// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2000-2005 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_bit.h"
#include "xfs_mount.h"
#include "xfs_inode.h"
#include "xfs_bmap.h"
#include "xfs_trans.h"
#include "xfs_rtalloc.h"
#include "xfs_error.h"

/*
 * Realtime allocator bitmap functions shared with userspace.
 */

/*
 * Real time buffers need verifiers to avoid runtime warnings during IO.
 * We don't have anything to verify, however, so these are just dummy
 * operations.
 */
static void
xfs_rtbuf_verify_read(
        struct xfs_buf  *bp)
{
        return;
}

static void
xfs_rtbuf_verify_write(
        struct xfs_buf  *bp)
{
        return;
}

const struct xfs_buf_ops xfs_rtbuf_ops = {
        .name = "rtbuf",
        .verify_read = xfs_rtbuf_verify_read,
        .verify_write = xfs_rtbuf_verify_write,
};

/*
 * Get a buffer for the bitmap or summary file block specified.
 * The buffer is returned read and locked.
 */
int
xfs_rtbuf_get(
        xfs_mount_t     *mp,            /* file system mount structure */
        xfs_trans_t     *tp,            /* transaction pointer */
        xfs_rtblock_t   block,          /* block number in bitmap or summary */
        int             issum,          /* is summary not bitmap */
        struct xfs_buf  **bpp)          /* output: buffer for the block */
{
        struct xfs_buf  *bp;            /* block buffer, result */
        xfs_inode_t     *ip;            /* bitmap or summary inode */
        xfs_bmbt_irec_t map;
        int             nmap = 1;
        int             error;          /* error value */

        ip = issum ? mp->m_rsumip : mp->m_rbmip;

        error = xfs_bmapi_read(ip, block, 1, &map, &nmap, 0);
        if (error)
                return error;

        if (XFS_IS_CORRUPT(mp, nmap == 0 || !xfs_bmap_is_written_extent(&map)))
                return -EFSCORRUPTED;

        ASSERT(map.br_startblock != NULLFSBLOCK);
        error = xfs_trans_read_buf(mp, tp, mp->m_ddev_targp,
                                   XFS_FSB_TO_DADDR(mp, map.br_startblock),
                                   mp->m_bsize, 0, &bp, &xfs_rtbuf_ops);
        if (error)
                return error;

        xfs_trans_buf_set_type(tp, bp, issum ? XFS_BLFT_RTSUMMARY_BUF
                                             : XFS_BLFT_RTBITMAP_BUF);
        *bpp = bp;
        return 0;
}

/*
 * Searching backward from start to limit, find the first block whose
 * allocated/free state is different from start's.
 */
int
xfs_rtfind_back(
        xfs_mount_t     *mp,            /* file system mount point */
        xfs_trans_t     *tp,            /* transaction pointer */
        xfs_rtblock_t   start,          /* starting block to look at */
        xfs_rtblock_t   limit,          /* last block to look at */
        xfs_rtblock_t   *rtblock)       /* out: start block found */
{
        xfs_rtword_t    *b;             /* current word in buffer */
        int             bit;            /* bit number in the word */
        xfs_rtblock_t   block;          /* bitmap block number */
        struct xfs_buf  *bp;            /* buf for the block */
        xfs_rtword_t    *bufp;          /* starting word in buffer */
        int             error;          /* error value */
        xfs_rtblock_t   firstbit;       /* first useful bit in the word */
        xfs_rtblock_t   i;              /* current bit number rel. to start */
        xfs_rtblock_t   len;            /* length of inspected area */
        xfs_rtword_t    mask;           /* mask of relevant bits for value */
        xfs_rtword_t    want;           /* mask for "good" values */
        xfs_rtword_t    wdiff;          /* difference from wanted value */
        int             word;           /* word number in the buffer */

