/*
 * 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

#ifdef CONFIG_ZRAM_DEBUG
#define DEBUG
#endif

#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;
static struct zram *zram_devices;

/* Module params (documentation at end) */
static unsigned int num_devices = 1;

static inline struct zram *dev_to_zram(struct device *dev)
{
        return (struct zram *)dev_to_disk(dev)->private_data;
}

static ssize_t disksize_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);

        return sprintf(buf, "%llu\n", zram->disksize);
}

static ssize_t initstate_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);

        return sprintf(buf, "%u\n", zram->init_done);
}

static ssize_t num_reads_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);

        return sprintf(buf, "%llu\n",
                        (u64)atomic64_read(&zram->stats.num_reads));
}

static ssize_t num_writes_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);

        return sprintf(buf, "%llu\n",
                        (u64)atomic64_read(&zram->stats.num_writes));
}

static ssize_t invalid_io_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);

        return sprintf(buf, "%llu\n",
                        (u64)atomic64_read(&zram->stats.invalid_io));
}

static ssize_t notify_free_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);

        return sprintf(buf, "%llu\n",
                        (u64)atomic64_read(&zram->stats.notify_free));
}

static ssize_t zero_pages_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);

        return sprintf(buf, "%u\n", zram->stats.pages_zero);
}

static ssize_t orig_data_size_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);

        return sprintf(buf, "%llu\n",
                (u64)(zram->stats.pages_stored) << PAGE_SHIFT);
}

static ssize_t compr_data_size_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);

        return sprintf(buf, "%llu\n",
                        (u64)atomic64_read(&zram->stats.compr_size));
}

static ssize_t mem_used_total_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        u64 val = 0;
        struct zram *zram = dev_to_zram(dev);
        struct zram_meta *meta = zram->meta;

        down_read(&zram->init_lock);
        if (zram->init_done)
                val = zs_get_total_size_bytes(meta->mem_pool);
        up_read(&zram->init_lock);

        return sprintf(buf, "%llu\n", val);
}

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

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

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

static inline int is_partial_io(struct bio_vec *bvec)
{
        return bvec->bv_len != PAGE_SIZE;
}

/*
 * Check if request is within bounds and aligned on zram logical blocks.
 */
static inline int valid_io_request(struct zram *zram, struct bio *bio)
{
        u64 start, end, bound;

        /* unaligned request */
        if (unlikely(bio->bi_sector & (ZRAM_SECTOR_PER_LOGICAL_BLOCK - 1)))
                return 0;
        if (unlikely(bio->bi_size & (ZRAM_LOGICAL_BLOCK_SIZE - 1)))
                return 0;

        start = bio->bi_sector;
        end = start + (bio->bi_size >> SECTOR_SHIFT);
        bound = zram->disksize >> SECTOR_SHIFT;
        /* out of range range */
        if (unlikely(start >= bound || end > bound || start > end))
                return 0;

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

static void zram_meta_free(struct zram_meta *meta)
{
        zs_destroy_pool(meta->mem_pool);
        kfree(meta->compress_workmem);
        free_pages((unsigned long)meta->compress_buffer, 1);
        vfree(meta->table);
        kfree(meta);
}

static struct zram_meta *zram_meta_alloc(u64 disksize)
{
        size_t num_pages;
        struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
        if (!meta)
                goto out;

        meta->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
        if (!meta->compress_workmem)
                goto free_meta;

        meta->compress_buffer =
                (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
        if (!meta->compress_buffer) {
                pr_err("Error allocating compressor buffer space\n");
                goto free_workmem;
        }

        num_pages = disksize >> PAGE_SHIFT;
        meta->table = vzalloc(num_pages * sizeof(*meta->table));
        if (!meta->table) {
                pr_err("Error allocating zram address table\n");
                goto free_buffer;
        }

        meta->mem_pool = zs_create_pool(GFP_NOIO | __GFP_HIGHMEM);
        if (!meta->mem_pool) {
                pr_err("Error creating memory pool\n");
                goto free_table;
        }

        return meta;

free_table:
        vfree(meta->table);
free_buffer:
        free_pages((unsigned long)meta->compress_buffer, 1);
free_workmem:
        kfree(meta->compress_workmem);
free_meta:
        kfree(meta);
        meta = NULL;
out:
        return meta;
}

static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
{
        if (*offset + bvec->bv_len >= PAGE_SIZE)
                (*index)++;
        *offset = (*offset + bvec->bv_len) % PAGE_SIZE;
}

