// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2000-2006 Silicon Graphics, Inc.
 * All Rights Reserved.
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_inode.h"
#include "xfs_errortag.h"
#include "xfs_error.h"
#include "xfs_icache.h"
#include "xfs_trans.h"
#include "xfs_ialloc.h"
#include "xfs_dir2.h"

#include <linux/iversion.h>

/*
 * If we are doing readahead on an inode buffer, we might be in log recovery
 * reading an inode allocation buffer that hasn't yet been replayed, and hence
 * has not had the inode cores stamped into it. Hence for readahead, the buffer
 * may be potentially invalid.
 *
 * If the readahead buffer is invalid, we need to mark it with an error and
 * clear the DONE status of the buffer so that a followup read will re-read it
 * from disk. We don't report the error otherwise to avoid warnings during log
 * recovery and we don't get unnecessary panics on debug kernels. We use EIO here
 * because all we want to do is say readahead failed; there is no-one to report
 * the error to, so this will distinguish it from a non-ra verifier failure.
 * Changes to this readahead error behaviour also need to be reflected in
 * xfs_dquot_buf_readahead_verify().
 */
static void
xfs_inode_buf_verify(
        struct xfs_buf  *bp,
        bool            readahead)
{
        struct xfs_mount *mp = bp->b_mount;
        xfs_agnumber_t  agno;
        int             i;
        int             ni;

        /*
         * Validate the magic number and version of every inode in the buffer
         */
        agno = xfs_daddr_to_agno(mp, xfs_buf_daddr(bp));
        ni = XFS_BB_TO_FSB(mp, bp->b_length) * mp->m_sb.sb_inopblock;
        for (i = 0; i < ni; i++) {
                int             di_ok;
                xfs_dinode_t    *dip;
                xfs_agino_t     unlinked_ino;

                dip = xfs_buf_offset(bp, (i << mp->m_sb.sb_inodelog));
                unlinked_ino = be32_to_cpu(dip->di_next_unlinked);
                di_ok = xfs_verify_magic16(bp, dip->di_magic) &&
                        xfs_dinode_good_version(mp, dip->di_version) &&
                        xfs_verify_agino_or_null(mp, agno, unlinked_ino);
                if (unlikely(XFS_TEST_ERROR(!di_ok, mp,
                                                XFS_ERRTAG_ITOBP_INOTOBP))) {
                        if (readahead) {
                                bp->b_flags &= ~XBF_DONE;
                                xfs_buf_ioerror(bp, -EIO);
                                return;
                        }

#ifdef DEBUG
                        xfs_alert(mp,
                                "bad inode magic/vsn daddr %lld #%d (magic=%x)",
                                (unsigned long long)xfs_buf_daddr(bp), i,
                                be16_to_cpu(dip->di_magic));
#endif
                        xfs_buf_verifier_error(bp, -EFSCORRUPTED,
                                        __func__, dip, sizeof(*dip),
                                        NULL);
                        return;
                }
        }
}


static void
xfs_inode_buf_read_verify(
        struct xfs_buf  *bp)
{
        xfs_inode_buf_verify(bp, false);
}

static void
xfs_inode_buf_readahead_verify(
        struct xfs_buf  *bp)
{
        xfs_inode_buf_verify(bp, true);
}

static void
xfs_inode_buf_write_verify(
        struct xfs_buf  *bp)
{
        xfs_inode_buf_verify(bp, false);
}

const struct xfs_buf_ops xfs_inode_buf_ops = {
        .name = "xfs_inode",
        .magic16 = { cpu_to_be16(XFS_DINODE_MAGIC),
                     cpu_to_be16(XFS_DINODE_MAGIC) },
        .verify_read = xfs_inode_buf_read_verify,
        .verify_write = xfs_inode_buf_write_verify,
};

const struct xfs_buf_ops xfs_inode_buf_ra_ops = {
        .name = "xfs_inode_ra",
        .magic16 = { cpu_to_be16(XFS_DINODE_MAGIC),
                     cpu_to_be16(XFS_DINODE_MAGIC) },
        .verify_read = xfs_inode_buf_readahead_verify,
        .verify_write = xfs_inode_buf_write_verify,
};


