drivers: remove struct module * setting from struct class

[linux-2.6-microblaze.git] / drivers / block / zram / zram_drv.c

/*
 * Compressed RAM block device
 *
 * Copyright (C) 2008, 2009, 2010  Nitin Gupta
 *               2012, 2013 Minchan Kim
 *
 * 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
 *
 */

#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/highmem.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/string.h>
#include <linux/vmalloc.h>
#include <linux/err.h>
#include <linux/idr.h>
#include <linux/sysfs.h>
#include <linux/debugfs.h>
#include <linux/cpuhotplug.h>
#include <linux/part_stat.h>

#include "zram_drv.h"

static DEFINE_IDR(zram_index_idr);
/* idr index must be protected */
static DEFINE_MUTEX(zram_index_mutex);

static int zram_major;
static const char *default_compressor = CONFIG_ZRAM_DEF_COMP;

/* Module params (documentation at end) */
static unsigned int num_devices = 1;
/*
 * Pages that compress to sizes equals or greater than this are stored
 * uncompressed in memory.
 */
static size_t huge_class_size;

static const struct block_device_operations zram_devops;

static void zram_free_page(struct zram *zram, size_t index);
static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
                                u32 index, int offset, struct bio *bio);


static int zram_slot_trylock(struct zram *zram, u32 index)
{
        return bit_spin_trylock(ZRAM_LOCK, &zram->table[index].flags);
}

static void zram_slot_lock(struct zram *zram, u32 index)
{
        bit_spin_lock(ZRAM_LOCK, &zram->table[index].flags);
}

static void zram_slot_unlock(struct zram *zram, u32 index)
{
        bit_spin_unlock(ZRAM_LOCK, &zram->table[index].flags);
}

static inline bool init_done(struct zram *zram)
{
        return zram->disksize;
}

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

static unsigned long zram_get_handle(struct zram *zram, u32 index)
{
        return zram->table[index].handle;
}

static void zram_set_handle(struct zram *zram, u32 index, unsigned long handle)
{
        zram->table[index].handle = handle;
}

/* flag operations require table entry bit_spin_lock() being held */
static bool 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 inline void zram_set_element(struct zram *zram, u32 index,
                        unsigned long element)
{
        zram->table[index].element = element;
}

static unsigned long zram_get_element(struct zram *zram, u32 index)
{
        return zram->table[index].element;
}

static size_t zram_get_obj_size(struct zram *zram, u32 index)
{
        return zram->table[index].flags & (BIT(ZRAM_FLAG_SHIFT) - 1);
}

static void zram_set_obj_size(struct zram *zram,
                                        u32 index, size_t size)
{
        unsigned long flags = zram->table[index].flags >> ZRAM_FLAG_SHIFT;

        zram->table[index].flags = (flags << ZRAM_FLAG_SHIFT) | size;
}

static inline bool zram_allocated(struct zram *zram, u32 index)
{
        return zram_get_obj_size(zram, index) ||
                        zram_test_flag(zram, index, ZRAM_SAME) ||
                        zram_test_flag(zram, index, ZRAM_WB);
}

#if PAGE_SIZE != 4096
static inline bool is_partial_io(struct bio_vec *bvec)
{
        return bvec->bv_len != PAGE_SIZE;
}
#else
static inline bool is_partial_io(struct bio_vec *bvec)
{
        return false;
}
#endif

static inline void zram_set_priority(struct zram *zram, u32 index, u32 prio)
{
        prio &= ZRAM_COMP_PRIORITY_MASK;
        /*
         * Clear previous priority value first, in case if we recompress
         * further an already recompressed page
         */
        zram->table[index].flags &= ~(ZRAM_COMP_PRIORITY_MASK <<
                                      ZRAM_COMP_PRIORITY_BIT1);
        zram->table[index].flags |= (prio << ZRAM_COMP_PRIORITY_BIT1);
}

static inline u32 zram_get_priority(struct zram *zram, u32 index)
{
        u32 prio = zram->table[index].flags >> ZRAM_COMP_PRIORITY_BIT1;

        return prio & ZRAM_COMP_PRIORITY_MASK;
}

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

        /* unaligned request */
        if (unlikely(start & (ZRAM_SECTOR_PER_LOGICAL_BLOCK - 1)))
                return false;
        if (unlikely(size & (ZRAM_LOGICAL_BLOCK_SIZE - 1)))
                return false;

        end = start + (size >> SECTOR_SHIFT);
        bound = zram->disksize >> SECTOR_SHIFT;
        /* out of range */
        if (unlikely(start >= bound || end > bound || start > end))
                return false;

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

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

static inline void update_used_max(struct zram *zram,
                                        const unsigned long pages)
{
        unsigned long cur_max = atomic_long_read(&zram->stats.max_used_pages);

        do {
                if (cur_max >= pages)
                        return;
        } while (!atomic_long_try_cmpxchg(&zram->stats.max_used_pages,
                                          &cur_max, pages));
}

static inline void zram_fill_page(void *ptr, unsigned long len,
                                        unsigned long value)
{
        WARN_ON_ONCE(!IS_ALIGNED(len, sizeof(unsigned long)));
        memset_l(ptr, value, len / sizeof(unsigned long));
}

static bool page_same_filled(void *ptr, unsigned long *element)
{
        unsigned long *page;
        unsigned long val;
        unsigned int pos, last_pos = PAGE_SIZE / sizeof(*page) - 1;

        page = (unsigned long *)ptr;
        val = page[0];

        if (val != page[last_pos])
                return false;

        for (pos = 1; pos < last_pos; pos++) {
                if (val != page[pos])
                        return false;
        }

        *element = val;

        return true;
}

static ssize_t initstate_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        u32 val;
        struct zram *zram = dev_to_zram(dev);

        down_read(&zram->init_lock);
        val = init_done(zram);
        up_read(&zram->init_lock);

        return scnprintf(buf, PAGE_SIZE, "%u\n", val);
}

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

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

static ssize_t mem_limit_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        u64 limit;
        char *tmp;
        struct zram *zram = dev_to_zram(dev);

        limit = memparse(buf, &tmp);
        if (buf == tmp) /* no chars parsed, invalid input */
                return -EINVAL;

        down_write(&zram->init_lock);
        zram->limit_pages = PAGE_ALIGN(limit) >> PAGE_SHIFT;
        up_write(&zram->init_lock);

        return len;
}

static ssize_t mem_used_max_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        int err;
        unsigned long val;
        struct zram *zram = dev_to_zram(dev);

        err = kstrtoul(buf, 10, &val);
        if (err || val != 0)
                return -EINVAL;

        down_read(&zram->init_lock);
        if (init_done(zram)) {
                atomic_long_set(&zram->stats.max_used_pages,
                                zs_get_total_pages(zram->mem_pool));
        }
        up_read(&zram->init_lock);

        return len;
}

/*
 * Mark all pages which are older than or equal to cutoff as IDLE.
 * Callers should hold the zram init lock in read mode
 */
static void mark_idle(struct zram *zram, ktime_t cutoff)
{
        int is_idle = 1;
        unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
        int index;

        for (index = 0; index < nr_pages; index++) {
                /*
                 * Do not mark ZRAM_UNDER_WB slot as ZRAM_IDLE to close race.
                 * See the comment in writeback_store.
                 */
                zram_slot_lock(zram, index);
                if (zram_allocated(zram, index) &&
                                !zram_test_flag(zram, index, ZRAM_UNDER_WB)) {
#ifdef CONFIG_ZRAM_MEMORY_TRACKING
                        is_idle = !cutoff || ktime_after(cutoff, zram->table[index].ac_time);
#endif
                        if (is_idle)
                                zram_set_flag(zram, index, ZRAM_IDLE);
                }
                zram_slot_unlock(zram, index);
        }
}

static ssize_t idle_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        ktime_t cutoff_time = 0;
        ssize_t rv = -EINVAL;

        if (!sysfs_streq(buf, "all")) {
                /*
                 * If it did not parse as 'all' try to treat it as an integer
                 * when we have memory tracking enabled.
                 */
                u64 age_sec;

                if (IS_ENABLED(CONFIG_ZRAM_MEMORY_TRACKING) && !kstrtoull(buf, 0, &age_sec))
                        cutoff_time = ktime_sub(ktime_get_boottime(),
                                        ns_to_ktime(age_sec * NSEC_PER_SEC));
                else
                        goto out;
        }