        /*
         * Compute and read in starting bitmap block for starting block.
         */
        block = XFS_BITTOBLOCK(mp, start);
        error = xfs_rtbuf_get(mp, tp, block, 0, &bp);
        if (error) {
                return error;
        }
        bufp = bp->b_addr;
        /*
         * Get the first word's index & point to it.
         */
        word = XFS_BITTOWORD(mp, start);
        b = &bufp[word];
        bit = (int)(start & (XFS_NBWORD - 1));
        len = start - limit + 1;
        /*
         * Compute match value, based on the bit at start: if 1 (free)
         * then all-ones, else all-zeroes.
         */
        want = (*b & ((xfs_rtword_t)1 << bit)) ? -1 : 0;
        /*
         * If the starting position is not word-aligned, deal with the
         * partial word.
         */
        if (bit < XFS_NBWORD - 1) {
                /*
                 * Calculate first (leftmost) bit number to look at,
                 * and mask for all the relevant bits in this word.
                 */
                firstbit = XFS_RTMAX((xfs_srtblock_t)(bit - len + 1), 0);
                mask = (((xfs_rtword_t)1 << (bit - firstbit + 1)) - 1) <<
                        firstbit;
                /*
                 * Calculate the difference between the value there
                 * and what we're looking for.
                 */
                if ((wdiff = (*b ^ want) & mask)) {
                        /*
                         * Different.  Mark where we are and return.
                         */
                        xfs_trans_brelse(tp, bp);
                        i = bit - XFS_RTHIBIT(wdiff);
                        *rtblock = start - i + 1;
                        return 0;
                }
                i = bit - firstbit + 1;
                /*
                 * Go on to previous block if that's where the previous word is
                 * and we need the previous word.
                 */
                if (--word == -1 && i < len) {
                        /*
                         * If done with this block, get the previous one.
                         */
                        xfs_trans_brelse(tp, bp);
                        error = xfs_rtbuf_get(mp, tp, --block, 0, &bp);
                        if (error) {
                                return error;
                        }
                        bufp = bp->b_addr;
                        word = XFS_BLOCKWMASK(mp);
                        b = &bufp[word];
                } else {
                        /*
                         * Go on to the previous word in the buffer.
                         */
                        b--;
                }
        } else {
                /*
                 * Starting on a word boundary, no partial word.
                 */
                i = 0;
        }
        /*
         * Loop over whole words in buffers.  When we use up one buffer
         * we move on to the previous one.
         */
        while (len - i >= XFS_NBWORD) {
                /*
                 * Compute difference between actual and desired value.
                 */
                if ((wdiff = *b ^ want)) {
                        /*
                         * Different, mark where we are and return.
                         */
                        xfs_trans_brelse(tp, bp);
                        i += XFS_NBWORD - 1 - XFS_RTHIBIT(wdiff);
                        *rtblock = start - i + 1;
                        return 0;
                }
                i += XFS_NBWORD;
                /*
                 * Go on to previous block if that's where the previous word is
                 * and we need the previous word.
                 */
                if (--word == -1 && i < len) {
                        /*
                         * If done with this block, get the previous one.
                         */
                        xfs_trans_brelse(tp, bp);
                        error = xfs_rtbuf_get(mp, tp, --block, 0, &bp);
                        if (error) {
                                return error;
                        }
                        bufp = bp->b_addr;
                        word = XFS_BLOCKWMASK(mp);
                        b = &bufp[word];
                } else {
                        /*
                         * Go on to the previous word in the buffer.
                         */
                        b--;
                }
        }
        /*
         * If not ending on a word boundary, deal with the last
         * (partial) word.
         */
        if (len - i) {
                /*
                 * Calculate first (leftmost) bit number to look at,
                 * and mask for all the relevant bits in this word.
                 */
                firstbit = XFS_NBWORD - (len - i);
                mask = (((xfs_rtword_t)1 << (len - i)) - 1) << firstbit;
                /*
                 * Compute difference between actual and desired value.
                 */
                if ((wdiff = (*b ^ want) & mask)) {
                        /*
                         * Different, mark where we are and return.
                         */
                        xfs_trans_brelse(tp, bp);
                        i += XFS_NBWORD - 1 - XFS_RTHIBIT(wdiff);
                        *rtblock = start - i + 1;
                        return 0;
                } else
                        i = len;
        }
        /*
         * No match, return that we scanned the whole area.
         */
        xfs_trans_brelse(tp, bp);
        *rtblock = start - i + 1;
        return 0;
}

