// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2019 Oracle.  All Rights Reserved.
 * Author: Darrick J. Wong <darrick.wong@oracle.com>
 */
#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_btree.h"
#include "xfs_ialloc.h"
#include "xfs_ialloc_btree.h"
#include "xfs_iwalk.h"
#include "xfs_error.h"
#include "xfs_trace.h"
#include "xfs_icache.h"
#include "xfs_health.h"
#include "xfs_trans.h"
#include "xfs_pwork.h"
#include "xfs_ag.h"

/*
 * Walking Inodes in the Filesystem
 * ================================
 *
 * This iterator function walks a subset of filesystem inodes in increasing
 * order from @startino until there are no more inodes.  For each allocated
 * inode it finds, it calls a walk function with the relevant inode number and
 * a pointer to caller-provided data.  The walk function can return the usual
 * negative error code to stop the iteration; 0 to continue the iteration; or
 * -ECANCELED to stop the iteration.  This return value is returned to the
 * caller.
 *
 * Internally, we allow the walk function to do anything, which means that we
 * cannot maintain the inobt cursor or our lock on the AGI buffer.  We
 * therefore cache the inobt records in kernel memory and only call the walk
 * function when our memory buffer is full.  @nr_recs is the number of records
 * that we've cached, and @sz_recs is the size of our cache.
 *
 * It is the responsibility of the walk function to ensure it accesses
 * allocated inodes, as the inobt records may be stale by the time they are
 * acted upon.
 */

struct xfs_iwalk_ag {
        /* parallel work control data; will be null if single threaded */
        struct xfs_pwork                pwork;

        struct xfs_mount                *mp;
        struct xfs_trans                *tp;
        struct xfs_perag                *pag;

        /* Where do we start the traversal? */
        xfs_ino_t                       startino;

        /* What was the last inode number we saw when iterating the inobt? */
        xfs_ino_t                       lastino;

        /* Array of inobt records we cache. */
        struct xfs_inobt_rec_incore     *recs;

        /* Number of entries allocated for the @recs array. */
        unsigned int                    sz_recs;

        /* Number of entries in the @recs array that are in use. */
        unsigned int                    nr_recs;

        /* Inode walk function and data pointer. */
        xfs_iwalk_fn                    iwalk_fn;
        xfs_inobt_walk_fn               inobt_walk_fn;
        void                            *data;

        /*
         * Make it look like the inodes up to startino are free so that
         * bulkstat can start its inode iteration at the correct place without
         * needing to special case everywhere.
         */
        unsigned int                    trim_start:1;

        /* Skip empty inobt records? */
        unsigned int                    skip_empty:1;

        /* Drop the (hopefully empty) transaction when calling iwalk_fn. */
        unsigned int                    drop_trans:1;
};

/*
 * Loop over all clusters in a chunk for a given incore inode allocation btree
 * record.  Do a readahead if there are any allocated inodes in that cluster.
 */
STATIC void
xfs_iwalk_ichunk_ra(
        struct xfs_mount                *mp,
        struct xfs_perag                *pag,
        struct xfs_inobt_rec_incore     *irec)
{
        struct xfs_ino_geometry         *igeo = M_IGEO(mp);
        xfs_agblock_t                   agbno;
        struct blk_plug                 plug;
        int                             i;      /* inode chunk index */

        agbno = XFS_AGINO_TO_AGBNO(mp, irec->ir_startino);

        blk_start_plug(&plug);
        for (i = 0; i < XFS_INODES_PER_CHUNK; i += igeo->inodes_per_cluster) {
                xfs_inofree_t   imask;

                imask = xfs_inobt_maskn(i, igeo->inodes_per_cluster);
                if (imask & ~irec->ir_free) {
                        xfs_btree_reada_bufs(mp, pag->pag_agno, agbno,
                                        igeo->blocks_per_cluster,
                                        &xfs_inode_buf_ops);
                }
                agbno += igeo->blocks_per_cluster;
        }
        blk_finish_plug(&plug);
}

/*
 * Set the bits in @irec's free mask that correspond to the inodes before
 * @agino so that we skip them.  This is how we restart an inode walk that was
 * interrupted in the middle of an inode record.
 */
STATIC void
xfs_iwalk_adjust_start(
        xfs_agino_t                     agino,  /* starting inode of chunk */
        struct xfs_inobt_rec_incore     *irec)  /* btree record */
{
        int                             idx;    /* index into inode chunk */
        int                             i;

        idx = agino - irec->ir_startino;

