/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2017, Fedor Uporov
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD$
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/vnode.h>
#include <sys/bio.h>
#include <sys/buf.h>
#include <sys/endian.h>
#include <sys/conf.h>
#include <sys/mount.h>

#include <vfs/ext2fs/fs.h>
#include <vfs/ext2fs/ext2fs.h>
#include <vfs/ext2fs/ext2_dinode.h>
#include <vfs/ext2fs/inode.h>
#include <vfs/ext2fs/ext2_dir.h>
#include <vfs/ext2fs/htree.h>
#include <vfs/ext2fs/ext2_extern.h>

SDT_PROVIDER_DECLARE(ext2fs);
/*
 * ext2fs trace probe:
 * arg0: verbosity. Higher numbers give more verbose messages
 * arg1: Textual message
 */
SDT_PROBE_DEFINE2(ext2fs, , trace, csum, "int", "char*");

#define EXT2_BG_INODE_BITMAP_CSUM_HI_END        \
        (offsetof(struct ext2_gd, ext4bgd_i_bmap_csum_hi) + \
         sizeof(uint16_t))

#define EXT2_INODE_CSUM_HI_EXTRA_END    \
        (offsetof(struct ext2fs_dinode, e2di_chksum_hi) + sizeof(uint16_t) - \
         E2FS_REV0_INODE_SIZE)

#define EXT2_BG_BLOCK_BITMAP_CSUM_HI_LOCATION   \
        (offsetof(struct ext2_gd, ext4bgd_b_bmap_csum_hi) + \
         sizeof(uint16_t))

void
ext2_sb_csum_set_seed(struct m_ext2fs *fs)
{

        if (EXT2_HAS_INCOMPAT_FEATURE(fs, EXT2F_INCOMPAT_CSUM_SEED))
                fs->e2fs_csum_seed = le32toh(fs->e2fs->e4fs_chksum_seed);
        else if (EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM)) {
                fs->e2fs_csum_seed = calculate_crc32c(~0, fs->e2fs->e2fs_uuid,
                    sizeof(fs->e2fs->e2fs_uuid));
        }
        else
                fs->e2fs_csum_seed = 0;
}

int
ext2_sb_csum_verify(struct m_ext2fs *fs)
{

        if (fs->e2fs->e4fs_chksum_type != EXT4_CRC32C_CHKSUM) {
                printf(
"WARNING: mount of %s denied due bad sb csum type\n", fs->e2fs_fsmnt);
                return (EINVAL);
        }
        if (le32toh(fs->e2fs->e4fs_sbchksum) !=
            calculate_crc32c(~0, (const char *)fs->e2fs,
            offsetof(struct ext2fs, e4fs_sbchksum))) {
                printf(
"WARNING: mount of %s denied due bad sb csum=0x%x, expected=0x%x - run fsck\n",
                    fs->e2fs_fsmnt, le32toh(fs->e2fs->e4fs_sbchksum),
                    calculate_crc32c(~0, (const char *)fs->e2fs,
                    offsetof(struct ext2fs, e4fs_sbchksum)));
                return (EINVAL);
        }

        return (0);
}

void
ext2_sb_csum_set(struct m_ext2fs *fs)
{

        fs->e2fs->e4fs_sbchksum =
            htole32(calculate_crc32c(~0, (const char *)fs->e2fs,
            offsetof(struct ext2fs, e4fs_sbchksum)));
}

void
ext2_init_dirent_tail(struct ext2fs_direct_tail *tp)
{
        memset(tp, 0, sizeof(struct ext2fs_direct_tail));
        tp->e2dt_rec_len = le16toh(sizeof(struct ext2fs_direct_tail));
        tp->e2dt_reserved_ft = EXT2_FT_DIR_CSUM;
}

int
ext2_is_dirent_tail(struct inode *ip, struct ext2fs_direct_2 *ep)
{
        struct m_ext2fs *fs;
        struct ext2fs_direct_tail *tp;

        fs = ip->i_e2fs;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return (0);