/*
 * Searching forward from start to limit, find the first block whose
 * allocated/free state is different from start's.
 */
int
xfs_rtfind_forw(
        xfs_mount_t     *mp,            /* file system mount point */
        xfs_trans_t     *tp,            /* transaction pointer */
        xfs_rtblock_t   start,          /* starting block to look at */
        xfs_rtblock_t   limit,          /* last block to look at */
        xfs_rtblock_t   *rtblock)       /* out: start block found */
{
        xfs_rtword_t    *b;             /* current word in buffer */
        int             bit;            /* bit number in the word */
        xfs_rtblock_t   block;          /* bitmap block number */
        struct xfs_buf  *bp;            /* buf for the block */
        xfs_rtword_t    *bufp;          /* starting word in buffer */
        int             error;          /* error value */
        xfs_rtblock_t   i;              /* current bit number rel. to start */
        xfs_rtblock_t   lastbit;        /* last useful bit in the word */
        xfs_rtblock_t   len;            /* length of inspected area */
        xfs_rtword_t    mask;           /* mask of relevant bits for value */
        xfs_rtword_t    want;           /* mask for "good" values */
        xfs_rtword_t    wdiff;          /* difference from wanted value */
        int             word;           /* word number in the buffer */

        /*
         * Compute and read in starting bitmap block for starting block.
         */
        block = XFS_BITTOBLOCK(mp, start);
        error = xfs_rtbuf_get(mp, tp, block, 0, &bp);
        if (error) {
                return error;
        }
        bufp = bp->b_addr;
        /*
         * Get the first word's index & point to it.
         */
        word = XFS_BITTOWORD(mp, start);
        b = &bufp[word];
        bit = (int)(start & (XFS_NBWORD - 1));
        len = limit - start + 1;
        /*
         * Compute match value, based on the bit at start: if 1 (free)
         * then all-ones, else all-zeroes.
         */
        want = (*b & ((xfs_rtword_t)1 << bit)) ? -1 : 0;
        /*
         * If the starting position is not word-aligned, deal with the
         * partial word.
         */
        if (bit) {
                /*
                 * Calculate last (rightmost) bit number to look at,
                 * and mask for all the relevant bits in this word.
                 */
                lastbit = XFS_RTMIN(bit + len, XFS_NBWORD);
                mask = (((xfs_rtword_t)1 << (lastbit - bit)) - 1) << bit;
                /*
                 * Calculate the difference between the value there
                 * and what we're looking for.
                 */
                if ((wdiff = (*b ^ want) & mask)) {
                        /*
                         * Different.  Mark where we are and return.
                         */
                        xfs_trans_brelse(tp, bp);
                        i = XFS_RTLOBIT(wdiff) - bit;
                        *rtblock = start + i - 1;
                        return 0;
                }
                i = lastbit - bit;
                /*
                 * Go on to next block if that's where the next word is
                 * and we need the next word.
                 */
                if (++word == XFS_BLOCKWSIZE(mp) && i < len) {
                        /*
                         * If done with this block, get the previous one.
                         */
                        xfs_trans_brelse(tp, bp);
                        error = xfs_rtbuf_get(mp, tp, ++block, 0, &bp);
                        if (error) {
                                return error;
                        }
                        b = bufp = bp->b_addr;
                        word = 0;
                } else {
                        /*
                         * Go on to the previous word in the buffer.
                         */
                        b++;
                }
        } else {
                /*
                 * Starting on a word boundary, no partial word.
                 */
                i = 0;
        }
        /*
         * Loop over whole words in buffers.  When we use up one buffer
         * we move on to the next one.
         */
        while (len - i >= XFS_NBWORD) {
                /*
                 * Compute difference between actual and desired value.
                 */
                if ((wdiff = *b ^ want)) {
                        /*
                         * Different, mark where we are and return.
                         */
                        xfs_trans_brelse(tp, bp);
                        i += XFS_RTLOBIT(wdiff);
                        *rtblock = start + i - 1;
                        return 0;
                }
                i += XFS_NBWORD;
                /*
                 * Go on to next block if that's where the next word is
                 * and we need the next word.
                 */
                if (++word == XFS_BLOCKWSIZE(mp) && i < len) {
                        /*
                         * If done with this block, get the next one.
                         */
                        xfs_trans_brelse(tp, bp);
                        error = xfs_rtbuf_get(mp, tp, ++block, 0, &bp);
                        if (error) {
                                return error;
                        }
                        b = bufp = bp->b_addr;
                        word = 0;
                } else {
                        /*
                         * Go on to the next word in the buffer.
                         */
                        b++;
                }
        }
        /*
         * If not ending on a word boundary, deal with the last
         * (partial) word.
         */
        if ((lastbit = len - i)) {
                /*
                 * Calculate mask for all the relevant bits in this word.
                 */
                mask = ((xfs_rtword_t)1 << lastbit) - 1;
                /*
                 * Compute difference between actual and desired value.
                 */
                if ((wdiff = (*b ^ want) & mask)) {
                        /*
                         * Different, mark where we are and return.
                         */
                        xfs_trans_brelse(tp, bp);
                        i += XFS_RTLOBIT(wdiff);
                        *rtblock = start + i - 1;
                        return 0;
                } else
                        i = len;
        }
        /*
         * No match, return that we scanned the whole area.
         */
        xfs_trans_brelse(tp, bp);
        *rtblock = start + i - 1;
        return 0;
}