/*
 * This routine is called to map an inode to the buffer containing the on-disk
 * version of the inode.  It returns a pointer to the buffer containing the
 * on-disk inode in the bpp parameter.
 */
int
xfs_imap_to_bp(
        struct xfs_mount        *mp,
        struct xfs_trans        *tp,
        struct xfs_imap         *imap,
        struct xfs_buf          **bpp)
{
        return xfs_trans_read_buf(mp, tp, mp->m_ddev_targp, imap->im_blkno,
                                   imap->im_len, XBF_UNMAPPED, bpp,
                                   &xfs_inode_buf_ops);
}

static inline struct timespec64 xfs_inode_decode_bigtime(uint64_t ts)
{
        struct timespec64       tv;
        uint32_t                n;

        tv.tv_sec = xfs_bigtime_to_unix(div_u64_rem(ts, NSEC_PER_SEC, &n));
        tv.tv_nsec = n;

        return tv;
}

/* Convert an ondisk timestamp to an incore timestamp. */
struct timespec64
xfs_inode_from_disk_ts(
        struct xfs_dinode               *dip,
        const xfs_timestamp_t           ts)
{
        struct timespec64               tv;
        struct xfs_legacy_timestamp     *lts;

        if (xfs_dinode_has_bigtime(dip))
                return xfs_inode_decode_bigtime(be64_to_cpu(ts));

        lts = (struct xfs_legacy_timestamp *)&ts;
        tv.tv_sec = (int)be32_to_cpu(lts->t_sec);
        tv.tv_nsec = (int)be32_to_cpu(lts->t_nsec);

        return tv;
}

int
xfs_inode_from_disk(
        struct xfs_inode        *ip,
        struct xfs_dinode       *from)
{
        struct inode            *inode = VFS_I(ip);
        int                     error;
        xfs_failaddr_t          fa;

        ASSERT(ip->i_cowfp == NULL);
        ASSERT(ip->i_afp == NULL);

        fa = xfs_dinode_verify(ip->i_mount, ip->i_ino, from);
        if (fa) {
                xfs_inode_verifier_error(ip, -EFSCORRUPTED, "dinode", from,
                                sizeof(*from), fa);
                return -EFSCORRUPTED;
        }

        /*
         * First get the permanent information that is needed to allocate an
         * inode. If the inode is unused, mode is zero and we shouldn't mess
         * with the uninitialized part of it.
         */
        if (!xfs_has_v3inodes(ip->i_mount))
                ip->i_flushiter = be16_to_cpu(from->di_flushiter);
        inode->i_generation = be32_to_cpu(from->di_gen);
        inode->i_mode = be16_to_cpu(from->di_mode);
        if (!inode->i_mode)
                return 0;

        /*
         * Convert v1 inodes immediately to v2 inode format as this is the
         * minimum inode version format we support in the rest of the code.
         * They will also be unconditionally written back to disk as v2 inodes.
         */
        if (unlikely(from->di_version == 1)) {
                set_nlink(inode, be16_to_cpu(from->di_onlink));
                ip->i_projid = 0;
        } else {
                set_nlink(inode, be32_to_cpu(from->di_nlink));
                ip->i_projid = (prid_t)be16_to_cpu(from->di_projid_hi) << 16 |
                                        be16_to_cpu(from->di_projid_lo);
        }

        i_uid_write(inode, be32_to_cpu(from->di_uid));
        i_gid_write(inode, be32_to_cpu(from->di_gid));

        /*
         * Time is signed, so need to convert to signed 32 bit before
         * storing in inode timestamp which may be 64 bit. Otherwise
         * a time before epoch is converted to a time long after epoch
         * on 64 bit systems.
         */
        inode->i_atime = xfs_inode_from_disk_ts(from, from->di_atime);
        inode->i_mtime = xfs_inode_from_disk_ts(from, from->di_mtime);
        inode->i_ctime = xfs_inode_from_disk_ts(from, from->di_ctime);

        ip->i_disk_size = be64_to_cpu(from->di_size);
        ip->i_nblocks = be64_to_cpu(from->di_nblocks);
        ip->i_extsize = be32_to_cpu(from->di_extsize);
        ip->i_forkoff = from->di_forkoff;
        ip->i_diflags   = be16_to_cpu(from->di_flags);

        if (from->di_dmevmask || from->di_dmstate)
                xfs_iflags_set(ip, XFS_IPRESERVE_DM_FIELDS);

