UBUNTU: Ubuntu-4.13.0-45.50

[mirror_ubuntu-artful-kernel.git] / drivers / nvdimm / btt.c

/*
 * Block Translation Table
 * Copyright (c) 2014-2015, Intel Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 */
#include <linux/highmem.h>
#include <linux/debugfs.h>
#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/mutex.h>
#include <linux/hdreg.h>
#include <linux/genhd.h>
#include <linux/sizes.h>
#include <linux/ndctl.h>
#include <linux/fs.h>
#include <linux/nd.h>
#include "btt.h"
#include "nd.h"

enum log_ent_request {
        LOG_NEW_ENT = 0,
        LOG_OLD_ENT
};

static u64 adjust_initial_offset(struct nd_btt *nd_btt, u64 offset)
{
        return offset + nd_btt->initial_offset;
}

static int arena_read_bytes(struct arena_info *arena, resource_size_t offset,
                void *buf, size_t n, unsigned long flags)
{
        struct nd_btt *nd_btt = arena->nd_btt;
        struct nd_namespace_common *ndns = nd_btt->ndns;

        /* arena offsets may be shifted from the base of the device */
        offset = adjust_initial_offset(nd_btt, offset);
        return nvdimm_read_bytes(ndns, offset, buf, n, flags);
}

static int arena_write_bytes(struct arena_info *arena, resource_size_t offset,
                void *buf, size_t n, unsigned long flags)
{
        struct nd_btt *nd_btt = arena->nd_btt;
        struct nd_namespace_common *ndns = nd_btt->ndns;

        /* arena offsets may be shifted from the base of the device */
        offset = adjust_initial_offset(nd_btt, offset);
        return nvdimm_write_bytes(ndns, offset, buf, n, flags);
}

static int btt_info_write(struct arena_info *arena, struct btt_sb *super)
{
        int ret;

        /*
         * infooff and info2off should always be at least 512B aligned.
         * We rely on that to make sure rw_bytes does error clearing
         * correctly, so make sure that is the case.
         */
        WARN_ON_ONCE(!IS_ALIGNED(arena->infooff, 512));
        WARN_ON_ONCE(!IS_ALIGNED(arena->info2off, 512));

        ret = arena_write_bytes(arena, arena->info2off, super,
                        sizeof(struct btt_sb), 0);
        if (ret)
                return ret;

        return arena_write_bytes(arena, arena->infooff, super,
                        sizeof(struct btt_sb), 0);
}

static int btt_info_read(struct arena_info *arena, struct btt_sb *super)
{
        WARN_ON(!super);
        return arena_read_bytes(arena, arena->infooff, super,
                        sizeof(struct btt_sb), 0);
}

/*
 * 'raw' version of btt_map write
 * Assumptions:
 *   mapping is in little-endian
 *   mapping contains 'E' and 'Z' flags as desired
 */
static int __btt_map_write(struct arena_info *arena, u32 lba, __le32 mapping,
                unsigned long flags)
{
        u64 ns_off = arena->mapoff + (lba * MAP_ENT_SIZE);

        WARN_ON(lba >= arena->external_nlba);
        return arena_write_bytes(arena, ns_off, &mapping, MAP_ENT_SIZE, flags);
}

static int btt_map_write(struct arena_info *arena, u32 lba, u32 mapping,
                        u32 z_flag, u32 e_flag, unsigned long rwb_flags)
{
        u32 ze;
        __le32 mapping_le;

        /*
         * This 'mapping' is supposed to be just the LBA mapping, without
         * any flags set, so strip the flag bits.
         */
        mapping = ent_lba(mapping);

        ze = (z_flag << 1) + e_flag;
        switch (ze) {
        case 0:
                /*
                 * We want to set neither of the Z or E flags, and
                 * in the actual layout, this means setting the bit
                 * positions of both to '1' to indicate a 'normal'
                 * map entry
                 */
                mapping |= MAP_ENT_NORMAL;
                break;
        case 1:
                mapping |= (1 << MAP_ERR_SHIFT);
                break;
        case 2:
                mapping |= (1 << MAP_TRIM_SHIFT);
                break;
        default:
                /*
                 * The case where Z and E are both sent in as '1' could be
                 * construed as a valid 'normal' case, but we decide not to,
                 * to avoid confusion
                 */
                WARN_ONCE(1, "Invalid use of Z and E flags\n");
                return -EIO;
        }

        mapping_le = cpu_to_le32(mapping);
        return __btt_map_write(arena, lba, mapping_le, rwb_flags);
}

static int btt_map_read(struct arena_info *arena, u32 lba, u32 *mapping,
                        int *trim, int *error, unsigned long rwb_flags)
{
        int ret;
        __le32 in;
        u32 raw_mapping, postmap, ze, z_flag, e_flag;
        u64 ns_off = arena->mapoff + (lba * MAP_ENT_SIZE);

        WARN_ON(lba >= arena->external_nlba);

        ret = arena_read_bytes(arena, ns_off, &in, MAP_ENT_SIZE, rwb_flags);
        if (ret)
                return ret;

        raw_mapping = le32_to_cpu(in);

        z_flag = ent_z_flag(raw_mapping);
        e_flag = ent_e_flag(raw_mapping);
        ze = (z_flag << 1) + e_flag;
        postmap = ent_lba(raw_mapping);

        /* Reuse the {z,e}_flag variables for *trim and *error */
        z_flag = 0;
        e_flag = 0;

        switch (ze) {
        case 0:
                /* Initial state. Return postmap = premap */
                *mapping = lba;
                break;
        case 1:
                *mapping = postmap;
                e_flag = 1;
                break;
        case 2:
                *mapping = postmap;
                z_flag = 1;
                break;
        case 3:
                *mapping = postmap;
                break;
        default:
                return -EIO;
        }

        if (trim)
                *trim = z_flag;
        if (error)
                *error = e_flag;

        return ret;
}

static int btt_log_read_pair(struct arena_info *arena, u32 lane,
                        struct log_entry *ent)
{
        WARN_ON(!ent);
        return arena_read_bytes(arena,
                        arena->logoff + (2 * lane * LOG_ENT_SIZE), ent,
                        2 * LOG_ENT_SIZE, 0);
}

static struct dentry *debugfs_root;

static void arena_debugfs_init(struct arena_info *a, struct dentry *parent,
                                int idx)
{
        char dirname[32];
        struct dentry *d;

