// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2004, OGAWA Hirofumi
 */

#include <linux/blkdev.h>
#include <linux/sched/signal.h>
#include <linux/backing-dev-defs.h>
#include "fat.h"

struct fatent_operations {
        void (*ent_blocknr)(struct super_block *, int, int *, sector_t *);
        void (*ent_set_ptr)(struct fat_entry *, int);
        int (*ent_bread)(struct super_block *, struct fat_entry *,
                         int, sector_t);
        int (*ent_get)(struct fat_entry *);
        void (*ent_put)(struct fat_entry *, int);
        int (*ent_next)(struct fat_entry *);
};

static DEFINE_SPINLOCK(fat12_entry_lock);

static void fat12_ent_blocknr(struct super_block *sb, int entry,
                              int *offset, sector_t *blocknr)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        int bytes = entry + (entry >> 1);
        WARN_ON(!fat_valid_entry(sbi, entry));
        *offset = bytes & (sb->s_blocksize - 1);
        *blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
}

static void fat_ent_blocknr(struct super_block *sb, int entry,
                            int *offset, sector_t *blocknr)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        int bytes = (entry << sbi->fatent_shift);
        WARN_ON(!fat_valid_entry(sbi, entry));
        *offset = bytes & (sb->s_blocksize - 1);
        *blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
}

static void fat12_ent_set_ptr(struct fat_entry *fatent, int offset)
{
        struct buffer_head **bhs = fatent->bhs;
        if (fatent->nr_bhs == 1) {
                WARN_ON(offset >= (bhs[0]->b_size - 1));
                fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
                fatent->u.ent12_p[1] = bhs[0]->b_data + (offset + 1);
        } else {
                WARN_ON(offset != (bhs[0]->b_size - 1));
                fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
                fatent->u.ent12_p[1] = bhs[1]->b_data;
        }
}

static void fat16_ent_set_ptr(struct fat_entry *fatent, int offset)
{
        WARN_ON(offset & (2 - 1));
        fatent->u.ent16_p = (__le16 *)(fatent->bhs[0]->b_data + offset);
}

static void fat32_ent_set_ptr(struct fat_entry *fatent, int offset)
{
        WARN_ON(offset & (4 - 1));
        fatent->u.ent32_p = (__le32 *)(fatent->bhs[0]->b_data + offset);
}

static int fat12_ent_bread(struct super_block *sb, struct fat_entry *fatent,
                           int offset, sector_t blocknr)
{
        struct buffer_head **bhs = fatent->bhs;

        WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
        fatent->fat_inode = MSDOS_SB(sb)->fat_inode;

        bhs[0] = sb_bread(sb, blocknr);
        if (!bhs[0])
                goto err;

        if ((offset + 1) < sb->s_blocksize)
                fatent->nr_bhs = 1;
        else {
                /* This entry is block boundary, it needs the next block */
                blocknr++;
                bhs[1] = sb_bread(sb, blocknr);
                if (!bhs[1])
                        goto err_brelse;
                fatent->nr_bhs = 2;
        }
        fat12_ent_set_ptr(fatent, offset);
        return 0;

err_brelse:
        brelse(bhs[0]);
err:
        fat_msg_ratelimit(sb, KERN_ERR, "FAT read failed (blocknr %llu)",
                          (llu)blocknr);
        return -EIO;
}

static int fat_ent_bread(struct super_block *sb, struct fat_entry *fatent,
                         int offset, sector_t blocknr)
{
        const struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;

        WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
        fatent->fat_inode = MSDOS_SB(sb)->fat_inode;
        fatent->bhs[0] = sb_bread(sb, blocknr);
        if (!fatent->bhs[0]) {
                fat_msg_ratelimit(sb, KERN_ERR, "FAT read failed (blocknr %llu)",
                                  (llu)blocknr);
                return -EIO;
        }
        fatent->nr_bhs = 1;
        ops->ent_set_ptr(fatent, offset);
        return 0;
}

static int fat12_ent_get(struct fat_entry *fatent)
{
        u8 **ent12_p = fatent->u.ent12_p;
        int next;

        spin_lock(&fat12_entry_lock);
        if (fatent->entry & 1)
                next = (*ent12_p[0] >> 4) | (*ent12_p[1] << 4);
        else
                next = (*ent12_p[1] << 8) | *ent12_p[0];
        spin_unlock(&fat12_entry_lock);

        next &= 0x0fff;
        if (next >= BAD_FAT12)
                next = FAT_ENT_EOF;
        return next;
}

static int fat16_ent_get(struct fat_entry *fatent)
{
        int next = le16_to_cpu(*fatent->u.ent16_p);
        WARN_ON((unsigned long)fatent->u.ent16_p & (2 - 1));
        if (next >= BAD_FAT16)
                next = FAT_ENT_EOF;
        return next;
}

static int fat32_ent_get(struct fat_entry *fatent)
{
        int next = le32_to_cpu(*fatent->u.ent32_p) & 0x0fffffff;
        WARN_ON((unsigned long)fatent->u.ent32_p & (4 - 1));
        if (next >= BAD_FAT32)
                next = FAT_ENT_EOF;
        return next;
}

static void fat12_ent_put(struct fat_entry *fatent, int new)
{
        u8 **ent12_p = fatent->u.ent12_p;

        if (new == FAT_ENT_EOF)
                new = EOF_FAT12;

        spin_lock(&fat12_entry_lock);
        if (fatent->entry & 1) {
                *ent12_p[0] = (new << 4) | (*ent12_p[0] & 0x0f);
                *ent12_p[1] = new >> 4;
        } else {
                *ent12_p[0] = new & 0xff;
                *ent12_p[1] = (*ent12_p[1] & 0xf0) | (new >> 8);
        }
        spin_unlock(&fat12_entry_lock);

        mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
        if (fatent->nr_bhs == 2)
                mark_buffer_dirty_inode(fatent->bhs[1], fatent->fat_inode);
}

static void fat16_ent_put(struct fat_entry *fatent, int new)
{
        if (new == FAT_ENT_EOF)
                new = EOF_FAT16;

        *fatent->u.ent16_p = cpu_to_le16(new);
        mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
}

static void fat32_ent_put(struct fat_entry *fatent, int new)
{
        WARN_ON(new & 0xf0000000);
        new |= le32_to_cpu(*fatent->u.ent32_p) & ~0x0fffffff;
        *fatent->u.ent32_p = cpu_to_le32(new);
        mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
}

static int fat12_ent_next(struct fat_entry *fatent)
{
        u8 **ent12_p = fatent->u.ent12_p;
        struct buffer_head **bhs = fatent->bhs;
        u8 *nextp = ent12_p[1] + 1 + (fatent->entry & 1);

        fatent->entry++;
        if (fatent->nr_bhs == 1) {
                WARN_ON(ent12_p[0] > (u8 *)(bhs[0]->b_data +
                                                        (bhs[0]->b_size - 2)));
                WARN_ON(ent12_p[1] > (u8 *)(bhs[0]->b_data +
                                                        (bhs[0]->b_size - 1)));
                if (nextp < (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1))) {
                        ent12_p[0] = nextp - 1;
                        ent12_p[1] = nextp;
                        return 1;
                }
        } else {
                WARN_ON(ent12_p[0] != (u8 *)(bhs[0]->b_data +
                                                        (bhs[0]->b_size - 1)));
                WARN_ON(ent12_p[1] != (u8 *)bhs[1]->b_data);
                ent12_p[0] = nextp - 1;
                ent12_p[1] = nextp;
                brelse(bhs[0]);
                bhs[0] = bhs[1];
                fatent->nr_bhs = 1;
                return 1;
        }
        ent12_p[0] = NULL;
        ent12_p[1] = NULL;
        return 0;
}