        tp = (struct ext2fs_direct_tail *)ep;
        if (tp->e2dt_reserved_zero1 == 0 &&
            le16toh(tp->e2dt_rec_len) == sizeof(struct ext2fs_direct_tail) &&
            tp->e2dt_reserved_zero2 == 0 &&
            tp->e2dt_reserved_ft == EXT2_FT_DIR_CSUM)
                return (1);

        return (0);
}

struct ext2fs_direct_tail *
ext2_dirent_get_tail(struct inode *ip, struct ext2fs_direct_2 *ep)
{
        struct ext2fs_direct_2 *dep;
        void *top;
        unsigned int rec_len;

        dep = ep;
        top = EXT2_DIRENT_TAIL(ep, ip->i_e2fs->e2fs_bsize);
        rec_len = le16toh(dep->e2d_reclen);

        while (rec_len && !(rec_len & 0x3)) {
                dep = (struct ext2fs_direct_2 *)(((char *)dep) + rec_len);
                if ((void *)dep >= top)
                        break;
                rec_len = le16toh(dep->e2d_reclen);
        }

        if (dep != top)
                return (NULL);

        if (ext2_is_dirent_tail(ip, dep))
                return ((struct ext2fs_direct_tail *)dep);

        return (NULL);
}

static uint32_t
ext2_dirent_csum(struct inode *ip, struct ext2fs_direct_2 *ep, int size)
{
        struct m_ext2fs *fs;
        char *buf;
        uint32_t inum, gen, crc;

        fs = ip->i_e2fs;

        buf = (char *)ep;

        inum = htole32(ip->i_number);
        gen = htole32(ip->i_gen);
        crc = calculate_crc32c(fs->e2fs_csum_seed, (uint8_t *)&inum, sizeof(inum));
        crc = calculate_crc32c(crc, (uint8_t *)&gen, sizeof(gen));
        crc = calculate_crc32c(crc, (uint8_t *)buf, size);

        return (crc);
}

int
ext2_dirent_csum_verify(struct inode *ip, struct ext2fs_direct_2 *ep)
{
        uint32_t calculated;
        struct ext2fs_direct_tail *tp;

        tp = ext2_dirent_get_tail(ip, ep);
        if (tp == NULL)
                return (0);

        calculated = ext2_dirent_csum(ip, ep, (char *)tp - (char *)ep);
        if (calculated != le32toh(tp->e2dt_checksum))
                return (EIO);

        return (0);
}

static struct ext2fs_htree_count *
ext2_get_dx_count(struct inode *ip, struct ext2fs_direct_2 *ep, int *offset)
{
        struct ext2fs_direct_2 *dp;
        struct ext2fs_htree_root_info *root;
        int count_offset;

        if (le16toh(ep->e2d_reclen) == EXT2_BLOCK_SIZE(ip->i_e2fs))
                count_offset = 8;
        else if (le16toh(ep->e2d_reclen) == 12) {
                dp = (struct ext2fs_direct_2 *)(((char *)ep) + 12);
                if (le16toh(dp->e2d_reclen) != EXT2_BLOCK_SIZE(ip->i_e2fs) - 12)
                        return (NULL);

                root = (struct ext2fs_htree_root_info *)(((char *)dp + 12));
                if (root->h_reserved1 ||
                    root->h_info_len != sizeof(struct ext2fs_htree_root_info))
                        return (NULL);

                count_offset = 32;
        } else
                return (NULL);

        if (offset)
                *offset = count_offset;

        return ((struct ext2fs_htree_count *)(((char *)ep) + count_offset));
}

static uint32_t
ext2_dx_csum(struct inode *ip, struct ext2fs_direct_2 *ep, int count_offset,
    int count, struct ext2fs_htree_tail *tp)
{
        struct m_ext2fs *fs;
        char *buf;
        int size;
        uint32_t inum, old_csum, gen, crc;

        fs = ip->i_e2fs;

        buf = (char *)ep;

        size = count_offset + (count * sizeof(struct ext2fs_htree_entry));
        old_csum = tp->ht_checksum;
        tp->ht_checksum = 0;