        if (xfs_has_v3inodes(ip->i_mount)) {
                inode_set_iversion_queried(inode,
                                           be64_to_cpu(from->di_changecount));
                ip->i_crtime = xfs_inode_from_disk_ts(from, from->di_crtime);
                ip->i_diflags2 = be64_to_cpu(from->di_flags2);
                ip->i_cowextsize = be32_to_cpu(from->di_cowextsize);
        }

        error = xfs_iformat_data_fork(ip, from);
        if (error)
                return error;
        if (from->di_forkoff) {
                error = xfs_iformat_attr_fork(ip, from);
                if (error)
                        goto out_destroy_data_fork;
        }
        if (xfs_is_reflink_inode(ip))
                xfs_ifork_init_cow(ip);
        return 0;

out_destroy_data_fork:
        xfs_idestroy_fork(&ip->i_df);
        return error;
}

/* Convert an incore timestamp to an ondisk timestamp. */
static inline xfs_timestamp_t
xfs_inode_to_disk_ts(
        struct xfs_inode                *ip,
        const struct timespec64         tv)
{
        struct xfs_legacy_timestamp     *lts;
        xfs_timestamp_t                 ts;

        if (xfs_inode_has_bigtime(ip))
                return cpu_to_be64(xfs_inode_encode_bigtime(tv));

        lts = (struct xfs_legacy_timestamp *)&ts;
        lts->t_sec = cpu_to_be32(tv.tv_sec);
        lts->t_nsec = cpu_to_be32(tv.tv_nsec);

        return ts;
}

void
xfs_inode_to_disk(
        struct xfs_inode        *ip,
        struct xfs_dinode       *to,
        xfs_lsn_t               lsn)
{
        struct inode            *inode = VFS_I(ip);

        to->di_magic = cpu_to_be16(XFS_DINODE_MAGIC);
        to->di_onlink = 0;

        to->di_format = xfs_ifork_format(&ip->i_df);
        to->di_uid = cpu_to_be32(i_uid_read(inode));
        to->di_gid = cpu_to_be32(i_gid_read(inode));
        to->di_projid_lo = cpu_to_be16(ip->i_projid & 0xffff);
        to->di_projid_hi = cpu_to_be16(ip->i_projid >> 16);

        memset(to->di_pad, 0, sizeof(to->di_pad));
        to->di_atime = xfs_inode_to_disk_ts(ip, inode->i_atime);
        to->di_mtime = xfs_inode_to_disk_ts(ip, inode->i_mtime);
        to->di_ctime = xfs_inode_to_disk_ts(ip, inode->i_ctime);
        to->di_nlink = cpu_to_be32(inode->i_nlink);
        to->di_gen = cpu_to_be32(inode->i_generation);
        to->di_mode = cpu_to_be16(inode->i_mode);

        to->di_size = cpu_to_be64(ip->i_disk_size);
        to->di_nblocks = cpu_to_be64(ip->i_nblocks);
        to->di_extsize = cpu_to_be32(ip->i_extsize);
        to->di_nextents = cpu_to_be32(xfs_ifork_nextents(&ip->i_df));
        to->di_anextents = cpu_to_be16(xfs_ifork_nextents(ip->i_afp));
        to->di_forkoff = ip->i_forkoff;
        to->di_aformat = xfs_ifork_format(ip->i_afp);
        to->di_flags = cpu_to_be16(ip->i_diflags);

        if (xfs_has_v3inodes(ip->i_mount)) {
                to->di_version = 3;
                to->di_changecount = cpu_to_be64(inode_peek_iversion(inode));
                to->di_crtime = xfs_inode_to_disk_ts(ip, ip->i_crtime);
                to->di_flags2 = cpu_to_be64(ip->i_diflags2);
                to->di_cowextsize = cpu_to_be32(ip->i_cowextsize);
                to->di_ino = cpu_to_be64(ip->i_ino);
                to->di_lsn = cpu_to_be64(lsn);
                memset(to->di_pad2, 0, sizeof(to->di_pad2));
                uuid_copy(&to->di_uuid, &ip->i_mount->m_sb.sb_meta_uuid);
                to->di_flushiter = 0;
        } else {
                to->di_version = 2;
                to->di_flushiter = cpu_to_be16(ip->i_flushiter);
        }
}

