/*
 * Compressed RAM block device
 *
 * Copyright (C) 2008, 2009, 2010  Nitin Gupta
 *
 * This code is released using a dual license strategy: BSD/GPL
 * You can choose the licence that better fits your requirements.
 *
 * Released under the terms of 3-clause BSD License
 * Released under the terms of GNU General Public License Version 2.0
 *
 * Project home: http://compcache.googlecode.com
 */

#define KMSG_COMPONENT "zram"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/bio.h>
#include <linux/bitops.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h>
#include <linux/device.h>
#include <linux/genhd.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/lzo.h>
#include <linux/string.h>
#include <linux/vmalloc.h>

#include "zram_drv.h"

/* Globals */
static int zram_major;
struct zram *devices;

/* Module params (documentation at end) */
unsigned int num_devices;

static void zram_stat_inc(u32 *v)
{
        *v = *v + 1;
}

static void zram_stat_dec(u32 *v)
{
        *v = *v - 1;
}

static void zram_stat64_add(struct zram *zram, u64 *v, u64 inc)
{
        spin_lock(&zram->stat64_lock);
        *v = *v + inc;
        spin_unlock(&zram->stat64_lock);
}

static void zram_stat64_sub(struct zram *zram, u64 *v, u64 dec)
{
        spin_lock(&zram->stat64_lock);
        *v = *v - dec;
        spin_unlock(&zram->stat64_lock);
}

static void zram_stat64_inc(struct zram *zram, u64 *v)
{
        zram_stat64_add(zram, v, 1);
}

static int zram_test_flag(struct zram *zram, u32 index,
                        enum zram_pageflags flag)
{
        return zram->table[index].flags & BIT(flag);
}

static void zram_set_flag(struct zram *zram, u32 index,
                        enum zram_pageflags flag)
{
        zram->table[index].flags |= BIT(flag);
}

static void zram_clear_flag(struct zram *zram, u32 index,
                        enum zram_pageflags flag)
{
        zram->table[index].flags &= ~BIT(flag);
}

static int page_zero_filled(void *ptr)
{
        unsigned int pos;
        unsigned long *page;

        page = (unsigned long *)ptr;

        for (pos = 0; pos != PAGE_SIZE / sizeof(*page); pos++) {
                if (page[pos])
                        return 0;
        }

        return 1;
}

static void zram_set_disksize(struct zram *zram, size_t totalram_bytes)
{
        if (!zram->disksize) {
                pr_info(
                "disk size not provided. You can use disksize_kb module "
                "param to specify size.\nUsing default: (%u%% of RAM).\n",
                default_disksize_perc_ram
                );
                zram->disksize = default_disksize_perc_ram *
                                        (totalram_bytes / 100);
        }

        if (zram->disksize > 2 * (totalram_bytes)) {
                pr_info(
                "There is little point creating a zram of greater than "
                "twice the size of memory since we expect a 2:1 compression "
                "ratio. Note that zram uses about 0.1%% of the size of "
                "the disk when not in use so a huge zram is "
                "wasteful.\n"
                "\tMemory Size: %zu kB\n"
                "\tSize you selected: %llu kB\n"
                "Continuing anyway ...\n",
                totalram_bytes >> 10, zram->disksize
                );
        }

        zram->disksize &= PAGE_MASK;
}

static void zram_free_page(struct zram *zram, size_t index)
{
        u32 clen;
        void *obj;

        struct page *page = zram->table[index].page;
        u32 offset = zram->table[index].offset;

        if (unlikely(!page)) {
                /*
                 * No memory is allocated for zero filled pages.
                 * Simply clear zero page flag.
                 */
                if (zram_test_flag(zram, index, ZRAM_ZERO)) {
                        zram_clear_flag(zram, index, ZRAM_ZERO);
                        zram_stat_dec(&zram->stats.pages_zero);
                }
                return;
        }

        if (unlikely(zram_test_flag(zram, index, ZRAM_UNCOMPRESSED))) {
                clen = PAGE_SIZE;
                __free_page(page);
                zram_clear_flag(zram, index, ZRAM_UNCOMPRESSED);
                zram_stat_dec(&zram->stats.pages_expand);
                goto out;
        }