/*
 * Read and/or modify the summary information for a given extent size,
 * bitmap block combination.
 * Keeps track of a current summary block, so we don't keep reading
 * it from the buffer cache.
 *
 * Summary information is returned in *sum if specified.
 * If no delta is specified, returns summary only.
 */
int
xfs_rtmodify_summary_int(
        xfs_mount_t     *mp,            /* file system mount structure */
        xfs_trans_t     *tp,            /* transaction pointer */
        int             log,            /* log2 of extent size */
        xfs_rtblock_t   bbno,           /* bitmap block number */
        int             delta,          /* change to make to summary info */
        struct xfs_buf  **rbpp,         /* in/out: summary block buffer */
        xfs_fsblock_t   *rsb,           /* in/out: summary block number */
        xfs_suminfo_t   *sum)           /* out: summary info for this block */
{
        struct xfs_buf  *bp;            /* buffer for the summary block */
        int             error;          /* error value */
        xfs_fsblock_t   sb;             /* summary fsblock */
        int             so;             /* index into the summary file */
        xfs_suminfo_t   *sp;            /* pointer to returned data */

        /*
         * Compute entry number in the summary file.
         */
        so = XFS_SUMOFFS(mp, log, bbno);
        /*
         * Compute the block number in the summary file.
         */
        sb = XFS_SUMOFFSTOBLOCK(mp, so);
        /*
         * If we have an old buffer, and the block number matches, use that.
         */
        if (*rbpp && *rsb == sb)
                bp = *rbpp;
        /*
         * Otherwise we have to get the buffer.
         */
        else {
                /*
                 * If there was an old one, get rid of it first.
                 */
                if (*rbpp)
                        xfs_trans_brelse(tp, *rbpp);
                error = xfs_rtbuf_get(mp, tp, sb, 1, &bp);
                if (error) {
                        return error;
                }
                /*
                 * Remember this buffer and block for the next call.
                 */
                *rbpp = bp;
                *rsb = sb;
        }
        /*
         * Point to the summary information, modify/log it, and/or copy it out.
         */
        sp = XFS_SUMPTR(mp, bp, so);
        if (delta) {
                uint first = (uint)((char *)sp - (char *)bp->b_addr);

                *sp += delta;
                if (mp->m_rsum_cache) {
                        if (*sp == 0 && log == mp->m_rsum_cache[bbno])
                                mp->m_rsum_cache[bbno]++;
                        if (*sp != 0 && log < mp->m_rsum_cache[bbno])
                                mp->m_rsum_cache[bbno] = log;
                }
                xfs_trans_log_buf(tp, bp, first, first + sizeof(*sp) - 1);
        }
        if (sum)
                *sum = *sp;
        return 0;
}

int
xfs_rtmodify_summary(
        xfs_mount_t     *mp,            /* file system mount structure */
        xfs_trans_t     *tp,            /* transaction pointer */
        int             log,            /* log2 of extent size */
        xfs_rtblock_t   bbno,           /* bitmap block number */
        int             delta,          /* change to make to summary info */
        struct xfs_buf  **rbpp,         /* in/out: summary block buffer */
        xfs_fsblock_t   *rsb)           /* in/out: summary block number */
{
        return xfs_rtmodify_summary_int(mp, tp, log, bbno,
                                        delta, rbpp, rsb, NULL);
}

/*
 * Set the given range of bitmap bits to the given value.
 * Do whatever I/O and logging is required.
 */
int
xfs_rtmodify_range(
        xfs_mount_t     *mp,            /* file system mount point */
        xfs_trans_t     *tp,            /* transaction pointer */
        xfs_rtblock_t   start,          /* starting block to modify */
        xfs_extlen_t    len,            /* length of extent to modify */
        int             val)            /* 1 for free, 0 for allocated */
{
        xfs_rtword_t    *b;             /* current word in buffer */
        int             bit;            /* bit number in the word */
        xfs_rtblock_t   block;          /* bitmap block number */
        struct xfs_buf  *bp;            /* buf for the block */
        xfs_rtword_t    *bufp;          /* starting word in buffer */
        int             error;          /* error value */
        xfs_rtword_t    *first;         /* first used word in the buffer */
        int             i;              /* current bit number rel. to start */
        int             lastbit;        /* last useful bit in word */
        xfs_rtword_t    mask;           /* mask o frelevant bits for value */
        int             word;           /* word number in the buffer */