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

        /*
         * A cutoff_time of 0 marks everything as idle, this is the
         * "all" behavior.
         */
        mark_idle(zram, cutoff_time);
        rv = len;

out_unlock:
        up_read(&zram->init_lock);
out:
        return rv;
}

#ifdef CONFIG_ZRAM_WRITEBACK
static ssize_t writeback_limit_enable_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        u64 val;
        ssize_t ret = -EINVAL;

        if (kstrtoull(buf, 10, &val))
                return ret;

        down_read(&zram->init_lock);
        spin_lock(&zram->wb_limit_lock);
        zram->wb_limit_enable = val;
        spin_unlock(&zram->wb_limit_lock);
        up_read(&zram->init_lock);
        ret = len;

        return ret;
}

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

        down_read(&zram->init_lock);
        spin_lock(&zram->wb_limit_lock);
        val = zram->wb_limit_enable;
        spin_unlock(&zram->wb_limit_lock);
        up_read(&zram->init_lock);

        return scnprintf(buf, PAGE_SIZE, "%d\n", val);
}

static ssize_t writeback_limit_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        u64 val;
        ssize_t ret = -EINVAL;

        if (kstrtoull(buf, 10, &val))
                return ret;

        down_read(&zram->init_lock);
        spin_lock(&zram->wb_limit_lock);
        zram->bd_wb_limit = val;
        spin_unlock(&zram->wb_limit_lock);
        up_read(&zram->init_lock);
        ret = len;

        return ret;
}

static ssize_t writeback_limit_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        u64 val;
        struct zram *zram = dev_to_zram(dev);

        down_read(&zram->init_lock);
        spin_lock(&zram->wb_limit_lock);
        val = zram->bd_wb_limit;
        spin_unlock(&zram->wb_limit_lock);
        up_read(&zram->init_lock);

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

static void reset_bdev(struct zram *zram)
{
        struct block_device *bdev;

        if (!zram->backing_dev)
                return;

        bdev = zram->bdev;
        blkdev_put(bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
        /* hope filp_close flush all of IO */
        filp_close(zram->backing_dev, NULL);
        zram->backing_dev = NULL;
        zram->bdev = NULL;
        zram->disk->fops = &zram_devops;
        kvfree(zram->bitmap);
        zram->bitmap = NULL;
}

static ssize_t backing_dev_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct file *file;
        struct zram *zram = dev_to_zram(dev);
        char *p;
        ssize_t ret;

        down_read(&zram->init_lock);
        file = zram->backing_dev;
        if (!file) {
                memcpy(buf, "none\n", 5);
                up_read(&zram->init_lock);
                return 5;
        }

        p = file_path(file, buf, PAGE_SIZE - 1);
        if (IS_ERR(p)) {
                ret = PTR_ERR(p);
                goto out;
        }

        ret = strlen(p);
        memmove(buf, p, ret);
        buf[ret++] = '\n';
out:
        up_read(&zram->init_lock);
        return ret;
}

static ssize_t backing_dev_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        char *file_name;
        size_t sz;
        struct file *backing_dev = NULL;
        struct inode *inode;
        struct address_space *mapping;
        unsigned int bitmap_sz;
        unsigned long nr_pages, *bitmap = NULL;
        struct block_device *bdev = NULL;
        int err;
        struct zram *zram = dev_to_zram(dev);

        file_name = kmalloc(PATH_MAX, GFP_KERNEL);
        if (!file_name)
                return -ENOMEM;

        down_write(&zram->init_lock);
        if (init_done(zram)) {
                pr_info("Can't setup backing device for initialized device\n");
                err = -EBUSY;
                goto out;
        }

        strscpy(file_name, buf, PATH_MAX);
        /* ignore trailing newline */
        sz = strlen(file_name);
        if (sz > 0 && file_name[sz - 1] == '\n')
                file_name[sz - 1] = 0x00;

        backing_dev = filp_open(file_name, O_RDWR|O_LARGEFILE, 0);
        if (IS_ERR(backing_dev)) {
                err = PTR_ERR(backing_dev);
                backing_dev = NULL;
                goto out;
        }

        mapping = backing_dev->f_mapping;
        inode = mapping->host;

        /* Support only block device in this moment */
        if (!S_ISBLK(inode->i_mode)) {
                err = -ENOTBLK;
                goto out;
        }

        bdev = blkdev_get_by_dev(inode->i_rdev,
                        FMODE_READ | FMODE_WRITE | FMODE_EXCL, zram);
        if (IS_ERR(bdev)) {
                err = PTR_ERR(bdev);
                bdev = NULL;
                goto out;
        }

        nr_pages = i_size_read(inode) >> PAGE_SHIFT;
        bitmap_sz = BITS_TO_LONGS(nr_pages) * sizeof(long);
        bitmap = kvzalloc(bitmap_sz, GFP_KERNEL);
        if (!bitmap) {
                err = -ENOMEM;
                goto out;
        }

        reset_bdev(zram);

        zram->bdev = bdev;
        zram->backing_dev = backing_dev;
        zram->bitmap = bitmap;
        zram->nr_pages = nr_pages;
        up_write(&zram->init_lock);

        pr_info("setup backing device %s\n", file_name);
        kfree(file_name);

        return len;
out:
        kvfree(bitmap);

        if (bdev)
                blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);

        if (backing_dev)
                filp_close(backing_dev, NULL);

        up_write(&zram->init_lock);

        kfree(file_name);

        return err;
}

static unsigned long alloc_block_bdev(struct zram *zram)
{
        unsigned long blk_idx = 1;
retry:
        /* skip 0 bit to confuse zram.handle = 0 */
        blk_idx = find_next_zero_bit(zram->bitmap, zram->nr_pages, blk_idx);
        if (blk_idx == zram->nr_pages)
                return 0;

        if (test_and_set_bit(blk_idx, zram->bitmap))
                goto retry;

        atomic64_inc(&zram->stats.bd_count);
        return blk_idx;
}

static void free_block_bdev(struct zram *zram, unsigned long blk_idx)
{
        int was_set;

        was_set = test_and_clear_bit(blk_idx, zram->bitmap);
        WARN_ON_ONCE(!was_set);
        atomic64_dec(&zram->stats.bd_count);
}

static void zram_page_end_io(struct bio *bio)
{
        struct page *page = bio_first_page_all(bio);

        page_endio(page, op_is_write(bio_op(bio)),
                        blk_status_to_errno(bio->bi_status));
        bio_put(bio);
}

/*
 * Returns 1 if the submission is successful.
 */
static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
                        unsigned long entry, struct bio *parent)
{
        struct bio *bio;

        bio = bio_alloc(zram->bdev, 1, parent ? parent->bi_opf : REQ_OP_READ,
                        GFP_NOIO);
        if (!bio)
                return -ENOMEM;

        bio->bi_iter.bi_sector = entry * (PAGE_SIZE >> 9);
        if (!bio_add_page(bio, bvec->bv_page, bvec->bv_len, bvec->bv_offset)) {
                bio_put(bio);
                return -EIO;
        }

        if (!parent)
                bio->bi_end_io = zram_page_end_io;
        else
                bio_chain(bio, parent);

        submit_bio(bio);
        return 1;
}

#define PAGE_WB_SIG "page_index="

#define PAGE_WRITEBACK                  0
#define HUGE_WRITEBACK                  (1<<0)
#define IDLE_WRITEBACK                  (1<<1)
#define INCOMPRESSIBLE_WRITEBACK        (1<<2)

static ssize_t writeback_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
        unsigned long index = 0;
        struct bio bio;
        struct bio_vec bio_vec;
        struct page *page;
        ssize_t ret = len;
        int mode, err;
        unsigned long blk_idx = 0;

        if (sysfs_streq(buf, "idle"))
                mode = IDLE_WRITEBACK;
        else if (sysfs_streq(buf, "huge"))
                mode = HUGE_WRITEBACK;
        else if (sysfs_streq(buf, "huge_idle"))
                mode = IDLE_WRITEBACK | HUGE_WRITEBACK;
        else if (sysfs_streq(buf, "incompressible"))
                mode = INCOMPRESSIBLE_WRITEBACK;
        else {
                if (strncmp(buf, PAGE_WB_SIG, sizeof(PAGE_WB_SIG) - 1))
                        return -EINVAL;

                if (kstrtol(buf + sizeof(PAGE_WB_SIG) - 1, 10, &index) ||
                                index >= nr_pages)
                        return -EINVAL;

                nr_pages = 1;
                mode = PAGE_WRITEBACK;
        }

        down_read(&zram->init_lock);
        if (!init_done(zram)) {
                ret = -EINVAL;
                goto release_init_lock;
        }

        if (!zram->backing_dev) {
                ret = -ENODEV;
                goto release_init_lock;
        }

        page = alloc_page(GFP_KERNEL);
        if (!page) {
                ret = -ENOMEM;
                goto release_init_lock;
        }

        for (; nr_pages != 0; index++, nr_pages--) {
                struct bio_vec bvec;

                bvec_set_page(&bvec, page, PAGE_SIZE, 0);

                spin_lock(&zram->wb_limit_lock);
                if (zram->wb_limit_enable && !zram->bd_wb_limit) {
                        spin_unlock(&zram->wb_limit_lock);
                        ret = -EIO;
                        break;
                }
                spin_unlock(&zram->wb_limit_lock);

                if (!blk_idx) {
                        blk_idx = alloc_block_bdev(zram);
                        if (!blk_idx) {
                                ret = -ENOSPC;
                                break;
                        }
                }

                zram_slot_lock(zram, index);
                if (!zram_allocated(zram, index))
                        goto next;

                if (zram_test_flag(zram, index, ZRAM_WB) ||
                                zram_test_flag(zram, index, ZRAM_SAME) ||
                                zram_test_flag(zram, index, ZRAM_UNDER_WB))
                        goto next;

                if (mode & IDLE_WRITEBACK &&
                    !zram_test_flag(zram, index, ZRAM_IDLE))
                        goto next;
                if (mode & HUGE_WRITEBACK &&
                    !zram_test_flag(zram, index, ZRAM_HUGE))
                        goto next;
                if (mode & INCOMPRESSIBLE_WRITEBACK &&
                    !zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
                        goto next;