        /* If for some reason, parent bttN was not created, exit */
        if (!parent)
                return;

        snprintf(dirname, 32, "arena%d", idx);
        d = debugfs_create_dir(dirname, parent);
        if (IS_ERR_OR_NULL(d))
                return;
        a->debugfs_dir = d;

        debugfs_create_x64("size", S_IRUGO, d, &a->size);
        debugfs_create_x64("external_lba_start", S_IRUGO, d,
                                &a->external_lba_start);
        debugfs_create_x32("internal_nlba", S_IRUGO, d, &a->internal_nlba);
        debugfs_create_u32("internal_lbasize", S_IRUGO, d,
                                &a->internal_lbasize);
        debugfs_create_x32("external_nlba", S_IRUGO, d, &a->external_nlba);
        debugfs_create_u32("external_lbasize", S_IRUGO, d,
                                &a->external_lbasize);
        debugfs_create_u32("nfree", S_IRUGO, d, &a->nfree);
        debugfs_create_u16("version_major", S_IRUGO, d, &a->version_major);
        debugfs_create_u16("version_minor", S_IRUGO, d, &a->version_minor);
        debugfs_create_x64("nextoff", S_IRUGO, d, &a->nextoff);
        debugfs_create_x64("infooff", S_IRUGO, d, &a->infooff);
        debugfs_create_x64("dataoff", S_IRUGO, d, &a->dataoff);
        debugfs_create_x64("mapoff", S_IRUGO, d, &a->mapoff);
        debugfs_create_x64("logoff", S_IRUGO, d, &a->logoff);
        debugfs_create_x64("info2off", S_IRUGO, d, &a->info2off);
        debugfs_create_x32("flags", S_IRUGO, d, &a->flags);
}

static void btt_debugfs_init(struct btt *btt)
{
        int i = 0;
        struct arena_info *arena;

        btt->debugfs_dir = debugfs_create_dir(dev_name(&btt->nd_btt->dev),
                                                debugfs_root);
        if (IS_ERR_OR_NULL(btt->debugfs_dir))
                return;

        list_for_each_entry(arena, &btt->arena_list, list) {
                arena_debugfs_init(arena, btt->debugfs_dir, i);
                i++;
        }
}

/*
 * This function accepts two log entries, and uses the
 * sequence number to find the 'older' entry.
 * It also updates the sequence number in this old entry to
 * make it the 'new' one if the mark_flag is set.
 * Finally, it returns which of the entries was the older one.
 *
 * TODO The logic feels a bit kludge-y. make it better..
 */
static int btt_log_get_old(struct log_entry *ent)
{
        int old;

        /*
         * the first ever time this is seen, the entry goes into [0]
         * the next time, the following logic works out to put this
         * (next) entry into [1]
         */
        if (ent[0].seq == 0) {
                ent[0].seq = cpu_to_le32(1);
                return 0;
        }

        if (ent[0].seq == ent[1].seq)
                return -EINVAL;
        if (le32_to_cpu(ent[0].seq) + le32_to_cpu(ent[1].seq) > 5)
                return -EINVAL;

        if (le32_to_cpu(ent[0].seq) < le32_to_cpu(ent[1].seq)) {
                if (le32_to_cpu(ent[1].seq) - le32_to_cpu(ent[0].seq) == 1)
                        old = 0;
                else
                        old = 1;
        } else {
                if (le32_to_cpu(ent[0].seq) - le32_to_cpu(ent[1].seq) == 1)
                        old = 1;
                else
                        old = 0;
        }

        return old;
}

static struct device *to_dev(struct arena_info *arena)
{
        return &arena->nd_btt->dev;
}

/*
 * This function copies the desired (old/new) log entry into ent if
 * it is not NULL. It returns the sub-slot number (0 or 1)
 * where the desired log entry was found. Negative return values
 * indicate errors.
 */
static int btt_log_read(struct arena_info *arena, u32 lane,
                        struct log_entry *ent, int old_flag)
{
        int ret;
        int old_ent, ret_ent;
        struct log_entry log[2];

        ret = btt_log_read_pair(arena, lane, log);
        if (ret)
                return -EIO;

        old_ent = btt_log_get_old(log);
        if (old_ent < 0 || old_ent > 1) {
                dev_err(to_dev(arena),
                                "log corruption (%d): lane %d seq [%d, %d]\n",
                        old_ent, lane, log[0].seq, log[1].seq);
                /* TODO set error state? */
                return -EIO;
        }

        ret_ent = (old_flag ? old_ent : (1 - old_ent));

        if (ent != NULL)
                memcpy(ent, &log[ret_ent], LOG_ENT_SIZE);

        return ret_ent;
}

/*
 * This function commits a log entry to media
 * It does _not_ prepare the freelist entry for the next write
 * btt_flog_write is the wrapper for updating the freelist elements
 */
static int __btt_log_write(struct arena_info *arena, u32 lane,
                        u32 sub, struct log_entry *ent, unsigned long flags)
{
        int ret;
        /*
         * Ignore the padding in log_entry for calculating log_half.
         * The entry is 'committed' when we write the sequence number,
         * and we want to ensure that that is the last thing written.
         * We don't bother writing the padding as that would be extra
         * media wear and write amplification
         */
        unsigned int log_half = (LOG_ENT_SIZE - 2 * sizeof(u64)) / 2;
        u64 ns_off = arena->logoff + (((2 * lane) + sub) * LOG_ENT_SIZE);
        void *src = ent;

        /* split the 16B write into atomic, durable halves */
        ret = arena_write_bytes(arena, ns_off, src, log_half, flags);
        if (ret)
                return ret;

        ns_off += log_half;
        src += log_half;
        return arena_write_bytes(arena, ns_off, src, log_half, flags);
}

static int btt_flog_write(struct arena_info *arena, u32 lane, u32 sub,
                        struct log_entry *ent)
{
        int ret;

        ret = __btt_log_write(arena, lane, sub, ent, NVDIMM_IO_ATOMIC);
        if (ret)
                return ret;

