/*
 * Bad block management
 *
 * - Heavily based on MD badblocks code from Neil Brown
 *
 * Copyright (c) 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/badblocks.h>
#include <linux/seqlock.h>
#include <linux/device.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/stddef.h>
#include <linux/types.h>
#include <linux/slab.h>

/**
 * badblocks_check() - check a given range for bad sectors
 * @bb:         the badblocks structure that holds all badblock information
 * @s:          sector (start) at which to check for badblocks
 * @sectors:    number of sectors to check for badblocks
 * @first_bad:  pointer to store location of the first badblock
 * @bad_sectors: pointer to store number of badblocks after @first_bad
 *
 * We can record which blocks on each device are 'bad' and so just
 * fail those blocks, or that stripe, rather than the whole device.
 * Entries in the bad-block table are 64bits wide.  This comprises:
 * Length of bad-range, in sectors: 0-511 for lengths 1-512
 * Start of bad-range, sector offset, 54 bits (allows 8 exbibytes)
 *  A 'shift' can be set so that larger blocks are tracked and
 *  consequently larger devices can be covered.
 * 'Acknowledged' flag - 1 bit. - the most significant bit.
 *
 * Locking of the bad-block table uses a seqlock so badblocks_check
 * might need to retry if it is very unlucky.
 * We will sometimes want to check for bad blocks in a bi_end_io function,
 * so we use the write_seqlock_irq variant.
 *
 * When looking for a bad block we specify a range and want to
 * know if any block in the range is bad.  So we binary-search
 * to the last range that starts at-or-before the given endpoint,
 * (or "before the sector after the target range")
 * then see if it ends after the given start.
 *
 * Return:
 *  0: there are no known bad blocks in the range
 *  1: there are known bad block which are all acknowledged
 * -1: there are bad blocks which have not yet been acknowledged in metadata.
 * plus the start/length of the first bad section we overlap.
 */
int badblocks_check(struct badblocks *bb, sector_t s, int sectors,
                        sector_t *first_bad, int *bad_sectors)
{
        int hi;
        int lo;
        u64 *p = bb->page;
        int rv;
        sector_t target = s + sectors;
        unsigned seq;

        if (bb->shift > 0) {
                /* round the start down, and the end up */
                s >>= bb->shift;
                target += (1<<bb->shift) - 1;
                target >>= bb->shift;
                sectors = target - s;
        }
        /* 'target' is now the first block after the bad range */

retry:
        seq = read_seqbegin(&bb->lock);
        lo = 0;
        rv = 0;
        hi = bb->count;

        /* Binary search between lo and hi for 'target'
         * i.e. for the last range that starts before 'target'
         */
        /* INVARIANT: ranges before 'lo' and at-or-after 'hi'
         * are known not to be the last range before target.
         * VARIANT: hi-lo is the number of possible
         * ranges, and decreases until it reaches 1
         */
        while (hi - lo > 1) {
                int mid = (lo + hi) / 2;
                sector_t a = BB_OFFSET(p[mid]);

                if (a < target)
                        /* This could still be the one, earlier ranges
                         * could not.
                         */
                        lo = mid;
                else
                        /* This and later ranges are definitely out. */
                        hi = mid;
        }
        /* 'lo' might be the last that started before target, but 'hi' isn't */
        if (hi > lo) {
                /* need to check all range that end after 's' to see if
                 * any are unacknowledged.
                 */
                while (lo >= 0 &&
                       BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > s) {
                        if (BB_OFFSET(p[lo]) < target) {
                                /* starts before the end, and finishes after
                                 * the start, so they must overlap
                                 */
                                if (rv != -1 && BB_ACK(p[lo]))
                                        rv = 1;
                                else
                                        rv = -1;
                                *first_bad = BB_OFFSET(p[lo]);
                                *bad_sectors = BB_LEN(p[lo]);
                        }
                        lo--;
                }
        }

        if (read_seqretry(&bb->lock, seq))
                goto retry;

        return rv;
}
EXPORT_SYMBOL_GPL(badblocks_check);

static void badblocks_update_acked(struct badblocks *bb)
{
        u64 *p = bb->page;
        int i;
        bool unacked = false;

        if (!bb->unacked_exist)
                return;

        for (i = 0; i < bb->count ; i++) {
                if (!BB_ACK(p[i])) {
                        unacked = true;
                        break;
                }
        }