        inum = htole32(ip->i_number);
        gen = htole32(ip->i_gen);
        crc = calculate_crc32c(fs->e2fs_csum_seed, (uint8_t *)&inum, sizeof(inum));
        crc = calculate_crc32c(crc, (uint8_t *)&gen, sizeof(gen));
        crc = calculate_crc32c(crc, (uint8_t *)buf, size);
        crc = calculate_crc32c(crc, (uint8_t *)tp, sizeof(struct ext2fs_htree_tail));
        tp->ht_checksum = old_csum;

        return htole32(crc);
}

int
ext2_dx_csum_verify(struct inode *ip, struct ext2fs_direct_2 *ep)
{
        uint32_t calculated;
        struct ext2fs_htree_count *cp;
        struct ext2fs_htree_tail *tp;
        int count_offset, limit, count;

        cp = ext2_get_dx_count(ip, ep, &count_offset);
        if (cp == NULL)
                return (0);

        limit = le16toh(cp->h_entries_max);
        count = le16toh(cp->h_entries_num);
        if (count_offset + (limit * sizeof(struct ext2fs_htree_entry)) >
            ip->i_e2fs->e2fs_bsize - sizeof(struct ext2fs_htree_tail))
                return (EIO);

        tp = (struct ext2fs_htree_tail *)(((struct ext2fs_htree_entry *)cp) + limit);
        calculated = ext2_dx_csum(ip, ep,  count_offset, count, tp);

        if (tp->ht_checksum != calculated)
                return (EIO);

        return (0);
}

int
ext2_dir_blk_csum_verify(struct inode *ip, struct buf *bp)
{
        struct m_ext2fs *fs;
        struct ext2fs_direct_2 *ep;
        int error = 0;

        fs = ip->i_e2fs;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return (error);

        ep = (struct ext2fs_direct_2 *)bp->b_data;

        if (ext2_dirent_get_tail(ip, ep) != NULL)
                error = ext2_dirent_csum_verify(ip, ep);
        else if (ext2_get_dx_count(ip, ep, NULL) != NULL)
                error = ext2_dx_csum_verify(ip, ep);

        if (error)
                SDT_PROBE2(ext2fs, , trace, csum, 1, "bad directory csum detected");

        return (error);
}

void
ext2_dirent_csum_set(struct inode *ip, struct ext2fs_direct_2 *ep)
{
        struct m_ext2fs *fs;
        struct ext2fs_direct_tail *tp;

        fs = ip->i_e2fs;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return;

        tp = ext2_dirent_get_tail(ip, ep);
        if (tp == NULL)
                return;

        tp->e2dt_checksum =
            htole32(ext2_dirent_csum(ip, ep, (char *)tp - (char *)ep));
}

void
ext2_dx_csum_set(struct inode *ip, struct ext2fs_direct_2 *ep)
{
        struct m_ext2fs *fs;
        struct ext2fs_htree_count *cp;
        struct ext2fs_htree_tail *tp;
        int count_offset, limit, count;

        fs = ip->i_e2fs;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return;

        cp = ext2_get_dx_count(ip, ep, &count_offset);
        if (cp == NULL)
                return;

        limit = le16toh(cp->h_entries_max);
        count = le16toh(cp->h_entries_num);
        if (count_offset + (limit * sizeof(struct ext2fs_htree_entry)) >
            ip->i_e2fs->e2fs_bsize - sizeof(struct ext2fs_htree_tail))
                return;

        tp = (struct ext2fs_htree_tail *)(((struct ext2fs_htree_entry *)cp) + limit);
        tp->ht_checksum = ext2_dx_csum(ip, ep,  count_offset, count, tp);
}

static uint32_t
ext2_extent_blk_csum(struct inode *ip, struct ext4_extent_header *ehp)
{
        struct m_ext2fs *fs;
        size_t size;
        uint32_t inum, gen, crc;

        fs = ip->i_e2fs;

        size = EXT4_EXTENT_TAIL_OFFSET(ehp) +
            offsetof(struct ext4_extent_tail, et_checksum);

        inum = htole32(ip->i_number);
        gen = htole32(ip->i_gen);
        crc = calculate_crc32c(fs->e2fs_csum_seed, (uint8_t *)&inum, sizeof(inum));
        crc = calculate_crc32c(crc, (uint8_t *)&gen, sizeof(gen));
        crc = calculate_crc32c(crc, (uint8_t *)ehp, size);

