// SPDX-License-Identifier: GPL-2.0
/*
 *
 * Copyright (C) 2019-2021 Paragon Software GmbH, All rights reserved.
 *
 * This code builds two trees of free clusters extents.
 * Trees are sorted by start of extent and by length of extent.
 * NTFS_MAX_WND_EXTENTS defines the maximum number of elements in trees.
 * In extreme case code reads on-disk bitmap to find free clusters.
 *
 */

#include <linux/buffer_head.h>
#include <linux/fs.h>
#include <linux/kernel.h>

#include "ntfs.h"
#include "ntfs_fs.h"

/*
 * Maximum number of extents in tree.
 */
#define NTFS_MAX_WND_EXTENTS (32u * 1024u)

struct rb_node_key {
        struct rb_node node;
        size_t key;
};

struct e_node {
        struct rb_node_key start; /* Tree sorted by start. */
        struct rb_node_key count; /* Tree sorted by len. */
};

static int wnd_rescan(struct wnd_bitmap *wnd);
static struct buffer_head *wnd_map(struct wnd_bitmap *wnd, size_t iw);
static bool wnd_is_free_hlp(struct wnd_bitmap *wnd, size_t bit, size_t bits);

static struct kmem_cache *ntfs_enode_cachep;

int __init ntfs3_init_bitmap(void)
{
        ntfs_enode_cachep =
                kmem_cache_create("ntfs3_enode_cache", sizeof(struct e_node), 0,
                                  SLAB_RECLAIM_ACCOUNT, NULL);
        return ntfs_enode_cachep ? 0 : -ENOMEM;
}

void ntfs3_exit_bitmap(void)
{
        kmem_cache_destroy(ntfs_enode_cachep);
}

static inline u32 wnd_bits(const struct wnd_bitmap *wnd, size_t i)
{
        return i + 1 == wnd->nwnd ? wnd->bits_last : wnd->sb->s_blocksize * 8;
}

/*
 * wnd_scan
 *
 * b_pos + b_len - biggest fragment.
 * Scan range [wpos wbits) window @buf.
 *
 * Return: -1 if not found.
 */
static size_t wnd_scan(const ulong *buf, size_t wbit, u32 wpos, u32 wend,
                       size_t to_alloc, size_t *prev_tail, size_t *b_pos,
                       size_t *b_len)
{
        while (wpos < wend) {
                size_t free_len;
                u32 free_bits, end;
                u32 used = find_next_zero_bit(buf, wend, wpos);

                if (used >= wend) {
                        if (*b_len < *prev_tail) {
                                *b_pos = wbit - *prev_tail;
                                *b_len = *prev_tail;
                        }

                        *prev_tail = 0;
                        return -1;
                }

                if (used > wpos) {
                        wpos = used;
                        if (*b_len < *prev_tail) {
                                *b_pos = wbit - *prev_tail;
                                *b_len = *prev_tail;
                        }

                        *prev_tail = 0;
                }

                /*
                 * Now we have a fragment [wpos, wend) staring with 0.
                 */
                end = wpos + to_alloc - *prev_tail;
                free_bits = find_next_bit(buf, min(end, wend), wpos);

                free_len = *prev_tail + free_bits - wpos;

                if (*b_len < free_len) {
                        *b_pos = wbit + wpos - *prev_tail;
                        *b_len = free_len;
                }

                if (free_len >= to_alloc)
                        return wbit + wpos - *prev_tail;

                if (free_bits >= wend) {
                        *prev_tail += free_bits - wpos;
                        return -1;
                }

                wpos = free_bits + 1;

                *prev_tail = 0;
        }

        return -1;
}

/*
 * wnd_close - Frees all resources.
 */
void wnd_close(struct wnd_bitmap *wnd)
{
        struct rb_node *node, *next;

        kfree(wnd->free_bits);
        run_close(&wnd->run);

        node = rb_first(&wnd->start_tree);

        while (node) {
                next = rb_next(node);
                rb_erase(node, &wnd->start_tree);
                kmem_cache_free(ntfs_enode_cachep,
                                rb_entry(node, struct e_node, start.node));
                node = next;
        }
}

static struct rb_node *rb_lookup(struct rb_root *root, size_t v)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *r = NULL;

        while (*p) {
                struct rb_node_key *k;

                k = rb_entry(*p, struct rb_node_key, node);
                if (v < k->key) {
                        p = &(*p)->rb_left;
                } else if (v > k->key) {
                        r = &k->node;
                        p = &(*p)->rb_right;
                } else {
                        return &k->node;
                }
        }

        return r;
}

/*
 * rb_insert_count - Helper function to insert special kind of 'count' tree.
 */
static inline bool rb_insert_count(struct rb_root *root, struct e_node *e)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        size_t e_ckey = e->count.key;
        size_t e_skey = e->start.key;

        while (*p) {
                struct e_node *k =
                        rb_entry(parent = *p, struct e_node, count.node);

                if (e_ckey > k->count.key) {
                        p = &(*p)->rb_left;
                } else if (e_ckey < k->count.key) {
                        p = &(*p)->rb_right;
                } else if (e_skey < k->start.key) {
                        p = &(*p)->rb_left;
                } else if (e_skey > k->start.key) {
                        p = &(*p)->rb_right;
                } else {
                        WARN_ON(1);
                        return false;
                }
        }

        rb_link_node(&e->count.node, parent, p);
        rb_insert_color(&e->count.node, root);
        return true;
}