        /*
         * We got a right chunk with some left inodes allocated at it.  Grab
         * the chunk record.  Mark all the uninteresting inodes free because
         * they're before our start point.
         */
        for (i = 0; i < idx; i++) {
                if (XFS_INOBT_MASK(i) & ~irec->ir_free)
                        irec->ir_freecount++;
        }

        irec->ir_free |= xfs_inobt_maskn(0, idx);
}

/* Allocate memory for a walk. */
STATIC int
xfs_iwalk_alloc(
        struct xfs_iwalk_ag     *iwag)
{
        size_t                  size;

        ASSERT(iwag->recs == NULL);
        iwag->nr_recs = 0;

        /* Allocate a prefetch buffer for inobt records. */
        size = iwag->sz_recs * sizeof(struct xfs_inobt_rec_incore);
        iwag->recs = kmem_alloc(size, KM_MAYFAIL);
        if (iwag->recs == NULL)
                return -ENOMEM;

        return 0;
}

/* Free memory we allocated for a walk. */
STATIC void
xfs_iwalk_free(
        struct xfs_iwalk_ag     *iwag)
{
        kmem_free(iwag->recs);
        iwag->recs = NULL;
}

/* For each inuse inode in each cached inobt record, call our function. */
STATIC int
xfs_iwalk_ag_recs(
        struct xfs_iwalk_ag     *iwag)
{
        struct xfs_mount        *mp = iwag->mp;
        struct xfs_trans        *tp = iwag->tp;
        struct xfs_perag        *pag = iwag->pag;
        xfs_ino_t               ino;
        unsigned int            i, j;
        int                     error;

        for (i = 0; i < iwag->nr_recs; i++) {
                struct xfs_inobt_rec_incore     *irec = &iwag->recs[i];

                trace_xfs_iwalk_ag_rec(mp, pag->pag_agno, irec);

                if (xfs_pwork_want_abort(&iwag->pwork))
                        return 0;

                if (iwag->inobt_walk_fn) {
                        error = iwag->inobt_walk_fn(mp, tp, pag->pag_agno, irec,
                                        iwag->data);
                        if (error)
                                return error;
                }

                if (!iwag->iwalk_fn)
                        continue;

                for (j = 0; j < XFS_INODES_PER_CHUNK; j++) {
                        if (xfs_pwork_want_abort(&iwag->pwork))
                                return 0;

                        /* Skip if this inode is free */
                        if (XFS_INOBT_MASK(j) & irec->ir_free)
                                continue;

                        /* Otherwise call our function. */
                        ino = XFS_AGINO_TO_INO(mp, pag->pag_agno,
                                                irec->ir_startino + j);
                        error = iwag->iwalk_fn(mp, tp, ino, iwag->data);
                        if (error)
                                return error;
                }
        }

        return 0;
}

/* Delete cursor and let go of AGI. */
static inline void
xfs_iwalk_del_inobt(
        struct xfs_trans        *tp,
        struct xfs_btree_cur    **curpp,
        struct xfs_buf          **agi_bpp,
        int                     error)
{
        if (*curpp) {
                xfs_btree_del_cursor(*curpp, error);
                *curpp = NULL;
        }
        if (*agi_bpp) {
                xfs_trans_brelse(tp, *agi_bpp);
                *agi_bpp = NULL;
        }
}

/*
 * Set ourselves up for walking inobt records starting from a given point in
 * the filesystem.
 *
 * If caller passed in a nonzero start inode number, load the record from the
 * inobt and make the record look like all the inodes before agino are free so
 * that we skip them, and then move the cursor to the next inobt record.  This
 * is how we support starting an iwalk in the middle of an inode chunk.
 *
 * If the caller passed in a start number of zero, move the cursor to the first
 * inobt record.
 *
 * The caller is responsible for cleaning up the cursor and buffer pointer
 * regardless of the error status.
 */
STATIC int
xfs_iwalk_ag_start(
        struct xfs_iwalk_ag     *iwag,
        xfs_agino_t             agino,
        struct xfs_btree_cur    **curpp,
        struct xfs_buf          **agi_bpp,
        int                     *has_more)
{
        struct xfs_mount        *mp = iwag->mp;
        struct xfs_trans        *tp = iwag->tp;
        struct xfs_perag        *pag = iwag->pag;
        struct xfs_inobt_rec_incore *irec;
        int                     error;

        /* Set up a fresh cursor and empty the inobt cache. */
        iwag->nr_recs = 0;
        error = xfs_inobt_cur(mp, tp, pag, XFS_BTNUM_INO, curpp, agi_bpp);
        if (error)
                return error;

        /* Starting at the beginning of the AG?  That's easy! */
        if (agino == 0)
                return xfs_inobt_lookup(*curpp, 0, XFS_LOOKUP_GE, has_more);