        /* prepare the next free entry */
        arena->freelist[lane].sub = 1 - arena->freelist[lane].sub;
        if (++(arena->freelist[lane].seq) == 4)
                arena->freelist[lane].seq = 1;
        if (ent_e_flag(ent->old_map))
                arena->freelist[lane].has_err = 1;
        arena->freelist[lane].block = le32_to_cpu(ent_lba(ent->old_map));

        return ret;
}

/*
 * This function initializes the BTT map to the initial state, which is
 * all-zeroes, and indicates an identity mapping
 */
static int btt_map_init(struct arena_info *arena)
{
        int ret = -EINVAL;
        void *zerobuf;
        size_t offset = 0;
        size_t chunk_size = SZ_2M;
        size_t mapsize = arena->logoff - arena->mapoff;

        zerobuf = kzalloc(chunk_size, GFP_KERNEL);
        if (!zerobuf)
                return -ENOMEM;

        /*
         * mapoff should always be at least 512B  aligned. We rely on that to
         * make sure rw_bytes does error clearing correctly, so make sure that
         * is the case.
         */
        WARN_ON_ONCE(!IS_ALIGNED(arena->mapoff, 512));

        while (mapsize) {
                size_t size = min(mapsize, chunk_size);

                WARN_ON_ONCE(size < 512);
                ret = arena_write_bytes(arena, arena->mapoff + offset, zerobuf,
                                size, 0);
                if (ret)
                        goto free;

                offset += size;
                mapsize -= size;
                cond_resched();
        }

 free:
        kfree(zerobuf);
        return ret;
}

/*
 * This function initializes the BTT log with 'fake' entries pointing
 * to the initial reserved set of blocks as being free
 */
static int btt_log_init(struct arena_info *arena)
{
        size_t logsize = arena->info2off - arena->logoff;
        size_t chunk_size = SZ_4K, offset = 0;
        struct log_entry log;
        void *zerobuf;
        int ret;
        u32 i;

        zerobuf = kzalloc(chunk_size, GFP_KERNEL);
        if (!zerobuf)
                return -ENOMEM;
        /*
         * logoff should always be at least 512B  aligned. We rely on that to
         * make sure rw_bytes does error clearing correctly, so make sure that
         * is the case.
         */
        WARN_ON_ONCE(!IS_ALIGNED(arena->logoff, 512));

        while (logsize) {
                size_t size = min(logsize, chunk_size);

                WARN_ON_ONCE(size < 512);
                ret = arena_write_bytes(arena, arena->logoff + offset, zerobuf,
                                size, 0);
                if (ret)
                        goto free;

                offset += size;
                logsize -= size;
                cond_resched();
        }

        for (i = 0; i < arena->nfree; i++) {
                log.lba = cpu_to_le32(i);
                log.old_map = cpu_to_le32(arena->external_nlba + i);
                log.new_map = cpu_to_le32(arena->external_nlba + i);
                log.seq = cpu_to_le32(LOG_SEQ_INIT);
                ret = __btt_log_write(arena, i, 0, &log, 0);
                if (ret)
                        goto free;
        }

 free:
        kfree(zerobuf);
        return ret;
}

static u64 to_namespace_offset(struct arena_info *arena, u64 lba)
{
        return arena->dataoff + ((u64)lba * arena->internal_lbasize);
}

static int arena_clear_freelist_error(struct arena_info *arena, u32 lane)
{
        int ret = 0;

        if (arena->freelist[lane].has_err) {
                void *zero_page = page_address(ZERO_PAGE(0));
                u32 lba = arena->freelist[lane].block;
                u64 nsoff = to_namespace_offset(arena, lba);
                unsigned long len = arena->sector_size;

                mutex_lock(&arena->err_lock);

                while (len) {
                        unsigned long chunk = min(len, PAGE_SIZE);

                        ret = arena_write_bytes(arena, nsoff, zero_page,
                                chunk, 0);
                        if (ret)
                                break;
                        len -= chunk;
                        nsoff += chunk;
                        if (len == 0)
                                arena->freelist[lane].has_err = 0;
                }
                mutex_unlock(&arena->err_lock);
        }
        return ret;
}

static int btt_freelist_init(struct arena_info *arena)
{
        int old, new, ret;
        u32 i, map_entry;
        struct log_entry log_new, log_old;

        arena->freelist = kcalloc(arena->nfree, sizeof(struct free_entry),
                                        GFP_KERNEL);
        if (!arena->freelist)
                return -ENOMEM;

        for (i = 0; i < arena->nfree; i++) {
                old = btt_log_read(arena, i, &log_old, LOG_OLD_ENT);
                if (old < 0)
                        return old;

                new = btt_log_read(arena, i, &log_new, LOG_NEW_ENT);
                if (new < 0)
                        return new;

                /* sub points to the next one to be overwritten */
                arena->freelist[i].sub = 1 - new;
                arena->freelist[i].seq = nd_inc_seq(le32_to_cpu(log_new.seq));
                arena->freelist[i].block = le32_to_cpu(log_new.old_map);

                /*
                 * FIXME: if error clearing fails during init, we want to make
                 * the BTT read-only
                 */
                if (ent_e_flag(log_new.old_map)) {
                        ret = arena_clear_freelist_error(arena, i);
                        if (ret)
                                WARN_ONCE(1, "Unable to clear known errors\n");
                }

                /* This implies a newly created or untouched flog entry */
                if (log_new.old_map == log_new.new_map)
                        continue;

                /* Check if map recovery is needed */
                ret = btt_map_read(arena, le32_to_cpu(log_new.lba), &map_entry,
                                NULL, NULL, 0);
                if (ret)
                        return ret;
                if ((le32_to_cpu(log_new.new_map) != map_entry) &&
                                (le32_to_cpu(log_new.old_map) == map_entry)) {
                        /*
                         * Last transaction wrote the flog, but wasn't able
                         * to complete the map write. So fix up the map.
                         */
                        ret = btt_map_write(arena, le32_to_cpu(log_new.lba),
                                        le32_to_cpu(log_new.new_map), 0, 0, 0);
                        if (ret)
                                return ret;
                }
        }

        return 0;
}

static int btt_rtt_init(struct arena_info *arena)
{
        arena->rtt = kcalloc(arena->nfree, sizeof(u32), GFP_KERNEL);
        if (arena->rtt == NULL)
                return -ENOMEM;

        return 0;
}

static int btt_maplocks_init(struct arena_info *arena)
{
        u32 i;

        arena->map_locks = kcalloc(arena->nfree, sizeof(struct aligned_lock),
                                GFP_KERNEL);
        if (!arena->map_locks)
                return -ENOMEM;