                /*
                 * Clearing ZRAM_UNDER_WB is duty of caller.
                 * IOW, zram_free_page never clear it.
                 */
                zram_set_flag(zram, index, ZRAM_UNDER_WB);
                /* Need for hugepage writeback racing */
                zram_set_flag(zram, index, ZRAM_IDLE);
                zram_slot_unlock(zram, index);
                if (zram_bvec_read(zram, &bvec, index, 0, NULL)) {
                        zram_slot_lock(zram, index);
                        zram_clear_flag(zram, index, ZRAM_UNDER_WB);
                        zram_clear_flag(zram, index, ZRAM_IDLE);
                        zram_slot_unlock(zram, index);
                        continue;
                }

                bio_init(&bio, zram->bdev, &bio_vec, 1,
                         REQ_OP_WRITE | REQ_SYNC);
                bio.bi_iter.bi_sector = blk_idx * (PAGE_SIZE >> 9);

                bio_add_page(&bio, bvec.bv_page, bvec.bv_len,
                                bvec.bv_offset);
                /*
                 * XXX: A single page IO would be inefficient for write
                 * but it would be not bad as starter.
                 */
                err = submit_bio_wait(&bio);
                if (err) {
                        zram_slot_lock(zram, index);
                        zram_clear_flag(zram, index, ZRAM_UNDER_WB);
                        zram_clear_flag(zram, index, ZRAM_IDLE);
                        zram_slot_unlock(zram, index);
                        /*
                         * BIO errors are not fatal, we continue and simply
                         * attempt to writeback the remaining objects (pages).
                         * At the same time we need to signal user-space that
                         * some writes (at least one, but also could be all of
                         * them) were not successful and we do so by returning
                         * the most recent BIO error.
                         */
                        ret = err;
                        continue;
                }

                atomic64_inc(&zram->stats.bd_writes);
                /*
                 * We released zram_slot_lock so need to check if the slot was
                 * changed. If there is freeing for the slot, we can catch it
                 * easily by zram_allocated.
                 * A subtle case is the slot is freed/reallocated/marked as
                 * ZRAM_IDLE again. To close the race, idle_store doesn't
                 * mark ZRAM_IDLE once it found the slot was ZRAM_UNDER_WB.
                 * Thus, we could close the race by checking ZRAM_IDLE bit.
                 */
                zram_slot_lock(zram, index);
                if (!zram_allocated(zram, index) ||
                          !zram_test_flag(zram, index, ZRAM_IDLE)) {
                        zram_clear_flag(zram, index, ZRAM_UNDER_WB);
                        zram_clear_flag(zram, index, ZRAM_IDLE);
                        goto next;
                }

                zram_free_page(zram, index);
                zram_clear_flag(zram, index, ZRAM_UNDER_WB);
                zram_set_flag(zram, index, ZRAM_WB);
                zram_set_element(zram, index, blk_idx);
                blk_idx = 0;
                atomic64_inc(&zram->stats.pages_stored);
                spin_lock(&zram->wb_limit_lock);
                if (zram->wb_limit_enable && zram->bd_wb_limit > 0)
                        zram->bd_wb_limit -=  1UL << (PAGE_SHIFT - 12);
                spin_unlock(&zram->wb_limit_lock);
next:
                zram_slot_unlock(zram, index);
        }

        if (blk_idx)
                free_block_bdev(zram, blk_idx);
        __free_page(page);
release_init_lock:
        up_read(&zram->init_lock);

        return ret;
}

struct zram_work {
        struct work_struct work;
        struct zram *zram;
        unsigned long entry;
        struct bio *bio;
        struct bio_vec bvec;
};

#if PAGE_SIZE != 4096
static void zram_sync_read(struct work_struct *work)
{
        struct zram_work *zw = container_of(work, struct zram_work, work);
        struct zram *zram = zw->zram;
        unsigned long entry = zw->entry;
        struct bio *bio = zw->bio;

        read_from_bdev_async(zram, &zw->bvec, entry, bio);
}

/*
 * Block layer want one ->submit_bio to be active at a time, so if we use
 * chained IO with parent IO in same context, it's a deadlock. To avoid that,
 * use a worker thread context.
 */
static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
                                unsigned long entry, struct bio *bio)
{
        struct zram_work work;

        work.bvec = *bvec;
        work.zram = zram;
        work.entry = entry;
        work.bio = bio;

        INIT_WORK_ONSTACK(&work.work, zram_sync_read);
        queue_work(system_unbound_wq, &work.work);
        flush_work(&work.work);
        destroy_work_on_stack(&work.work);

        return 1;
}
#else
static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
                                unsigned long entry, struct bio *bio)
{
        WARN_ON(1);
        return -EIO;
}
#endif

static int read_from_bdev(struct zram *zram, struct bio_vec *bvec,
                        unsigned long entry, struct bio *parent, bool sync)
{
        atomic64_inc(&zram->stats.bd_reads);
        if (sync)
                return read_from_bdev_sync(zram, bvec, entry, parent);
        else
                return read_from_bdev_async(zram, bvec, entry, parent);
}
#else
static inline void reset_bdev(struct zram *zram) {};
static int read_from_bdev(struct zram *zram, struct bio_vec *bvec,
                        unsigned long entry, struct bio *parent, bool sync)
{
        return -EIO;
}

static void free_block_bdev(struct zram *zram, unsigned long blk_idx) {};
#endif

#ifdef CONFIG_ZRAM_MEMORY_TRACKING

static struct dentry *zram_debugfs_root;

static void zram_debugfs_create(void)
{
        zram_debugfs_root = debugfs_create_dir("zram", NULL);
}

static void zram_debugfs_destroy(void)
{
        debugfs_remove_recursive(zram_debugfs_root);
}

static void zram_accessed(struct zram *zram, u32 index)
{
        zram_clear_flag(zram, index, ZRAM_IDLE);
        zram->table[index].ac_time = ktime_get_boottime();
}

static ssize_t read_block_state(struct file *file, char __user *buf,
                                size_t count, loff_t *ppos)
{
        char *kbuf;
        ssize_t index, written = 0;
        struct zram *zram = file->private_data;
        unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
        struct timespec64 ts;

        kbuf = kvmalloc(count, GFP_KERNEL);
        if (!kbuf)
                return -ENOMEM;

        down_read(&zram->init_lock);
        if (!init_done(zram)) {
                up_read(&zram->init_lock);
                kvfree(kbuf);
                return -EINVAL;
        }

        for (index = *ppos; index < nr_pages; index++) {
                int copied;

                zram_slot_lock(zram, index);
                if (!zram_allocated(zram, index))
                        goto next;

                ts = ktime_to_timespec64(zram->table[index].ac_time);
                copied = snprintf(kbuf + written, count,
                        "%12zd %12lld.%06lu %c%c%c%c%c%c\n",
                        index, (s64)ts.tv_sec,
                        ts.tv_nsec / NSEC_PER_USEC,
                        zram_test_flag(zram, index, ZRAM_SAME) ? 's' : '.',
                        zram_test_flag(zram, index, ZRAM_WB) ? 'w' : '.',
                        zram_test_flag(zram, index, ZRAM_HUGE) ? 'h' : '.',
                        zram_test_flag(zram, index, ZRAM_IDLE) ? 'i' : '.',
                        zram_get_priority(zram, index) ? 'r' : '.',
                        zram_test_flag(zram, index,
                                       ZRAM_INCOMPRESSIBLE) ? 'n' : '.');

                if (count <= copied) {
                        zram_slot_unlock(zram, index);
                        break;
                }
                written += copied;
                count -= copied;
next:
                zram_slot_unlock(zram, index);
                *ppos += 1;
        }

        up_read(&zram->init_lock);
        if (copy_to_user(buf, kbuf, written))
                written = -EFAULT;
        kvfree(kbuf);

        return written;
}

static const struct file_operations proc_zram_block_state_op = {
        .open = simple_open,
        .read = read_block_state,
        .llseek = default_llseek,
};

static void zram_debugfs_register(struct zram *zram)
{
        if (!zram_debugfs_root)
                return;

        zram->debugfs_dir = debugfs_create_dir(zram->disk->disk_name,
                                                zram_debugfs_root);
        debugfs_create_file("block_state", 0400, zram->debugfs_dir,
                                zram, &proc_zram_block_state_op);
}

static void zram_debugfs_unregister(struct zram *zram)
{
        debugfs_remove_recursive(zram->debugfs_dir);
}
#else
static void zram_debugfs_create(void) {};
static void zram_debugfs_destroy(void) {};
static void zram_accessed(struct zram *zram, u32 index)
{
        zram_clear_flag(zram, index, ZRAM_IDLE);
};
static void zram_debugfs_register(struct zram *zram) {};
static void zram_debugfs_unregister(struct zram *zram) {};
#endif

