/*
 *  Copyright (c) 2013
 *  Minchan Kim <minchan@kernel.org>
 *
 *  This work is licensed under the terms of the GNU GPL, version 2. See
 *  the COPYING file in the top-level directory.
 */
#include <linux/types.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/buffer_head.h>
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/cpumask.h>

#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "decompressor.h"
#include "squashfs.h"

/*
 * This file implements multi-threaded decompression in the
 * decompressor framework
 */


/*
 * The reason that multiply two is that a CPU can request new I/O
 * while it is waiting previous request.
 */
#define MAX_DECOMPRESSOR        (num_online_cpus() * 2)


int squashfs_max_decompressors(void)
{
        return MAX_DECOMPRESSOR;
}


struct squashfs_stream {
        void                    *comp_opts;
        struct list_head        strm_list;
        struct mutex            mutex;
        int                     avail_decomp;
        wait_queue_head_t       wait;
};


struct decomp_stream {
        void *stream;
        struct list_head list;
};


static void put_decomp_stream(struct decomp_stream *decomp_strm,
                                struct squashfs_stream *stream)
{
        mutex_lock(&stream->mutex);
        list_add(&decomp_strm->list, &stream->strm_list);
        mutex_unlock(&stream->mutex);
        wake_up(&stream->wait);
}

void *squashfs_decompressor_create(struct squashfs_sb_info *msblk,
                                void *comp_opts)
{
        struct squashfs_stream *stream;
        struct decomp_stream *decomp_strm = NULL;
        int err = -ENOMEM;

        stream = kzalloc(sizeof(*stream), GFP_KERNEL);
        if (!stream)
                goto out;

        stream->comp_opts = comp_opts;
        mutex_init(&stream->mutex);
        INIT_LIST_HEAD(&stream->strm_list);
        init_waitqueue_head(&stream->wait);

        /*
         * We should have a decompressor at least as default
         * so if we fail to allocate new decompressor dynamically,
         * we could always fall back to default decompressor and
         * file system works.
         */
        decomp_strm = kmalloc(sizeof(*decomp_strm), GFP_KERNEL);
        if (!decomp_strm)
                goto out;

        decomp_strm->stream = msblk->decompressor->init(msblk,
                                                stream->comp_opts);
        if (IS_ERR(decomp_strm->stream)) {
                err = PTR_ERR(decomp_strm->stream);
                goto out;
        }

        list_add(&decomp_strm->list, &stream->strm_list);
        stream->avail_decomp = 1;
        return stream;

out:
        kfree(decomp_strm);
        kfree(stream);
        return ERR_PTR(err);
}


void squashfs_decompressor_destroy(struct squashfs_sb_info *msblk)
{
        struct squashfs_stream *stream = msblk->stream;
        if (stream) {
                struct decomp_stream *decomp_strm;

                while (!list_empty(&stream->strm_list)) {
                        decomp_strm = list_entry(stream->strm_list.prev,
                                                struct decomp_stream, list);
                        list_del(&decomp_strm->list);
                        msblk->decompressor->free(decomp_strm->stream);
                        kfree(decomp_strm);
                        stream->avail_decomp--;
                }
                WARN_ON(stream->avail_decomp);
                kfree(stream->comp_opts);
                kfree(stream);
        }
}


static struct decomp_stream *get_decomp_stream(struct squashfs_sb_info *msblk,
                                        struct squashfs_stream *stream)
{
        struct decomp_stream *decomp_strm;

        while (1) {
                mutex_lock(&stream->mutex);

                /* There is available decomp_stream */
                if (!list_empty(&stream->strm_list)) {
                        decomp_strm = list_entry(stream->strm_list.prev,
                                struct decomp_stream, list);
                        list_del(&decomp_strm->list);
                        mutex_unlock(&stream->mutex);
                        break;
                }

                /*
                 * If there is no available decomp and already full,
                 * let's wait for releasing decomp from other users.
                 */
                if (stream->avail_decomp >= MAX_DECOMPRESSOR)
                        goto wait;

                /* Let's allocate new decomp */
                decomp_strm = kmalloc(sizeof(*decomp_strm), GFP_KERNEL);
                if (!decomp_strm)
                        goto wait;

                decomp_strm->stream = msblk->decompressor->init(msblk,
                                                stream->comp_opts);
                if (IS_ERR(decomp_strm->stream)) {
                        kfree(decomp_strm);
                        goto wait;
                }

                stream->avail_decomp++;
                WARN_ON(stream->avail_decomp > MAX_DECOMPRESSOR);

                mutex_unlock(&stream->mutex);
                break;
wait:
                /*
                 * If system memory is tough, let's for other's
                 * releasing instead of hurting VM because it could
                 * make page cache thrashing.
                 */
                mutex_unlock(&stream->mutex);
                wait_event(stream->wait,
                        !list_empty(&stream->strm_list));
        }

        return decomp_strm;
}


int squashfs_decompress(struct squashfs_sb_info *msblk, struct buffer_head **bh,
        int b, int offset, int length, struct squashfs_page_actor *output)
{
        int res;
        struct squashfs_stream *stream = msblk->stream;
        struct decomp_stream *decomp_stream = get_decomp_stream(msblk, stream);
        res = msblk->decompressor->decompress(msblk, decomp_stream->stream,
                bh, b, offset, length, output);
        put_decomp_stream(decomp_stream, stream);
        if (res < 0)
                ERROR("%s decompression failed, data probably corrupt\n",
                        msblk->decompressor->name);
        return res;
}