        return (crc);
}

int
ext2_extent_blk_csum_verify(struct inode *ip, void *data)
{
        struct m_ext2fs *fs;
        struct ext4_extent_header *ehp;
        struct ext4_extent_tail *etp;
        uint32_t provided, calculated;

        fs = ip->i_e2fs;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return (0);

        ehp = (struct ext4_extent_header *)data;
        etp = (struct ext4_extent_tail *)(((char *)ehp) +
            EXT4_EXTENT_TAIL_OFFSET(ehp));

        provided = le32toh(etp->et_checksum);
        calculated = ext2_extent_blk_csum(ip, ehp);

        if (provided != calculated) {
                SDT_PROBE2(ext2fs, , trace, csum, 1, "bad extent csum detected");
                return (EIO);
        }

        return (0);
}

void
ext2_extent_blk_csum_set(struct inode *ip, void *data)
{
        struct m_ext2fs *fs;
        struct ext4_extent_header *ehp;
        struct ext4_extent_tail *etp;

        fs = ip->i_e2fs;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return;

        ehp = (struct ext4_extent_header *)data;
        etp = (struct ext4_extent_tail *)(((char *)data) +
            EXT4_EXTENT_TAIL_OFFSET(ehp));

        etp->et_checksum = htole32(ext2_extent_blk_csum(ip,
            (struct ext4_extent_header *)data));
}

int
ext2_gd_i_bitmap_csum_verify(struct m_ext2fs *fs, int cg, struct buf *bp)
{
        uint32_t hi, provided, calculated;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return (0);

        provided = le16toh(fs->e2fs_gd[cg].ext4bgd_i_bmap_csum);
        calculated = calculate_crc32c(fs->e2fs_csum_seed, bp->b_data,
            fs->e2fs_ipg / 8);
        if (le16toh(fs->e2fs->e3fs_desc_size) >=
            EXT2_BG_INODE_BITMAP_CSUM_HI_END) {
                hi = le16toh(fs->e2fs_gd[cg].ext4bgd_i_bmap_csum_hi);
                provided |= (hi << 16);
        } else
                calculated &= 0xFFFF;

        if (provided != calculated) {
                SDT_PROBE2(ext2fs, , trace, csum, 1, "bad inode bitmap csum detected");
                return (EIO);
        }

        return (0);
}

void
ext2_gd_i_bitmap_csum_set(struct m_ext2fs *fs, int cg, struct buf *bp)
{
        uint32_t csum;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return;

        csum = calculate_crc32c(fs->e2fs_csum_seed, bp->b_data,
            fs->e2fs_ipg / 8);
        fs->e2fs_gd[cg].ext4bgd_i_bmap_csum = htole16(csum & 0xFFFF);
        if (le16toh(fs->e2fs->e3fs_desc_size) >= EXT2_BG_INODE_BITMAP_CSUM_HI_END)
                fs->e2fs_gd[cg].ext4bgd_i_bmap_csum_hi = htole16(csum >> 16);
}

int
ext2_gd_b_bitmap_csum_verify(struct m_ext2fs *fs, int cg, struct buf *bp)
{
        uint32_t hi, provided, calculated, size;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return (0);

        size = fs->e2fs_fpg / 8;
        provided = le16toh(fs->e2fs_gd[cg].ext4bgd_b_bmap_csum);
        calculated = calculate_crc32c(fs->e2fs_csum_seed, bp->b_data, size);
        if (le16toh(fs->e2fs->e3fs_desc_size) >=
            EXT2_BG_BLOCK_BITMAP_CSUM_HI_LOCATION) {
                hi = le16toh(fs->e2fs_gd[cg].ext4bgd_b_bmap_csum_hi);
                provided |= (hi << 16);
        } else
                calculated &= 0xFFFF;

        if (provided != calculated) {
                SDT_PROBE2(ext2fs, , trace, csum, 1, "bad block bitmap csum detected");
                return (EIO);
        }

        return (0);
}

void
ext2_gd_b_bitmap_csum_set(struct m_ext2fs *fs, int cg, struct buf *bp)
{
        uint32_t csum, size;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return;