/*
 * We switched to per-cpu streams and this attr is not needed anymore.
 * However, we will keep it around for some time, because:
 * a) we may revert per-cpu streams in the future
 * b) it's visible to user space and we need to follow our 2 years
 *    retirement rule; but we already have a number of 'soon to be
 *    altered' attrs, so max_comp_streams need to wait for the next
 *    layoff cycle.
 */
static ssize_t max_comp_streams_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        return scnprintf(buf, PAGE_SIZE, "%d\n", num_online_cpus());
}

static ssize_t max_comp_streams_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        return len;
}

static void comp_algorithm_set(struct zram *zram, u32 prio, const char *alg)
{
        /* Do not free statically defined compression algorithms */
        if (zram->comp_algs[prio] != default_compressor)
                kfree(zram->comp_algs[prio]);

        zram->comp_algs[prio] = alg;
}

static ssize_t __comp_algorithm_show(struct zram *zram, u32 prio, char *buf)
{
        ssize_t sz;

        down_read(&zram->init_lock);
        sz = zcomp_available_show(zram->comp_algs[prio], buf);
        up_read(&zram->init_lock);

        return sz;
}

static int __comp_algorithm_store(struct zram *zram, u32 prio, const char *buf)
{
        char *compressor;
        size_t sz;

        sz = strlen(buf);
        if (sz >= CRYPTO_MAX_ALG_NAME)
                return -E2BIG;

        compressor = kstrdup(buf, GFP_KERNEL);
        if (!compressor)
                return -ENOMEM;

        /* ignore trailing newline */
        if (sz > 0 && compressor[sz - 1] == '\n')
                compressor[sz - 1] = 0x00;

        if (!zcomp_available_algorithm(compressor)) {
                kfree(compressor);
                return -EINVAL;
        }

        down_write(&zram->init_lock);
        if (init_done(zram)) {
                up_write(&zram->init_lock);
                kfree(compressor);
                pr_info("Can't change algorithm for initialized device\n");
                return -EBUSY;
        }

        comp_algorithm_set(zram, prio, compressor);
        up_write(&zram->init_lock);
        return 0;
}

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

        return __comp_algorithm_show(zram, ZRAM_PRIMARY_COMP, buf);
}

static ssize_t comp_algorithm_store(struct device *dev,
                                    struct device_attribute *attr,
                                    const char *buf,
                                    size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        int ret;

        ret = __comp_algorithm_store(zram, ZRAM_PRIMARY_COMP, buf);
        return ret ? ret : len;
}

#ifdef CONFIG_ZRAM_MULTI_COMP
static ssize_t recomp_algorithm_show(struct device *dev,
                                     struct device_attribute *attr,
                                     char *buf)
{
        struct zram *zram = dev_to_zram(dev);
        ssize_t sz = 0;
        u32 prio;

        for (prio = ZRAM_SECONDARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
                if (!zram->comp_algs[prio])
                        continue;

                sz += scnprintf(buf + sz, PAGE_SIZE - sz - 2, "#%d: ", prio);
                sz += __comp_algorithm_show(zram, prio, buf + sz);
        }

        return sz;
}

static ssize_t recomp_algorithm_store(struct device *dev,
                                      struct device_attribute *attr,
                                      const char *buf,
                                      size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        int prio = ZRAM_SECONDARY_COMP;
        char *args, *param, *val;
        char *alg = NULL;
        int ret;

        args = skip_spaces(buf);
        while (*args) {
                args = next_arg(args, &param, &val);

                if (!val || !*val)
                        return -EINVAL;

                if (!strcmp(param, "algo")) {
                        alg = val;
                        continue;
                }

                if (!strcmp(param, "priority")) {
                        ret = kstrtoint(val, 10, &prio);
                        if (ret)
                                return ret;
                        continue;
                }
        }

        if (!alg)
                return -EINVAL;

        if (prio < ZRAM_SECONDARY_COMP || prio >= ZRAM_MAX_COMPS)
                return -EINVAL;

        ret = __comp_algorithm_store(zram, prio, alg);
        return ret ? ret : len;
}
#endif

static ssize_t compact_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);

        down_read(&zram->init_lock);
        if (!init_done(zram)) {
                up_read(&zram->init_lock);
                return -EINVAL;
        }

        zs_compact(zram->mem_pool);
        up_read(&zram->init_lock);

        return len;
}

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

        down_read(&zram->init_lock);
        ret = scnprintf(buf, PAGE_SIZE,
                        "%8llu %8llu %8llu %8llu\n",
                        (u64)atomic64_read(&zram->stats.failed_reads),
                        (u64)atomic64_read(&zram->stats.failed_writes),
                        (u64)atomic64_read(&zram->stats.invalid_io),
                        (u64)atomic64_read(&zram->stats.notify_free));
        up_read(&zram->init_lock);

        return ret;
}

static ssize_t mm_stat_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);
        struct zs_pool_stats pool_stats;
        u64 orig_size, mem_used = 0;
        long max_used;
        ssize_t ret;

        memset(&pool_stats, 0x00, sizeof(struct zs_pool_stats));

        down_read(&zram->init_lock);
        if (init_done(zram)) {
                mem_used = zs_get_total_pages(zram->mem_pool);
                zs_pool_stats(zram->mem_pool, &pool_stats);
        }

        orig_size = atomic64_read(&zram->stats.pages_stored);
        max_used = atomic_long_read(&zram->stats.max_used_pages);

        ret = scnprintf(buf, PAGE_SIZE,
                        "%8llu %8llu %8llu %8lu %8ld %8llu %8lu %8llu %8llu\n",
                        orig_size << PAGE_SHIFT,
                        (u64)atomic64_read(&zram->stats.compr_data_size),
                        mem_used << PAGE_SHIFT,
                        zram->limit_pages << PAGE_SHIFT,
                        max_used << PAGE_SHIFT,
                        (u64)atomic64_read(&zram->stats.same_pages),
                        atomic_long_read(&pool_stats.pages_compacted),
                        (u64)atomic64_read(&zram->stats.huge_pages),
                        (u64)atomic64_read(&zram->stats.huge_pages_since));
        up_read(&zram->init_lock);

        return ret;
}

#ifdef CONFIG_ZRAM_WRITEBACK
#define FOUR_K(x) ((x) * (1 << (PAGE_SHIFT - 12)))
static ssize_t bd_stat_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);
        ssize_t ret;

        down_read(&zram->init_lock);
        ret = scnprintf(buf, PAGE_SIZE,
                "%8llu %8llu %8llu\n",
                        FOUR_K((u64)atomic64_read(&zram->stats.bd_count)),
                        FOUR_K((u64)atomic64_read(&zram->stats.bd_reads)),
                        FOUR_K((u64)atomic64_read(&zram->stats.bd_writes)));
        up_read(&zram->init_lock);

        return ret;
}
#endif

static ssize_t debug_stat_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        int version = 1;
        struct zram *zram = dev_to_zram(dev);
        ssize_t ret;

        down_read(&zram->init_lock);
        ret = scnprintf(buf, PAGE_SIZE,
                        "version: %d\n%8llu %8llu\n",
                        version,
                        (u64)atomic64_read(&zram->stats.writestall),
                        (u64)atomic64_read(&zram->stats.miss_free));
        up_read(&zram->init_lock);

        return ret;
}

static DEVICE_ATTR_RO(io_stat);
static DEVICE_ATTR_RO(mm_stat);
#ifdef CONFIG_ZRAM_WRITEBACK
static DEVICE_ATTR_RO(bd_stat);
#endif
static DEVICE_ATTR_RO(debug_stat);

static void zram_meta_free(struct zram *zram, u64 disksize)
{
        size_t num_pages = disksize >> PAGE_SHIFT;
        size_t index;

        /* Free all pages that are still in this zram device */
        for (index = 0; index < num_pages; index++)
                zram_free_page(zram, index);

        zs_destroy_pool(zram->mem_pool);
        vfree(zram->table);
}

static bool zram_meta_alloc(struct zram *zram, u64 disksize)
{
        size_t num_pages;

        num_pages = disksize >> PAGE_SHIFT;
        zram->table = vzalloc(array_size(num_pages, sizeof(*zram->table)));
        if (!zram->table)
                return false;

        zram->mem_pool = zs_create_pool(zram->disk->disk_name);
        if (!zram->mem_pool) {
                vfree(zram->table);
                return false;
        }

        if (!huge_class_size)
                huge_class_size = zs_huge_class_size(zram->mem_pool);
        return true;
}

