[mirror_ubuntu-artful-kernel.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/genhd.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/vmalloc.h>
#include <linux/err.h>
#include <linux/idr.h>
#include <linux/sysfs.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 = "lzo";

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

static inline void deprecated_attr_warn(const char *name)
{
        pr_warn_once("%d (%s) Attribute %s (and others) will be removed. %s\n",
                        task_pid_nr(current),
                        current->comm,
                        name,
                        "See zram documentation.");
}

#define ZRAM_ATTR_RO(name)                                              \
static ssize_t name##_show(struct device *d,                            \
                                struct device_attribute *attr, char *b) \
{                                                                       \
        struct zram *zram = dev_to_zram(d);                             \
                                                                        \
        deprecated_attr_warn(__stringify(name));                        \
        return scnprintf(b, PAGE_SIZE, "%llu\n",                        \
                (u64)atomic64_read(&zram->stats.name));                 \
}                                                                       \
static DEVICE_ATTR_RO(name);

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;
}

/* flag operations require table entry bit_spin_lock() being held */
static int zram_test_flag(struct zram_meta *meta, u32 index,
                        enum zram_pageflags flag)
{
        return meta->table[index].value & BIT(flag);
}

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

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

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

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

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

static inline bool 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 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 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)
{
        if (*offset + bvec->bv_len >= PAGE_SIZE)
                (*index)++;
        *offset = (*offset + bvec->bv_len) % PAGE_SIZE;
}

static inline void update_used_max(struct zram *zram,
                                        const unsigned long pages)
{
        unsigned long old_max, cur_max;

        old_max = atomic_long_read(&zram->stats.max_used_pages);

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

static bool 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 false;
        }

        return true;
}

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

        deprecated_attr_warn("orig_data_size");
        return scnprintf(buf, PAGE_SIZE, "%llu\n",
                (u64)(atomic64_read(&zram->stats.pages_stored)) << PAGE_SHIFT);
}

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);

        deprecated_attr_warn("mem_used_total");
        down_read(&zram->init_lock);
        if (init_done(zram)) {
                struct zram_meta *meta = zram->meta;
                val = zs_get_total_pages(meta->mem_pool);
        }
        up_read(&zram->init_lock);

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

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

        deprecated_attr_warn("mem_limit");
        down_read(&zram->init_lock);
        val = zram->limit_pages;
        up_read(&zram->init_lock);

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

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_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        u64 val = 0;
        struct zram *zram = dev_to_zram(dev);

        deprecated_attr_warn("mem_used_max");
        down_read(&zram->init_lock);
        if (init_done(zram))
                val = atomic_long_read(&zram->stats.max_used_pages);
        up_read(&zram->init_lock);

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

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)) {
                struct zram_meta *meta = zram->meta;
                atomic_long_set(&zram->stats.max_used_pages,
                                zs_get_total_pages(meta->mem_pool));
        }
        up_read(&zram->init_lock);

        return len;
}

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

        down_read(&zram->init_lock);
        sz = zcomp_available_show(zram->compressor, buf);
        up_read(&zram->init_lock);

        return sz;
}

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);
        size_t sz;

        if (!zcomp_available_algorithm(buf))
                return -EINVAL;

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

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

        up_write(&zram->init_lock);
        return len;
}

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);
        struct zram_meta *meta;

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

        meta = zram->meta;
        zs_compact(meta->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->meta->mem_pool);
                zs_pool_stats(zram->meta->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\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.zero_pages),
                        pool_stats.pages_compacted);
        up_read(&zram->init_lock);

        return ret;
}

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\n",
                        version,
                        (u64)atomic64_read(&zram->stats.writestall));
        up_read(&zram->init_lock);