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 handle_zero_page(struct bio_vec *bvec)
{
        struct page *page = bvec->bv_page;
        void *user_mem;

        user_mem = kmap_atomic(page);
        if (is_partial_io(bvec))
                memset(user_mem + bvec->bv_offset, 0, bvec->bv_len);
        else
                clear_page(user_mem);
        kunmap_atomic(user_mem);

        flush_dcache_page(page);
}

static void zram_free_page(struct zram *zram, size_t index)
{
        struct zram_meta *meta = zram->meta;
        unsigned long handle = meta->table[index].handle;
        u16 size = meta->table[index].size;

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

        if (unlikely(size > max_zpage_size))
                zram->stats.bad_compress--;

        zs_free(meta->mem_pool, handle);

        if (size <= PAGE_SIZE / 2)
                zram->stats.good_compress--;

        atomic64_sub(meta->table[index].size, &zram->stats.compr_size);
        zram->stats.pages_stored--;

        meta->table[index].handle = 0;
        meta->table[index].size = 0;
}

static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
{
        int ret = LZO_E_OK;
        size_t clen = PAGE_SIZE;
        unsigned char *cmem;
        struct zram_meta *meta = zram->meta;
        unsigned long handle = meta->table[index].handle;

        if (!handle || zram_test_flag(meta, index, ZRAM_ZERO)) {
                clear_page(mem);
                return 0;
        }

        cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_RO);
        if (meta->table[index].size == PAGE_SIZE)
                copy_page(mem, cmem);
        else
                ret = lzo1x_decompress_safe(cmem, meta->table[index].size,
                                                mem, &clen);
        zs_unmap_object(meta->mem_pool, handle);

        /* 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);
                atomic64_inc(&zram->stats.failed_reads);
                return ret;
        }

        return 0;
}

static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
                          u32 index, int offset, struct bio *bio)
{
        int ret;
        struct page *page;
        unsigned char *user_mem, *uncmem = NULL;
        struct zram_meta *meta = zram->meta;
        page = bvec->bv_page;

        if (unlikely(!meta->table[index].handle) ||
                        zram_test_flag(meta, index, ZRAM_ZERO)) {
                handle_zero_page(bvec);
                return 0;
        }

        if (is_partial_io(bvec))
                /* Use  a temporary buffer to decompress the page */
                uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);

        user_mem = kmap_atomic(page);
        if (!is_partial_io(bvec))
                uncmem = user_mem;

        if (!uncmem) {
                pr_info("Unable to allocate temp memory\n");
                ret = -ENOMEM;
                goto out_cleanup;
        }

        ret = zram_decompress_page(zram, uncmem, index);
        /* Should NEVER happen. Return bio error if it does. */
        if (unlikely(ret != LZO_E_OK))
                goto out_cleanup;

        if (is_partial_io(bvec))
                memcpy(user_mem + bvec->bv_offset, uncmem + offset,
                                bvec->bv_len);

        flush_dcache_page(page);
        ret = 0;
out_cleanup:
        kunmap_atomic(user_mem);
        if (is_partial_io(bvec))
                kfree(uncmem);
        return ret;
}

static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
                           int offset)
{
        int ret = 0;
        size_t clen;
        unsigned long handle;
        struct page *page;
        unsigned char *user_mem, *cmem, *src, *uncmem = NULL;
        struct zram_meta *meta = zram->meta;