        for (i = 0; i < arena->nfree; i++)
                spin_lock_init(&arena->map_locks[i].lock);

        return 0;
}

static struct arena_info *alloc_arena(struct btt *btt, size_t size,
                                size_t start, size_t arena_off)
{
        struct arena_info *arena;
        u64 logsize, mapsize, datasize;
        u64 available = size;

        arena = kzalloc(sizeof(struct arena_info), GFP_KERNEL);
        if (!arena)
                return NULL;
        arena->nd_btt = btt->nd_btt;
        arena->sector_size = btt->sector_size;

        if (!size)
                return arena;

        arena->size = size;
        arena->external_lba_start = start;
        arena->external_lbasize = btt->lbasize;
        arena->internal_lbasize = roundup(arena->external_lbasize,
                                        INT_LBASIZE_ALIGNMENT);
        arena->nfree = BTT_DEFAULT_NFREE;
        arena->version_major = btt->nd_btt->version_major;
        arena->version_minor = btt->nd_btt->version_minor;

        if (available % BTT_PG_SIZE)
                available -= (available % BTT_PG_SIZE);

        /* Two pages are reserved for the super block and its copy */
        available -= 2 * BTT_PG_SIZE;

        /* The log takes a fixed amount of space based on nfree */
        logsize = roundup(2 * arena->nfree * sizeof(struct log_entry),
                                BTT_PG_SIZE);
        available -= logsize;

        /* Calculate optimal split between map and data area */
        arena->internal_nlba = div_u64(available - BTT_PG_SIZE,
                        arena->internal_lbasize + MAP_ENT_SIZE);
        arena->external_nlba = arena->internal_nlba - arena->nfree;

        mapsize = roundup((arena->external_nlba * MAP_ENT_SIZE), BTT_PG_SIZE);
        datasize = available - mapsize;

        /* 'Absolute' values, relative to start of storage space */
        arena->infooff = arena_off;
        arena->dataoff = arena->infooff + BTT_PG_SIZE;
        arena->mapoff = arena->dataoff + datasize;
        arena->logoff = arena->mapoff + mapsize;
        arena->info2off = arena->logoff + logsize;
        return arena;
}

static void free_arenas(struct btt *btt)
{
        struct arena_info *arena, *next;

        list_for_each_entry_safe(arena, next, &btt->arena_list, list) {
                list_del(&arena->list);
                kfree(arena->rtt);
                kfree(arena->map_locks);
                kfree(arena->freelist);
                debugfs_remove_recursive(arena->debugfs_dir);
                kfree(arena);
        }
}

/*
 * This function reads an existing valid btt superblock and
 * populates the corresponding arena_info struct
 */
static void parse_arena_meta(struct arena_info *arena, struct btt_sb *super,
                                u64 arena_off)
{
        arena->internal_nlba = le32_to_cpu(super->internal_nlba);
        arena->internal_lbasize = le32_to_cpu(super->internal_lbasize);
        arena->external_nlba = le32_to_cpu(super->external_nlba);
        arena->external_lbasize = le32_to_cpu(super->external_lbasize);
        arena->nfree = le32_to_cpu(super->nfree);
        arena->version_major = le16_to_cpu(super->version_major);
        arena->version_minor = le16_to_cpu(super->version_minor);

        arena->nextoff = (super->nextoff == 0) ? 0 : (arena_off +
                        le64_to_cpu(super->nextoff));
        arena->infooff = arena_off;
        arena->dataoff = arena_off + le64_to_cpu(super->dataoff);
        arena->mapoff = arena_off + le64_to_cpu(super->mapoff);
        arena->logoff = arena_off + le64_to_cpu(super->logoff);
        arena->info2off = arena_off + le64_to_cpu(super->info2off);

        arena->size = (le64_to_cpu(super->nextoff) > 0)
                ? (le64_to_cpu(super->nextoff))
                : (arena->info2off - arena->infooff + BTT_PG_SIZE);

        arena->flags = le32_to_cpu(super->flags);
}

static int discover_arenas(struct btt *btt)
{
        int ret = 0;
        struct arena_info *arena;
        struct btt_sb *super;
        size_t remaining = btt->rawsize;
        u64 cur_nlba = 0;
        size_t cur_off = 0;
        int num_arenas = 0;

        super = kzalloc(sizeof(*super), GFP_KERNEL);
        if (!super)
                return -ENOMEM;

        while (remaining) {
                /* Alloc memory for arena */
                arena = alloc_arena(btt, 0, 0, 0);
                if (!arena) {
                        ret = -ENOMEM;
                        goto out_super;
                }

                arena->infooff = cur_off;
                ret = btt_info_read(arena, super);
                if (ret)
                        goto out;

                if (!nd_btt_arena_is_valid(btt->nd_btt, super)) {
                        if (remaining == btt->rawsize) {
                                btt->init_state = INIT_NOTFOUND;
                                dev_info(to_dev(arena), "No existing arenas\n");
                                goto out;
                        } else {
                                dev_err(to_dev(arena),
                                                "Found corrupted metadata!\n");
                                ret = -ENODEV;
                                goto out;
                        }
                }

                arena->external_lba_start = cur_nlba;
                parse_arena_meta(arena, super, cur_off);

                mutex_init(&arena->err_lock);
                ret = btt_freelist_init(arena);
                if (ret)
                        goto out;

                ret = btt_rtt_init(arena);
                if (ret)
                        goto out;

                ret = btt_maplocks_init(arena);
                if (ret)
                        goto out;

                list_add_tail(&arena->list, &btt->arena_list);

                remaining -= arena->size;
                cur_off += arena->size;
                cur_nlba += arena->external_nlba;
                num_arenas++;

                if (arena->nextoff == 0)
                        break;
        }
        btt->num_arenas = num_arenas;
        btt->nlba = cur_nlba;
        btt->init_state = INIT_READY;

        kfree(super);
        return ret;

 out:
        kfree(arena);
        free_arenas(btt);
 out_super:
        kfree(super);
        return ret;
}

static int create_arenas(struct btt *btt)
{
        size_t remaining = btt->rawsize;
        size_t cur_off = 0;

        while (remaining) {
                struct arena_info *arena;
                size_t arena_size = min_t(u64, ARENA_MAX_SIZE, remaining);

                remaining -= arena_size;
                if (arena_size < ARENA_MIN_SIZE)
                        break;