/*
 * rb_insert_start - Helper function to insert special kind of 'count' tree.
 */
static inline bool rb_insert_start(struct rb_root *root, struct e_node *e)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        size_t e_skey = e->start.key;

        while (*p) {
                struct e_node *k;

                parent = *p;

                k = rb_entry(parent, struct e_node, start.node);
                if (e_skey < k->start.key) {
                        p = &(*p)->rb_left;
                } else if (e_skey > k->start.key) {
                        p = &(*p)->rb_right;
                } else {
                        WARN_ON(1);
                        return false;
                }
        }

        rb_link_node(&e->start.node, parent, p);
        rb_insert_color(&e->start.node, root);
        return true;
}

/*
 * wnd_add_free_ext - Adds a new extent of free space.
 * @build:      1 when building tree.
 */
static void wnd_add_free_ext(struct wnd_bitmap *wnd, size_t bit, size_t len,
                             bool build)
{
        struct e_node *e, *e0 = NULL;
        size_t ib, end_in = bit + len;
        struct rb_node *n;

        if (build) {
                /* Use extent_min to filter too short extents. */
                if (wnd->count >= NTFS_MAX_WND_EXTENTS &&
                    len <= wnd->extent_min) {
                        wnd->uptodated = -1;
                        return;
                }
        } else {
                /* Try to find extent before 'bit'. */
                n = rb_lookup(&wnd->start_tree, bit);

                if (!n) {
                        n = rb_first(&wnd->start_tree);
                } else {
                        e = rb_entry(n, struct e_node, start.node);
                        n = rb_next(n);
                        if (e->start.key + e->count.key == bit) {
                                /* Remove left. */
                                bit = e->start.key;
                                len += e->count.key;
                                rb_erase(&e->start.node, &wnd->start_tree);
                                rb_erase(&e->count.node, &wnd->count_tree);
                                wnd->count -= 1;
                                e0 = e;
                        }
                }

                while (n) {
                        size_t next_end;

                        e = rb_entry(n, struct e_node, start.node);
                        next_end = e->start.key + e->count.key;
                        if (e->start.key > end_in)
                                break;

                        /* Remove right. */
                        n = rb_next(n);
                        len += next_end - end_in;
                        end_in = next_end;
                        rb_erase(&e->start.node, &wnd->start_tree);
                        rb_erase(&e->count.node, &wnd->count_tree);
                        wnd->count -= 1;

                        if (!e0)
                                e0 = e;
                        else
                                kmem_cache_free(ntfs_enode_cachep, e);
                }

                if (wnd->uptodated != 1) {
                        /* Check bits before 'bit'. */
                        ib = wnd->zone_bit == wnd->zone_end ||
                                             bit < wnd->zone_end
                                     ? 0
                                     : wnd->zone_end;

                        while (bit > ib && wnd_is_free_hlp(wnd, bit - 1, 1)) {
                                bit -= 1;
                                len += 1;
                        }

                        /* Check bits after 'end_in'. */
                        ib = wnd->zone_bit == wnd->zone_end ||
                                             end_in > wnd->zone_bit
                                     ? wnd->nbits
                                     : wnd->zone_bit;

                        while (end_in < ib && wnd_is_free_hlp(wnd, end_in, 1)) {
                                end_in += 1;
                                len += 1;
                        }
                }
        }
        /* Insert new fragment. */
        if (wnd->count >= NTFS_MAX_WND_EXTENTS) {
                if (e0)
                        kmem_cache_free(ntfs_enode_cachep, e0);

                wnd->uptodated = -1;

                /* Compare with smallest fragment. */
                n = rb_last(&wnd->count_tree);
                e = rb_entry(n, struct e_node, count.node);
                if (len <= e->count.key)
                        goto out; /* Do not insert small fragments. */

                if (build) {
                        struct e_node *e2;

                        n = rb_prev(n);
                        e2 = rb_entry(n, struct e_node, count.node);
                        /* Smallest fragment will be 'e2->count.key'. */
                        wnd->extent_min = e2->count.key;
                }

                /* Replace smallest fragment by new one. */
                rb_erase(&e->start.node, &wnd->start_tree);
                rb_erase(&e->count.node, &wnd->count_tree);
                wnd->count -= 1;
        } else {
                e = e0 ? e0 : kmem_cache_alloc(ntfs_enode_cachep, GFP_ATOMIC);
                if (!e) {
                        wnd->uptodated = -1;
                        goto out;
                }

                if (build && len <= wnd->extent_min)
                        wnd->extent_min = len;
        }
        e->start.key = bit;
        e->count.key = len;
        if (len > wnd->extent_max)
                wnd->extent_max = len;

        rb_insert_start(&wnd->start_tree, e);
        rb_insert_count(&wnd->count_tree, e);
        wnd->count += 1;

out:;
}

/*
 * wnd_remove_free_ext - Remove a run from the cached free space.
 */
static void wnd_remove_free_ext(struct wnd_bitmap *wnd, size_t bit, size_t len)
{
        struct rb_node *n, *n3;
        struct e_node *e, *e3;
        size_t end_in = bit + len;
        size_t end3, end, new_key, new_len, max_new_len;

        /* Try to find extent before 'bit'. */
        n = rb_lookup(&wnd->start_tree, bit);

        if (!n)
                return;

        e = rb_entry(n, struct e_node, start.node);
        end = e->start.key + e->count.key;

        new_key = new_len = 0;
        len = e->count.key;