        if (!unacked)
                bb->unacked_exist = 0;
}

/**
 * badblocks_set() - Add a range of bad blocks to the table.
 * @bb:         the badblocks structure that holds all badblock information
 * @s:          first sector to mark as bad
 * @sectors:    number of sectors to mark as bad
 * @acknowledged: weather to mark the bad sectors as acknowledged
 *
 * This might extend the table, or might contract it if two adjacent ranges
 * can be merged. We binary-search to find the 'insertion' point, then
 * decide how best to handle it.
 *
 * Return:
 *  0: success
 *  1: failed to set badblocks (out of space)
 */
int badblocks_set(struct badblocks *bb, sector_t s, int sectors,
                        int acknowledged)
{
        u64 *p;
        int lo, hi;
        int rv = 0;
        unsigned long flags;

        if (bb->shift < 0)
                /* badblocks are disabled */
                return 1;

        if (bb->shift) {
                /* round the start down, and the end up */
                sector_t next = s + sectors;

                s >>= bb->shift;
                next += (1<<bb->shift) - 1;
                next >>= bb->shift;
                sectors = next - s;
        }

        write_seqlock_irqsave(&bb->lock, flags);

        p = bb->page;
        lo = 0;
        hi = bb->count;
        /* Find the last range that starts at-or-before 's' */
        while (hi - lo > 1) {
                int mid = (lo + hi) / 2;
                sector_t a = BB_OFFSET(p[mid]);

                if (a <= s)
                        lo = mid;
                else
                        hi = mid;
        }
        if (hi > lo && BB_OFFSET(p[lo]) > s)
                hi = lo;

        if (hi > lo) {
                /* we found a range that might merge with the start
                 * of our new range
                 */
                sector_t a = BB_OFFSET(p[lo]);
                sector_t e = a + BB_LEN(p[lo]);
                int ack = BB_ACK(p[lo]);

                if (e >= s) {
                        /* Yes, we can merge with a previous range */
                        if (s == a && s + sectors >= e)
                                /* new range covers old */
                                ack = acknowledged;
                        else
                                ack = ack && acknowledged;

                        if (e < s + sectors)
                                e = s + sectors;
                        if (e - a <= BB_MAX_LEN) {
                                p[lo] = BB_MAKE(a, e-a, ack);
                                s = e;
                        } else {
                                /* does not all fit in one range,
                                 * make p[lo] maximal
                                 */
                                if (BB_LEN(p[lo]) != BB_MAX_LEN)
                                        p[lo] = BB_MAKE(a, BB_MAX_LEN, ack);
                                s = a + BB_MAX_LEN;
                        }
                        sectors = e - s;
                }
        }
        if (sectors && hi < bb->count) {
                /* 'hi' points to the first range that starts after 's'.
                 * Maybe we can merge with the start of that range
                 */
                sector_t a = BB_OFFSET(p[hi]);
                sector_t e = a + BB_LEN(p[hi]);
                int ack = BB_ACK(p[hi]);

                if (a <= s + sectors) {
                        /* merging is possible */
                        if (e <= s + sectors) {
                                /* full overlap */
                                e = s + sectors;
                                ack = acknowledged;
                        } else
                                ack = ack && acknowledged;

                        a = s;
                        if (e - a <= BB_MAX_LEN) {
                                p[hi] = BB_MAKE(a, e-a, ack);
                                s = e;
                        } else {
                                p[hi] = BB_MAKE(a, BB_MAX_LEN, ack);
                                s = a + BB_MAX_LEN;
                        }
                        sectors = e - s;
                        lo = hi;
                        hi++;
                }
        }
        if (sectors == 0 && hi < bb->count) {
                /* we might be able to combine lo and hi */
                /* Note: 's' is at the end of 'lo' */
                sector_t a = BB_OFFSET(p[hi]);
                int lolen = BB_LEN(p[lo]);
                int hilen = BB_LEN(p[hi]);
                int newlen = lolen + hilen - (s - a);

                if (s >= a && newlen < BB_MAX_LEN) {
                        /* yes, we can combine them */
                        int ack = BB_ACK(p[lo]) && BB_ACK(p[hi]);

                        p[lo] = BB_MAKE(BB_OFFSET(p[lo]), newlen, ack);
                        memmove(p + hi, p + hi + 1,
                                (bb->count - hi - 1) * 8);
                        bb->count--;
                }
        }
        while (sectors) {
                /* didn't merge (it all).
                 * Need to add a range just before 'hi'
                 */
                if (bb->count >= MAX_BADBLOCKS) {
                        /* No room for more */
                        rv = 1;
                        break;
                } else {
                        int this_sectors = sectors;