        /*
         * Compute starting bitmap block number.
         */
        block = XFS_BITTOBLOCK(mp, start);
        /*
         * Read the bitmap block, and point to its data.
         */
        error = xfs_rtbuf_get(mp, tp, block, 0, &bp);
        if (error) {
                return error;
        }
        bufp = bp->b_addr;
        /*
         * Compute the starting word's address, and starting bit.
         */
        word = XFS_BITTOWORD(mp, start);
        first = b = &bufp[word];
        bit = (int)(start & (XFS_NBWORD - 1));
        /*
         * 0 (allocated) => all zeroes; 1 (free) => all ones.
         */
        val = -val;
        /*
         * If not starting on a word boundary, deal with the first
         * (partial) word.
         */
        if (bit) {
                /*
                 * Compute first bit not changed and mask of relevant bits.
                 */
                lastbit = XFS_RTMIN(bit + len, XFS_NBWORD);
                mask = (((xfs_rtword_t)1 << (lastbit - bit)) - 1) << bit;
                /*
                 * Set/clear the active bits.
                 */
                if (val)
                        *b |= mask;
                else
                        *b &= ~mask;
                i = lastbit - bit;
                /*
                 * Go on to the next block if that's where the next word is
                 * and we need the next word.
                 */
                if (++word == XFS_BLOCKWSIZE(mp) && i < len) {
                        /*
                         * Log the changed part of this block.
                         * Get the next one.
                         */
                        xfs_trans_log_buf(tp, bp,
                                (uint)((char *)first - (char *)bufp),
                                (uint)((char *)b - (char *)bufp));
                        error = xfs_rtbuf_get(mp, tp, ++block, 0, &bp);
                        if (error) {
                                return error;
                        }
                        first = b = bufp = bp->b_addr;
                        word = 0;
                } else {
                        /*
                         * Go on to the next word in the buffer
                         */
                        b++;
                }
        } else {
                /*
                 * Starting on a word boundary, no partial word.
                 */
                i = 0;
        }
        /*
         * Loop over whole words in buffers.  When we use up one buffer
         * we move on to the next one.
         */
        while (len - i >= XFS_NBWORD) {
                /*
                 * Set the word value correctly.
                 */
                *b = val;
                i += XFS_NBWORD;
                /*
                 * Go on to the next block if that's where the next word is
                 * and we need the next word.
                 */
                if (++word == XFS_BLOCKWSIZE(mp) && i < len) {
                        /*
                         * Log the changed part of this block.
                         * Get the next one.
                         */
                        xfs_trans_log_buf(tp, bp,
                                (uint)((char *)first - (char *)bufp),
                                (uint)((char *)b - (char *)bufp));
                        error = xfs_rtbuf_get(mp, tp, ++block, 0, &bp);
                        if (error) {
                                return error;
                        }
                        first = b = bufp = bp->b_addr;
                        word = 0;
                } else {
                        /*
                         * Go on to the next word in the buffer
                         */
                        b++;
                }
        }
        /*
         * If not ending on a word boundary, deal with the last
         * (partial) word.
         */
        if ((lastbit = len - i)) {
                /*
                 * Compute a mask of relevant bits.
                 */
                mask = ((xfs_rtword_t)1 << lastbit) - 1;
                /*
                 * Set/clear the active bits.
                 */
                if (val)
                        *b |= mask;
                else
                        *b &= ~mask;
                b++;
        }
        /*
         * Log any remaining changed bytes.
         */
        if (b > first)
                xfs_trans_log_buf(tp, bp, (uint)((char *)first - (char *)bufp),
                        (uint)((char *)b - (char *)bufp - 1));
        return 0;
}