        obj = kmap_atomic(page, KM_USER0) + offset;
        clen = xv_get_object_size(obj) - sizeof(struct zobj_header);
        kunmap_atomic(obj, KM_USER0);

        xv_free(zram->mem_pool, page, offset);
        if (clen <= PAGE_SIZE / 2)
                zram_stat_dec(&zram->stats.good_compress);

out:
        zram_stat64_sub(zram, &zram->stats.compr_size, clen);
        zram_stat_dec(&zram->stats.pages_stored);

        zram->table[index].page = NULL;
        zram->table[index].offset = 0;
}

static void handle_zero_page(struct page *page)
{
        void *user_mem;

        user_mem = kmap_atomic(page, KM_USER0);
        memset(user_mem, 0, PAGE_SIZE);
        kunmap_atomic(user_mem, KM_USER0);

        flush_dcache_page(page);
}

static void handle_uncompressed_page(struct zram *zram,
                                struct page *page, u32 index)
{
        unsigned char *user_mem, *cmem;

        user_mem = kmap_atomic(page, KM_USER0);
        cmem = kmap_atomic(zram->table[index].page, KM_USER1) +
                        zram->table[index].offset;

        memcpy(user_mem, cmem, PAGE_SIZE);
        kunmap_atomic(user_mem, KM_USER0);
        kunmap_atomic(cmem, KM_USER1);

        flush_dcache_page(page);
}

static int zram_read(struct zram *zram, struct bio *bio)
{

        int i;
        u32 index;
        struct bio_vec *bvec;

        if (unlikely(!zram->init_done)) {
                set_bit(BIO_UPTODATE, &bio->bi_flags);
                bio_endio(bio, 0);
                return 0;
        }

        zram_stat64_inc(zram, &zram->stats.num_reads);
        index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;

        bio_for_each_segment(bvec, bio, i) {
                int ret;
                size_t clen;
                struct page *page;
                struct zobj_header *zheader;
                unsigned char *user_mem, *cmem;

                page = bvec->bv_page;

                if (zram_test_flag(zram, index, ZRAM_ZERO)) {
                        handle_zero_page(page);
                        index++;
                        continue;
                }

                /* Requested page is not present in compressed area */
                if (unlikely(!zram->table[index].page)) {
                        pr_debug("Read before write: sector=%lu, size=%u",
                                (ulong)(bio->bi_sector), bio->bi_size);
                        /* Do nothing */
                        index++;
                        continue;
                }

                /* Page is stored uncompressed since it's incompressible */
                if (unlikely(zram_test_flag(zram, index, ZRAM_UNCOMPRESSED))) {
                        handle_uncompressed_page(zram, page, index);
                        index++;
                        continue;
                }

                user_mem = kmap_atomic(page, KM_USER0);
                clen = PAGE_SIZE;

                cmem = kmap_atomic(zram->table[index].page, KM_USER1) +
                                zram->table[index].offset;

                ret = lzo1x_decompress_safe(
                        cmem + sizeof(*zheader),
                        xv_get_object_size(cmem) - sizeof(*zheader),
                        user_mem, &clen);

                kunmap_atomic(user_mem, KM_USER0);
                kunmap_atomic(cmem, KM_USER1);

                /* Should NEVER happen. Return bio error if it does. */
                if (unlikely(ret != LZO_E_OK)) {
                        pr_err("Decompression failed! err=%d, page=%u\n",
                                ret, index);
                        zram_stat64_inc(zram, &zram->stats.failed_reads);
                        goto out;
                }

                flush_dcache_page(page);
                index++;
        }

        set_bit(BIO_UPTODATE, &bio->bi_flags);
        bio_endio(bio, 0);
        return 0;

out:
        bio_io_error(bio);
        return 0;
}

static int zram_write(struct zram *zram, struct bio *bio)
{
        int i, ret;
        u32 index;
        struct bio_vec *bvec;

        if (unlikely(!zram->init_done)) {
                ret = zram_init_device(zram);
                if (ret)
                        goto out;
        }

        zram_stat64_inc(zram, &zram->stats.num_writes);
        index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;

        bio_for_each_segment(bvec, bio, i) {
                u32 offset;
                size_t clen;
                struct zobj_header *zheader;
                struct page *page, *page_store;
                unsigned char *user_mem, *cmem, *src;

                page = bvec->bv_page;
                src = zram->compress_buffer;