                        memmove(p + hi + 1, p + hi,
                                (bb->count - hi) * 8);
                        bb->count++;

                        if (this_sectors > BB_MAX_LEN)
                                this_sectors = BB_MAX_LEN;
                        p[hi] = BB_MAKE(s, this_sectors, acknowledged);
                        sectors -= this_sectors;
                        s += this_sectors;
                }
        }

        bb->changed = 1;
        if (!acknowledged)
                bb->unacked_exist = 1;
        else
                badblocks_update_acked(bb);
        write_sequnlock_irqrestore(&bb->lock, flags);

        return rv;
}
EXPORT_SYMBOL_GPL(badblocks_set);

/**
 * badblocks_clear() - Remove a range of bad blocks to the table.
 * @bb:         the badblocks structure that holds all badblock information
 * @s:          first sector to mark as bad
 * @sectors:    number of sectors to mark as bad
 *
 * This may involve extending the table if we spilt a region,
 * but it must not fail.  So if the table becomes full, we just
 * drop the remove request.
 *
 * Return:
 *  0: success
 *  1: failed to clear badblocks
 */
int badblocks_clear(struct badblocks *bb, sector_t s, int sectors)
{
        u64 *p;
        int lo, hi;
        sector_t target = s + sectors;
        int rv = 0;

        if (bb->shift > 0) {
                /* When clearing we round the start up and the end down.
                 * This should not matter as the shift should align with
                 * the block size and no rounding should ever be needed.
                 * However it is better the think a block is bad when it
                 * isn't than to think a block is not bad when it is.
                 */
                s += (1<<bb->shift) - 1;
                s >>= bb->shift;
                target >>= bb->shift;
                sectors = target - s;
        }

        write_seqlock_irq(&bb->lock);

        p = bb->page;
        lo = 0;
        hi = bb->count;
        /* Find the last range that starts before 'target' */
        while (hi - lo > 1) {
                int mid = (lo + hi) / 2;
                sector_t a = BB_OFFSET(p[mid]);

                if (a < target)
                        lo = mid;
                else
                        hi = mid;
        }
        if (hi > lo) {
                /* p[lo] is the last range that could overlap the
                 * current range.  Earlier ranges could also overlap,
                 * but only this one can overlap the end of the range.
                 */
                if ((BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > target) &&
                    (BB_OFFSET(p[lo]) < target)) {
                        /* Partial overlap, leave the tail of this range */
                        int ack = BB_ACK(p[lo]);
                        sector_t a = BB_OFFSET(p[lo]);
                        sector_t end = a + BB_LEN(p[lo]);

                        if (a < s) {
                                /* we need to split this range */
                                if (bb->count >= MAX_BADBLOCKS) {
                                        rv = -ENOSPC;
                                        goto out;
                                }
                                memmove(p+lo+1, p+lo, (bb->count - lo) * 8);
                                bb->count++;
                                p[lo] = BB_MAKE(a, s-a, ack);
                                lo++;
                        }
                        p[lo] = BB_MAKE(target, end - target, ack);
                        /* there is no longer an overlap */
                        hi = lo;
                        lo--;
                }
                while (lo >= 0 &&
                       (BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > s) &&
                       (BB_OFFSET(p[lo]) < target)) {
                        /* This range does overlap */
                        if (BB_OFFSET(p[lo]) < s) {
                                /* Keep the early parts of this range. */
                                int ack = BB_ACK(p[lo]);
                                sector_t start = BB_OFFSET(p[lo]);

                                p[lo] = BB_MAKE(start, s - start, ack);
                                /* now low doesn't overlap, so.. */
                                break;
                        }
                        lo--;
                }
                /* 'lo' is strictly before, 'hi' is strictly after,
                 * anything between needs to be discarded
                 */
                if (hi - lo > 1) {
                        memmove(p+lo+1, p+hi, (bb->count - hi) * 8);
                        bb->count -= (hi - lo - 1);
                }
        }

        badblocks_update_acked(bb);
        bb->changed = 1;
out:
        write_sequnlock_irq(&bb->lock);
        return rv;
}
EXPORT_SYMBOL_GPL(badblocks_clear);

/**
 * ack_all_badblocks() - Acknowledge all bad blocks in a list.
 * @bb:         the badblocks structure that holds all badblock information
 *
 * This only succeeds if ->changed is clear.  It is used by
 * in-kernel metadata updates
 */
void ack_all_badblocks(struct badblocks *bb)
{
        if (bb->page == NULL || bb->changed)
                /* no point even trying */
                return;
        write_seqlock_irq(&bb->lock);

        if (bb->changed == 0 && bb->unacked_exist) {
                u64 *p = bb->page;
                int i;

                for (i = 0; i < bb->count ; i++) {
                        if (!BB_ACK(p[i])) {
                                sector_t start = BB_OFFSET(p[i]);
                                int len = BB_LEN(p[i]);