static xfs_failaddr_t
xfs_dinode_verify_fork(
        struct xfs_dinode       *dip,
        struct xfs_mount        *mp,
        int                     whichfork)
{
        uint32_t                di_nextents = XFS_DFORK_NEXTENTS(dip, whichfork);

        switch (XFS_DFORK_FORMAT(dip, whichfork)) {
        case XFS_DINODE_FMT_LOCAL:
                /*
                 * no local regular files yet
                 */
                if (whichfork == XFS_DATA_FORK) {
                        if (S_ISREG(be16_to_cpu(dip->di_mode)))
                                return __this_address;
                        if (be64_to_cpu(dip->di_size) >
                                        XFS_DFORK_SIZE(dip, mp, whichfork))
                                return __this_address;
                }
                if (di_nextents)
                        return __this_address;
                break;
        case XFS_DINODE_FMT_EXTENTS:
                if (di_nextents > XFS_DFORK_MAXEXT(dip, mp, whichfork))
                        return __this_address;
                break;
        case XFS_DINODE_FMT_BTREE:
                if (whichfork == XFS_ATTR_FORK) {
                        if (di_nextents > MAXAEXTNUM)
                                return __this_address;
                } else if (di_nextents > MAXEXTNUM) {
                        return __this_address;
                }
                break;
        default:
                return __this_address;
        }
        return NULL;
}

static xfs_failaddr_t
xfs_dinode_verify_forkoff(
        struct xfs_dinode       *dip,
        struct xfs_mount        *mp)
{
        if (!dip->di_forkoff)
                return NULL;

        switch (dip->di_format)  {
        case XFS_DINODE_FMT_DEV:
                if (dip->di_forkoff != (roundup(sizeof(xfs_dev_t), 8) >> 3))
                        return __this_address;
                break;
        case XFS_DINODE_FMT_LOCAL:      /* fall through ... */
        case XFS_DINODE_FMT_EXTENTS:    /* fall through ... */
        case XFS_DINODE_FMT_BTREE:
                if (dip->di_forkoff >= (XFS_LITINO(mp) >> 3))
                        return __this_address;
                break;
        default:
                return __this_address;
        }
        return NULL;
}

xfs_failaddr_t
xfs_dinode_verify(
        struct xfs_mount        *mp,
        xfs_ino_t               ino,
        struct xfs_dinode       *dip)
{
        xfs_failaddr_t          fa;
        uint16_t                mode;
        uint16_t                flags;
        uint64_t                flags2;
        uint64_t                di_size;

        if (dip->di_magic != cpu_to_be16(XFS_DINODE_MAGIC))
                return __this_address;

        /* Verify v3 integrity information first */
        if (dip->di_version >= 3) {
                if (!xfs_has_v3inodes(mp))
                        return __this_address;
                if (!xfs_verify_cksum((char *)dip, mp->m_sb.sb_inodesize,
                                      XFS_DINODE_CRC_OFF))
                        return __this_address;
                if (be64_to_cpu(dip->di_ino) != ino)
                        return __this_address;
                if (!uuid_equal(&dip->di_uuid, &mp->m_sb.sb_meta_uuid))
                        return __this_address;
        }

        /* don't allow invalid i_size */
        di_size = be64_to_cpu(dip->di_size);
        if (di_size & (1ULL << 63))
                return __this_address;

        mode = be16_to_cpu(dip->di_mode);
        if (mode && xfs_mode_to_ftype(mode) == XFS_DIR3_FT_UNKNOWN)
                return __this_address;

        /* No zero-length symlinks/dirs. */
        if ((S_ISLNK(mode) || S_ISDIR(mode)) && di_size == 0)
                return __this_address;

        /* Fork checks carried over from xfs_iformat_fork */
        if (mode &&
            be32_to_cpu(dip->di_nextents) + be16_to_cpu(dip->di_anextents) >
                        be64_to_cpu(dip->di_nblocks))
                return __this_address;

        if (mode && XFS_DFORK_BOFF(dip) > mp->m_sb.sb_inodesize)
                return __this_address;

        flags = be16_to_cpu(dip->di_flags);

        if (mode && (flags & XFS_DIFLAG_REALTIME) && !mp->m_rtdev_targp)
                return __this_address;

        /* check for illegal values of forkoff */
        fa = xfs_dinode_verify_forkoff(dip, mp);
        if (fa)
                return fa;