static int fat16_ent_next(struct fat_entry *fatent)
{
        const struct buffer_head *bh = fatent->bhs[0];
        fatent->entry++;
        if (fatent->u.ent16_p < (__le16 *)(bh->b_data + (bh->b_size - 2))) {
                fatent->u.ent16_p++;
                return 1;
        }
        fatent->u.ent16_p = NULL;
        return 0;
}

static int fat32_ent_next(struct fat_entry *fatent)
{
        const struct buffer_head *bh = fatent->bhs[0];
        fatent->entry++;
        if (fatent->u.ent32_p < (__le32 *)(bh->b_data + (bh->b_size - 4))) {
                fatent->u.ent32_p++;
                return 1;
        }
        fatent->u.ent32_p = NULL;
        return 0;
}

static const struct fatent_operations fat12_ops = {
        .ent_blocknr    = fat12_ent_blocknr,
        .ent_set_ptr    = fat12_ent_set_ptr,
        .ent_bread      = fat12_ent_bread,
        .ent_get        = fat12_ent_get,
        .ent_put        = fat12_ent_put,
        .ent_next       = fat12_ent_next,
};

static const struct fatent_operations fat16_ops = {
        .ent_blocknr    = fat_ent_blocknr,
        .ent_set_ptr    = fat16_ent_set_ptr,
        .ent_bread      = fat_ent_bread,
        .ent_get        = fat16_ent_get,
        .ent_put        = fat16_ent_put,
        .ent_next       = fat16_ent_next,
};

static const struct fatent_operations fat32_ops = {
        .ent_blocknr    = fat_ent_blocknr,
        .ent_set_ptr    = fat32_ent_set_ptr,
        .ent_bread      = fat_ent_bread,
        .ent_get        = fat32_ent_get,
        .ent_put        = fat32_ent_put,
        .ent_next       = fat32_ent_next,
};

static inline void lock_fat(struct msdos_sb_info *sbi)
{
        mutex_lock(&sbi->fat_lock);
}

static inline void unlock_fat(struct msdos_sb_info *sbi)
{
        mutex_unlock(&sbi->fat_lock);
}

void fat_ent_access_init(struct super_block *sb)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);

        mutex_init(&sbi->fat_lock);

        if (is_fat32(sbi)) {
                sbi->fatent_shift = 2;
                sbi->fatent_ops = &fat32_ops;
        } else if (is_fat16(sbi)) {
                sbi->fatent_shift = 1;
                sbi->fatent_ops = &fat16_ops;
        } else if (is_fat12(sbi)) {
                sbi->fatent_shift = -1;
                sbi->fatent_ops = &fat12_ops;
        } else {
                fat_fs_error(sb, "invalid FAT variant, %u bits", sbi->fat_bits);
        }
}

static void mark_fsinfo_dirty(struct super_block *sb)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);

        if (sb_rdonly(sb) || !is_fat32(sbi))
                return;

        __mark_inode_dirty(sbi->fsinfo_inode, I_DIRTY_SYNC);
}

static inline int fat_ent_update_ptr(struct super_block *sb,
                                     struct fat_entry *fatent,
                                     int offset, sector_t blocknr)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        const struct fatent_operations *ops = sbi->fatent_ops;
        struct buffer_head **bhs = fatent->bhs;

        /* Is this fatent's blocks including this entry? */
        if (!fatent->nr_bhs || bhs[0]->b_blocknr != blocknr)
                return 0;
        if (is_fat12(sbi)) {
                if ((offset + 1) < sb->s_blocksize) {
                        /* This entry is on bhs[0]. */
                        if (fatent->nr_bhs == 2) {
                                brelse(bhs[1]);
                                fatent->nr_bhs = 1;
                        }
                } else {
                        /* This entry needs the next block. */
                        if (fatent->nr_bhs != 2)
                                return 0;
                        if (bhs[1]->b_blocknr != (blocknr + 1))
                                return 0;
                }
        }
        ops->ent_set_ptr(fatent, offset);
        return 1;
}

int fat_ent_read(struct inode *inode, struct fat_entry *fatent, int entry)
{
        struct super_block *sb = inode->i_sb;
        struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
        const struct fatent_operations *ops = sbi->fatent_ops;
        int err, offset;
        sector_t blocknr;