        /*
         * Otherwise, we have to grab the inobt record where we left off, stuff
         * the record into our cache, and then see if there are more records.
         * We require a lookup cache of at least two elements so that the
         * caller doesn't have to deal with tearing down the cursor to walk the
         * records.
         */
        error = xfs_inobt_lookup(*curpp, agino, XFS_LOOKUP_LE, has_more);
        if (error)
                return error;

        /*
         * If the LE lookup at @agino yields no records, jump ahead to the
         * inobt cursor increment to see if there are more records to process.
         */
        if (!*has_more)
                goto out_advance;

        /* Get the record, should always work */
        irec = &iwag->recs[iwag->nr_recs];
        error = xfs_inobt_get_rec(*curpp, irec, has_more);
        if (error)
                return error;
        if (XFS_IS_CORRUPT(mp, *has_more != 1))
                return -EFSCORRUPTED;

        iwag->lastino = XFS_AGINO_TO_INO(mp, pag->pag_agno,
                                irec->ir_startino + XFS_INODES_PER_CHUNK - 1);

        /*
         * If the LE lookup yielded an inobt record before the cursor position,
         * skip it and see if there's another one after it.
         */
        if (irec->ir_startino + XFS_INODES_PER_CHUNK <= agino)
                goto out_advance;

        /*
         * If agino fell in the middle of the inode record, make it look like
         * the inodes up to agino are free so that we don't return them again.
         */
        if (iwag->trim_start)
                xfs_iwalk_adjust_start(agino, irec);

        /*
         * The prefetch calculation is supposed to give us a large enough inobt
         * record cache that grab_ichunk can stage a partial first record and
         * the loop body can cache a record without having to check for cache
         * space until after it reads an inobt record.
         */
        iwag->nr_recs++;
        ASSERT(iwag->nr_recs < iwag->sz_recs);

out_advance:
        return xfs_btree_increment(*curpp, 0, has_more);
}

/*
 * The inobt record cache is full, so preserve the inobt cursor state and
 * run callbacks on the cached inobt records.  When we're done, restore the
 * cursor state to wherever the cursor would have been had the cache not been
 * full (and therefore we could've just incremented the cursor) if *@has_more
 * is true.  On exit, *@has_more will indicate whether or not the caller should
 * try for more inode records.
 */
STATIC int
xfs_iwalk_run_callbacks(
        struct xfs_iwalk_ag             *iwag,
        struct xfs_btree_cur            **curpp,
        struct xfs_buf                  **agi_bpp,
        int                             *has_more)
{
        struct xfs_mount                *mp = iwag->mp;
        struct xfs_inobt_rec_incore     *irec;
        xfs_agino_t                     next_agino;
        int                             error;

        next_agino = XFS_INO_TO_AGINO(mp, iwag->lastino) + 1;

        ASSERT(iwag->nr_recs > 0);

        /* Delete cursor but remember the last record we cached... */
        xfs_iwalk_del_inobt(iwag->tp, curpp, agi_bpp, 0);
        irec = &iwag->recs[iwag->nr_recs - 1];
        ASSERT(next_agino >= irec->ir_startino + XFS_INODES_PER_CHUNK);

        if (iwag->drop_trans) {
                xfs_trans_cancel(iwag->tp);
                iwag->tp = NULL;
        }

        error = xfs_iwalk_ag_recs(iwag);
        if (error)
                return error;

        /* ...empty the cache... */
        iwag->nr_recs = 0;

        if (!has_more)
                return 0;

        if (iwag->drop_trans) {
                error = xfs_trans_alloc_empty(mp, &iwag->tp);
                if (error)
                        return error;
        }

        /* ...and recreate the cursor just past where we left off. */
        error = xfs_inobt_cur(mp, iwag->tp, iwag->pag, XFS_BTNUM_INO, curpp,
                        agi_bpp);
        if (error)
                return error;

        return xfs_inobt_lookup(*curpp, next_agino, XFS_LOOKUP_GE, has_more);
}

/* Walk all inodes in a single AG, from @iwag->startino to the end of the AG. */
STATIC int
xfs_iwalk_ag(
        struct xfs_iwalk_ag             *iwag)
{
        struct xfs_mount                *mp = iwag->mp;
        struct xfs_perag                *pag = iwag->pag;
        struct xfs_buf                  *agi_bp = NULL;
        struct xfs_btree_cur            *cur = NULL;
        xfs_agino_t                     agino;
        int                             has_more;
        int                             error = 0;