/*
 * To protect concurrent access to the same index entry,
 * caller should hold this table index entry's bit_spinlock to
 * indicate this index entry is accessing.
 */
static void zram_free_page(struct zram *zram, size_t index)
{
        unsigned long handle;

#ifdef CONFIG_ZRAM_MEMORY_TRACKING
        zram->table[index].ac_time = 0;
#endif
        if (zram_test_flag(zram, index, ZRAM_IDLE))
                zram_clear_flag(zram, index, ZRAM_IDLE);

        if (zram_test_flag(zram, index, ZRAM_HUGE)) {
                zram_clear_flag(zram, index, ZRAM_HUGE);
                atomic64_dec(&zram->stats.huge_pages);
        }

        if (zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
                zram_clear_flag(zram, index, ZRAM_INCOMPRESSIBLE);

        zram_set_priority(zram, index, 0);

        if (zram_test_flag(zram, index, ZRAM_WB)) {
                zram_clear_flag(zram, index, ZRAM_WB);
                free_block_bdev(zram, zram_get_element(zram, index));
                goto out;
        }

        /*
         * No memory is allocated for same element filled pages.
         * Simply clear same page flag.
         */
        if (zram_test_flag(zram, index, ZRAM_SAME)) {
                zram_clear_flag(zram, index, ZRAM_SAME);
                atomic64_dec(&zram->stats.same_pages);
                goto out;
        }

        handle = zram_get_handle(zram, index);
        if (!handle)
                return;

        zs_free(zram->mem_pool, handle);

        atomic64_sub(zram_get_obj_size(zram, index),
                        &zram->stats.compr_data_size);
out:
        atomic64_dec(&zram->stats.pages_stored);
        zram_set_handle(zram, index, 0);
        zram_set_obj_size(zram, index, 0);
        WARN_ON_ONCE(zram->table[index].flags &
                ~(1UL << ZRAM_LOCK | 1UL << ZRAM_UNDER_WB));
}

/*
 * Reads a page from the writeback devices. Corresponding ZRAM slot
 * should be unlocked.
 */
static int zram_bvec_read_from_bdev(struct zram *zram, struct page *page,
                                    u32 index, struct bio *bio, bool partial_io)
{
        struct bio_vec bvec;

        bvec_set_page(&bvec, page, PAGE_SIZE, 0);
        return read_from_bdev(zram, &bvec, zram_get_element(zram, index), bio,
                              partial_io);
}

/*
 * Reads (decompresses if needed) a page from zspool (zsmalloc).
 * Corresponding ZRAM slot should be locked.
 */
static int zram_read_from_zspool(struct zram *zram, struct page *page,
                                 u32 index)
{
        struct zcomp_strm *zstrm;
        unsigned long handle;
        unsigned int size;
        void *src, *dst;
        u32 prio;
        int ret;

        handle = zram_get_handle(zram, index);
        if (!handle || zram_test_flag(zram, index, ZRAM_SAME)) {
                unsigned long value;
                void *mem;

                value = handle ? zram_get_element(zram, index) : 0;
                mem = kmap_atomic(page);
                zram_fill_page(mem, PAGE_SIZE, value);
                kunmap_atomic(mem);
                return 0;
        }

        size = zram_get_obj_size(zram, index);

        if (size != PAGE_SIZE) {
                prio = zram_get_priority(zram, index);
                zstrm = zcomp_stream_get(zram->comps[prio]);
        }

        src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
        if (size == PAGE_SIZE) {
                dst = kmap_atomic(page);
                memcpy(dst, src, PAGE_SIZE);
                kunmap_atomic(dst);
                ret = 0;
        } else {
                dst = kmap_atomic(page);
                ret = zcomp_decompress(zstrm, src, size, dst);
                kunmap_atomic(dst);
                zcomp_stream_put(zram->comps[prio]);
        }
        zs_unmap_object(zram->mem_pool, handle);
        return ret;
}

static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
                            struct bio *bio, bool partial_io)
{
        int ret;

        zram_slot_lock(zram, index);
        if (!zram_test_flag(zram, index, ZRAM_WB)) {
                /* Slot should be locked through out the function call */
                ret = zram_read_from_zspool(zram, page, index);
                zram_slot_unlock(zram, index);
        } else {
                /* Slot should be unlocked before the function call */
                zram_slot_unlock(zram, index);

                ret = zram_bvec_read_from_bdev(zram, page, index, bio,
                                               partial_io);
        }

        /* Should NEVER happen. Return bio error if it does. */
        if (WARN_ON(ret < 0))
                pr_err("Decompression failed! err=%d, page=%u\n", ret, index);

        return ret;
}

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

        page = bvec->bv_page;
        if (is_partial_io(bvec)) {
                /* Use a temporary buffer to decompress the page */
                page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
                if (!page)
                        return -ENOMEM;
        }

        ret = __zram_bvec_read(zram, page, index, bio, is_partial_io(bvec));
        if (unlikely(ret))
                goto out;

        if (is_partial_io(bvec)) {
                void *src = kmap_atomic(page);

                memcpy_to_bvec(bvec, src + offset);
                kunmap_atomic(src);
        }
out:
        if (is_partial_io(bvec))
                __free_page(page);

        return ret;
}

static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
                                u32 index, struct bio *bio)
{
        int ret = 0;
        unsigned long alloced_pages;
        unsigned long handle = -ENOMEM;
        unsigned int comp_len = 0;
        void *src, *dst, *mem;
        struct zcomp_strm *zstrm;
        struct page *page = bvec->bv_page;
        unsigned long element = 0;
        enum zram_pageflags flags = 0;

        mem = kmap_atomic(page);
        if (page_same_filled(mem, &element)) {
                kunmap_atomic(mem);
                /* Free memory associated with this sector now. */
                flags = ZRAM_SAME;
                atomic64_inc(&zram->stats.same_pages);
                goto out;
        }
        kunmap_atomic(mem);

compress_again:
        zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
        src = kmap_atomic(page);
        ret = zcomp_compress(zstrm, src, &comp_len);
        kunmap_atomic(src);

        if (unlikely(ret)) {
                zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
                pr_err("Compression failed! err=%d\n", ret);
                zs_free(zram->mem_pool, handle);
                return ret;
        }

        if (comp_len >= huge_class_size)
                comp_len = PAGE_SIZE;
        /*
         * handle allocation has 2 paths:
         * a) fast path is executed with preemption disabled (for
         *  per-cpu streams) and has __GFP_DIRECT_RECLAIM bit clear,
         *  since we can't sleep;
         * b) slow path enables preemption and attempts to allocate
         *  the page with __GFP_DIRECT_RECLAIM bit set. we have to
         *  put per-cpu compression stream and, thus, to re-do
         *  the compression once handle is allocated.
         *
         * if we have a 'non-null' handle here then we are coming
         * from the slow path and handle has already been allocated.
         */
        if (IS_ERR_VALUE(handle))
                handle = zs_malloc(zram->mem_pool, comp_len,
                                __GFP_KSWAPD_RECLAIM |
                                __GFP_NOWARN |
                                __GFP_HIGHMEM |
                                __GFP_MOVABLE);
        if (IS_ERR_VALUE(handle)) {
                zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
                atomic64_inc(&zram->stats.writestall);
                handle = zs_malloc(zram->mem_pool, comp_len,
                                GFP_NOIO | __GFP_HIGHMEM |
                                __GFP_MOVABLE);
                if (IS_ERR_VALUE(handle))
                        return PTR_ERR((void *)handle);

                if (comp_len != PAGE_SIZE)
                        goto compress_again;
                /*
                 * If the page is not compressible, you need to acquire the
                 * lock and execute the code below. The zcomp_stream_get()
                 * call is needed to disable the cpu hotplug and grab the
                 * zstrm buffer back. It is necessary that the dereferencing
                 * of the zstrm variable below occurs correctly.
                 */
                zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
        }

        alloced_pages = zs_get_total_pages(zram->mem_pool);
        update_used_max(zram, alloced_pages);

        if (zram->limit_pages && alloced_pages > zram->limit_pages) {
                zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
                zs_free(zram->mem_pool, handle);
                return -ENOMEM;
        }

        dst = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);

        src = zstrm->buffer;
        if (comp_len == PAGE_SIZE)
                src = kmap_atomic(page);
        memcpy(dst, src, comp_len);
        if (comp_len == PAGE_SIZE)
                kunmap_atomic(src);

        zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
        zs_unmap_object(zram->mem_pool, handle);
        atomic64_add(comp_len, &zram->stats.compr_data_size);
out:
        /*
         * Free memory associated with this sector
         * before overwriting unused sectors.
         */
        zram_slot_lock(zram, index);
        zram_free_page(zram, index);

        if (comp_len == PAGE_SIZE) {
                zram_set_flag(zram, index, ZRAM_HUGE);
                atomic64_inc(&zram->stats.huge_pages);
                atomic64_inc(&zram->stats.huge_pages_since);
        }

        if (flags) {
                zram_set_flag(zram, index, flags);
                zram_set_element(zram, index, element);
        }  else {
                zram_set_handle(zram, index, handle);
                zram_set_obj_size(zram, index, comp_len);
        }
        zram_slot_unlock(zram, index);