        /* Do we have appropriate data fork formats for the mode? */
        switch (mode & S_IFMT) {
        case S_IFIFO:
        case S_IFCHR:
        case S_IFBLK:
        case S_IFSOCK:
                if (dip->di_format != XFS_DINODE_FMT_DEV)
                        return __this_address;
                break;
        case S_IFREG:
        case S_IFLNK:
        case S_IFDIR:
                fa = xfs_dinode_verify_fork(dip, mp, XFS_DATA_FORK);
                if (fa)
                        return fa;
                break;
        case 0:
                /* Uninitialized inode ok. */
                break;
        default:
                return __this_address;
        }

        if (dip->di_forkoff) {
                fa = xfs_dinode_verify_fork(dip, mp, XFS_ATTR_FORK);
                if (fa)
                        return fa;
        } else {
                /*
                 * If there is no fork offset, this may be a freshly-made inode
                 * in a new disk cluster, in which case di_aformat is zeroed.
                 * Otherwise, such an inode must be in EXTENTS format; this goes
                 * for freed inodes as well.
                 */
                switch (dip->di_aformat) {
                case 0:
                case XFS_DINODE_FMT_EXTENTS:
                        break;
                default:
                        return __this_address;
                }
                if (dip->di_anextents)
                        return __this_address;
        }

        /* extent size hint validation */
        fa = xfs_inode_validate_extsize(mp, be32_to_cpu(dip->di_extsize),
                        mode, flags);
        if (fa)
                return fa;

        /* only version 3 or greater inodes are extensively verified here */
        if (dip->di_version < 3)
                return NULL;

        flags2 = be64_to_cpu(dip->di_flags2);

        /* don't allow reflink/cowextsize if we don't have reflink */
        if ((flags2 & (XFS_DIFLAG2_REFLINK | XFS_DIFLAG2_COWEXTSIZE)) &&
             !xfs_has_reflink(mp))
                return __this_address;

        /* only regular files get reflink */
        if ((flags2 & XFS_DIFLAG2_REFLINK) && (mode & S_IFMT) != S_IFREG)
                return __this_address;

        /* don't let reflink and realtime mix */
        if ((flags2 & XFS_DIFLAG2_REFLINK) && (flags & XFS_DIFLAG_REALTIME))
                return __this_address;

        /* COW extent size hint validation */
        fa = xfs_inode_validate_cowextsize(mp, be32_to_cpu(dip->di_cowextsize),
                        mode, flags, flags2);
        if (fa)
                return fa;

        /* bigtime iflag can only happen on bigtime filesystems */
        if (xfs_dinode_has_bigtime(dip) &&
            !xfs_has_bigtime(mp))
                return __this_address;

        return NULL;
}

void
xfs_dinode_calc_crc(
        struct xfs_mount        *mp,
        struct xfs_dinode       *dip)
{
        uint32_t                crc;

        if (dip->di_version < 3)
                return;

        ASSERT(xfs_has_crc(mp));
        crc = xfs_start_cksum_update((char *)dip, mp->m_sb.sb_inodesize,
                              XFS_DINODE_CRC_OFF);
        dip->di_crc = xfs_end_cksum(crc);
}

/*
 * Validate di_extsize hint.
 *
 * 1. Extent size hint is only valid for directories and regular files.
 * 2. FS_XFLAG_EXTSIZE is only valid for regular files.
 * 3. FS_XFLAG_EXTSZINHERIT is only valid for directories.
 * 4. Hint cannot be larger than MAXTEXTLEN.
 * 5. Can be changed on directories at any time.
 * 6. Hint value of 0 turns off hints, clears inode flags.
 * 7. Extent size must be a multiple of the appropriate block size.
 *    For realtime files, this is the rt extent size.
 * 8. For non-realtime files, the extent size hint must be limited
 *    to half the AG size to avoid alignment extending the extent beyond the
 *    limits of the AG.
 */
xfs_failaddr_t
xfs_inode_validate_extsize(
        struct xfs_mount                *mp,
        uint32_t                        extsize,
        uint16_t                        mode,
        uint16_t                        flags)
{
        bool                            rt_flag;
        bool                            hint_flag;
        bool                            inherit_flag;
        uint32_t                        extsize_bytes;
        uint32_t                        blocksize_bytes;

        rt_flag = (flags & XFS_DIFLAG_REALTIME);
        hint_flag = (flags & XFS_DIFLAG_EXTSIZE);
        inherit_flag = (flags & XFS_DIFLAG_EXTSZINHERIT);
        extsize_bytes = XFS_FSB_TO_B(mp, extsize);