                /*
                 * System overwrites unused sectors. Free memory associated
                 * with this sector now.
                 */
                if (zram->table[index].page ||
                                zram_test_flag(zram, index, ZRAM_ZERO))
                        zram_free_page(zram, index);

                mutex_lock(&zram->lock);

                user_mem = kmap_atomic(page, KM_USER0);
                if (page_zero_filled(user_mem)) {
                        kunmap_atomic(user_mem, KM_USER0);
                        mutex_unlock(&zram->lock);
                        zram_stat_inc(&zram->stats.pages_zero);
                        zram_set_flag(zram, index, ZRAM_ZERO);
                        index++;
                        continue;
                }

                ret = lzo1x_1_compress(user_mem, PAGE_SIZE, src, &clen,
                                        zram->compress_workmem);

                kunmap_atomic(user_mem, KM_USER0);

                if (unlikely(ret != LZO_E_OK)) {
                        mutex_unlock(&zram->lock);
                        pr_err("Compression failed! err=%d\n", ret);
                        zram_stat64_inc(zram, &zram->stats.failed_writes);
                        goto out;
                }

                /*
                 * Page is incompressible. Store it as-is (uncompressed)
                 * since we do not want to return too many disk write
                 * errors which has side effect of hanging the system.
                 */
                if (unlikely(clen > max_zpage_size)) {
                        clen = PAGE_SIZE;
                        page_store = alloc_page(GFP_NOIO | __GFP_HIGHMEM);
                        if (unlikely(!page_store)) {
                                mutex_unlock(&zram->lock);
                                pr_info("Error allocating memory for "
                                        "incompressible page: %u\n", index);
                                zram_stat64_inc(zram,
                                        &zram->stats.failed_writes);
                                goto out;
                        }

                        offset = 0;
                        zram_set_flag(zram, index, ZRAM_UNCOMPRESSED);
                        zram_stat_inc(&zram->stats.pages_expand);
                        zram->table[index].page = page_store;
                        src = kmap_atomic(page, KM_USER0);
                        goto memstore;
                }

                if (xv_malloc(zram->mem_pool, clen + sizeof(*zheader),
                                &zram->table[index].page, &offset,
                                GFP_NOIO | __GFP_HIGHMEM)) {
                        mutex_unlock(&zram->lock);
                        pr_info("Error allocating memory for compressed "
                                "page: %u, size=%zu\n", index, clen);
                        zram_stat64_inc(zram, &zram->stats.failed_writes);
                        goto out;
                }

memstore:
                zram->table[index].offset = offset;

                cmem = kmap_atomic(zram->table[index].page, KM_USER1) +
                                zram->table[index].offset;

#if 0
                /* Back-reference needed for memory defragmentation */
                if (!zram_test_flag(zram, index, ZRAM_UNCOMPRESSED)) {
                        zheader = (struct zobj_header *)cmem;
                        zheader->table_idx = index;
                        cmem += sizeof(*zheader);
                }
#endif

                memcpy(cmem, src, clen);

                kunmap_atomic(cmem, KM_USER1);
                if (unlikely(zram_test_flag(zram, index, ZRAM_UNCOMPRESSED)))
                        kunmap_atomic(src, KM_USER0);