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

static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
                                u32 index, int offset, struct bio *bio)
{
        int ret;
        struct page *page = NULL;
        struct bio_vec vec;

        vec = *bvec;
        if (is_partial_io(bvec)) {
                void *dst;
                /*
                 * This is a partial IO. We need to read the full page
                 * before to write the changes.
                 */
                page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
                if (!page)
                        return -ENOMEM;

                ret = __zram_bvec_read(zram, page, index, bio, true);
                if (ret)
                        goto out;

                dst = kmap_atomic(page);
                memcpy_from_bvec(dst + offset, bvec);
                kunmap_atomic(dst);

                bvec_set_page(&vec, page, PAGE_SIZE, 0);
        }

        ret = __zram_bvec_write(zram, &vec, index, bio);
out:
        if (is_partial_io(bvec))
                __free_page(page);
        return ret;
}

#ifdef CONFIG_ZRAM_MULTI_COMP
/*
 * This function will decompress (unless it's ZRAM_HUGE) the page and then
 * attempt to compress it using provided compression algorithm priority
 * (which is potentially more effective).
 *
 * Corresponding ZRAM slot should be locked.
 */
static int zram_recompress(struct zram *zram, u32 index, struct page *page,
                           u32 threshold, u32 prio, u32 prio_max)
{
        struct zcomp_strm *zstrm = NULL;
        unsigned long handle_old;
        unsigned long handle_new;
        unsigned int comp_len_old;
        unsigned int comp_len_new;
        unsigned int class_index_old;
        unsigned int class_index_new;
        u32 num_recomps = 0;
        void *src, *dst;
        int ret;

        handle_old = zram_get_handle(zram, index);
        if (!handle_old)
                return -EINVAL;

        comp_len_old = zram_get_obj_size(zram, index);
        /*
         * Do not recompress objects that are already "small enough".
         */
        if (comp_len_old < threshold)
                return 0;

        ret = zram_read_from_zspool(zram, page, index);
        if (ret)
                return ret;

        class_index_old = zs_lookup_class_index(zram->mem_pool, comp_len_old);
        /*
         * Iterate the secondary comp algorithms list (in order of priority)
         * and try to recompress the page.
         */
        for (; prio < prio_max; prio++) {
                if (!zram->comps[prio])
                        continue;

                /*
                 * Skip if the object is already re-compressed with a higher
                 * priority algorithm (or same algorithm).
                 */
                if (prio <= zram_get_priority(zram, index))
                        continue;

                num_recomps++;
                zstrm = zcomp_stream_get(zram->comps[prio]);
                src = kmap_atomic(page);
                ret = zcomp_compress(zstrm, src, &comp_len_new);
                kunmap_atomic(src);

                if (ret) {
                        zcomp_stream_put(zram->comps[prio]);
                        return ret;
                }

                class_index_new = zs_lookup_class_index(zram->mem_pool,
                                                        comp_len_new);

                /* Continue until we make progress */
                if (class_index_new >= class_index_old ||
                    (threshold && comp_len_new >= threshold)) {
                        zcomp_stream_put(zram->comps[prio]);
                        continue;
                }

                /* Recompression was successful so break out */
                break;
        }

        /*
         * We did not try to recompress, e.g. when we have only one
         * secondary algorithm and the page is already recompressed
         * using that algorithm
         */
        if (!zstrm)
                return 0;

        if (class_index_new >= class_index_old) {
                /*
                 * Secondary algorithms failed to re-compress the page
                 * in a way that would save memory, mark the object as
                 * incompressible so that we will not try to compress
                 * it again.
                 *
                 * We need to make sure that all secondary algorithms have
                 * failed, so we test if the number of recompressions matches
                 * the number of active secondary algorithms.
                 */
                if (num_recomps == zram->num_active_comps - 1)
                        zram_set_flag(zram, index, ZRAM_INCOMPRESSIBLE);
                return 0;
        }

        /* Successful recompression but above threshold */
        if (threshold && comp_len_new >= threshold)
                return 0;

        /*
         * No direct reclaim (slow path) for handle allocation and no
         * re-compression attempt (unlike in __zram_bvec_write()) since
         * we already have stored that object in zsmalloc. If we cannot
         * alloc memory for recompressed object then we bail out and
         * simply keep the old (existing) object in zsmalloc.
         */
        handle_new = zs_malloc(zram->mem_pool, comp_len_new,
                               __GFP_KSWAPD_RECLAIM |
                               __GFP_NOWARN |
                               __GFP_HIGHMEM |
                               __GFP_MOVABLE);
        if (IS_ERR_VALUE(handle_new)) {
                zcomp_stream_put(zram->comps[prio]);
                return PTR_ERR((void *)handle_new);
        }

        dst = zs_map_object(zram->mem_pool, handle_new, ZS_MM_WO);
        memcpy(dst, zstrm->buffer, comp_len_new);
        zcomp_stream_put(zram->comps[prio]);

        zs_unmap_object(zram->mem_pool, handle_new);

        zram_free_page(zram, index);
        zram_set_handle(zram, index, handle_new);
        zram_set_obj_size(zram, index, comp_len_new);
        zram_set_priority(zram, index, prio);

        atomic64_add(comp_len_new, &zram->stats.compr_data_size);
        atomic64_inc(&zram->stats.pages_stored);

        return 0;
}

#define RECOMPRESS_IDLE         (1 << 0)
#define RECOMPRESS_HUGE         (1 << 1)

static ssize_t recompress_store(struct device *dev,
                                struct device_attribute *attr,
                                const char *buf, size_t len)
{
        u32 prio = ZRAM_SECONDARY_COMP, prio_max = ZRAM_MAX_COMPS;
        struct zram *zram = dev_to_zram(dev);
        unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
        char *args, *param, *val, *algo = NULL;
        u32 mode = 0, threshold = 0;
        unsigned long index;
        struct page *page;
        ssize_t ret;

        args = skip_spaces(buf);
        while (*args) {
                args = next_arg(args, &param, &val);

                if (!val || !*val)
                        return -EINVAL;

                if (!strcmp(param, "type")) {
                        if (!strcmp(val, "idle"))
                                mode = RECOMPRESS_IDLE;
                        if (!strcmp(val, "huge"))
                                mode = RECOMPRESS_HUGE;
                        if (!strcmp(val, "huge_idle"))
                                mode = RECOMPRESS_IDLE | RECOMPRESS_HUGE;
                        continue;
                }

                if (!strcmp(param, "threshold")) {
                        /*
                         * We will re-compress only idle objects equal or
                         * greater in size than watermark.
                         */
                        ret = kstrtouint(val, 10, &threshold);
                        if (ret)
                                return ret;
                        continue;
                }

                if (!strcmp(param, "algo")) {
                        algo = val;
                        continue;
                }
        }

        if (threshold >= PAGE_SIZE)
                return -EINVAL;

        down_read(&zram->init_lock);
        if (!init_done(zram)) {
                ret = -EINVAL;
                goto release_init_lock;
        }

        if (algo) {
                bool found = false;

                for (; prio < ZRAM_MAX_COMPS; prio++) {
                        if (!zram->comp_algs[prio])
                                continue;

                        if (!strcmp(zram->comp_algs[prio], algo)) {
                                prio_max = min(prio + 1, ZRAM_MAX_COMPS);
                                found = true;
                                break;
                        }
                }

                if (!found) {
                        ret = -EINVAL;
                        goto release_init_lock;
                }
        }

        page = alloc_page(GFP_KERNEL);
        if (!page) {
                ret = -ENOMEM;
                goto release_init_lock;
        }

        ret = len;
        for (index = 0; index < nr_pages; index++) {
                int err = 0;

                zram_slot_lock(zram, index);

                if (!zram_allocated(zram, index))
                        goto next;

                if (mode & RECOMPRESS_IDLE &&
                    !zram_test_flag(zram, index, ZRAM_IDLE))
                        goto next;

                if (mode & RECOMPRESS_HUGE &&
                    !zram_test_flag(zram, index, ZRAM_HUGE))
                        goto next;

                if (zram_test_flag(zram, index, ZRAM_WB) ||
                    zram_test_flag(zram, index, ZRAM_UNDER_WB) ||
                    zram_test_flag(zram, index, ZRAM_SAME) ||
                    zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
                        goto next;

                err = zram_recompress(zram, index, page, threshold,
                                      prio, prio_max);
next:
                zram_slot_unlock(zram, index);
                if (err) {
                        ret = err;
                        break;
                }

                cond_resched();
        }

        __free_page(page);

release_init_lock:
        up_read(&zram->init_lock);
        return ret;
}
#endif