        /* Set up our cursor at the right place in the inode btree. */
        ASSERT(pag->pag_agno == XFS_INO_TO_AGNO(mp, iwag->startino));
        agino = XFS_INO_TO_AGINO(mp, iwag->startino);
        error = xfs_iwalk_ag_start(iwag, agino, &cur, &agi_bp, &has_more);

        while (!error && has_more) {
                struct xfs_inobt_rec_incore     *irec;
                xfs_ino_t                       rec_fsino;

                cond_resched();
                if (xfs_pwork_want_abort(&iwag->pwork))
                        goto out;

                /* Fetch the inobt record. */
                irec = &iwag->recs[iwag->nr_recs];
                error = xfs_inobt_get_rec(cur, irec, &has_more);
                if (error || !has_more)
                        break;

                /* Make sure that we always move forward. */
                rec_fsino = XFS_AGINO_TO_INO(mp, pag->pag_agno, irec->ir_startino);
                if (iwag->lastino != NULLFSINO &&
                    XFS_IS_CORRUPT(mp, iwag->lastino >= rec_fsino)) {
                        error = -EFSCORRUPTED;
                        goto out;
                }
                iwag->lastino = rec_fsino + XFS_INODES_PER_CHUNK - 1;

                /* No allocated inodes in this chunk; skip it. */
                if (iwag->skip_empty && irec->ir_freecount == irec->ir_count) {
                        error = xfs_btree_increment(cur, 0, &has_more);
                        if (error)
                                break;
                        continue;
                }

                /*
                 * Start readahead for this inode chunk in anticipation of
                 * walking the inodes.
                 */
                if (iwag->iwalk_fn)
                        xfs_iwalk_ichunk_ra(mp, pag, irec);

                /*
                 * If there's space in the buffer for more records, increment
                 * the btree cursor and grab more.
                 */
                if (++iwag->nr_recs < iwag->sz_recs) {
                        error = xfs_btree_increment(cur, 0, &has_more);
                        if (error || !has_more)
                                break;
                        continue;
                }

                /*
                 * Otherwise, we need to save cursor state and run the callback
                 * function on the cached records.  The run_callbacks function
                 * is supposed to return a cursor pointing to the record where
                 * we would be if we had been able to increment like above.
                 */
                ASSERT(has_more);
                error = xfs_iwalk_run_callbacks(iwag, &cur, &agi_bp, &has_more);
        }

        if (iwag->nr_recs == 0 || error)
                goto out;

        /* Walk the unprocessed records in the cache. */
        error = xfs_iwalk_run_callbacks(iwag, &cur, &agi_bp, &has_more);

out:
        xfs_iwalk_del_inobt(iwag->tp, &cur, &agi_bp, error);
        return error;
}

/*
 * We experimentally determined that the reduction in ioctl call overhead
 * diminishes when userspace asks for more than 2048 inodes, so we'll cap
 * prefetch at this point.
 */
#define IWALK_MAX_INODE_PREFETCH        (2048U)

/*
 * Given the number of inodes to prefetch, set the number of inobt records that
 * we cache in memory, which controls the number of inodes we try to read
 * ahead.  Set the maximum if @inodes == 0.
 */
static inline unsigned int
xfs_iwalk_prefetch(
        unsigned int            inodes)
{
        unsigned int            inobt_records;

        /*
         * If the caller didn't tell us the number of inodes they wanted,
         * assume the maximum prefetch possible for best performance.
         * Otherwise, cap prefetch at that maximum so that we don't start an
         * absurd amount of prefetch.
         */
        if (inodes == 0)
                inodes = IWALK_MAX_INODE_PREFETCH;
        inodes = min(inodes, IWALK_MAX_INODE_PREFETCH);

        /* Round the inode count up to a full chunk. */
        inodes = round_up(inodes, XFS_INODES_PER_CHUNK);

        /*
         * In order to convert the number of inodes to prefetch into an
         * estimate of the number of inobt records to cache, we require a
         * conversion factor that reflects our expectations of the average
         * loading factor of an inode chunk.  Based on data gathered, most
         * (but not all) filesystems manage to keep the inode chunks totally
         * full, so we'll underestimate slightly so that our readahead will
         * still deliver the performance we want on aging filesystems:
         *
         * inobt = inodes / (INODES_PER_CHUNK * (4 / 5));
         *
         * The funny math is to avoid integer division.
         */
        inobt_records = (inodes * 5) / (4 * XFS_INODES_PER_CHUNK);

        /*
         * Allocate enough space to prefetch at least two inobt records so that
         * we can cache both the record where the iwalk started and the next
         * record.  This simplifies the AG inode walk loop setup code.
         */
        return max(inobt_records, 2U);
}