        if (!fat_valid_entry(sbi, entry)) {
                fatent_brelse(fatent);
                fat_fs_error_ratelimit(sb, "invalid access to FAT (entry 0x%08x)", entry);
                return -EIO;
        }

        fatent_set_entry(fatent, entry);
        ops->ent_blocknr(sb, entry, &offset, &blocknr);

        if (!fat_ent_update_ptr(sb, fatent, offset, blocknr)) {
                fatent_brelse(fatent);
                err = ops->ent_bread(sb, fatent, offset, blocknr);
                if (err)
                        return err;
        }
        return ops->ent_get(fatent);
}

/* FIXME: We can write the blocks as more big chunk. */
static int fat_mirror_bhs(struct super_block *sb, struct buffer_head **bhs,
                          int nr_bhs)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        struct buffer_head *c_bh;
        int err, n, copy;

        err = 0;
        for (copy = 1; copy < sbi->fats; copy++) {
                sector_t backup_fat = sbi->fat_length * copy;

                for (n = 0; n < nr_bhs; n++) {
                        c_bh = sb_getblk(sb, backup_fat + bhs[n]->b_blocknr);
                        if (!c_bh) {
                                err = -ENOMEM;
                                goto error;
                        }
                        /* Avoid race with userspace read via bdev */
                        lock_buffer(c_bh);
                        memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize);
                        set_buffer_uptodate(c_bh);
                        unlock_buffer(c_bh);
                        mark_buffer_dirty_inode(c_bh, sbi->fat_inode);
                        if (sb->s_flags & SB_SYNCHRONOUS)
                                err = sync_dirty_buffer(c_bh);
                        brelse(c_bh);
                        if (err)
                                goto error;
                }
        }
error:
        return err;
}

int fat_ent_write(struct inode *inode, struct fat_entry *fatent,
                  int new, int wait)
{
        struct super_block *sb = inode->i_sb;
        const struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
        int err;

        ops->ent_put(fatent, new);
        if (wait) {
                err = fat_sync_bhs(fatent->bhs, fatent->nr_bhs);
                if (err)
                        return err;
        }
        return fat_mirror_bhs(sb, fatent->bhs, fatent->nr_bhs);
}

static inline int fat_ent_next(struct msdos_sb_info *sbi,
                               struct fat_entry *fatent)
{
        if (sbi->fatent_ops->ent_next(fatent)) {
                if (fatent->entry < sbi->max_cluster)
                        return 1;
        }
        return 0;
}

static inline int fat_ent_read_block(struct super_block *sb,
                                     struct fat_entry *fatent)
{
        const struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
        sector_t blocknr;
        int offset;

        fatent_brelse(fatent);
        ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
        return ops->ent_bread(sb, fatent, offset, blocknr);
}

static void fat_collect_bhs(struct buffer_head **bhs, int *nr_bhs,
                            struct fat_entry *fatent)
{
        int n, i;

        for (n = 0; n < fatent->nr_bhs; n++) {
                for (i = 0; i < *nr_bhs; i++) {
                        if (fatent->bhs[n] == bhs[i])
                                break;
                }
                if (i == *nr_bhs) {
                        get_bh(fatent->bhs[n]);
                        bhs[i] = fatent->bhs[n];
                        (*nr_bhs)++;
                }
        }
}

int fat_alloc_clusters(struct inode *inode, int *cluster, int nr_cluster)
{
        struct super_block *sb = inode->i_sb;
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        const struct fatent_operations *ops = sbi->fatent_ops;
        struct fat_entry fatent, prev_ent;
        struct buffer_head *bhs[MAX_BUF_PER_PAGE];
        int i, count, err, nr_bhs, idx_clus;