        /* Range [bit,end_in) must be inside 'e' or outside 'e' and 'n'. */
        if (e->start.key > bit)
                ;
        else if (end_in <= end) {
                /* Range [bit,end_in) inside 'e'. */
                new_key = end_in;
                new_len = end - end_in;
                len = bit - e->start.key;
        } else if (bit > end) {
                bool bmax = false;

                n3 = rb_next(n);

                while (n3) {
                        e3 = rb_entry(n3, struct e_node, start.node);
                        if (e3->start.key >= end_in)
                                break;

                        if (e3->count.key == wnd->extent_max)
                                bmax = true;

                        end3 = e3->start.key + e3->count.key;
                        if (end3 > end_in) {
                                e3->start.key = end_in;
                                rb_erase(&e3->count.node, &wnd->count_tree);
                                e3->count.key = end3 - end_in;
                                rb_insert_count(&wnd->count_tree, e3);
                                break;
                        }

                        n3 = rb_next(n3);
                        rb_erase(&e3->start.node, &wnd->start_tree);
                        rb_erase(&e3->count.node, &wnd->count_tree);
                        wnd->count -= 1;
                        kmem_cache_free(ntfs_enode_cachep, e3);
                }
                if (!bmax)
                        return;
                n3 = rb_first(&wnd->count_tree);
                wnd->extent_max =
                        n3 ? rb_entry(n3, struct e_node, count.node)->count.key
                           : 0;
                return;
        }

        if (e->count.key != wnd->extent_max) {
                ;
        } else if (rb_prev(&e->count.node)) {
                ;
        } else {
                n3 = rb_next(&e->count.node);
                max_new_len = max(len, new_len);
                if (!n3) {
                        wnd->extent_max = max_new_len;
                } else {
                        e3 = rb_entry(n3, struct e_node, count.node);
                        wnd->extent_max = max(e3->count.key, max_new_len);
                }
        }

        if (!len) {
                if (new_len) {
                        e->start.key = new_key;
                        rb_erase(&e->count.node, &wnd->count_tree);
                        e->count.key = new_len;
                        rb_insert_count(&wnd->count_tree, e);
                } else {
                        rb_erase(&e->start.node, &wnd->start_tree);
                        rb_erase(&e->count.node, &wnd->count_tree);
                        wnd->count -= 1;
                        kmem_cache_free(ntfs_enode_cachep, e);
                }
                goto out;
        }
        rb_erase(&e->count.node, &wnd->count_tree);
        e->count.key = len;
        rb_insert_count(&wnd->count_tree, e);

        if (!new_len)
                goto out;

        if (wnd->count >= NTFS_MAX_WND_EXTENTS) {
                wnd->uptodated = -1;

                /* Get minimal extent. */
                e = rb_entry(rb_last(&wnd->count_tree), struct e_node,
                             count.node);
                if (e->count.key > new_len)
                        goto out;

                /* Replace minimum. */
                rb_erase(&e->start.node, &wnd->start_tree);
                rb_erase(&e->count.node, &wnd->count_tree);
                wnd->count -= 1;
        } else {
                e = kmem_cache_alloc(ntfs_enode_cachep, GFP_ATOMIC);
                if (!e)
                        wnd->uptodated = -1;
        }

        if (e) {
                e->start.key = new_key;
                e->count.key = new_len;
                rb_insert_start(&wnd->start_tree, e);
                rb_insert_count(&wnd->count_tree, e);
                wnd->count += 1;
        }

out:
        if (!wnd->count && 1 != wnd->uptodated)
                wnd_rescan(wnd);
}

/*
 * wnd_rescan - Scan all bitmap. Used while initialization.
 */
static int wnd_rescan(struct wnd_bitmap *wnd)
{
        int err = 0;
        size_t prev_tail = 0;
        struct super_block *sb = wnd->sb;
        struct ntfs_sb_info *sbi = sb->s_fs_info;
        u64 lbo, len = 0;
        u32 blocksize = sb->s_blocksize;
        u8 cluster_bits = sbi->cluster_bits;
        u32 wbits = 8 * sb->s_blocksize;
        u32 used, frb;
        const ulong *buf;
        size_t wpos, wbit, iw, vbo;
        struct buffer_head *bh = NULL;
        CLST lcn, clen;

        wnd->uptodated = 0;
        wnd->extent_max = 0;
        wnd->extent_min = MINUS_ONE_T;
        wnd->total_zeroes = 0;

        vbo = 0;

        for (iw = 0; iw < wnd->nwnd; iw++) {
                if (iw + 1 == wnd->nwnd)
                        wbits = wnd->bits_last;

                if (wnd->inited) {
                        if (!wnd->free_bits[iw]) {
                                /* All ones. */
                                if (prev_tail) {
                                        wnd_add_free_ext(wnd,
                                                         vbo * 8 - prev_tail,
                                                         prev_tail, true);
                                        prev_tail = 0;
                                }
                                goto next_wnd;
                        }
                        if (wbits == wnd->free_bits[iw]) {
                                /* All zeroes. */
                                prev_tail += wbits;
                                wnd->total_zeroes += wbits;
                                goto next_wnd;
                        }
                }

                if (!len) {
                        u32 off = vbo & sbi->cluster_mask;