        return ret;
}

static DEVICE_ATTR_RO(io_stat);
static DEVICE_ATTR_RO(mm_stat);
static DEVICE_ATTR_RO(debug_stat);
ZRAM_ATTR_RO(num_reads);
ZRAM_ATTR_RO(num_writes);
ZRAM_ATTR_RO(failed_reads);
ZRAM_ATTR_RO(failed_writes);
ZRAM_ATTR_RO(invalid_io);
ZRAM_ATTR_RO(notify_free);
ZRAM_ATTR_RO(zero_pages);
ZRAM_ATTR_RO(compr_data_size);

static inline bool zram_meta_get(struct zram *zram)
{
        if (atomic_inc_not_zero(&zram->refcount))
                return true;
        return false;
}

static inline void zram_meta_put(struct zram *zram)
{
        atomic_dec(&zram->refcount);
}

static void zram_meta_free(struct zram_meta *meta, 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++) {
                unsigned long handle = meta->table[index].handle;

                if (!handle)
                        continue;

                zs_free(meta->mem_pool, handle);
        }

        zs_destroy_pool(meta->mem_pool);
        vfree(meta->table);
        kfree(meta);
}

static struct zram_meta *zram_meta_alloc(char *pool_name, u64 disksize)
{
        size_t num_pages;
        struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);

        if (!meta)
                return NULL;

        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 out_error;
        }

        meta->mem_pool = zs_create_pool(pool_name);
        if (!meta->mem_pool) {
                pr_err("Error creating memory pool\n");
                goto out_error;
        }

        return meta;

out_error:
        vfree(meta->table);
        kfree(meta);
        return NULL;
}

/*
 * 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)
{
        struct zram_meta *meta = zram->meta;
        unsigned long handle = meta->table[index].handle;

        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);
                        atomic64_dec(&zram->stats.zero_pages);
                }
                return;
        }

        zs_free(meta->mem_pool, handle);

        atomic64_sub(zram_get_obj_size(meta, index),
                        &zram->stats.compr_data_size);
        atomic64_dec(&zram->stats.pages_stored);

        meta->table[index].handle = 0;
        zram_set_obj_size(meta, index, 0);
}

static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
{
        int ret = 0;
        unsigned char *cmem;
        struct zram_meta *meta = zram->meta;
        unsigned long handle;
        size_t size;

        bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
        handle = meta->table[index].handle;
        size = zram_get_obj_size(meta, index);

        if (!handle || zram_test_flag(meta, index, ZRAM_ZERO)) {
                bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
                clear_page(mem);
                return 0;
        }

        cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_RO);
        if (size == PAGE_SIZE)
                copy_page(mem, cmem);
        else
                ret = zcomp_decompress(zram->comp, cmem, size, mem);
        zs_unmap_object(meta->mem_pool, handle);
        bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);

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

        return 0;
}

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

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

        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_err("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))
                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 = 0;
        struct page *page;
        unsigned char *user_mem, *cmem, *src, *uncmem = NULL;
        struct zram_meta *meta = zram->meta;
        struct zcomp_strm *zstrm = NULL;
        unsigned long alloced_pages;

        page = bvec->bv_page;
        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;
        }

compress_again:
        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)) {
                if (user_mem)
                        kunmap_atomic(user_mem);
                /* Free memory associated with this sector now. */
                bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
                zram_free_page(zram, index);
                zram_set_flag(meta, index, ZRAM_ZERO);
                bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);

                atomic64_inc(&zram->stats.zero_pages);
                ret = 0;
                goto out;
        }

        zstrm = zcomp_strm_find(zram->comp);
        ret = zcomp_compress(zram->comp, zstrm, uncmem, &clen);
        if (!is_partial_io(bvec)) {
                kunmap_atomic(user_mem);
                user_mem = NULL;
                uncmem = NULL;
        }

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

        src = zstrm->buffer;
        if (unlikely(clen > max_zpage_size)) {
                clen = PAGE_SIZE;
                if (is_partial_io(bvec))
                        src = uncmem;
        }