                arena = alloc_arena(btt, arena_size, btt->nlba, cur_off);
                if (!arena) {
                        free_arenas(btt);
                        return -ENOMEM;
                }
                btt->nlba += arena->external_nlba;
                if (remaining >= ARENA_MIN_SIZE)
                        arena->nextoff = arena->size;
                else
                        arena->nextoff = 0;
                cur_off += arena_size;
                list_add_tail(&arena->list, &btt->arena_list);
        }

        return 0;
}

/*
 * This function completes arena initialization by writing
 * all the metadata.
 * It is only called for an uninitialized arena when a write
 * to that arena occurs for the first time.
 */
static int btt_arena_write_layout(struct arena_info *arena)
{
        int ret;
        u64 sum;
        struct btt_sb *super;
        struct nd_btt *nd_btt = arena->nd_btt;
        const u8 *parent_uuid = nd_dev_to_uuid(&nd_btt->ndns->dev);

        ret = btt_map_init(arena);
        if (ret)
                return ret;

        ret = btt_log_init(arena);
        if (ret)
                return ret;

        super = kzalloc(sizeof(struct btt_sb), GFP_NOIO);
        if (!super)
                return -ENOMEM;

        strncpy(super->signature, BTT_SIG, BTT_SIG_LEN);
        memcpy(super->uuid, nd_btt->uuid, 16);
        memcpy(super->parent_uuid, parent_uuid, 16);
        super->flags = cpu_to_le32(arena->flags);
        super->version_major = cpu_to_le16(arena->version_major);
        super->version_minor = cpu_to_le16(arena->version_minor);
        super->external_lbasize = cpu_to_le32(arena->external_lbasize);
        super->external_nlba = cpu_to_le32(arena->external_nlba);
        super->internal_lbasize = cpu_to_le32(arena->internal_lbasize);
        super->internal_nlba = cpu_to_le32(arena->internal_nlba);
        super->nfree = cpu_to_le32(arena->nfree);
        super->infosize = cpu_to_le32(sizeof(struct btt_sb));
        super->nextoff = cpu_to_le64(arena->nextoff);
        /*
         * Subtract arena->infooff (arena start) so numbers are relative
         * to 'this' arena
         */
        super->dataoff = cpu_to_le64(arena->dataoff - arena->infooff);
        super->mapoff = cpu_to_le64(arena->mapoff - arena->infooff);
        super->logoff = cpu_to_le64(arena->logoff - arena->infooff);
        super->info2off = cpu_to_le64(arena->info2off - arena->infooff);

        super->flags = 0;
        sum = nd_sb_checksum((struct nd_gen_sb *) super);
        super->checksum = cpu_to_le64(sum);

        ret = btt_info_write(arena, super);

        kfree(super);
        return ret;
}

/*
 * This function completes the initialization for the BTT namespace
 * such that it is ready to accept IOs
 */
static int btt_meta_init(struct btt *btt)
{
        int ret = 0;
        struct arena_info *arena;

        mutex_lock(&btt->init_lock);
        list_for_each_entry(arena, &btt->arena_list, list) {
                ret = btt_arena_write_layout(arena);
                if (ret)
                        goto unlock;

                ret = btt_freelist_init(arena);
                if (ret)
                        goto unlock;

                ret = btt_rtt_init(arena);
                if (ret)
                        goto unlock;

                ret = btt_maplocks_init(arena);
                if (ret)
                        goto unlock;
        }

        btt->init_state = INIT_READY;

 unlock:
        mutex_unlock(&btt->init_lock);
        return ret;
}

static u32 btt_meta_size(struct btt *btt)
{
        return btt->lbasize - btt->sector_size;
}

/*
 * This function calculates the arena in which the given LBA lies
 * by doing a linear walk. This is acceptable since we expect only
 * a few arenas. If we have backing devices that get much larger,
 * we can construct a balanced binary tree of arenas at init time
 * so that this range search becomes faster.
 */
static int lba_to_arena(struct btt *btt, sector_t sector, __u32 *premap,
                                struct arena_info **arena)
{
        struct arena_info *arena_list;
        __u64 lba = div_u64(sector << SECTOR_SHIFT, btt->sector_size);

        list_for_each_entry(arena_list, &btt->arena_list, list) {
                if (lba < arena_list->external_nlba) {
                        *arena = arena_list;
                        *premap = lba;
                        return 0;
                }
                lba -= arena_list->external_nlba;
        }

        return -EIO;
}

/*
 * The following (lock_map, unlock_map) are mostly just to improve
 * readability, since they index into an array of locks
 */
static void lock_map(struct arena_info *arena, u32 premap)
                __acquires(&arena->map_locks[idx].lock)
{
        u32 idx = (premap * MAP_ENT_SIZE / L1_CACHE_BYTES) % arena->nfree;

        spin_lock(&arena->map_locks[idx].lock);
}

static void unlock_map(struct arena_info *arena, u32 premap)
                __releases(&arena->map_locks[idx].lock)
{
        u32 idx = (premap * MAP_ENT_SIZE / L1_CACHE_BYTES) % arena->nfree;

        spin_unlock(&arena->map_locks[idx].lock);
}

static int btt_data_read(struct arena_info *arena, struct page *page,
                        unsigned int off, u32 lba, u32 len)
{
        int ret;
        u64 nsoff = to_namespace_offset(arena, lba);
        void *mem = kmap_atomic(page);

        ret = arena_read_bytes(arena, nsoff, mem + off, len, NVDIMM_IO_ATOMIC);
        kunmap_atomic(mem);

        return ret;
}

static int btt_data_write(struct arena_info *arena, u32 lba,
                        struct page *page, unsigned int off, u32 len)
{
        int ret;
        u64 nsoff = to_namespace_offset(arena, lba);
        void *mem = kmap_atomic(page);

        ret = arena_write_bytes(arena, nsoff, mem + off, len, NVDIMM_IO_ATOMIC);
        kunmap_atomic(mem);

        return ret;
}

static void zero_fill_data(struct page *page, unsigned int off, u32 len)
{
        void *mem = kmap_atomic(page);

        memset(mem + off, 0, len);
        kunmap_atomic(mem);
}

#ifdef CONFIG_BLK_DEV_INTEGRITY
static int btt_rw_integrity(struct btt *btt, struct bio_integrity_payload *bip,
                        struct arena_info *arena, u32 postmap, int rw)
{
        unsigned int len = btt_meta_size(btt);
        u64 meta_nsoff;
        int ret = 0;