        BUG_ON(nr_cluster > (MAX_BUF_PER_PAGE / 2));    /* fixed limit */

        lock_fat(sbi);
        if (sbi->free_clusters != -1 && sbi->free_clus_valid &&
            sbi->free_clusters < nr_cluster) {
                unlock_fat(sbi);
                return -ENOSPC;
        }

        err = nr_bhs = idx_clus = 0;
        count = FAT_START_ENT;
        fatent_init(&prev_ent);
        fatent_init(&fatent);
        fatent_set_entry(&fatent, sbi->prev_free + 1);
        while (count < sbi->max_cluster) {
                if (fatent.entry >= sbi->max_cluster)
                        fatent.entry = FAT_START_ENT;
                fatent_set_entry(&fatent, fatent.entry);
                err = fat_ent_read_block(sb, &fatent);
                if (err)
                        goto out;

                /* Find the free entries in a block */
                do {
                        if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
                                int entry = fatent.entry;

                                /* make the cluster chain */
                                ops->ent_put(&fatent, FAT_ENT_EOF);
                                if (prev_ent.nr_bhs)
                                        ops->ent_put(&prev_ent, entry);

                                fat_collect_bhs(bhs, &nr_bhs, &fatent);

                                sbi->prev_free = entry;
                                if (sbi->free_clusters != -1)
                                        sbi->free_clusters--;

                                cluster[idx_clus] = entry;
                                idx_clus++;
                                if (idx_clus == nr_cluster)
                                        goto out;

                                /*
                                 * fat_collect_bhs() gets ref-count of bhs,
                                 * so we can still use the prev_ent.
                                 */
                                prev_ent = fatent;
                        }
                        count++;
                        if (count == sbi->max_cluster)
                                break;
                } while (fat_ent_next(sbi, &fatent));
        }

        /* Couldn't allocate the free entries */
        sbi->free_clusters = 0;
        sbi->free_clus_valid = 1;
        err = -ENOSPC;

out:
        unlock_fat(sbi);
        mark_fsinfo_dirty(sb);
        fatent_brelse(&fatent);
        if (!err) {
                if (inode_needs_sync(inode))
                        err = fat_sync_bhs(bhs, nr_bhs);
                if (!err)
                        err = fat_mirror_bhs(sb, bhs, nr_bhs);
        }
        for (i = 0; i < nr_bhs; i++)
                brelse(bhs[i]);

        if (err && idx_clus)
                fat_free_clusters(inode, cluster[0]);

        return err;
}

int fat_free_clusters(struct inode *inode, int cluster)
{
        struct super_block *sb = inode->i_sb;
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        const struct fatent_operations *ops = sbi->fatent_ops;
        struct fat_entry fatent;
        struct buffer_head *bhs[MAX_BUF_PER_PAGE];
        int i, err, nr_bhs;
        int first_cl = cluster, dirty_fsinfo = 0;

        nr_bhs = 0;
        fatent_init(&fatent);
        lock_fat(sbi);
        do {
                cluster = fat_ent_read(inode, &fatent, cluster);
                if (cluster < 0) {
                        err = cluster;
                        goto error;
                } else if (cluster == FAT_ENT_FREE) {
                        fat_fs_error(sb, "%s: deleting FAT entry beyond EOF",
                                     __func__);
                        err = -EIO;
                        goto error;
                }

                if (sbi->options.discard) {
                        /*
                         * Issue discard for the sectors we no longer
                         * care about, batching contiguous clusters
                         * into one request
                         */
                        if (cluster != fatent.entry + 1) {
                                int nr_clus = fatent.entry - first_cl + 1;

                                sb_issue_discard(sb,
                                        fat_clus_to_blknr(sbi, first_cl),
                                        nr_clus * sbi->sec_per_clus,
                                        GFP_NOFS, 0);