/*
 * zram_bio_discard - handler on discard request
 * @index: physical block index in PAGE_SIZE units
 * @offset: byte offset within physical block
 */
static void zram_bio_discard(struct zram *zram, u32 index,
                             int offset, struct bio *bio)
{
        size_t n = bio->bi_iter.bi_size;

        /*
         * zram manages data in physical block size units. Because logical block
         * size isn't identical with physical block size on some arch, we
         * could get a discard request pointing to a specific offset within a
         * certain physical block.  Although we can handle this request by
         * reading that physiclal block and decompressing and partially zeroing
         * and re-compressing and then re-storing it, this isn't reasonable
         * because our intent with a discard request is to save memory.  So
         * skipping this logical block is appropriate here.
         */
        if (offset) {
                if (n <= (PAGE_SIZE - offset))
                        return;

                n -= (PAGE_SIZE - offset);
                index++;
        }

        while (n >= PAGE_SIZE) {
                zram_slot_lock(zram, index);
                zram_free_page(zram, index);
                zram_slot_unlock(zram, index);
                atomic64_inc(&zram->stats.notify_free);
                index++;
                n -= PAGE_SIZE;
        }
}

/*
 * Returns errno if it has some problem. Otherwise return 0 or 1.
 * Returns 0 if IO request was done synchronously
 * Returns 1 if IO request was successfully submitted.
 */
static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
                        int offset, enum req_op op, struct bio *bio)
{
        int ret;

        if (!op_is_write(op)) {
                ret = zram_bvec_read(zram, bvec, index, offset, bio);
                flush_dcache_page(bvec->bv_page);
        } else {
                ret = zram_bvec_write(zram, bvec, index, offset, bio);
        }

        zram_slot_lock(zram, index);
        zram_accessed(zram, index);
        zram_slot_unlock(zram, index);

        if (unlikely(ret < 0)) {
                if (!op_is_write(op))
                        atomic64_inc(&zram->stats.failed_reads);
                else
                        atomic64_inc(&zram->stats.failed_writes);
        }

        return ret;
}

static void __zram_make_request(struct zram *zram, struct bio *bio)
{
        int offset;
        u32 index;
        struct bio_vec bvec;
        struct bvec_iter iter;
        unsigned long start_time;

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

        switch (bio_op(bio)) {
        case REQ_OP_DISCARD:
        case REQ_OP_WRITE_ZEROES:
                zram_bio_discard(zram, index, offset, bio);
                bio_endio(bio);
                return;
        default:
                break;
        }

        start_time = bio_start_io_acct(bio);
        bio_for_each_segment(bvec, bio, iter) {
                struct bio_vec bv = bvec;
                unsigned int unwritten = bvec.bv_len;

                do {
                        bv.bv_len = min_t(unsigned int, PAGE_SIZE - offset,
                                                        unwritten);
                        if (zram_bvec_rw(zram, &bv, index, offset,
                                         bio_op(bio), bio) < 0) {
                                bio->bi_status = BLK_STS_IOERR;
                                break;
                        }

                        bv.bv_offset += bv.bv_len;
                        unwritten -= bv.bv_len;

                        update_position(&index, &offset, &bv);
                } while (unwritten);
        }
        bio_end_io_acct(bio, start_time);
        bio_endio(bio);
}

/*
 * Handler function for all zram I/O requests.
 */
static void zram_submit_bio(struct bio *bio)
{
        struct zram *zram = bio->bi_bdev->bd_disk->private_data;

        if (!valid_io_request(zram, bio->bi_iter.bi_sector,
                                        bio->bi_iter.bi_size)) {
                atomic64_inc(&zram->stats.invalid_io);
                bio_io_error(bio);
                return;
        }

        __zram_make_request(zram, bio);
}

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

        zram = bdev->bd_disk->private_data;

        atomic64_inc(&zram->stats.notify_free);
        if (!zram_slot_trylock(zram, index)) {
                atomic64_inc(&zram->stats.miss_free);
                return;
        }

        zram_free_page(zram, index);
        zram_slot_unlock(zram, index);
}

static void zram_destroy_comps(struct zram *zram)
{
        u32 prio;

        for (prio = 0; prio < ZRAM_MAX_COMPS; prio++) {
                struct zcomp *comp = zram->comps[prio];

                zram->comps[prio] = NULL;
                if (!comp)
                        continue;
                zcomp_destroy(comp);
                zram->num_active_comps--;
        }
}

static void zram_reset_device(struct zram *zram)
{
        down_write(&zram->init_lock);

        zram->limit_pages = 0;

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

        set_capacity_and_notify(zram->disk, 0);
        part_stat_set_all(zram->disk->part0, 0);

        /* I/O operation under all of CPU are done so let's free */
        zram_meta_free(zram, zram->disksize);
        zram->disksize = 0;
        zram_destroy_comps(zram);
        memset(&zram->stats, 0, sizeof(zram->stats));
        reset_bdev(zram);

        comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);
        up_write(&zram->init_lock);
}

static ssize_t disksize_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        u64 disksize;
        struct zcomp *comp;
        struct zram *zram = dev_to_zram(dev);
        int err;
        u32 prio;

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

        down_write(&zram->init_lock);
        if (init_done(zram)) {
                pr_info("Cannot change disksize for initialized device\n");
                err = -EBUSY;
                goto out_unlock;
        }

        disksize = PAGE_ALIGN(disksize);
        if (!zram_meta_alloc(zram, disksize)) {
                err = -ENOMEM;
                goto out_unlock;
        }

        for (prio = 0; prio < ZRAM_MAX_COMPS; prio++) {
                if (!zram->comp_algs[prio])
                        continue;

                comp = zcomp_create(zram->comp_algs[prio]);
                if (IS_ERR(comp)) {
                        pr_err("Cannot initialise %s compressing backend\n",
                               zram->comp_algs[prio]);
                        err = PTR_ERR(comp);
                        goto out_free_comps;
                }

                zram->comps[prio] = comp;
                zram->num_active_comps++;
        }
        zram->disksize = disksize;
        set_capacity_and_notify(zram->disk, zram->disksize >> SECTOR_SHIFT);
        up_write(&zram->init_lock);

        return len;

out_free_comps:
        zram_destroy_comps(zram);
        zram_meta_free(zram, disksize);
out_unlock:
        up_write(&zram->init_lock);
        return err;
}

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 gendisk *disk;

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

        if (!do_reset)
                return -EINVAL;

        zram = dev_to_zram(dev);
        disk = zram->disk;

        mutex_lock(&disk->open_mutex);
        /* Do not reset an active device or claimed device */
        if (disk_openers(disk) || zram->claim) {
                mutex_unlock(&disk->open_mutex);
                return -EBUSY;
        }

        /* From now on, anyone can't open /dev/zram[0-9] */
        zram->claim = true;
        mutex_unlock(&disk->open_mutex);

        /* Make sure all the pending I/O are finished */
        sync_blockdev(disk->part0);
        zram_reset_device(zram);

        mutex_lock(&disk->open_mutex);
        zram->claim = false;
        mutex_unlock(&disk->open_mutex);

        return len;
}

static int zram_open(struct block_device *bdev, fmode_t mode)
{
        int ret = 0;
        struct zram *zram;

        WARN_ON(!mutex_is_locked(&bdev->bd_disk->open_mutex));

        zram = bdev->bd_disk->private_data;
        /* zram was claimed to reset so open request fails */
        if (zram->claim)
                ret = -EBUSY;

        return ret;
}

static const struct block_device_operations zram_devops = {
        .open = zram_open,
        .submit_bio = zram_submit_bio,
        .swap_slot_free_notify = zram_slot_free_notify,
        .owner = THIS_MODULE
};

static DEVICE_ATTR_WO(compact);
static DEVICE_ATTR_RW(disksize);
static DEVICE_ATTR_RO(initstate);
static DEVICE_ATTR_WO(reset);
static DEVICE_ATTR_WO(mem_limit);
static DEVICE_ATTR_WO(mem_used_max);
static DEVICE_ATTR_WO(idle);
static DEVICE_ATTR_RW(max_comp_streams);
static DEVICE_ATTR_RW(comp_algorithm);
#ifdef CONFIG_ZRAM_WRITEBACK
static DEVICE_ATTR_RW(backing_dev);
static DEVICE_ATTR_WO(writeback);
static DEVICE_ATTR_RW(writeback_limit);
static DEVICE_ATTR_RW(writeback_limit_enable);
#endif
#ifdef CONFIG_ZRAM_MULTI_COMP
static DEVICE_ATTR_RW(recomp_algorithm);
static DEVICE_ATTR_WO(recompress);
#endif

static struct attribute *zram_disk_attrs[] = {
        &dev_attr_disksize.attr,
        &dev_attr_initstate.attr,
        &dev_attr_reset.attr,
        &dev_attr_compact.attr,
        &dev_attr_mem_limit.attr,
        &dev_attr_mem_used_max.attr,
        &dev_attr_idle.attr,
        &dev_attr_max_comp_streams.attr,
        &dev_attr_comp_algorithm.attr,
#ifdef CONFIG_ZRAM_WRITEBACK
        &dev_attr_backing_dev.attr,
        &dev_attr_writeback.attr,
        &dev_attr_writeback_limit.attr,
        &dev_attr_writeback_limit_enable.attr,
#endif
        &dev_attr_io_stat.attr,
        &dev_attr_mm_stat.attr,
#ifdef CONFIG_ZRAM_WRITEBACK
        &dev_attr_bd_stat.attr,
#endif
        &dev_attr_debug_stat.attr,
#ifdef CONFIG_ZRAM_MULTI_COMP
        &dev_attr_recomp_algorithm.attr,
        &dev_attr_recompress.attr,
#endif
        NULL,
};