        /*
         * 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 (!handle)
                handle = zs_malloc(meta->mem_pool, clen,
                                __GFP_KSWAPD_RECLAIM |
                                __GFP_NOWARN |
                                __GFP_HIGHMEM);
        if (!handle) {
                zcomp_strm_release(zram->comp, zstrm);
                zstrm = NULL;

                atomic64_inc(&zram->stats.writestall);

                handle = zs_malloc(meta->mem_pool, clen,
                                GFP_NOIO | __GFP_HIGHMEM);
                if (handle)
                        goto compress_again;

                pr_err("Error allocating memory for compressed page: %u, size=%zu\n",
                        index, clen);
                ret = -ENOMEM;
                goto out;
        }

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

        if (zram->limit_pages && alloced_pages > zram->limit_pages) {
                zs_free(meta->mem_pool, handle);
                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);
        }

        zcomp_strm_release(zram->comp, zstrm);
        zstrm = NULL;
        zs_unmap_object(meta->mem_pool, handle);

        /*
         * Free memory associated with this sector
         * before overwriting unused sectors.
         */
        bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
        zram_free_page(zram, index);

        meta->table[index].handle = handle;
        zram_set_obj_size(meta, index, clen);
        bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);

        /* Update stats */
        atomic64_add(clen, &zram->stats.compr_data_size);
        atomic64_inc(&zram->stats.pages_stored);
out:
        if (zstrm)
                zcomp_strm_release(zram->comp, zstrm);
        if (is_partial_io(bvec))
                kfree(uncmem);
        return ret;
}

/*
 * 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;
        struct zram_meta *meta = zram->meta;

        /*
         * 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) {
                bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
                zram_free_page(zram, index);
                bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
                atomic64_inc(&zram->stats.notify_free);
                index++;
                n -= PAGE_SIZE;
        }
}

static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
                        int offset, int rw)
{
        unsigned long start_time = jiffies;
        int ret;

        generic_start_io_acct(rw, bvec->bv_len >> SECTOR_SHIFT,
                        &zram->disk->part0);

        if (rw == READ) {
                atomic64_inc(&zram->stats.num_reads);
                ret = zram_bvec_read(zram, bvec, index, offset);
        } else {
                atomic64_inc(&zram->stats.num_writes);
                ret = zram_bvec_write(zram, bvec, index, offset);
        }

        generic_end_io_acct(rw, &zram->disk->part0, start_time);

        if (unlikely(ret)) {
                if (rw == READ)
                        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, rw;
        u32 index;
        struct bio_vec bvec;
        struct bvec_iter iter;

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

        if (unlikely(bio->bi_rw & REQ_DISCARD)) {
                zram_bio_discard(zram, index, offset, bio);
                bio_endio(bio);
                return;
        }

        rw = bio_data_dir(bio);
        bio_for_each_segment(bvec, bio, iter) {
                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, 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, rw) < 0)
                                goto out;
                } else
                        if (zram_bvec_rw(zram, &bvec, index, offset, rw) < 0)
                                goto out;

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

        bio_endio(bio);
        return;

out:
        bio_io_error(bio);
}

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

        if (unlikely(!zram_meta_get(zram)))
                goto error;

        blk_queue_split(queue, &bio, queue->bio_split);

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

        __zram_make_request(zram, bio);
        zram_meta_put(zram);
        return BLK_QC_T_NONE;
put_zram:
        zram_meta_put(zram);
error:
        bio_io_error(bio);
        return BLK_QC_T_NONE;
}

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

        zram = bdev->bd_disk->private_data;
        meta = zram->meta;

        bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value);
        zram_free_page(zram, index);
        bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value);
        atomic64_inc(&zram->stats.notify_free);
}

static int zram_rw_page(struct block_device *bdev, sector_t sector,
                       struct page *page, int rw)
{
        int offset, err = -EIO;
        u32 index;
        struct zram *zram;
        struct bio_vec bv;

        zram = bdev->bd_disk->private_data;
        if (unlikely(!zram_meta_get(zram)))
                goto out;

        if (!valid_io_request(zram, sector, PAGE_SIZE)) {
                atomic64_inc(&zram->stats.invalid_io);
                err = -EINVAL;
                goto put_zram;
        }