                                p[i] = BB_MAKE(start, len, 1);
                        }
                }
                bb->unacked_exist = 0;
        }
        write_sequnlock_irq(&bb->lock);
}
EXPORT_SYMBOL_GPL(ack_all_badblocks);

/**
 * badblocks_show() - sysfs access to bad-blocks list
 * @bb:         the badblocks structure that holds all badblock information
 * @page:       buffer received from sysfs
 * @unack:      weather to show unacknowledged badblocks
 *
 * Return:
 *  Length of returned data
 */
ssize_t badblocks_show(struct badblocks *bb, char *page, int unack)
{
        size_t len;
        int i;
        u64 *p = bb->page;
        unsigned seq;

        if (bb->shift < 0)
                return 0;

retry:
        seq = read_seqbegin(&bb->lock);

        len = 0;
        i = 0;

        while (len < PAGE_SIZE && i < bb->count) {
                sector_t s = BB_OFFSET(p[i]);
                unsigned int length = BB_LEN(p[i]);
                int ack = BB_ACK(p[i]);

                i++;

                if (unack && ack)
                        continue;

                len += snprintf(page+len, PAGE_SIZE-len, "%llu %u\n",
                                (unsigned long long)s << bb->shift,
                                length << bb->shift);
        }
        if (unack && len == 0)
                bb->unacked_exist = 0;

        if (read_seqretry(&bb->lock, seq))
                goto retry;

        return len;
}
EXPORT_SYMBOL_GPL(badblocks_show);

/**
 * badblocks_store() - sysfs access to bad-blocks list
 * @bb:         the badblocks structure that holds all badblock information
 * @page:       buffer received from sysfs
 * @len:        length of data received from sysfs
 * @unack:      weather to show unacknowledged badblocks
 *
 * Return:
 *  Length of the buffer processed or -ve error.
 */
ssize_t badblocks_store(struct badblocks *bb, const char *page, size_t len,
                        int unack)
{
        unsigned long long sector;
        int length;
        char newline;

        switch (sscanf(page, "%llu %d%c", &sector, &length, &newline)) {
        case 3:
                if (newline != '\n')
                        return -EINVAL;
                /* fall through */
        case 2:
                if (length <= 0)
                        return -EINVAL;
                break;
        default:
                return -EINVAL;
        }

        if (badblocks_set(bb, sector, length, !unack))
                return -ENOSPC;
        else
                return len;
}
EXPORT_SYMBOL_GPL(badblocks_store);

static int __badblocks_init(struct device *dev, struct badblocks *bb,
                int enable)
{
        bb->dev = dev;
        bb->count = 0;
        if (enable)
                bb->shift = 0;
        else
                bb->shift = -1;
        if (dev)
                bb->page = devm_kzalloc(dev, PAGE_SIZE, GFP_KERNEL);
        else
                bb->page = kzalloc(PAGE_SIZE, GFP_KERNEL);
        if (!bb->page) {
                bb->shift = -1;
                return -ENOMEM;
        }
        seqlock_init(&bb->lock);

        return 0;
}

/**
 * badblocks_init() - initialize the badblocks structure
 * @bb:         the badblocks structure that holds all badblock information
 * @enable:     weather to enable badblocks accounting
 *
 * Return:
 *  0: success
 *  -ve errno: on error
 */
int badblocks_init(struct badblocks *bb, int enable)
{
        return __badblocks_init(NULL, bb, enable);
}
EXPORT_SYMBOL_GPL(badblocks_init);

int devm_init_badblocks(struct device *dev, struct badblocks *bb)
{
        if (!bb)
                return -EINVAL;
        return __badblocks_init(dev, bb, 1);
}
EXPORT_SYMBOL_GPL(devm_init_badblocks);

/**
 * badblocks_exit() - free the badblocks structure
 * @bb:         the badblocks structure that holds all badblock information
 */
void badblocks_exit(struct badblocks *bb)
{
        if (!bb)
                return;
        if (bb->dev)
                devm_kfree(bb->dev, bb->page);
        else
                kfree(bb->page);
        bb->page = NULL;
}
EXPORT_SYMBOL_GPL(badblocks_exit);