                                first_cl = cluster;
                        }
                }

                ops->ent_put(&fatent, FAT_ENT_FREE);
                if (sbi->free_clusters != -1) {
                        sbi->free_clusters++;
                        dirty_fsinfo = 1;
                }

                if (nr_bhs + fatent.nr_bhs > MAX_BUF_PER_PAGE) {
                        if (sb->s_flags & SB_SYNCHRONOUS) {
                                err = fat_sync_bhs(bhs, nr_bhs);
                                if (err)
                                        goto error;
                        }
                        err = fat_mirror_bhs(sb, bhs, nr_bhs);
                        if (err)
                                goto error;
                        for (i = 0; i < nr_bhs; i++)
                                brelse(bhs[i]);
                        nr_bhs = 0;
                }
                fat_collect_bhs(bhs, &nr_bhs, &fatent);
        } while (cluster != FAT_ENT_EOF);

        if (sb->s_flags & SB_SYNCHRONOUS) {
                err = fat_sync_bhs(bhs, nr_bhs);
                if (err)
                        goto error;
        }
        err = fat_mirror_bhs(sb, bhs, nr_bhs);
error:
        fatent_brelse(&fatent);
        for (i = 0; i < nr_bhs; i++)
                brelse(bhs[i]);
        unlock_fat(sbi);
        if (dirty_fsinfo)
                mark_fsinfo_dirty(sb);

        return err;
}
EXPORT_SYMBOL_GPL(fat_free_clusters);

struct fatent_ra {
        sector_t cur;
        sector_t limit;

        unsigned int ra_blocks;
        sector_t ra_advance;
        sector_t ra_next;
        sector_t ra_limit;
};

static void fat_ra_init(struct super_block *sb, struct fatent_ra *ra,
                        struct fat_entry *fatent, int ent_limit)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        const struct fatent_operations *ops = sbi->fatent_ops;
        sector_t blocknr, block_end;
        int offset;
        /*
         * This is the sequential read, so ra_pages * 2 (but try to
         * align the optimal hardware IO size).
         * [BTW, 128kb covers the whole sectors for FAT12 and FAT16]
         */
        unsigned long ra_pages = sb->s_bdi->ra_pages;
        unsigned int reada_blocks;

        if (fatent->entry >= ent_limit)
                return;

        if (ra_pages > sb->s_bdi->io_pages)
                ra_pages = rounddown(ra_pages, sb->s_bdi->io_pages);
        reada_blocks = ra_pages << (PAGE_SHIFT - sb->s_blocksize_bits + 1);

        /* Initialize the range for sequential read */
        ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
        ops->ent_blocknr(sb, ent_limit - 1, &offset, &block_end);
        ra->cur = 0;
        ra->limit = (block_end + 1) - blocknr;

        /* Advancing the window at half size */
        ra->ra_blocks = reada_blocks >> 1;
        ra->ra_advance = ra->cur;
        ra->ra_next = ra->cur;
        ra->ra_limit = ra->cur + min_t(sector_t, reada_blocks, ra->limit);
}

/* Assuming to be called before reading a new block (increments ->cur). */
static void fat_ent_reada(struct super_block *sb, struct fatent_ra *ra,
                          struct fat_entry *fatent)
{
        if (ra->ra_next >= ra->ra_limit)
                return;

        if (ra->cur >= ra->ra_advance) {
                struct msdos_sb_info *sbi = MSDOS_SB(sb);
                const struct fatent_operations *ops = sbi->fatent_ops;
                struct blk_plug plug;
                sector_t blocknr, diff;
                int offset;

                ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);

                diff = blocknr - ra->cur;
                blk_start_plug(&plug);
                /*
                 * FIXME: we would want to directly use the bio with
                 * pages to reduce the number of segments.
                 */
                for (; ra->ra_next < ra->ra_limit; ra->ra_next++)
                        sb_breadahead(sb, ra->ra_next + diff);
                blk_finish_plug(&plug);