                /* Update stats */
                zram_stat64_add(zram, &zram->stats.compr_size, clen);
                zram_stat_inc(&zram->stats.pages_stored);
                if (clen <= PAGE_SIZE / 2)
                        zram_stat_inc(&zram->stats.good_compress);

                mutex_unlock(&zram->lock);
                index++;
        }

        set_bit(BIO_UPTODATE, &bio->bi_flags);
        bio_endio(bio, 0);
        return 0;

out:
        bio_io_error(bio);
        return 0;
}

/*
 * Check if request is within bounds and page aligned.
 */
static inline int valid_io_request(struct zram *zram, struct bio *bio)
{
        if (unlikely(
                (bio->bi_sector >= (zram->disksize >> SECTOR_SHIFT)) ||
                (bio->bi_sector & (SECTORS_PER_PAGE - 1)) ||
                (bio->bi_size & (PAGE_SIZE - 1)))) {

                return 0;
        }

        /* I/O request is valid */
        return 1;
}

/*
 * Handler function for all zram I/O requests.
 */
static int zram_make_request(struct request_queue *queue, struct bio *bio)
{
        int ret = 0;
        struct zram *zram = queue->queuedata;

        if (!valid_io_request(zram, bio)) {
                zram_stat64_inc(zram, &zram->stats.invalid_io);
                bio_io_error(bio);
                return 0;
        }

        switch (bio_data_dir(bio)) {
        case READ:
                ret = zram_read(zram, bio);
                break;

        case WRITE:
                ret = zram_write(zram, bio);
                break;
        }

        return ret;
}

void zram_reset_device(struct zram *zram)
{
        size_t index;

        mutex_lock(&zram->init_lock);
        zram->init_done = 0;

        /* Free various per-device buffers */
        kfree(zram->compress_workmem);
        free_pages((unsigned long)zram->compress_buffer, 1);

        zram->compress_workmem = NULL;
        zram->compress_buffer = NULL;

        /* Free all pages that are still in this zram device */
        for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
                struct page *page;
                u16 offset;

                page = zram->table[index].page;
                offset = zram->table[index].offset;

                if (!page)
                        continue;

                if (unlikely(zram_test_flag(zram, index, ZRAM_UNCOMPRESSED)))
                        __free_page(page);
                else
                        xv_free(zram->mem_pool, page, offset);
        }

        vfree(zram->table);
        zram->table = NULL;

        xv_destroy_pool(zram->mem_pool);
        zram->mem_pool = NULL;

        /* Reset stats */
        memset(&zram->stats, 0, sizeof(zram->stats));

        zram->disksize = 0;
        mutex_unlock(&zram->init_lock);
}

int zram_init_device(struct zram *zram)
{
        int ret;
        size_t num_pages;

        mutex_lock(&zram->init_lock);

        if (zram->init_done) {
                mutex_unlock(&zram->init_lock);
                return 0;
        }

        zram_set_disksize(zram, totalram_pages << PAGE_SHIFT);

        zram->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
        if (!zram->compress_workmem) {
                pr_err("Error allocating compressor working memory!\n");
                ret = -ENOMEM;
                goto fail;
        }

        zram->compress_buffer = (void *)__get_free_pages(__GFP_ZERO, 1);
        if (!zram->compress_buffer) {
                pr_err("Error allocating compressor buffer space\n");
                ret = -ENOMEM;
                goto fail;
        }

        num_pages = zram->disksize >> PAGE_SHIFT;
        zram->table = vzalloc(num_pages * sizeof(*zram->table));
        if (!zram->table) {
                pr_err("Error allocating zram address table\n");
                /* To prevent accessing table entries during cleanup */
                zram->disksize = 0;
                ret = -ENOMEM;
                goto fail;
        }

        set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);

        /* zram devices sort of resembles non-rotational disks */
        queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);

        zram->mem_pool = xv_create_pool();
        if (!zram->mem_pool) {
                pr_err("Error creating memory pool\n");
                ret = -ENOMEM;
                goto fail;
        }

        zram->init_done = 1;
        mutex_unlock(&zram->init_lock);

        pr_debug("Initialization done!\n");
        return 0;

fail:
        mutex_unlock(&zram->init_lock);
        zram_reset_device(zram);

        pr_err("Initialization failed: err=%d\n", ret);
        return ret;
}

void zram_slot_free_notify(struct block_device *bdev, unsigned long index)
{
        struct zram *zram;

        zram = bdev->bd_disk->private_data;
        zram_free_page(zram, index);
        zram_stat64_inc(zram, &zram->stats.notify_free);
}