        /*
         * This comment describes a historic gap in this verifier function.
         *
         * For a directory with both RTINHERIT and EXTSZINHERIT flags set, this
         * function has never checked that the extent size hint is an integer
         * multiple of the realtime extent size.  Since we allow users to set
         * this combination  on non-rt filesystems /and/ to change the rt
         * extent size when adding a rt device to a filesystem, the net effect
         * is that users can configure a filesystem anticipating one rt
         * geometry and change their minds later.  Directories do not use the
         * extent size hint, so this is harmless for them.
         *
         * If a directory with a misaligned extent size hint is allowed to
         * propagate that hint into a new regular realtime file, the result
         * is that the inode cluster buffer verifier will trigger a corruption
         * shutdown the next time it is run, because the verifier has always
         * enforced the alignment rule for regular files.
         *
         * Because we allow administrators to set a new rt extent size when
         * adding a rt section, we cannot add a check to this verifier because
         * that will result a new source of directory corruption errors when
         * reading an existing filesystem.  Instead, we rely on callers to
         * decide when alignment checks are appropriate, and fix things up as
         * needed.
         */

        if (rt_flag)
                blocksize_bytes = XFS_FSB_TO_B(mp, mp->m_sb.sb_rextsize);
        else
                blocksize_bytes = mp->m_sb.sb_blocksize;

        if ((hint_flag || inherit_flag) && !(S_ISDIR(mode) || S_ISREG(mode)))
                return __this_address;

        if (hint_flag && !S_ISREG(mode))
                return __this_address;

        if (inherit_flag && !S_ISDIR(mode))
                return __this_address;

        if ((hint_flag || inherit_flag) && extsize == 0)
                return __this_address;

        /* free inodes get flags set to zero but extsize remains */
        if (mode && !(hint_flag || inherit_flag) && extsize != 0)
                return __this_address;

        if (extsize_bytes % blocksize_bytes)
                return __this_address;

        if (extsize > MAXEXTLEN)
                return __this_address;

        if (!rt_flag && extsize > mp->m_sb.sb_agblocks / 2)
                return __this_address;

        return NULL;
}

/*
 * Validate di_cowextsize hint.
 *
 * 1. CoW extent size hint can only be set if reflink is enabled on the fs.
 *    The inode does not have to have any shared blocks, but it must be a v3.
 * 2. FS_XFLAG_COWEXTSIZE is only valid for directories and regular files;
 *    for a directory, the hint is propagated to new files.
 * 3. Can be changed on files & directories at any time.
 * 4. Hint value of 0 turns off hints, clears inode flags.
 * 5. Extent size must be a multiple of the appropriate block size.
 * 6. The extent size hint must be limited to half the AG size to avoid
 *    alignment extending the extent beyond the limits of the AG.
 */
xfs_failaddr_t
xfs_inode_validate_cowextsize(
        struct xfs_mount                *mp,
        uint32_t                        cowextsize,
        uint16_t                        mode,
        uint16_t                        flags,
        uint64_t                        flags2)
{
        bool                            rt_flag;
        bool                            hint_flag;
        uint32_t                        cowextsize_bytes;

        rt_flag = (flags & XFS_DIFLAG_REALTIME);
        hint_flag = (flags2 & XFS_DIFLAG2_COWEXTSIZE);
        cowextsize_bytes = XFS_FSB_TO_B(mp, cowextsize);

        if (hint_flag && !xfs_has_reflink(mp))
                return __this_address;

        if (hint_flag && !(S_ISDIR(mode) || S_ISREG(mode)))
                return __this_address;

        if (hint_flag && cowextsize == 0)
                return __this_address;

        /* free inodes get flags set to zero but cowextsize remains */
        if (mode && !hint_flag && cowextsize != 0)
                return __this_address;

        if (hint_flag && rt_flag)
                return __this_address;

        if (cowextsize_bytes % mp->m_sb.sb_blocksize)
                return __this_address;

        if (cowextsize > MAXEXTLEN)
                return __this_address;

        if (cowextsize > mp->m_sb.sb_agblocks / 2)
                return __this_address;

        return NULL;
}