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

        bv.bv_page = page;
        bv.bv_len = PAGE_SIZE;
        bv.bv_offset = 0;

        err = zram_bvec_rw(zram, &bv, index, offset, rw);
put_zram:
        zram_meta_put(zram);
out:
        /*
         * If I/O fails, just return error(ie, non-zero) without
         * calling page_endio.
         * It causes resubmit the I/O with bio request by upper functions
         * of rw_page(e.g., swap_readpage, __swap_writepage) and
         * bio->bi_end_io does things to handle the error
         * (e.g., SetPageError, set_page_dirty and extra works).
         */
        if (err == 0)
                page_endio(page, rw, 0);
        return err;
}

static void zram_reset_device(struct zram *zram)
{
        struct zram_meta *meta;
        struct zcomp *comp;
        u64 disksize;

        down_write(&zram->init_lock);

        zram->limit_pages = 0;

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

        meta = zram->meta;
        comp = zram->comp;
        disksize = zram->disksize;
        /*
         * Refcount will go down to 0 eventually and r/w handler
         * cannot handle further I/O so it will bail out by
         * check zram_meta_get.
         */
        zram_meta_put(zram);
        /*
         * We want to free zram_meta in process context to avoid
         * deadlock between reclaim path and any other locks.
         */
        wait_event(zram->io_done, atomic_read(&zram->refcount) == 0);

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

        set_capacity(zram->disk, 0);
        part_stat_set_all(&zram->disk->part0, 0);

        up_write(&zram->init_lock);
        /* I/O operation under all of CPU are done so let's free */
        zram_meta_free(meta, disksize);
        zcomp_destroy(comp);
}

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_meta *meta;
        struct zram *zram = dev_to_zram(dev);
        int err;

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

        disksize = PAGE_ALIGN(disksize);
        meta = zram_meta_alloc(zram->disk->disk_name, disksize);
        if (!meta)
                return -ENOMEM;

        comp = zcomp_create(zram->compressor);
        if (IS_ERR(comp)) {
                pr_err("Cannot initialise %s compressing backend\n",
                                zram->compressor);
                err = PTR_ERR(comp);
                goto out_free_meta;
        }

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

        init_waitqueue_head(&zram->io_done);
        atomic_set(&zram->refcount, 1);
        zram->meta = meta;
        zram->comp = comp;
        zram->disksize = disksize;
        set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
        up_write(&zram->init_lock);

        /*
         * Revalidate disk out of the init_lock to avoid lockdep splat.
         * It's okay because disk's capacity is protected by init_lock
         * so that revalidate_disk always sees up-to-date capacity.
         */
        revalidate_disk(zram->disk);

        return len;

out_destroy_comp:
        up_write(&zram->init_lock);
        zcomp_destroy(comp);
out_free_meta:
        zram_meta_free(meta, disksize);
        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 block_device *bdev;

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

        if (!do_reset)
                return -EINVAL;

        zram = dev_to_zram(dev);
        bdev = bdget_disk(zram->disk, 0);
        if (!bdev)
                return -ENOMEM;

        mutex_lock(&bdev->bd_mutex);
        /* Do not reset an active device or claimed device */
        if (bdev->bd_openers || zram->claim) {
                mutex_unlock(&bdev->bd_mutex);
                bdput(bdev);
                return -EBUSY;
        }

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

        /* Make sure all the pending I/O are finished */
        fsync_bdev(bdev);
        zram_reset_device(zram);
        revalidate_disk(zram->disk);
        bdput(bdev);

        mutex_lock(&bdev->bd_mutex);
        zram->claim = false;
        mutex_unlock(&bdev->bd_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_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,
        .swap_slot_free_notify = zram_slot_free_notify,
        .rw_page = zram_rw_page,
        .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_RO(orig_data_size);
static DEVICE_ATTR_RO(mem_used_total);
static DEVICE_ATTR_RW(mem_limit);
static DEVICE_ATTR_RW(mem_used_max);
static DEVICE_ATTR_RW(max_comp_streams);
static DEVICE_ATTR_RW(comp_algorithm);