        if (bip == NULL)
                return 0;

        meta_nsoff = to_namespace_offset(arena, postmap) + btt->sector_size;

        while (len) {
                unsigned int cur_len;
                struct bio_vec bv;
                void *mem;

                bv = bvec_iter_bvec(bip->bip_vec, bip->bip_iter);
                /*
                 * The 'bv' obtained from bvec_iter_bvec has its .bv_len and
                 * .bv_offset already adjusted for iter->bi_bvec_done, and we
                 * can use those directly
                 */

                cur_len = min(len, bv.bv_len);
                mem = kmap_atomic(bv.bv_page);
                if (rw)
                        ret = arena_write_bytes(arena, meta_nsoff,
                                        mem + bv.bv_offset, cur_len,
                                        NVDIMM_IO_ATOMIC);
                else
                        ret = arena_read_bytes(arena, meta_nsoff,
                                        mem + bv.bv_offset, cur_len,
                                        NVDIMM_IO_ATOMIC);

                kunmap_atomic(mem);
                if (ret)
                        return ret;

                len -= cur_len;
                meta_nsoff += cur_len;
                if (!bvec_iter_advance(bip->bip_vec, &bip->bip_iter, cur_len))
                        return -EIO;
        }

        return ret;
}

#else /* CONFIG_BLK_DEV_INTEGRITY */
static int btt_rw_integrity(struct btt *btt, struct bio_integrity_payload *bip,
                        struct arena_info *arena, u32 postmap, int rw)
{
        return 0;
}
#endif

static int btt_read_pg(struct btt *btt, struct bio_integrity_payload *bip,
                        struct page *page, unsigned int off, sector_t sector,
                        unsigned int len)
{
        int ret = 0;
        int t_flag, e_flag;
        struct arena_info *arena = NULL;
        u32 lane = 0, premap, postmap;

        while (len) {
                u32 cur_len;

                lane = nd_region_acquire_lane(btt->nd_region);

                ret = lba_to_arena(btt, sector, &premap, &arena);
                if (ret)
                        goto out_lane;

                cur_len = min(btt->sector_size, len);

                ret = btt_map_read(arena, premap, &postmap, &t_flag, &e_flag,
                                NVDIMM_IO_ATOMIC);
                if (ret)
                        goto out_lane;

                /*
                 * We loop to make sure that the post map LBA didn't change
                 * from under us between writing the RTT and doing the actual
                 * read.
                 */
                while (1) {
                        u32 new_map;
                        int new_t, new_e;

                        if (t_flag) {
                                zero_fill_data(page, off, cur_len);
                                goto out_lane;
                        }

                        if (e_flag) {
                                ret = -EIO;
                                goto out_lane;
                        }

                        arena->rtt[lane] = RTT_VALID | postmap;
                        /*
                         * Barrier to make sure this write is not reordered
                         * to do the verification map_read before the RTT store
                         */
                        barrier();

                        ret = btt_map_read(arena, premap, &new_map, &new_t,
                                                &new_e, NVDIMM_IO_ATOMIC);
                        if (ret)
                                goto out_rtt;

                        if ((postmap == new_map) && (t_flag == new_t) &&
                                        (e_flag == new_e))
                                break;

                        postmap = new_map;
                        t_flag = new_t;
                        e_flag = new_e;
                }

                ret = btt_data_read(arena, page, off, postmap, cur_len);
                if (ret) {
                        int rc;

                        /* Media error - set the e_flag */
                        rc = btt_map_write(arena, premap, postmap, 0, 1,
                                NVDIMM_IO_ATOMIC);
                        goto out_rtt;
                }

                if (bip) {
                        ret = btt_rw_integrity(btt, bip, arena, postmap, READ);
                        if (ret)
                                goto out_rtt;
                }

                arena->rtt[lane] = RTT_INVALID;
                nd_region_release_lane(btt->nd_region, lane);

                len -= cur_len;
                off += cur_len;
                sector += btt->sector_size >> SECTOR_SHIFT;
        }

        return 0;

 out_rtt:
        arena->rtt[lane] = RTT_INVALID;
 out_lane:
        nd_region_release_lane(btt->nd_region, lane);
        return ret;
}

/*
 * Normally, arena_{read,write}_bytes will take care of the initial offset
 * adjustment, but in the case of btt_is_badblock, where we query is_bad_pmem,
 * we need the final, raw namespace offset here
 */
static bool btt_is_badblock(struct btt *btt, struct arena_info *arena,
                u32 postmap)
{
        u64 nsoff = adjust_initial_offset(arena->nd_btt,
                        to_namespace_offset(arena, postmap));
        sector_t phys_sector = nsoff >> 9;

        return is_bad_pmem(btt->phys_bb, phys_sector, arena->internal_lbasize);
}

static int btt_write_pg(struct btt *btt, struct bio_integrity_payload *bip,
                        sector_t sector, struct page *page, unsigned int off,
                        unsigned int len)
{
        int ret = 0;
        struct arena_info *arena = NULL;
        u32 premap = 0, old_postmap, new_postmap, lane = 0, i;
        struct log_entry log;
        int sub;

        while (len) {
                u32 cur_len;
                int e_flag;

 retry:
                lane = nd_region_acquire_lane(btt->nd_region);

                ret = lba_to_arena(btt, sector, &premap, &arena);
                if (ret)
                        goto out_lane;
                cur_len = min(btt->sector_size, len);

                if ((arena->flags & IB_FLAG_ERROR_MASK) != 0) {
                        ret = -EIO;
                        goto out_lane;
                }

                if (btt_is_badblock(btt, arena, arena->freelist[lane].block))
                        arena->freelist[lane].has_err = 1;

                if (mutex_is_locked(&arena->err_lock)
                                || arena->freelist[lane].has_err) {
                        nd_region_release_lane(btt->nd_region, lane);

                        ret = arena_clear_freelist_error(arena, lane);
                        if (ret)
                                return ret;

                        /* OK to acquire a different lane/free block */
                        goto retry;
                }

                new_postmap = arena->freelist[lane].block;