                        if (!run_lookup_entry(&wnd->run, vbo >> cluster_bits,
                                              &lcn, &clen, NULL)) {
                                err = -ENOENT;
                                goto out;
                        }

                        lbo = ((u64)lcn << cluster_bits) + off;
                        len = ((u64)clen << cluster_bits) - off;
                }

                bh = ntfs_bread(sb, lbo >> sb->s_blocksize_bits);
                if (!bh) {
                        err = -EIO;
                        goto out;
                }

                buf = (ulong *)bh->b_data;

                used = __bitmap_weight(buf, wbits);
                if (used < wbits) {
                        frb = wbits - used;
                        wnd->free_bits[iw] = frb;
                        wnd->total_zeroes += frb;
                }

                wpos = 0;
                wbit = vbo * 8;

                if (wbit + wbits > wnd->nbits)
                        wbits = wnd->nbits - wbit;

                do {
                        used = find_next_zero_bit(buf, wbits, wpos);

                        if (used > wpos && prev_tail) {
                                wnd_add_free_ext(wnd, wbit + wpos - prev_tail,
                                                 prev_tail, true);
                                prev_tail = 0;
                        }

                        wpos = used;

                        if (wpos >= wbits) {
                                /* No free blocks. */
                                prev_tail = 0;
                                break;
                        }

                        frb = find_next_bit(buf, wbits, wpos);
                        if (frb >= wbits) {
                                /* Keep last free block. */
                                prev_tail += frb - wpos;
                                break;
                        }

                        wnd_add_free_ext(wnd, wbit + wpos - prev_tail,
                                         frb + prev_tail - wpos, true);

                        /* Skip free block and first '1'. */
                        wpos = frb + 1;
                        /* Reset previous tail. */
                        prev_tail = 0;
                } while (wpos < wbits);

next_wnd:

                if (bh)
                        put_bh(bh);
                bh = NULL;

                vbo += blocksize;
                if (len) {
                        len -= blocksize;
                        lbo += blocksize;
                }
        }

        /* Add last block. */
        if (prev_tail)
                wnd_add_free_ext(wnd, wnd->nbits - prev_tail, prev_tail, true);

        /*
         * Before init cycle wnd->uptodated was 0.
         * If any errors or limits occurs while initialization then
         * wnd->uptodated will be -1.
         * If 'uptodated' is still 0 then Tree is really updated.
         */
        if (!wnd->uptodated)
                wnd->uptodated = 1;

        if (wnd->zone_bit != wnd->zone_end) {
                size_t zlen = wnd->zone_end - wnd->zone_bit;

                wnd->zone_end = wnd->zone_bit;
                wnd_zone_set(wnd, wnd->zone_bit, zlen);
        }

out:
        return err;
}

int wnd_init(struct wnd_bitmap *wnd, struct super_block *sb, size_t nbits)
{
        int err;
        u32 blocksize = sb->s_blocksize;
        u32 wbits = blocksize * 8;

        init_rwsem(&wnd->rw_lock);

        wnd->sb = sb;
        wnd->nbits = nbits;
        wnd->total_zeroes = nbits;
        wnd->extent_max = MINUS_ONE_T;
        wnd->zone_bit = wnd->zone_end = 0;
        wnd->nwnd = bytes_to_block(sb, bitmap_size(nbits));
        wnd->bits_last = nbits & (wbits - 1);
        if (!wnd->bits_last)
                wnd->bits_last = wbits;

        wnd->free_bits = kcalloc(wnd->nwnd, sizeof(u16), GFP_NOFS);
        if (!wnd->free_bits)
                return -ENOMEM;

        err = wnd_rescan(wnd);
        if (err)
                return err;

        wnd->inited = true;

        return 0;
}

/*
 * wnd_map - Call sb_bread for requested window.
 */
static struct buffer_head *wnd_map(struct wnd_bitmap *wnd, size_t iw)
{
        size_t vbo;
        CLST lcn, clen;
        struct super_block *sb = wnd->sb;
        struct ntfs_sb_info *sbi;
        struct buffer_head *bh;
        u64 lbo;

        sbi = sb->s_fs_info;
        vbo = (u64)iw << sb->s_blocksize_bits;

        if (!run_lookup_entry(&wnd->run, vbo >> sbi->cluster_bits, &lcn, &clen,
                              NULL)) {
                return ERR_PTR(-ENOENT);
        }

        lbo = ((u64)lcn << sbi->cluster_bits) + (vbo & sbi->cluster_mask);

        bh = ntfs_bread(wnd->sb, lbo >> sb->s_blocksize_bits);
        if (!bh)
                return ERR_PTR(-EIO);

        return bh;
}

/*
 * wnd_set_free - Mark the bits range from bit to bit + bits as free.
 */
int wnd_set_free(struct wnd_bitmap *wnd, size_t bit, size_t bits)
{
        int err = 0;
        struct super_block *sb = wnd->sb;
        size_t bits0 = bits;
        u32 wbits = 8 * sb->s_blocksize;
        size_t iw = bit >> (sb->s_blocksize_bits + 3);
        u32 wbit = bit & (wbits - 1);
        struct buffer_head *bh;

        while (iw < wnd->nwnd && bits) {
                u32 tail, op;
                ulong *buf;

                if (iw + 1 == wnd->nwnd)
                        wbits = wnd->bits_last;

                tail = wbits - wbit;
                op = min_t(u32, tail, bits);

                bh = wnd_map(wnd, iw);
                if (IS_ERR(bh)) {
                        err = PTR_ERR(bh);
                        break;
                }

                buf = (ulong *)bh->b_data;

                lock_buffer(bh);