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

        if (is_partial_io(bvec)) {
                /*
                 * This is a partial IO. We need to read the full page
                 * before to write the changes.
                 */
                uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
                if (!uncmem) {
                        ret = -ENOMEM;
                        goto out;
                }
                ret = zram_decompress_page(zram, uncmem, index);
                if (ret)
                        goto out;
        }

        user_mem = kmap_atomic(page);

        if (is_partial_io(bvec)) {
                memcpy(uncmem + offset, user_mem + bvec->bv_offset,
                       bvec->bv_len);
                kunmap_atomic(user_mem);
                user_mem = NULL;
        } else {
                uncmem = user_mem;
        }

        if (page_zero_filled(uncmem)) {
                kunmap_atomic(user_mem);
                /* Free memory associated with this sector now. */
                zram_free_page(zram, index);

                zram->stats.pages_zero++;
                zram_set_flag(meta, index, ZRAM_ZERO);
                ret = 0;
                goto out;
        }

        /*
         * zram_slot_free_notify could miss free so that let's
         * double check.
         */
        if (unlikely(meta->table[index].handle ||
                        zram_test_flag(meta, index, ZRAM_ZERO)))
                zram_free_page(zram, index);

        ret = lzo1x_1_compress(uncmem, PAGE_SIZE, src, &clen,
                               meta->compress_workmem);

        if (!is_partial_io(bvec)) {
                kunmap_atomic(user_mem);
                user_mem = NULL;
                uncmem = NULL;
        }

        if (unlikely(ret != LZO_E_OK)) {
                pr_err("Compression failed! err=%d\n", ret);
                goto out;
        }

        if (unlikely(clen > max_zpage_size)) {
                zram->stats.bad_compress++;
                clen = PAGE_SIZE;
                src = NULL;
                if (is_partial_io(bvec))
                        src = uncmem;
        }

        handle = zs_malloc(meta->mem_pool, clen);
        if (!handle) {
                pr_info("Error allocating memory for compressed page: %u, size=%zu\n",
                        index, clen);
                ret = -ENOMEM;
                goto out;
        }
        cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_WO);

        if ((clen == PAGE_SIZE) && !is_partial_io(bvec)) {
                src = kmap_atomic(page);
                copy_page(cmem, src);
                kunmap_atomic(src);
        } else {
                memcpy(cmem, src, clen);
        }

        zs_unmap_object(meta->mem_pool, handle);

        /*
         * Free memory associated with this sector
         * before overwriting unused sectors.
         */
        zram_free_page(zram, index);

        meta->table[index].handle = handle;
        meta->table[index].size = clen;

        /* Update stats */
        atomic64_add(clen, &zram->stats.compr_size);
        zram->stats.pages_stored++;
        if (clen <= PAGE_SIZE / 2)
                zram->stats.good_compress++;

out:
        if (is_partial_io(bvec))
                kfree(uncmem);

        if (ret)
                atomic64_inc(&zram->stats.failed_writes);
        return ret;
}

static void handle_pending_slot_free(struct zram *zram)
{
        struct zram_slot_free *free_rq;

        spin_lock(&zram->slot_free_lock);
        while (zram->slot_free_rq) {
                free_rq = zram->slot_free_rq;
                zram->slot_free_rq = free_rq->next;
                zram_free_page(zram, free_rq->index);
                kfree(free_rq);
        }
        spin_unlock(&zram->slot_free_lock);
}

static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
                        int offset, struct bio *bio, int rw)
{
        int ret;

        if (rw == READ) {
                down_read(&zram->lock);
                handle_pending_slot_free(zram);
                ret = zram_bvec_read(zram, bvec, index, offset, bio);
                up_read(&zram->lock);
        } else {
                down_write(&zram->lock);
                handle_pending_slot_free(zram);
                ret = zram_bvec_write(zram, bvec, index, offset);
                up_write(&zram->lock);
        }

        return ret;
}

static void zram_reset_device(struct zram *zram, bool reset_capacity)
{
        size_t index;
        struct zram_meta *meta;

        flush_work(&zram->free_work);

        down_write(&zram->init_lock);
        if (!zram->init_done) {
                up_write(&zram->init_lock);
                return;
        }

        meta = zram->meta;
        zram->init_done = 0;