                /* Wait if the new block is being read from */
                for (i = 0; i < arena->nfree; i++)
                        while (arena->rtt[i] == (RTT_VALID | new_postmap))
                                cpu_relax();


                if (new_postmap >= arena->internal_nlba) {
                        ret = -EIO;
                        goto out_lane;
                }

                ret = btt_data_write(arena, new_postmap, page, off, cur_len);
                if (ret)
                        goto out_lane;

                if (bip) {
                        ret = btt_rw_integrity(btt, bip, arena, new_postmap,
                                                WRITE);
                        if (ret)
                                goto out_lane;
                }

                lock_map(arena, premap);
                ret = btt_map_read(arena, premap, &old_postmap, NULL, &e_flag,
                                NVDIMM_IO_ATOMIC);
                if (ret)
                        goto out_map;
                if (old_postmap >= arena->internal_nlba) {
                        ret = -EIO;
                        goto out_map;
                }
                if (e_flag)
                        set_e_flag(old_postmap);

                log.lba = cpu_to_le32(premap);
                log.old_map = cpu_to_le32(old_postmap);
                log.new_map = cpu_to_le32(new_postmap);
                log.seq = cpu_to_le32(arena->freelist[lane].seq);
                sub = arena->freelist[lane].sub;
                ret = btt_flog_write(arena, lane, sub, &log);
                if (ret)
                        goto out_map;

                ret = btt_map_write(arena, premap, new_postmap, 0, 0,
                        NVDIMM_IO_ATOMIC);
                if (ret)
                        goto out_map;

                unlock_map(arena, premap);
                nd_region_release_lane(btt->nd_region, lane);

                if (e_flag) {
                        ret = arena_clear_freelist_error(arena, lane);
                        if (ret)
                                return ret;
                }

                len -= cur_len;
                off += cur_len;
                sector += btt->sector_size >> SECTOR_SHIFT;
        }

        return 0;

 out_map:
        unlock_map(arena, premap);
 out_lane:
        nd_region_release_lane(btt->nd_region, lane);
        return ret;
}

static int btt_do_bvec(struct btt *btt, struct bio_integrity_payload *bip,
                        struct page *page, unsigned int len, unsigned int off,
                        bool is_write, sector_t sector)
{
        int ret;

        if (!is_write) {
                ret = btt_read_pg(btt, bip, page, off, sector, len);
                flush_dcache_page(page);
        } else {
                flush_dcache_page(page);
                ret = btt_write_pg(btt, bip, sector, page, off, len);
        }

        return ret;
}

static blk_qc_t btt_make_request(struct request_queue *q, struct bio *bio)
{
        struct bio_integrity_payload *bip = bio_integrity(bio);
        struct btt *btt = q->queuedata;
        struct bvec_iter iter;
        unsigned long start;
        struct bio_vec bvec;
        int err = 0;
        bool do_acct;

        if (!bio_integrity_prep(bio))
                return BLK_QC_T_NONE;

        do_acct = nd_iostat_start(bio, &start);
        bio_for_each_segment(bvec, bio, iter) {
                unsigned int len = bvec.bv_len;

                BUG_ON(len > PAGE_SIZE);
                /* Make sure len is in multiples of sector size. */
                /* XXX is this right? */
                BUG_ON(len < btt->sector_size);
                BUG_ON(len % btt->sector_size);

                err = btt_do_bvec(btt, bip, bvec.bv_page, len, bvec.bv_offset,
                                  op_is_write(bio_op(bio)), iter.bi_sector);
                if (err) {
                        dev_err(&btt->nd_btt->dev,
                                        "io error in %s sector %lld, len %d,\n",
                                        (op_is_write(bio_op(bio))) ? "WRITE" :
                                        "READ",
                                        (unsigned long long) iter.bi_sector, len);
                        bio->bi_status = errno_to_blk_status(err);
                        break;
                }
        }
        if (do_acct)
                nd_iostat_end(bio, start);

        bio_endio(bio);
        return BLK_QC_T_NONE;
}

static int btt_rw_page(struct block_device *bdev, sector_t sector,
                struct page *page, bool is_write)
{
        struct btt *btt = bdev->bd_disk->private_data;
        int rc;

        rc = btt_do_bvec(btt, NULL, page, PAGE_SIZE, 0, is_write, sector);
        if (rc == 0)
                page_endio(page, is_write, 0);

        return rc;
}


static int btt_getgeo(struct block_device *bd, struct hd_geometry *geo)
{
        /* some standard values */
        geo->heads = 1 << 6;
        geo->sectors = 1 << 5;
        geo->cylinders = get_capacity(bd->bd_disk) >> 11;
        return 0;
}

static const struct block_device_operations btt_fops = {
        .owner =                THIS_MODULE,
        .rw_page =              btt_rw_page,
        .getgeo =               btt_getgeo,
        .revalidate_disk =      nvdimm_revalidate_disk,
};

static int btt_blk_init(struct btt *btt)
{
        struct nd_btt *nd_btt = btt->nd_btt;
        struct nd_namespace_common *ndns = nd_btt->ndns;

        /* create a new disk and request queue for btt */
        btt->btt_queue = blk_alloc_queue(GFP_KERNEL);
        if (!btt->btt_queue)
                return -ENOMEM;

        btt->btt_disk = alloc_disk(0);
        if (!btt->btt_disk) {
                blk_cleanup_queue(btt->btt_queue);
                return -ENOMEM;
        }

        nvdimm_namespace_disk_name(ndns, btt->btt_disk->disk_name);
        btt->btt_disk->first_minor = 0;
        btt->btt_disk->fops = &btt_fops;
        btt->btt_disk->private_data = btt;
        btt->btt_disk->queue = btt->btt_queue;
        btt->btt_disk->flags = GENHD_FL_EXT_DEVT;

        blk_queue_make_request(btt->btt_queue, btt_make_request);
        blk_queue_logical_block_size(btt->btt_queue, btt->sector_size);
        blk_queue_max_hw_sectors(btt->btt_queue, UINT_MAX);
        queue_flag_set_unlocked(QUEUE_FLAG_NONROT, btt->btt_queue);
        btt->btt_queue->queuedata = btt;

        set_capacity(btt->btt_disk, 0);
        device_add_disk(&btt->nd_btt->dev, btt->btt_disk);
        if (btt_meta_size(btt)) {
                int rc = nd_integrity_init(btt->btt_disk, btt_meta_size(btt));

                if (rc) {
                        del_gendisk(btt->btt_disk);
                        put_disk(btt->btt_disk);
                        blk_cleanup_queue(btt->btt_queue);
                        return rc;
                }
        }
        set_capacity(btt->btt_disk, btt->nlba * btt->sector_size >> 9);
        btt->nd_btt->size = btt->nlba * (u64)btt->sector_size;
        revalidate_disk(btt->btt_disk);

        return 0;
}

static void btt_blk_cleanup(struct btt *btt)
{
        del_gendisk(btt->btt_disk);
        put_disk(btt->btt_disk);
        blk_cleanup_queue(btt->btt_queue);
}