/*
 * Mark an extent specified by start and len freed.
 * Updates all the summary information as well as the bitmap.
 */
int
xfs_rtfree_range(
        xfs_mount_t     *mp,            /* file system mount point */
        xfs_trans_t     *tp,            /* transaction pointer */
        xfs_rtblock_t   start,          /* starting block to free */
        xfs_extlen_t    len,            /* length to free */
        struct xfs_buf  **rbpp,         /* in/out: summary block buffer */
        xfs_fsblock_t   *rsb)           /* in/out: summary block number */
{
        xfs_rtblock_t   end;            /* end of the freed extent */
        int             error;          /* error value */
        xfs_rtblock_t   postblock;      /* first block freed > end */
        xfs_rtblock_t   preblock;       /* first block freed < start */

        end = start + len - 1;
        /*
         * Modify the bitmap to mark this extent freed.
         */
        error = xfs_rtmodify_range(mp, tp, start, len, 1);
        if (error) {
                return error;
        }
        /*
         * Assume we're freeing out of the middle of an allocated extent.
         * We need to find the beginning and end of the extent so we can
         * properly update the summary.
         */
        error = xfs_rtfind_back(mp, tp, start, 0, &preblock);
        if (error) {
                return error;
        }
        /*
         * Find the next allocated block (end of allocated extent).
         */
        error = xfs_rtfind_forw(mp, tp, end, mp->m_sb.sb_rextents - 1,
                &postblock);
        if (error)
                return error;
        /*
         * If there are blocks not being freed at the front of the
         * old extent, add summary data for them to be allocated.
         */
        if (preblock < start) {
                error = xfs_rtmodify_summary(mp, tp,
                        XFS_RTBLOCKLOG(start - preblock),
                        XFS_BITTOBLOCK(mp, preblock), -1, rbpp, rsb);
                if (error) {
                        return error;
                }
        }
        /*
         * If there are blocks not being freed at the end of the
         * old extent, add summary data for them to be allocated.
         */
        if (postblock > end) {
                error = xfs_rtmodify_summary(mp, tp,
                        XFS_RTBLOCKLOG(postblock - end),
                        XFS_BITTOBLOCK(mp, end + 1), -1, rbpp, rsb);
                if (error) {
                        return error;
                }
        }
        /*
         * Increment the summary information corresponding to the entire
         * (new) free extent.
         */
        error = xfs_rtmodify_summary(mp, tp,
                XFS_RTBLOCKLOG(postblock + 1 - preblock),
                XFS_BITTOBLOCK(mp, preblock), 1, rbpp, rsb);
        return error;
}

/*
 * Check that the given range is either all allocated (val = 0) or
 * all free (val = 1).
 */
int
xfs_rtcheck_range(
        xfs_mount_t     *mp,            /* file system mount point */
        xfs_trans_t     *tp,            /* transaction pointer */
        xfs_rtblock_t   start,          /* starting block number of extent */
        xfs_extlen_t    len,            /* length of extent */
        int             val,            /* 1 for free, 0 for allocated */
        xfs_rtblock_t   *new,           /* out: first block not matching */
        int             *stat)          /* out: 1 for matches, 0 for not */
{
        xfs_rtword_t    *b;             /* current word in buffer */
        int             bit;            /* bit number in the word */
        xfs_rtblock_t   block;          /* bitmap block number */
        struct xfs_buf  *bp;            /* buf for the block */
        xfs_rtword_t    *bufp;          /* starting word in buffer */
        int             error;          /* error value */
        xfs_rtblock_t   i;              /* current bit number rel. to start */
        xfs_rtblock_t   lastbit;        /* last useful bit in word */
        xfs_rtword_t    mask;           /* mask of relevant bits for value */
        xfs_rtword_t    wdiff;          /* difference from wanted value */
        int             word;           /* word number in the buffer */