        size = fs->e2fs_fpg / 8;
        csum = calculate_crc32c(fs->e2fs_csum_seed, bp->b_data, size);
        fs->e2fs_gd[cg].ext4bgd_b_bmap_csum = htole16(csum & 0xFFFF);
        if (le16toh(fs->e2fs->e3fs_desc_size) >= EXT2_BG_BLOCK_BITMAP_CSUM_HI_LOCATION)
                fs->e2fs_gd[cg].ext4bgd_b_bmap_csum_hi = htole16(csum >> 16);
}

static uint32_t
ext2_ei_csum(struct inode *ip, struct ext2fs_dinode *ei)
{
        struct m_ext2fs *fs;
        uint32_t inode_csum_seed, inum, gen, crc;
        uint16_t dummy_csum = 0;
        unsigned int offset, csum_size;

        fs = ip->i_e2fs;
        offset = offsetof(struct ext2fs_dinode, e2di_chksum_lo);
        csum_size = sizeof(dummy_csum);
        inum = htole32(ip->i_number);
        crc = calculate_crc32c(fs->e2fs_csum_seed,
            (uint8_t *)&inum, sizeof(inum));
        gen = htole32(ip->i_gen);
        inode_csum_seed = calculate_crc32c(crc,
            (uint8_t *)&gen, sizeof(gen));

        crc = calculate_crc32c(inode_csum_seed, (uint8_t *)ei, offset);
        crc = calculate_crc32c(crc, (uint8_t *)&dummy_csum, csum_size);
        offset += csum_size;
        crc = calculate_crc32c(crc, (uint8_t *)ei + offset,
            E2FS_REV0_INODE_SIZE - offset);

        if (EXT2_INODE_SIZE(fs) > E2FS_REV0_INODE_SIZE) {
                offset = offsetof(struct ext2fs_dinode, e2di_chksum_hi);
                crc = calculate_crc32c(crc, (uint8_t *)ei +
                    E2FS_REV0_INODE_SIZE, offset - E2FS_REV0_INODE_SIZE);

                if ((EXT2_INODE_SIZE(ip->i_e2fs) > E2FS_REV0_INODE_SIZE &&
                    le16toh(ei->e2di_extra_isize) >=
                    EXT2_INODE_CSUM_HI_EXTRA_END)) {
                        crc = calculate_crc32c(crc, (uint8_t *)&dummy_csum,
                            csum_size);
                        offset += csum_size;
                }

                crc = calculate_crc32c(crc, (uint8_t *)ei + offset,
                    EXT2_INODE_SIZE(fs) - offset);
        }

        return (crc);
}

int
ext2_ei_csum_verify(struct inode *ip, struct ext2fs_dinode *ei)
{
        struct m_ext2fs *fs;
        static const struct ext2fs_dinode ei_zero;
        uint32_t hi, provided, calculated;

        fs = ip->i_e2fs;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return (0);

        provided = le16toh(ei->e2di_chksum_lo);
        calculated = ext2_ei_csum(ip, ei);

        if ((EXT2_INODE_SIZE(fs) > E2FS_REV0_INODE_SIZE &&
            le16toh(ei->e2di_extra_isize) >= EXT2_INODE_CSUM_HI_EXTRA_END)) {
                hi = le16toh(ei->e2di_chksum_hi);
                provided |= hi << 16;
        } else
                calculated &= 0xFFFF;

        if (provided != calculated) {
                /*
                 * If it is first time used dinode,
                 * it is expected that it will be zeroed
                 * and we will not return checksum error in this case.
                 */
                if (!memcmp(ei, &ei_zero, sizeof(struct ext2fs_dinode)))
                        return (0);