                /* Advance the readahead window */
                ra->ra_advance += ra->ra_blocks;
                ra->ra_limit += min_t(sector_t,
                                      ra->ra_blocks, ra->limit - ra->ra_limit);
        }
        ra->cur++;
}

int fat_count_free_clusters(struct super_block *sb)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        const struct fatent_operations *ops = sbi->fatent_ops;
        struct fat_entry fatent;
        struct fatent_ra fatent_ra;
        int err = 0, free;

        lock_fat(sbi);
        if (sbi->free_clusters != -1 && sbi->free_clus_valid)
                goto out;

        free = 0;
        fatent_init(&fatent);
        fatent_set_entry(&fatent, FAT_START_ENT);
        fat_ra_init(sb, &fatent_ra, &fatent, sbi->max_cluster);
        while (fatent.entry < sbi->max_cluster) {
                /* readahead of fat blocks */
                fat_ent_reada(sb, &fatent_ra, &fatent);

                err = fat_ent_read_block(sb, &fatent);
                if (err)
                        goto out;

                do {
                        if (ops->ent_get(&fatent) == FAT_ENT_FREE)
                                free++;
                } while (fat_ent_next(sbi, &fatent));
                cond_resched();
        }
        sbi->free_clusters = free;
        sbi->free_clus_valid = 1;
        mark_fsinfo_dirty(sb);
        fatent_brelse(&fatent);
out:
        unlock_fat(sbi);
        return err;
}

static int fat_trim_clusters(struct super_block *sb, u32 clus, u32 nr_clus)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        return sb_issue_discard(sb, fat_clus_to_blknr(sbi, clus),
                                nr_clus * sbi->sec_per_clus, GFP_NOFS, 0);
}

int fat_trim_fs(struct inode *inode, struct fstrim_range *range)
{
        struct super_block *sb = inode->i_sb;
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        const struct fatent_operations *ops = sbi->fatent_ops;
        struct fat_entry fatent;
        struct fatent_ra fatent_ra;
        u64 ent_start, ent_end, minlen, trimmed = 0;
        u32 free = 0;
        int err = 0;

        /*
         * FAT data is organized as clusters, trim at the granulary of cluster.
         *
         * fstrim_range is in byte, convert values to cluster index.
         * Treat sectors before data region as all used, not to trim them.
         */
        ent_start = max_t(u64, range->start>>sbi->cluster_bits, FAT_START_ENT);
        ent_end = ent_start + (range->len >> sbi->cluster_bits) - 1;
        minlen = range->minlen >> sbi->cluster_bits;

        if (ent_start >= sbi->max_cluster || range->len < sbi->cluster_size)
                return -EINVAL;
        if (ent_end >= sbi->max_cluster)
                ent_end = sbi->max_cluster - 1;

        fatent_init(&fatent);
        lock_fat(sbi);
        fatent_set_entry(&fatent, ent_start);
        fat_ra_init(sb, &fatent_ra, &fatent, ent_end + 1);
        while (fatent.entry <= ent_end) {
                /* readahead of fat blocks */
                fat_ent_reada(sb, &fatent_ra, &fatent);

                err = fat_ent_read_block(sb, &fatent);
                if (err)
                        goto error;
                do {
                        if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
                                free++;
                        } else if (free) {
                                if (free >= minlen) {
                                        u32 clus = fatent.entry - free;

                                        err = fat_trim_clusters(sb, clus, free);
                                        if (err && err != -EOPNOTSUPP)
                                                goto error;
                                        if (!err)
                                                trimmed += free;
                                        err = 0;
                                }
                                free = 0;
                        }
                } while (fat_ent_next(sbi, &fatent) && fatent.entry <= ent_end);

                if (fatal_signal_pending(current)) {
                        err = -ERESTARTSYS;
                        goto error;
                }

                if (need_resched()) {
                        fatent_brelse(&fatent);
                        unlock_fat(sbi);
                        cond_resched();
                        lock_fat(sbi);
                }
        }
        /* handle scenario when tail entries are all free */
        if (free && free >= minlen) {
                u32 clus = fatent.entry - free;

                err = fat_trim_clusters(sb, clus, free);
                if (err && err != -EOPNOTSUPP)
                        goto error;
                if (!err)
                        trimmed += free;
                err = 0;
        }

error:
        fatent_brelse(&fatent);
        unlock_fat(sbi);

        range->len = trimmed << sbi->cluster_bits;

        return err;
}