ATTRIBUTE_GROUPS(zram_disk);

/*
 * Allocate and initialize new zram device. the function returns
 * '>= 0' device_id upon success, and negative value otherwise.
 */
static int zram_add(void)
{
        struct zram *zram;
        int ret, device_id;

        zram = kzalloc(sizeof(struct zram), GFP_KERNEL);
        if (!zram)
                return -ENOMEM;

        ret = idr_alloc(&zram_index_idr, zram, 0, 0, GFP_KERNEL);
        if (ret < 0)
                goto out_free_dev;
        device_id = ret;

        init_rwsem(&zram->init_lock);
#ifdef CONFIG_ZRAM_WRITEBACK
        spin_lock_init(&zram->wb_limit_lock);
#endif

        /* gendisk structure */
        zram->disk = blk_alloc_disk(NUMA_NO_NODE);
        if (!zram->disk) {
                pr_err("Error allocating disk structure for device %d\n",
                        device_id);
                ret = -ENOMEM;
                goto out_free_idr;
        }

        zram->disk->major = zram_major;
        zram->disk->first_minor = device_id;
        zram->disk->minors = 1;
        zram->disk->flags |= GENHD_FL_NO_PART;
        zram->disk->fops = &zram_devops;
        zram->disk->private_data = zram;
        snprintf(zram->disk->disk_name, 16, "zram%d", device_id);

        /* Actual capacity set using sysfs (/sys/block/zram<id>/disksize */
        set_capacity(zram->disk, 0);
        /* zram devices sort of resembles non-rotational disks */
        blk_queue_flag_set(QUEUE_FLAG_NONROT, zram->disk->queue);
        blk_queue_flag_set(QUEUE_FLAG_SYNCHRONOUS, zram->disk->queue);
        blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, zram->disk->queue);

        /*
         * 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);
        zram->disk->queue->limits.discard_granularity = PAGE_SIZE;
        blk_queue_max_discard_sectors(zram->disk->queue, UINT_MAX);

        /*
         * zram_bio_discard() will clear all logical blocks if logical block
         * size is identical with physical block size(PAGE_SIZE). But if it is
         * different, we will skip discarding some parts of logical blocks in
         * the part of the request range which isn't aligned to physical block
         * size.  So we can't ensure that all discarded logical blocks are
         * zeroed.
         */
        if (ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE)
                blk_queue_max_write_zeroes_sectors(zram->disk->queue, UINT_MAX);

        blk_queue_flag_set(QUEUE_FLAG_STABLE_WRITES, zram->disk->queue);
        ret = device_add_disk(NULL, zram->disk, zram_disk_groups);
        if (ret)
                goto out_cleanup_disk;

        comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);

        zram_debugfs_register(zram);
        pr_info("Added device: %s\n", zram->disk->disk_name);
        return device_id;

out_cleanup_disk:
        put_disk(zram->disk);
out_free_idr:
        idr_remove(&zram_index_idr, device_id);
out_free_dev:
        kfree(zram);
        return ret;
}

static int zram_remove(struct zram *zram)
{
        bool claimed;

        mutex_lock(&zram->disk->open_mutex);
        if (disk_openers(zram->disk)) {
                mutex_unlock(&zram->disk->open_mutex);
                return -EBUSY;
        }

        claimed = zram->claim;
        if (!claimed)
                zram->claim = true;
        mutex_unlock(&zram->disk->open_mutex);

        zram_debugfs_unregister(zram);

        if (claimed) {
                /*
                 * If we were claimed by reset_store(), del_gendisk() will
                 * wait until reset_store() is done, so nothing need to do.
                 */
                ;
        } else {
                /* Make sure all the pending I/O are finished */
                sync_blockdev(zram->disk->part0);
                zram_reset_device(zram);
        }

        pr_info("Removed device: %s\n", zram->disk->disk_name);

        del_gendisk(zram->disk);

        /* del_gendisk drains pending reset_store */
        WARN_ON_ONCE(claimed && zram->claim);

        /*
         * disksize_store() may be called in between zram_reset_device()
         * and del_gendisk(), so run the last reset to avoid leaking
         * anything allocated with disksize_store()
         */
        zram_reset_device(zram);

        put_disk(zram->disk);
        kfree(zram);
        return 0;
}

/* zram-control sysfs attributes */

/*
 * NOTE: hot_add attribute is not the usual read-only sysfs attribute. In a
 * sense that reading from this file does alter the state of your system -- it
 * creates a new un-initialized zram device and returns back this device's
 * device_id (or an error code if it fails to create a new device).
 */
static ssize_t hot_add_show(struct class *class,
                        struct class_attribute *attr,
                        char *buf)
{
        int ret;

        mutex_lock(&zram_index_mutex);
        ret = zram_add();
        mutex_unlock(&zram_index_mutex);

        if (ret < 0)
                return ret;
        return scnprintf(buf, PAGE_SIZE, "%d\n", ret);
}
static struct class_attribute class_attr_hot_add =
        __ATTR(hot_add, 0400, hot_add_show, NULL);

static ssize_t hot_remove_store(struct class *class,
                        struct class_attribute *attr,
                        const char *buf,
                        size_t count)
{
        struct zram *zram;
        int ret, dev_id;

        /* dev_id is gendisk->first_minor, which is `int' */
        ret = kstrtoint(buf, 10, &dev_id);
        if (ret)
                return ret;
        if (dev_id < 0)
                return -EINVAL;

        mutex_lock(&zram_index_mutex);

        zram = idr_find(&zram_index_idr, dev_id);
        if (zram) {
                ret = zram_remove(zram);
                if (!ret)
                        idr_remove(&zram_index_idr, dev_id);
        } else {
                ret = -ENODEV;
        }

        mutex_unlock(&zram_index_mutex);
        return ret ? ret : count;
}
static CLASS_ATTR_WO(hot_remove);

static struct attribute *zram_control_class_attrs[] = {
        &class_attr_hot_add.attr,
        &class_attr_hot_remove.attr,
        NULL,
};
ATTRIBUTE_GROUPS(zram_control_class);

static struct class zram_control_class = {
        .name           = "zram-control",
        .class_groups   = zram_control_class_groups,
};

static int zram_remove_cb(int id, void *ptr, void *data)
{
        WARN_ON_ONCE(zram_remove(ptr));
        return 0;
}

static void destroy_devices(void)
{
        class_unregister(&zram_control_class);
        idr_for_each(&zram_index_idr, &zram_remove_cb, NULL);
        zram_debugfs_destroy();
        idr_destroy(&zram_index_idr);
        unregister_blkdev(zram_major, "zram");
        cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
}

static int __init zram_init(void)
{
        int ret;

        BUILD_BUG_ON(__NR_ZRAM_PAGEFLAGS > BITS_PER_LONG);

        ret = cpuhp_setup_state_multi(CPUHP_ZCOMP_PREPARE, "block/zram:prepare",
                                      zcomp_cpu_up_prepare, zcomp_cpu_dead);
        if (ret < 0)
                return ret;

        ret = class_register(&zram_control_class);
        if (ret) {
                pr_err("Unable to register zram-control class\n");
                cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
                return ret;
        }

        zram_debugfs_create();
        zram_major = register_blkdev(0, "zram");
        if (zram_major <= 0) {
                pr_err("Unable to get major number\n");
                class_unregister(&zram_control_class);
                cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
                return -EBUSY;
        }

        while (num_devices != 0) {
                mutex_lock(&zram_index_mutex);
                ret = zram_add();
                mutex_unlock(&zram_index_mutex);
                if (ret < 0)
                        goto out_error;
                num_devices--;
        }

        return 0;

out_error:
        destroy_devices();
        return ret;
}

static void __exit zram_exit(void)
{
        destroy_devices();
}

module_init(zram_init);
module_exit(zram_exit);

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

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