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_failed_reads.attr,
        &dev_attr_failed_writes.attr,
        &dev_attr_compact.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,
        &dev_attr_mem_limit.attr,
        &dev_attr_mem_used_max.attr,
        &dev_attr_max_comp_streams.attr,
        &dev_attr_comp_algorithm.attr,
        &dev_attr_io_stat.attr,
        &dev_attr_mm_stat.attr,
        &dev_attr_debug_stat.attr,
        NULL,
};

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

/*
 * 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;
        struct request_queue *queue;
        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);

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

        blk_queue_make_request(queue, zram_make_request);

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

        zram->disk->major = zram_major;
        zram->disk->first_minor = device_id;
        zram->disk->fops = &zram_devops;
        zram->disk->queue = queue;
        zram->disk->queue->queuedata = zram;
        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);
        /* zram devices sort of resembles non-rotational disks */
        queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
        queue_flag_clear_unlocked(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)
                zram->disk->queue->limits.discard_zeroes_data = 1;
        else
                zram->disk->queue->limits.discard_zeroes_data = 0;
        queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, zram->disk->queue);

        add_disk(zram->disk);

        ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj,
                                &zram_disk_attr_group);
        if (ret < 0) {
                pr_err("Error creating sysfs group for device %d\n",
                                device_id);
                goto out_free_disk;
        }
        strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));
        zram->meta = NULL;

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

out_free_disk:
        del_gendisk(zram->disk);
        put_disk(zram->disk);
out_free_queue:
        blk_cleanup_queue(queue);
out_free_idr:
        idr_remove(&zram_index_idr, device_id);
out_free_dev:
        kfree(zram);
        return ret;
}

static int zram_remove(struct zram *zram)
{
        struct block_device *bdev;

        bdev = bdget_disk(zram->disk, 0);
        if (!bdev)
                return -ENOMEM;

        mutex_lock(&bdev->bd_mutex);
        if (bdev->bd_openers || zram->claim) {
                mutex_unlock(&bdev->bd_mutex);
                bdput(bdev);
                return -EBUSY;
        }

        zram->claim = true;
        mutex_unlock(&bdev->bd_mutex);

        /*
         * Remove sysfs first, so no one will perform a disksize
         * store while we destroy the devices. This also helps during
         * hot_remove -- zram_reset_device() is the last holder of
         * ->init_lock, no later/concurrent disksize_store() or any
         * other sysfs handlers are possible.
         */
        sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
                        &zram_disk_attr_group);

        /* Make sure all the pending I/O are finished */
        fsync_bdev(bdev);
        zram_reset_device(zram);
        bdput(bdev);

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

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

/* zram-control sysfs attributes */
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 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);
                idr_remove(&zram_index_idr, dev_id);
        } else {
                ret = -ENODEV;
        }

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

static struct class_attribute zram_control_class_attrs[] = {
        __ATTR_RO(hot_add),
        __ATTR_WO(hot_remove),
        __ATTR_NULL,
};

static struct class zram_control_class = {
        .name           = "zram-control",
        .owner          = THIS_MODULE,
        .class_attrs    = zram_control_class_attrs,
};

static int zram_remove_cb(int id, void *ptr, void *data)
{
        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);
        idr_destroy(&zram_index_idr);
        unregister_blkdev(zram_major, "zram");
}

static int __init zram_init(void)
{
        int ret;

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

        zram_major = register_blkdev(0, "zram");
        if (zram_major <= 0) {
                pr_err("Unable to get major number\n");
                class_unregister(&zram_control_class);
                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");