        /*
         * Compute starting bitmap block number
         */
        block = XFS_BITTOBLOCK(mp, start);
        /*
         * Read the bitmap block.
         */
        error = xfs_rtbuf_get(mp, tp, block, 0, &bp);
        if (error) {
                return error;
        }
        bufp = bp->b_addr;
        /*
         * Compute the starting word's address, and starting bit.
         */
        word = XFS_BITTOWORD(mp, start);
        b = &bufp[word];
        bit = (int)(start & (XFS_NBWORD - 1));
        /*
         * 0 (allocated) => all zero's; 1 (free) => all one's.
         */
        val = -val;
        /*
         * If not starting on a word boundary, deal with the first
         * (partial) word.
         */
        if (bit) {
                /*
                 * Compute first bit not examined.
                 */
                lastbit = XFS_RTMIN(bit + len, XFS_NBWORD);
                /*
                 * Mask of relevant bits.
                 */
                mask = (((xfs_rtword_t)1 << (lastbit - bit)) - 1) << bit;
                /*
                 * Compute difference between actual and desired value.
                 */
                if ((wdiff = (*b ^ val) & mask)) {
                        /*
                         * Different, compute first wrong bit and return.
                         */
                        xfs_trans_brelse(tp, bp);
                        i = XFS_RTLOBIT(wdiff) - bit;
                        *new = start + i;
                        *stat = 0;
                        return 0;
                }
                i = lastbit - bit;
                /*
                 * Go on to next block if that's where the next word is
                 * and we need the next word.
                 */
                if (++word == XFS_BLOCKWSIZE(mp) && i < len) {
                        /*
                         * If done with this block, get the next one.
                         */
                        xfs_trans_brelse(tp, bp);
                        error = xfs_rtbuf_get(mp, tp, ++block, 0, &bp);
                        if (error) {
                                return error;
                        }
                        b = bufp = bp->b_addr;
                        word = 0;
                } else {
                        /*
                         * Go on to the next word in the buffer.
                         */
                        b++;
                }
        } else {
                /*
                 * Starting on a word boundary, no partial word.
                 */
                i = 0;
        }
        /*
         * Loop over whole words in buffers.  When we use up one buffer
         * we move on to the next one.
         */
        while (len - i >= XFS_NBWORD) {
                /*
                 * Compute difference between actual and desired value.
                 */
                if ((wdiff = *b ^ val)) {
                        /*
                         * Different, compute first wrong bit and return.
                         */
                        xfs_trans_brelse(tp, bp);
                        i += XFS_RTLOBIT(wdiff);
                        *new = start + i;
                        *stat = 0;
                        return 0;
                }
                i += XFS_NBWORD;
                /*
                 * Go on to next block if that's where the next word is
                 * and we need the next word.
                 */
                if (++word == XFS_BLOCKWSIZE(mp) && i < len) {
                        /*
                         * If done with this block, get the next one.
                         */
                        xfs_trans_brelse(tp, bp);
                        error = xfs_rtbuf_get(mp, tp, ++block, 0, &bp);
                        if (error) {
                                return error;
                        }
                        b = bufp = bp->b_addr;
                        word = 0;
                } else {
                        /*
                         * Go on to the next word in the buffer.
                         */
                        b++;
                }
        }
        /*
         * If not ending on a word boundary, deal with the last
         * (partial) word.
         */
        if ((lastbit = len - i)) {
                /*
                 * Mask of relevant bits.
                 */
                mask = ((xfs_rtword_t)1 << lastbit) - 1;
                /*
                 * Compute difference between actual and desired value.
                 */
                if ((wdiff = (*b ^ val) & mask)) {
                        /*
                         * Different, compute first wrong bit and return.
                         */
                        xfs_trans_brelse(tp, bp);
                        i += XFS_RTLOBIT(wdiff);
                        *new = start + i;
                        *stat = 0;
                        return 0;
                } else
                        i = len;
        }
        /*
         * Successful, return.
         */
        xfs_trans_brelse(tp, bp);
        *new = start + i;
        *stat = 1;
        return 0;
}

#ifdef DEBUG
/*
 * Check that the given extent (block range) is allocated already.
 */
STATIC int                              /* error */
xfs_rtcheck_alloc_range(
        xfs_mount_t     *mp,            /* file system mount point */
        xfs_trans_t     *tp,            /* transaction pointer */
        xfs_rtblock_t   bno,            /* starting block number of extent */
        xfs_extlen_t    len)            /* length of extent */
{
        xfs_rtblock_t   new;            /* dummy for xfs_rtcheck_range */
        int             stat;
        int             error;

        error = xfs_rtcheck_range(mp, tp, bno, len, 0, &new, &stat);
        if (error)
                return error;
        ASSERT(stat);
        return 0;
}
#else
#define xfs_rtcheck_alloc_range(m,t,b,l)        (0)
#endif
/*
 * Free an extent in the realtime subvolume.  Length is expressed in
 * realtime extents, as is the block number.
 */
int                                     /* error */
xfs_rtfree_extent(
        xfs_trans_t     *tp,            /* transaction pointer */
        xfs_rtblock_t   bno,            /* starting block number to free */
        xfs_extlen_t    len)            /* length of extent freed */
{
        int             error;          /* error value */
        xfs_mount_t     *mp;            /* file system mount structure */
        xfs_fsblock_t   sb;             /* summary file block number */
        struct xfs_buf  *sumbp = NULL;  /* summary file block buffer */

        mp = tp->t_mountp;