        /* Free all pages that are still in this zram device */
        for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
                unsigned long handle = meta->table[index].handle;
                if (!handle)
                        continue;

                zs_free(meta->mem_pool, handle);
        }

        zram_meta_free(zram->meta);
        zram->meta = NULL;
        /* Reset stats */
        memset(&zram->stats, 0, sizeof(zram->stats));

        zram->disksize = 0;
        if (reset_capacity)
                set_capacity(zram->disk, 0);
        up_write(&zram->init_lock);
}

static void zram_init_device(struct zram *zram, struct zram_meta *meta)
{
        if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
                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: %lu kB\n"
                "\tSize you selected: %llu kB\n"
                "Continuing anyway ...\n",
                (totalram_pages << PAGE_SHIFT) >> 10, zram->disksize >> 10
                );
        }

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

        zram->meta = meta;
        zram->init_done = 1;

        pr_debug("Initialization done!\n");
}

static ssize_t disksize_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        u64 disksize;
        struct zram_meta *meta;
        struct zram *zram = dev_to_zram(dev);

        disksize = memparse(buf, NULL);
        if (!disksize)
                return -EINVAL;

        disksize = PAGE_ALIGN(disksize);
        meta = zram_meta_alloc(disksize);
        down_write(&zram->init_lock);
        if (zram->init_done) {
                up_write(&zram->init_lock);
                zram_meta_free(meta);
                pr_info("Cannot change disksize for initialized device\n");
                return -EBUSY;
        }

        zram->disksize = disksize;
        set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
        zram_init_device(zram, meta);
        up_write(&zram->init_lock);

        return len;
}

static ssize_t reset_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        int ret;
        unsigned short do_reset;
        struct zram *zram;
        struct block_device *bdev;

        zram = dev_to_zram(dev);
        bdev = bdget_disk(zram->disk, 0);

        /* Do not reset an active device! */
        if (bdev->bd_holders)
                return -EBUSY;

        ret = kstrtou16(buf, 10, &do_reset);
        if (ret)
                return ret;

        if (!do_reset)
                return -EINVAL;

        /* Make sure all pending I/O is finished */
        if (bdev)
                fsync_bdev(bdev);

        zram_reset_device(zram, true);
        return len;
}

static void __zram_make_request(struct zram *zram, struct bio *bio, int rw)
{
        int i, offset;
        u32 index;
        struct bio_vec *bvec;

        switch (rw) {
        case READ:
                atomic64_inc(&zram->stats.num_reads);
                break;
        case WRITE:
                atomic64_inc(&zram->stats.num_writes);
                break;
        }

        index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;
        offset = (bio->bi_sector & (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;

        bio_for_each_segment(bvec, bio, i) {
                int max_transfer_size = PAGE_SIZE - offset;

                if (bvec->bv_len > max_transfer_size) {
                        /*
                         * zram_bvec_rw() can only make operation on a single
                         * zram page. Split the bio vector.
                         */
                        struct bio_vec bv;

                        bv.bv_page = bvec->bv_page;
                        bv.bv_len = max_transfer_size;
                        bv.bv_offset = bvec->bv_offset;

                        if (zram_bvec_rw(zram, &bv, index, offset, bio, rw) < 0)
                                goto out;

                        bv.bv_len = bvec->bv_len - max_transfer_size;
                        bv.bv_offset += max_transfer_size;
                        if (zram_bvec_rw(zram, &bv, index+1, 0, bio, rw) < 0)
                                goto out;
                } else
                        if (zram_bvec_rw(zram, bvec, index, offset, bio, rw)
                            < 0)
                                goto out;

                update_position(&index, &offset, bvec);
        }

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

out:
        bio_io_error(bio);
}

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

        down_read(&zram->init_lock);
        if (unlikely(!zram->init_done))
                goto error;

        if (!valid_io_request(zram, bio)) {
                atomic64_inc(&zram->stats.invalid_io);
                goto error;
        }

        __zram_make_request(zram, bio, bio_data_dir(bio));
        up_read(&zram->init_lock);

        return;

error:
        up_read(&zram->init_lock);
        bio_io_error(bio);
}

static void zram_slot_free(struct work_struct *work)
{
        struct zram *zram;

        zram = container_of(work, struct zram, free_work);
        down_write(&zram->lock);
        handle_pending_slot_free(zram);
        up_write(&zram->lock);
}

static void add_slot_free(struct zram *zram, struct zram_slot_free *free_rq)
{
        spin_lock(&zram->slot_free_lock);
        free_rq->next = zram->slot_free_rq;
        zram->slot_free_rq = free_rq;
        spin_unlock(&zram->slot_free_lock);
}