                SDT_PROBE2(ext2fs, , trace, csum, 1, "bad inode csum");

                return (EIO);
        }

        return (0);
}

void
ext2_ei_csum_set(struct inode *ip, struct ext2fs_dinode *ei)
{
        struct m_ext2fs *fs;
        uint32_t crc;

        fs = ip->i_e2fs;

        if (!EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM))
                return;

        crc = ext2_ei_csum(ip, ei);

        ei->e2di_chksum_lo = htole16(crc & 0xFFFF);
        if ((EXT2_INODE_SIZE(fs) > E2FS_REV0_INODE_SIZE &&
            le16toh(ei->e2di_extra_isize) >= EXT2_INODE_CSUM_HI_EXTRA_END))
                ei->e2di_chksum_hi = htole16(crc >> 16);
}

static uint16_t
ext2_crc16(uint16_t crc, const void *buffer, unsigned int len)
{
        const unsigned char *cp = buffer;
        /* CRC table for the CRC-16. The poly is 0x8005 (x16 + x15 + x2 + 1). */
        static uint16_t const crc16_table[256] = {
                0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
                0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
                0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
                0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
                0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
                0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
                0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
                0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
                0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
                0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
                0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
                0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
                0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
                0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
                0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
                0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
                0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
                0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
                0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
                0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
                0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
                0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
                0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
                0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
                0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
                0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
                0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
                0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
                0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
                0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
                0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
                0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
        };

        while (len--)
                crc = (((crc >> 8) & 0xffU) ^
                    crc16_table[(crc ^ *cp++) & 0xffU]) & 0x0000ffffU;
        return crc;
}

static uint16_t
ext2_gd_csum(struct m_ext2fs *fs, uint32_t block_group, struct ext2_gd *gd)
{
        size_t offset;
        uint32_t csum32;
        uint16_t crc, dummy_csum;

        offset = offsetof(struct ext2_gd, ext4bgd_csum);

        block_group = htole32(block_group);

        if (EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM)) {
                csum32 = calculate_crc32c(fs->e2fs_csum_seed,
                    (uint8_t *)&block_group, sizeof(block_group));
                csum32 = calculate_crc32c(csum32, (uint8_t *)gd, offset);
                dummy_csum = 0;
                csum32 = calculate_crc32c(csum32, (uint8_t *)&dummy_csum,
                    sizeof(dummy_csum));
                offset += sizeof(dummy_csum);
                if (offset < le16toh(fs->e2fs->e3fs_desc_size))
                        csum32 = calculate_crc32c(csum32, (uint8_t *)gd + offset,
                            le16toh(fs->e2fs->e3fs_desc_size) - offset);

                crc = csum32 & 0xFFFF;
                return (htole16(crc));
        } else if (EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_GDT_CSUM)) {
                crc = ext2_crc16(~0, fs->e2fs->e2fs_uuid,
                    sizeof(fs->e2fs->e2fs_uuid));
                crc = ext2_crc16(crc, (uint8_t *)&block_group,
                    sizeof(block_group));
                crc = ext2_crc16(crc, (uint8_t *)gd, offset);
                offset += sizeof(gd->ext4bgd_csum); /* skip checksum */
                if (EXT2_HAS_INCOMPAT_FEATURE(fs, EXT2F_INCOMPAT_64BIT) &&
                    offset < le16toh(fs->e2fs->e3fs_desc_size))
                        crc = ext2_crc16(crc, (uint8_t *)gd + offset,
                            le16toh(fs->e2fs->e3fs_desc_size) - offset);
                return (htole16(crc));
        }

        return (0);
}

int
ext2_gd_csum_verify(struct m_ext2fs *fs, struct cdev *dev)
{
        unsigned int i;
        int error = 0;

        for (i = 0; i < fs->e2fs_gcount; i++) {
                if (fs->e2fs_gd[i].ext4bgd_csum !=
                    ext2_gd_csum(fs, i, &fs->e2fs_gd[i])) {
                        printf(
"WARNING: mount of %s denied due bad gd=%d csum=0x%x, expected=0x%x - run fsck\n",
                            devtoname(dev), i, fs->e2fs_gd[i].ext4bgd_csum,
                            ext2_gd_csum(fs, i, &fs->e2fs_gd[i]));
                        error = EIO;
                        break;
                }
        }

        return (error);
}

void
ext2_gd_csum_set(struct m_ext2fs *fs)
{
        unsigned int i;

        for (i = 0; i < fs->e2fs_gcount; i++)
                fs->e2fs_gd[i].ext4bgd_csum = ext2_gd_csum(fs, i, &fs->e2fs_gd[i]);
}