                __bitmap_clear(buf, wbit, op);

                wnd->free_bits[iw] += op;

                set_buffer_uptodate(bh);
                mark_buffer_dirty(bh);
                unlock_buffer(bh);
                put_bh(bh);

                wnd->total_zeroes += op;
                bits -= op;
                wbit = 0;
                iw += 1;
        }

        wnd_add_free_ext(wnd, bit, bits0, false);

        return err;
}

/*
 * wnd_set_used - Mark the bits range from bit to bit + bits as used.
 */
int wnd_set_used(struct wnd_bitmap *wnd, size_t bit, size_t bits)
{
        int err = 0;
        struct super_block *sb = wnd->sb;
        size_t bits0 = bits;
        size_t iw = bit >> (sb->s_blocksize_bits + 3);
        u32 wbits = 8 * sb->s_blocksize;
        u32 wbit = bit & (wbits - 1);
        struct buffer_head *bh;

        while (iw < wnd->nwnd && bits) {
                u32 tail, op;
                ulong *buf;

                if (unlikely(iw + 1 == wnd->nwnd))
                        wbits = wnd->bits_last;

                tail = wbits - wbit;
                op = min_t(u32, tail, bits);

                bh = wnd_map(wnd, iw);
                if (IS_ERR(bh)) {
                        err = PTR_ERR(bh);
                        break;
                }
                buf = (ulong *)bh->b_data;

                lock_buffer(bh);

                __bitmap_set(buf, wbit, op);
                wnd->free_bits[iw] -= op;

                set_buffer_uptodate(bh);
                mark_buffer_dirty(bh);
                unlock_buffer(bh);
                put_bh(bh);

                wnd->total_zeroes -= op;
                bits -= op;
                wbit = 0;
                iw += 1;
        }

        if (!RB_EMPTY_ROOT(&wnd->start_tree))
                wnd_remove_free_ext(wnd, bit, bits0);

        return err;
}

/*
 * wnd_is_free_hlp
 *
 * Return: True if all clusters [bit, bit+bits) are free (bitmap only).
 */
static bool wnd_is_free_hlp(struct wnd_bitmap *wnd, size_t bit, size_t bits)
{
        struct super_block *sb = wnd->sb;
        size_t iw = bit >> (sb->s_blocksize_bits + 3);
        u32 wbits = 8 * sb->s_blocksize;
        u32 wbit = bit & (wbits - 1);

        while (iw < wnd->nwnd && bits) {
                u32 tail, op;

                if (unlikely(iw + 1 == wnd->nwnd))
                        wbits = wnd->bits_last;

                tail = wbits - wbit;
                op = min_t(u32, tail, bits);

                if (wbits != wnd->free_bits[iw]) {
                        bool ret;
                        struct buffer_head *bh = wnd_map(wnd, iw);

                        if (IS_ERR(bh))
                                return false;

                        ret = are_bits_clear((ulong *)bh->b_data, wbit, op);

                        put_bh(bh);
                        if (!ret)
                                return false;
                }

                bits -= op;
                wbit = 0;
                iw += 1;
        }

        return true;
}

/*
 * wnd_is_free
 *
 * Return: True if all clusters [bit, bit+bits) are free.
 */
bool wnd_is_free(struct wnd_bitmap *wnd, size_t bit, size_t bits)
{
        bool ret;
        struct rb_node *n;
        size_t end;
        struct e_node *e;

        if (RB_EMPTY_ROOT(&wnd->start_tree))
                goto use_wnd;

        n = rb_lookup(&wnd->start_tree, bit);
        if (!n)
                goto use_wnd;

        e = rb_entry(n, struct e_node, start.node);

        end = e->start.key + e->count.key;

        if (bit < end && bit + bits <= end)
                return true;

use_wnd:
        ret = wnd_is_free_hlp(wnd, bit, bits);

        return ret;
}

/*
 * wnd_is_used
 *
 * Return: True if all clusters [bit, bit+bits) are used.
 */
bool wnd_is_used(struct wnd_bitmap *wnd, size_t bit, size_t bits)
{
        bool ret = false;
        struct super_block *sb = wnd->sb;
        size_t iw = bit >> (sb->s_blocksize_bits + 3);
        u32 wbits = 8 * sb->s_blocksize;
        u32 wbit = bit & (wbits - 1);
        size_t end;
        struct rb_node *n;
        struct e_node *e;

        if (RB_EMPTY_ROOT(&wnd->start_tree))
                goto use_wnd;

        end = bit + bits;
        n = rb_lookup(&wnd->start_tree, end - 1);
        if (!n)
                goto use_wnd;

        e = rb_entry(n, struct e_node, start.node);
        if (e->start.key + e->count.key > bit)
                return false;

use_wnd:
        while (iw < wnd->nwnd && bits) {
                u32 tail, op;

                if (unlikely(iw + 1 == wnd->nwnd))
                        wbits = wnd->bits_last;

                tail = wbits - wbit;
                op = min_t(u32, tail, bits);

                if (wnd->free_bits[iw]) {
                        bool ret;
                        struct buffer_head *bh = wnd_map(wnd, iw);

                        if (IS_ERR(bh))
                                goto out;