        ASSERT(mp->m_rbmip->i_itemp != NULL);
        ASSERT(xfs_isilocked(mp->m_rbmip, XFS_ILOCK_EXCL));

        error = xfs_rtcheck_alloc_range(mp, tp, bno, len);
        if (error)
                return error;

        /*
         * Free the range of realtime blocks.
         */
        error = xfs_rtfree_range(mp, tp, bno, len, &sumbp, &sb);
        if (error) {
                return error;
        }
        /*
         * Mark more blocks free in the superblock.
         */
        xfs_trans_mod_sb(tp, XFS_TRANS_SB_FREXTENTS, (long)len);
        /*
         * If we've now freed all the blocks, reset the file sequence
         * number to 0.
         */
        if (tp->t_frextents_delta + mp->m_sb.sb_frextents ==
            mp->m_sb.sb_rextents) {
                if (!(mp->m_rbmip->i_d.di_flags & XFS_DIFLAG_NEWRTBM))

                        mp->m_rbmip->i_d.di_flags |= XFS_DIFLAG_NEWRTBM;
                *(uint64_t *)&VFS_I(mp->m_rbmip)->i_atime = 0;
                xfs_trans_log_inode(tp, mp->m_rbmip, XFS_ILOG_CORE);
        }
        return 0;
}

/* Find all the free records within a given range. */
int
xfs_rtalloc_query_range(
        struct xfs_trans                *tp,
        struct xfs_rtalloc_rec          *low_rec,
        struct xfs_rtalloc_rec          *high_rec,
        xfs_rtalloc_query_range_fn      fn,
        void                            *priv)
{
        struct xfs_rtalloc_rec          rec;
        struct xfs_mount                *mp = tp->t_mountp;
        xfs_rtblock_t                   rtstart;
        xfs_rtblock_t                   rtend;
        int                             is_free;
        int                             error = 0;

        if (low_rec->ar_startext > high_rec->ar_startext)
                return -EINVAL;
        if (low_rec->ar_startext >= mp->m_sb.sb_rextents ||
            low_rec->ar_startext == high_rec->ar_startext)
                return 0;
        high_rec->ar_startext = min(high_rec->ar_startext,
                        mp->m_sb.sb_rextents - 1);

        /* Iterate the bitmap, looking for discrepancies. */
        rtstart = low_rec->ar_startext;
        while (rtstart <= high_rec->ar_startext) {
                /* Is the first block free? */
                error = xfs_rtcheck_range(mp, tp, rtstart, 1, 1, &rtend,
                                &is_free);
                if (error)
                        break;

                /* How long does the extent go for? */
                error = xfs_rtfind_forw(mp, tp, rtstart,
                                high_rec->ar_startext, &rtend);
                if (error)
                        break;

                if (is_free) {
                        rec.ar_startext = rtstart;
                        rec.ar_extcount = rtend - rtstart + 1;

                        error = fn(tp, &rec, priv);
                        if (error)
                                break;
                }

                rtstart = rtend + 1;
        }

        return error;
}

/* Find all the free records. */
int
xfs_rtalloc_query_all(
        struct xfs_trans                *tp,
        xfs_rtalloc_query_range_fn      fn,
        void                            *priv)
{
        struct xfs_rtalloc_rec          keys[2];

        keys[0].ar_startext = 0;
        keys[1].ar_startext = tp->t_mountp->m_sb.sb_rextents - 1;
        keys[0].ar_extcount = keys[1].ar_extcount = 0;

        return xfs_rtalloc_query_range(tp, &keys[0], &keys[1], fn, priv);
}

/* Is the given extent all free? */
int
xfs_rtalloc_extent_is_free(
        struct xfs_mount                *mp,
        struct xfs_trans                *tp,
        xfs_rtblock_t                   start,
        xfs_extlen_t                    len,
        bool                            *is_free)
{
        xfs_rtblock_t                   end;
        int                             matches;
        int                             error;

        error = xfs_rtcheck_range(mp, tp, start, len, 1, &end, &matches);
        if (error)
                return error;

        *is_free = matches;
        return 0;
}