/**
 * btt_init - initialize a block translation table for the given device
 * @nd_btt:     device with BTT geometry and backing device info
 * @rawsize:    raw size in bytes of the backing device
 * @lbasize:    lba size of the backing device
 * @uuid:       A uuid for the backing device - this is stored on media
 * @maxlane:    maximum number of parallel requests the device can handle
 *
 * Initialize a Block Translation Table on a backing device to provide
 * single sector power fail atomicity.
 *
 * Context:
 * Might sleep.
 *
 * Returns:
 * Pointer to a new struct btt on success, NULL on failure.
 */
static struct btt *btt_init(struct nd_btt *nd_btt, unsigned long long rawsize,
                u32 lbasize, u8 *uuid, struct nd_region *nd_region)
{
        int ret;
        struct btt *btt;
        struct nd_namespace_io *nsio;
        struct device *dev = &nd_btt->dev;

        btt = devm_kzalloc(dev, sizeof(struct btt), GFP_KERNEL);
        if (!btt)
                return NULL;

        btt->nd_btt = nd_btt;
        btt->rawsize = rawsize;
        btt->lbasize = lbasize;
        btt->sector_size = ((lbasize >= 4096) ? 4096 : 512);
        INIT_LIST_HEAD(&btt->arena_list);
        mutex_init(&btt->init_lock);
        btt->nd_region = nd_region;
        nsio = to_nd_namespace_io(&nd_btt->ndns->dev);
        btt->phys_bb = &nsio->bb;

        ret = discover_arenas(btt);
        if (ret) {
                dev_err(dev, "init: error in arena_discover: %d\n", ret);
                return NULL;
        }

        if (btt->init_state != INIT_READY && nd_region->ro) {
                dev_warn(dev, "%s is read-only, unable to init btt metadata\n",
                                dev_name(&nd_region->dev));
                return NULL;
        } else if (btt->init_state != INIT_READY) {
                btt->num_arenas = (rawsize / ARENA_MAX_SIZE) +
                        ((rawsize % ARENA_MAX_SIZE) ? 1 : 0);
                dev_dbg(dev, "init: %d arenas for %llu rawsize\n",
                                btt->num_arenas, rawsize);

                ret = create_arenas(btt);
                if (ret) {
                        dev_info(dev, "init: create_arenas: %d\n", ret);
                        return NULL;
                }

                ret = btt_meta_init(btt);
                if (ret) {
                        dev_err(dev, "init: error in meta_init: %d\n", ret);
                        return NULL;
                }
        }

        ret = btt_blk_init(btt);
        if (ret) {
                dev_err(dev, "init: error in blk_init: %d\n", ret);
                return NULL;
        }

        btt_debugfs_init(btt);

        return btt;
}

/**
 * btt_fini - de-initialize a BTT
 * @btt:        the BTT handle that was generated by btt_init
 *
 * De-initialize a Block Translation Table on device removal
 *
 * Context:
 * Might sleep.
 */
static void btt_fini(struct btt *btt)
{
        if (btt) {
                btt_blk_cleanup(btt);
                free_arenas(btt);
                debugfs_remove_recursive(btt->debugfs_dir);
        }
}

int nvdimm_namespace_attach_btt(struct nd_namespace_common *ndns)
{
        struct nd_btt *nd_btt = to_nd_btt(ndns->claim);
        struct nd_region *nd_region;
        struct btt_sb *btt_sb;
        struct btt *btt;
        size_t rawsize;

        if (!nd_btt->uuid || !nd_btt->ndns || !nd_btt->lbasize) {
                dev_dbg(&nd_btt->dev, "incomplete btt configuration\n");
                return -ENODEV;
        }

        btt_sb = devm_kzalloc(&nd_btt->dev, sizeof(*btt_sb), GFP_KERNEL);
        if (!btt_sb)
                return -ENOMEM;

        /*
         * If this returns < 0, that is ok as it just means there wasn't
         * an existing BTT, and we're creating a new one. We still need to
         * call this as we need the version dependent fields in nd_btt to be
         * set correctly based on the holder class
         */
        nd_btt_version(nd_btt, ndns, btt_sb);

        rawsize = nvdimm_namespace_capacity(ndns) - nd_btt->initial_offset;
        if (rawsize < ARENA_MIN_SIZE) {
                dev_dbg(&nd_btt->dev, "%s must be at least %ld bytes\n",
                                dev_name(&ndns->dev),
                                ARENA_MIN_SIZE + nd_btt->initial_offset);
                return -ENXIO;
        }
        nd_region = to_nd_region(nd_btt->dev.parent);
        btt = btt_init(nd_btt, rawsize, nd_btt->lbasize, nd_btt->uuid,
                        nd_region);
        if (!btt)
                return -ENOMEM;
        nd_btt->btt = btt;

        return 0;
}
EXPORT_SYMBOL(nvdimm_namespace_attach_btt);

int nvdimm_namespace_detach_btt(struct nd_btt *nd_btt)
{
        struct btt *btt = nd_btt->btt;

        btt_fini(btt);
        nd_btt->btt = NULL;

        return 0;
}
EXPORT_SYMBOL(nvdimm_namespace_detach_btt);

static int __init nd_btt_init(void)
{
        int rc = 0;

        debugfs_root = debugfs_create_dir("btt", NULL);
        if (IS_ERR_OR_NULL(debugfs_root))
                rc = -ENXIO;

        return rc;
}

static void __exit nd_btt_exit(void)
{
        debugfs_remove_recursive(debugfs_root);
}

MODULE_ALIAS_ND_DEVICE(ND_DEVICE_BTT);
MODULE_AUTHOR("Vishal Verma <vishal.l.verma@linux.intel.com>");
MODULE_LICENSE("GPL v2");
module_init(nd_btt_init);
module_exit(nd_btt_exit);