                        ret = are_bits_set((ulong *)bh->b_data, wbit, op);
                        put_bh(bh);
                        if (!ret)
                                goto out;
                }

                bits -= op;
                wbit = 0;
                iw += 1;
        }
        ret = true;

out:
        return ret;
}

/*
 * wnd_find - Look for free space.
 *
 * - flags - BITMAP_FIND_XXX flags
 *
 * Return: 0 if not found.
 */
size_t wnd_find(struct wnd_bitmap *wnd, size_t to_alloc, size_t hint,
                size_t flags, size_t *allocated)
{
        struct super_block *sb;
        u32 wbits, wpos, wzbit, wzend;
        size_t fnd, max_alloc, b_len, b_pos;
        size_t iw, prev_tail, nwnd, wbit, ebit, zbit, zend;
        size_t to_alloc0 = to_alloc;
        const ulong *buf;
        const struct e_node *e;
        const struct rb_node *pr, *cr;
        u8 log2_bits;
        bool fbits_valid;
        struct buffer_head *bh;

        /* Fast checking for available free space. */
        if (flags & BITMAP_FIND_FULL) {
                size_t zeroes = wnd_zeroes(wnd);

                zeroes -= wnd->zone_end - wnd->zone_bit;
                if (zeroes < to_alloc0)
                        goto no_space;

                if (to_alloc0 > wnd->extent_max)
                        goto no_space;
        } else {
                if (to_alloc > wnd->extent_max)
                        to_alloc = wnd->extent_max;
        }

        if (wnd->zone_bit <= hint && hint < wnd->zone_end)
                hint = wnd->zone_end;

        max_alloc = wnd->nbits;
        b_len = b_pos = 0;

        if (hint >= max_alloc)
                hint = 0;

        if (RB_EMPTY_ROOT(&wnd->start_tree)) {
                if (wnd->uptodated == 1) {
                        /* Extents tree is updated -> No free space. */

                        goto no_space;
                }
                goto scan_bitmap;
        }

        e = NULL;
        if (!hint)
                goto allocate_biggest;

        /* Use hint: Enumerate extents by start >= hint. */
        pr = NULL;
        cr = wnd->start_tree.rb_node;

        for (;;) {
                e = rb_entry(cr, struct e_node, start.node);

                if (e->start.key == hint)
                        break;

                if (e->start.key < hint) {
                        pr = cr;
                        cr = cr->rb_right;
                        if (!cr)
                                break;
                        continue;
                }

                cr = cr->rb_left;
                if (!cr) {
                        e = pr ? rb_entry(pr, struct e_node, start.node) : NULL;
                        break;
                }
        }

        if (!e)
                goto allocate_biggest;

        if (e->start.key + e->count.key > hint) {
                /* We have found extension with 'hint' inside. */
                size_t len = e->start.key + e->count.key - hint;

                if (len >= to_alloc && hint + to_alloc <= max_alloc) {
                        fnd = hint;
                        goto found;
                }

                if (!(flags & BITMAP_FIND_FULL)) {
                        if (len > to_alloc)
                                len = to_alloc;

                        if (hint + len <= max_alloc) {
                                fnd = hint;
                                to_alloc = len;
                                goto found;
                        }
                }
        }

allocate_biggest:
        /* Allocate from biggest free extent. */
        e = rb_entry(rb_first(&wnd->count_tree), struct e_node, count.node);
        if (e->count.key != wnd->extent_max)
                wnd->extent_max = e->count.key;

        if (e->count.key < max_alloc) {
                if (e->count.key >= to_alloc) {
                        ;
                } else if (flags & BITMAP_FIND_FULL) {
                        if (e->count.key < to_alloc0) {
                                /* Biggest free block is less then requested. */
                                goto no_space;
                        }
                        to_alloc = e->count.key;
                } else if (-1 != wnd->uptodated) {
                        to_alloc = e->count.key;
                } else {
                        /* Check if we can use more bits. */
                        size_t op, max_check;
                        struct rb_root start_tree;

                        memcpy(&start_tree, &wnd->start_tree,
                               sizeof(struct rb_root));
                        memset(&wnd->start_tree, 0, sizeof(struct rb_root));

                        max_check = e->start.key + to_alloc;
                        if (max_check > max_alloc)
                                max_check = max_alloc;
                        for (op = e->start.key + e->count.key; op < max_check;
                             op++) {
                                if (!wnd_is_free(wnd, op, 1))
                                        break;
                        }
                        memcpy(&wnd->start_tree, &start_tree,
                               sizeof(struct rb_root));
                        to_alloc = op - e->start.key;
                }

                /* Prepare to return. */
                fnd = e->start.key;
                if (e->start.key + to_alloc > max_alloc)
                        to_alloc = max_alloc - e->start.key;
                goto found;
        }

        if (wnd->uptodated == 1) {
                /* Extents tree is updated -> no free space. */
                goto no_space;
        }

        b_len = e->count.key;
        b_pos = e->start.key;

scan_bitmap:
        sb = wnd->sb;
        log2_bits = sb->s_blocksize_bits + 3;

        /* At most two ranges [hint, max_alloc) + [0, hint). */
Again:

        /* TODO: Optimize request for case nbits > wbits. */
        iw = hint >> log2_bits;
        wbits = sb->s_blocksize * 8;
        wpos = hint & (wbits - 1);
        prev_tail = 0;
        fbits_valid = true;

        if (max_alloc == wnd->nbits) {
                nwnd = wnd->nwnd;
        } else {
                size_t t = max_alloc + wbits - 1;

                nwnd = likely(t > max_alloc) ? (t >> log2_bits) : wnd->nwnd;
        }

        /* Enumerate all windows. */
        for (; iw < nwnd; iw++) {
                wbit = iw << log2_bits;

                if (!wnd->free_bits[iw]) {
                        if (prev_tail > b_len) {
                                b_pos = wbit - prev_tail;
                                b_len = prev_tail;
                        }

                        /* Skip full used window. */
                        prev_tail = 0;
                        wpos = 0;
                        continue;
                }

                if (unlikely(iw + 1 == nwnd)) {
                        if (max_alloc == wnd->nbits) {
                                wbits = wnd->bits_last;
                        } else {
                                size_t t = max_alloc & (wbits - 1);

                                if (t) {
                                        wbits = t;
                                        fbits_valid = false;
                                }
                        }
                }

                if (wnd->zone_end > wnd->zone_bit) {
                        ebit = wbit + wbits;
                        zbit = max(wnd->zone_bit, wbit);
                        zend = min(wnd->zone_end, ebit);

                        /* Here we have a window [wbit, ebit) and zone [zbit, zend). */
                        if (zend <= zbit) {
                                /* Zone does not overlap window. */
                        } else {
                                wzbit = zbit - wbit;
                                wzend = zend - wbit;

                                /* Zone overlaps window. */
                                if (wnd->free_bits[iw] == wzend - wzbit) {
                                        prev_tail = 0;
                                        wpos = 0;
                                        continue;
                                }

                                /* Scan two ranges window: [wbit, zbit) and [zend, ebit). */
                                bh = wnd_map(wnd, iw);

                                if (IS_ERR(bh)) {
                                        /* TODO: Error */
                                        prev_tail = 0;
                                        wpos = 0;
                                        continue;
                                }

                                buf = (ulong *)bh->b_data;

                                /* Scan range [wbit, zbit). */
                                if (wpos < wzbit) {
                                        /* Scan range [wpos, zbit). */
                                        fnd = wnd_scan(buf, wbit, wpos, wzbit,
                                                       to_alloc, &prev_tail,
                                                       &b_pos, &b_len);
                                        if (fnd != MINUS_ONE_T) {
                                                put_bh(bh);
                                                goto found;
                                        }
                                }

                                prev_tail = 0;

                                /* Scan range [zend, ebit). */
                                if (wzend < wbits) {
                                        fnd = wnd_scan(buf, wbit,
                                                       max(wzend, wpos), wbits,
                                                       to_alloc, &prev_tail,
                                                       &b_pos, &b_len);
                                        if (fnd != MINUS_ONE_T) {
                                                put_bh(bh);
                                                goto found;
                                        }
                                }

                                wpos = 0;
                                put_bh(bh);
                                continue;
                        }
                }

                /* Current window does not overlap zone. */
                if (!wpos && fbits_valid && wnd->free_bits[iw] == wbits) {
                        /* Window is empty. */
                        if (prev_tail + wbits >= to_alloc) {
                                fnd = wbit + wpos - prev_tail;
                                goto found;
                        }

                        /* Increase 'prev_tail' and process next window. */
                        prev_tail += wbits;
                        wpos = 0;
                        continue;
                }

                /* Read window. */
                bh = wnd_map(wnd, iw);
                if (IS_ERR(bh)) {
                        // TODO: Error.
                        prev_tail = 0;
                        wpos = 0;
                        continue;
                }

                buf = (ulong *)bh->b_data;

                /* Scan range [wpos, eBits). */
                fnd = wnd_scan(buf, wbit, wpos, wbits, to_alloc, &prev_tail,
                               &b_pos, &b_len);
                put_bh(bh);
                if (fnd != MINUS_ONE_T)
                        goto found;
        }

        if (b_len < prev_tail) {
                /* The last fragment. */
                b_len = prev_tail;
                b_pos = max_alloc - prev_tail;
        }

        if (hint) {
                /*
                 * We have scanned range [hint max_alloc).
                 * Prepare to scan range [0 hint + to_alloc).
                 */
                size_t nextmax = hint + to_alloc;

                if (likely(nextmax >= hint) && nextmax < max_alloc)
                        max_alloc = nextmax;
                hint = 0;
                goto Again;
        }

        if (!b_len)
                goto no_space;

        wnd->extent_max = b_len;

        if (flags & BITMAP_FIND_FULL)
                goto no_space;

        fnd = b_pos;
        to_alloc = b_len;

found:
        if (flags & BITMAP_FIND_MARK_AS_USED) {
                /* TODO: Optimize remove extent (pass 'e'?). */
                if (wnd_set_used(wnd, fnd, to_alloc))
                        goto no_space;
        } else if (wnd->extent_max != MINUS_ONE_T &&
                   to_alloc > wnd->extent_max) {
                wnd->extent_max = to_alloc;
        }

        *allocated = fnd;
        return to_alloc;

no_space:
        return 0;
}

/*
 * wnd_extend - Extend bitmap ($MFT bitmap).
 */
int wnd_extend(struct wnd_bitmap *wnd, size_t new_bits)
{
        int err;
        struct super_block *sb = wnd->sb;
        struct ntfs_sb_info *sbi = sb->s_fs_info;
        u32 blocksize = sb->s_blocksize;
        u32 wbits = blocksize * 8;
        u32 b0, new_last;
        size_t bits, iw, new_wnd;
        size_t old_bits = wnd->nbits;
        u16 *new_free;

        if (new_bits <= old_bits)
                return -EINVAL;