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

        zram = bdev->bd_disk->private_data;
        atomic64_inc(&zram->stats.notify_free);

        free_rq = kmalloc(sizeof(struct zram_slot_free), GFP_ATOMIC);
        if (!free_rq)
                return;

        free_rq->index = index;
        add_slot_free(zram, free_rq);
        schedule_work(&zram->free_work);
}

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

static DEVICE_ATTR(disksize, S_IRUGO | S_IWUSR,
                disksize_show, disksize_store);
static DEVICE_ATTR(initstate, S_IRUGO, initstate_show, NULL);
static DEVICE_ATTR(reset, S_IWUSR, NULL, reset_store);
static DEVICE_ATTR(num_reads, S_IRUGO, num_reads_show, NULL);
static DEVICE_ATTR(num_writes, S_IRUGO, num_writes_show, NULL);
static DEVICE_ATTR(invalid_io, S_IRUGO, invalid_io_show, NULL);
static DEVICE_ATTR(notify_free, S_IRUGO, notify_free_show, NULL);
static DEVICE_ATTR(zero_pages, S_IRUGO, zero_pages_show, NULL);
static DEVICE_ATTR(orig_data_size, S_IRUGO, orig_data_size_show, NULL);
static DEVICE_ATTR(compr_data_size, S_IRUGO, compr_data_size_show, NULL);
static DEVICE_ATTR(mem_used_total, S_IRUGO, mem_used_total_show, NULL);

static struct attribute *zram_disk_attrs[] = {
        &dev_attr_disksize.attr,
        &dev_attr_initstate.attr,
        &dev_attr_reset.attr,
        &dev_attr_num_reads.attr,
        &dev_attr_num_writes.attr,
        &dev_attr_invalid_io.attr,
        &dev_attr_notify_free.attr,
        &dev_attr_zero_pages.attr,
        &dev_attr_orig_data_size.attr,
        &dev_attr_compr_data_size.attr,
        &dev_attr_mem_used_total.attr,
        NULL,
};

static struct attribute_group zram_disk_attr_group = {
        .attrs = zram_disk_attrs,
};

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

        init_rwsem(&zram->lock);
        init_rwsem(&zram->init_lock);

        INIT_WORK(&zram->free_work, zram_slot_free);
        spin_lock_init(&zram->slot_free_lock);
        zram->slot_free_rq = NULL;

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

        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,
                                        ZRAM_LOGICAL_BLOCK_SIZE);
        blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
        blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);

        add_disk(zram->disk);

        ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj,
                                &zram_disk_attr_group);
        if (ret < 0) {
                pr_warn("Error creating sysfs group");
                goto out_free_disk;
        }

        zram->init_done = 0;
        return 0;

out_free_disk:
        del_gendisk(zram->disk);
        put_disk(zram->disk);
out_free_queue:
        blk_cleanup_queue(zram->queue);
out:
        return ret;
}

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

        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_warn("Invalid value for num_devices: %u\n",
                                num_devices);
                ret = -EINVAL;
                goto out;
        }

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

        /* Allocate the device array and initialize each one */
        zram_devices = kzalloc(num_devices * sizeof(struct zram), GFP_KERNEL);
        if (!zram_devices) {
                ret = -ENOMEM;
                goto unregister;
        }

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

        pr_info("Created %u device(s) ...\n", num_devices);

        return 0;

free_devices:
        while (dev_id)
                destroy_device(&zram_devices[--dev_id]);
        kfree(zram_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 = &zram_devices[i];

                destroy_device(zram);
                /*
                 * Shouldn't access zram->disk after destroy_device
                 * because destroy_device already released zram->disk.
                 */
                zram_reset_device(zram, false);
        }

        unregister_blkdev(zram_major, "zram");

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

module_init(zram_init);
module_exit(zram_exit);

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

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