static const struct block_device_operations zram_devops = {
        .swap_slot_free_notify = zram_slot_free_notify,
        .owner = THIS_MODULE
};

static int create_device(struct zram *zram, int device_id)
{
        int ret = 0;

        mutex_init(&zram->lock);
        mutex_init(&zram->init_lock);
        spin_lock_init(&zram->stat64_lock);

        zram->queue = blk_alloc_queue(GFP_KERNEL);
        if (!zram->queue) {
                pr_err("Error allocating disk queue for device %d\n",
                        device_id);
                ret = -ENOMEM;
                goto out;
        }

        blk_queue_make_request(zram->queue, zram_make_request);
        zram->queue->queuedata = zram;

         /* gendisk structure */
        zram->disk = alloc_disk(1);
        if (!zram->disk) {
                blk_cleanup_queue(zram->queue);
                pr_warning("Error allocating disk structure for device %d\n",
                        device_id);
                ret = -ENOMEM;
                goto out;
        }

        zram->disk->major = zram_major;
        zram->disk->first_minor = device_id;
        zram->disk->fops = &zram_devops;
        zram->disk->queue = zram->queue;
        zram->disk->private_data = zram;
        snprintf(zram->disk->disk_name, 16, "zram%d", device_id);

        /* Actual capacity set using syfs (/sys/block/zram<id>/disksize */
        set_capacity(zram->disk, 0);

        /*
         * To ensure that we always get PAGE_SIZE aligned
         * and n*PAGE_SIZED sized I/O requests.
         */
        blk_queue_physical_block_size(zram->disk->queue, PAGE_SIZE);
        blk_queue_logical_block_size(zram->disk->queue, PAGE_SIZE);
        blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
        blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);

        add_disk(zram->disk);

#ifdef CONFIG_SYSFS
        ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj,
                                &zram_disk_attr_group);
        if (ret < 0) {
                pr_warning("Error creating sysfs group");
                goto out;
        }
#endif

        zram->init_done = 0;

out:
        return ret;
}

static void destroy_device(struct zram *zram)
{
#ifdef CONFIG_SYSFS
        sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
                        &zram_disk_attr_group);
#endif

        if (zram->disk) {
                del_gendisk(zram->disk);
                put_disk(zram->disk);
        }

        if (zram->queue)
                blk_cleanup_queue(zram->queue);
}

static int __init zram_init(void)
{
        int ret, dev_id;

        if (num_devices > max_num_devices) {
                pr_warning("Invalid value for num_devices: %u\n",
                                num_devices);
                ret = -EINVAL;
                goto out;
        }

        zram_major = register_blkdev(0, "zram");
        if (zram_major <= 0) {
                pr_warning("Unable to get major number\n");
                ret = -EBUSY;
                goto out;
        }

        if (!num_devices) {
                pr_info("num_devices not specified. Using default: 1\n");
                num_devices = 1;
        }

        /* Allocate the device array and initialize each one */
        pr_info("Creating %u devices ...\n", num_devices);
        devices = kzalloc(num_devices * sizeof(struct zram), GFP_KERNEL);
        if (!devices) {
                ret = -ENOMEM;
                goto unregister;
        }

        for (dev_id = 0; dev_id < num_devices; dev_id++) {
                ret = create_device(&devices[dev_id], dev_id);
                if (ret)
                        goto free_devices;
        }

        return 0;

free_devices:
        while (dev_id)
                destroy_device(&devices[--dev_id]);
        kfree(devices);
unregister:
        unregister_blkdev(zram_major, "zram");
out:
        return ret;
}

static void __exit zram_exit(void)
{
        int i;
        struct zram *zram;

        for (i = 0; i < num_devices; i++) {
                zram = &devices[i];

                destroy_device(zram);
                if (zram->init_done)
                        zram_reset_device(zram);
        }

        unregister_blkdev(zram_major, "zram");

        kfree(devices);
        pr_debug("Cleanup done!\n");
}

module_param(num_devices, uint, 0);
MODULE_PARM_DESC(num_devices, "Number of zram devices");

module_init(zram_init);
module_exit(zram_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");
MODULE_DESCRIPTION("Compressed RAM Block Device");