        /* Align to 8 byte boundary. */
        new_wnd = bytes_to_block(sb, bitmap_size(new_bits));
        new_last = new_bits & (wbits - 1);
        if (!new_last)
                new_last = wbits;

        if (new_wnd != wnd->nwnd) {
                new_free = kmalloc(new_wnd * sizeof(u16), GFP_NOFS);
                if (!new_free)
                        return -ENOMEM;

                if (new_free != wnd->free_bits)
                        memcpy(new_free, wnd->free_bits,
                               wnd->nwnd * sizeof(short));
                memset(new_free + wnd->nwnd, 0,
                       (new_wnd - wnd->nwnd) * sizeof(short));
                kfree(wnd->free_bits);
                wnd->free_bits = new_free;
        }

        /* Zero bits [old_bits,new_bits). */
        bits = new_bits - old_bits;
        b0 = old_bits & (wbits - 1);

        for (iw = old_bits >> (sb->s_blocksize_bits + 3); bits; iw += 1) {
                u32 op;
                size_t frb;
                u64 vbo, lbo, bytes;
                struct buffer_head *bh;
                ulong *buf;

                if (iw + 1 == new_wnd)
                        wbits = new_last;

                op = b0 + bits > wbits ? wbits - b0 : bits;
                vbo = (u64)iw * blocksize;

                err = ntfs_vbo_to_lbo(sbi, &wnd->run, vbo, &lbo, &bytes);
                if (err)
                        break;

                bh = ntfs_bread(sb, lbo >> sb->s_blocksize_bits);
                if (!bh)
                        return -EIO;

                lock_buffer(bh);
                buf = (ulong *)bh->b_data;

                __bitmap_clear(buf, b0, blocksize * 8 - b0);
                frb = wbits - __bitmap_weight(buf, wbits);
                wnd->total_zeroes += frb - wnd->free_bits[iw];
                wnd->free_bits[iw] = frb;

                set_buffer_uptodate(bh);
                mark_buffer_dirty(bh);
                unlock_buffer(bh);
                /* err = sync_dirty_buffer(bh); */

                b0 = 0;
                bits -= op;
        }

        wnd->nbits = new_bits;
        wnd->nwnd = new_wnd;
        wnd->bits_last = new_last;

        wnd_add_free_ext(wnd, old_bits, new_bits - old_bits, false);

        return 0;
}

void wnd_zone_set(struct wnd_bitmap *wnd, size_t lcn, size_t len)
{
        size_t zlen;

        zlen = wnd->zone_end - wnd->zone_bit;
        if (zlen)
                wnd_add_free_ext(wnd, wnd->zone_bit, zlen, false);

        if (!RB_EMPTY_ROOT(&wnd->start_tree) && len)
                wnd_remove_free_ext(wnd, lcn, len);

        wnd->zone_bit = lcn;
        wnd->zone_end = lcn + len;
}

int ntfs_trim_fs(struct ntfs_sb_info *sbi, struct fstrim_range *range)
{
        int err = 0;
        struct super_block *sb = sbi->sb;
        struct wnd_bitmap *wnd = &sbi->used.bitmap;
        u32 wbits = 8 * sb->s_blocksize;
        CLST len = 0, lcn = 0, done = 0;
        CLST minlen = bytes_to_cluster(sbi, range->minlen);
        CLST lcn_from = bytes_to_cluster(sbi, range->start);
        size_t iw = lcn_from >> (sb->s_blocksize_bits + 3);
        u32 wbit = lcn_from & (wbits - 1);
        const ulong *buf;
        CLST lcn_to;

        if (!minlen)
                minlen = 1;

        if (range->len == (u64)-1)
                lcn_to = wnd->nbits;
        else
                lcn_to = bytes_to_cluster(sbi, range->start + range->len);

        down_read_nested(&wnd->rw_lock, BITMAP_MUTEX_CLUSTERS);

        for (; iw < wnd->nbits; iw++, wbit = 0) {
                CLST lcn_wnd = iw * wbits;
                struct buffer_head *bh;

                if (lcn_wnd > lcn_to)
                        break;

                if (!wnd->free_bits[iw])
                        continue;

                if (iw + 1 == wnd->nwnd)
                        wbits = wnd->bits_last;

                if (lcn_wnd + wbits > lcn_to)
                        wbits = lcn_to - lcn_wnd;

                bh = wnd_map(wnd, iw);
                if (IS_ERR(bh)) {
                        err = PTR_ERR(bh);
                        break;
                }

                buf = (ulong *)bh->b_data;

                for (; wbit < wbits; wbit++) {
                        if (!test_bit(wbit, buf)) {
                                if (!len)
                                        lcn = lcn_wnd + wbit;
                                len += 1;
                                continue;
                        }
                        if (len >= minlen) {
                                err = ntfs_discard(sbi, lcn, len);
                                if (err)
                                        goto out;
                                done += len;
                        }
                        len = 0;
                }
                put_bh(bh);
        }

        /* Process the last fragment. */
        if (len >= minlen) {
                err = ntfs_discard(sbi, lcn, len);
                if (err)
                        goto out;
                done += len;
        }

out:
        range->len = (u64)done << sbi->cluster_bits;

        up_read(&wnd->rw_lock);

        return err;
}