(lp->page);
}

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

    mutex_lock(&lp->lock);
    if (!PageDirty(lp->page)) {
        goto unlock;
    }
    if (lbatpage_error(lp)) {
        ret = -EIO;
        goto unlock;
    }
    iopagev[0] = lp->page;
    pblk_write(lp->params->priv, lp->pblk, 1, iopagev);
    mutex_unlock(&lp->lock);

    return ret;

unlock:
    unlock_page(lp->page);
    mutex_unlock(&lp->lock);

    return ret;
}

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

    pagev[0] = lp->page;
    ret = pblk_read_wait(lp->params->priv, lp->pblk, 1, pagev);

    return ret;
}

static int
lbatpage_reset(struct lbatpage* lp, u64 pblk)
{
    int ret = 0;

    lock_page(lp->page);
    if (lp->pblk != pblk) {
        lp->pblk = pblk;
        ret = lbatpage_read(lp);
    }

    if (ret) {
        unlock_page(lp->page);
        lp->pblk = PBLK_NONE;
    }

    return ret;
}

u8*
lbatpage_get_buf(struct lbatpage* lp, bool rw)
{
    mutex_lock(&lp->lock);
    if (rw) {
        SetPageDirty(lp->page);
    }

    return lp->buf;
}

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

struct lbatpagecache {
    struct mutex                lock;
    struct cbd_params*          params;
    struct list_head            cache_head;
    unsigned int                cache_len;
    struct lbatpage*            cache;
};

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

bool
lbatpagecache_ctr(struct lbatpagecache* lpc,
        struct cbd_params* params, u32 cache_pages)
{
    struct lbatpage* cache;
    u32 cache_len;
    u32 n;

    memset(lpc, 0, sizeof(struct lbatpagecache));
    mutex_init(&lpc->lock);
    lpc->params = params;

    /* lbatpagecache gets 15/32 of cache pages */
    cache_len = (cache_pages * 15 / 32);
    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 lbatpage), GFP_KERNEL);
    if (!cache) {
        return false;
    }
    INIT_LIST_HEAD(&lpc->cache_head);
    lpc->cache_len = cache_len;
    lpc->cache = cache;
    for (n = 0; n < cache_len; ++n) {
        if (!lbatpage_ctr(&cache[n], lpc->params)) {
            return false;
        }
        list_add_tail(&cache[n].list, &lpc->cache_head);
    }

    return true;
}

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

    for (n = 0; n < lpc->cache_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(lpc->cache);
    lpc->cache = NULL;
    lpc->cache_len = 0;
    INIT_LIST_HEAD(&lpc->cache_head);
    lpc->params = NULL;
}

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

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

found:
    mutex_unlock(&lpc->lock);
    if (lbatpage_reset(lp, pblk) != 0) {
        mutex_unlock(&lp->reflock);
        return NULL;
    }
    lp->ref = 1;
    mutex_unlock(&lp->reflock);

    return lp;
}

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

    if (!lp) {
        return 0;
    }
    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);

    return ret;
}