/*
 * Walk all inodes in the filesystem starting from @startino.  The @iwalk_fn
 * will be called for each allocated inode, being passed the inode's number and
 * @data.  @max_prefetch controls how many inobt records' worth of inodes we
 * try to readahead.
 */
int
xfs_iwalk(
        struct xfs_mount        *mp,
        struct xfs_trans        *tp,
        xfs_ino_t               startino,
        unsigned int            flags,
        xfs_iwalk_fn            iwalk_fn,
        unsigned int            inode_records,
        void                    *data)
{
        struct xfs_iwalk_ag     iwag = {
                .mp             = mp,
                .tp             = tp,
                .iwalk_fn       = iwalk_fn,
                .data           = data,
                .startino       = startino,
                .sz_recs        = xfs_iwalk_prefetch(inode_records),
                .trim_start     = 1,
                .skip_empty     = 1,
                .pwork          = XFS_PWORK_SINGLE_THREADED,
                .lastino        = NULLFSINO,
        };
        struct xfs_perag        *pag;
        xfs_agnumber_t          agno = XFS_INO_TO_AGNO(mp, startino);
        int                     error;

        ASSERT(agno < mp->m_sb.sb_agcount);
        ASSERT(!(flags & ~XFS_IWALK_FLAGS_ALL));

        error = xfs_iwalk_alloc(&iwag);
        if (error)
                return error;

        for_each_perag_from(mp, agno, pag) {
                iwag.pag = pag;
                error = xfs_iwalk_ag(&iwag);
                if (error)
                        break;
                iwag.startino = XFS_AGINO_TO_INO(mp, agno + 1, 0);
                if (flags & XFS_INOBT_WALK_SAME_AG)
                        break;
                iwag.pag = NULL;
        }

        if (iwag.pag)
                xfs_perag_put(pag);
        xfs_iwalk_free(&iwag);
        return error;
}

/* Run per-thread iwalk work. */
static int
xfs_iwalk_ag_work(
        struct xfs_mount        *mp,
        struct xfs_pwork        *pwork)
{
        struct xfs_iwalk_ag     *iwag;
        int                     error = 0;

        iwag = container_of(pwork, struct xfs_iwalk_ag, pwork);
        if (xfs_pwork_want_abort(pwork))
                goto out;

        error = xfs_iwalk_alloc(iwag);
        if (error)
                goto out;
        /*
         * Grab an empty transaction so that we can use its recursive buffer
         * locking abilities to detect cycles in the inobt without deadlocking.
         */
        error = xfs_trans_alloc_empty(mp, &iwag->tp);
        if (error)
                goto out;
        iwag->drop_trans = 1;

        error = xfs_iwalk_ag(iwag);
        if (iwag->tp)
                xfs_trans_cancel(iwag->tp);
        xfs_iwalk_free(iwag);
out:
        xfs_perag_put(iwag->pag);
        kmem_free(iwag);
        return error;
}

/*
 * Walk all the inodes in the filesystem using multiple threads to process each
 * AG.
 */
int
xfs_iwalk_threaded(
        struct xfs_mount        *mp,
        xfs_ino_t               startino,
        unsigned int            flags,
        xfs_iwalk_fn            iwalk_fn,
        unsigned int            inode_records,
        bool                    polled,
        void                    *data)
{
        struct xfs_pwork_ctl    pctl;
        struct xfs_perag        *pag;
        xfs_agnumber_t          agno = XFS_INO_TO_AGNO(mp, startino);
        int                     error;

        ASSERT(agno < mp->m_sb.sb_agcount);
        ASSERT(!(flags & ~XFS_IWALK_FLAGS_ALL));

        error = xfs_pwork_init(mp, &pctl, xfs_iwalk_ag_work, "xfs_iwalk");
        if (error)
                return error;

        for_each_perag_from(mp, agno, pag) {
                struct xfs_iwalk_ag     *iwag;

                if (xfs_pwork_ctl_want_abort(&pctl))
                        break;

                iwag = kmem_zalloc(sizeof(struct xfs_iwalk_ag), 0);
                iwag->mp = mp;

                /*
                 * perag is being handed off to async work, so take another
                 * reference for the async work to release.
                 */
                atomic_inc(&pag->pag_ref);
                iwag->pag = pag;
                iwag->iwalk_fn = iwalk_fn;
                iwag->data = data;
                iwag->startino = startino;
                iwag->sz_recs = xfs_iwalk_prefetch(inode_records);
                iwag->lastino = NULLFSINO;
                xfs_pwork_queue(&pctl, &iwag->pwork);
                startino = XFS_AGINO_TO_INO(mp, pag->pag_agno + 1, 0);
                if (flags & XFS_INOBT_WALK_SAME_AG)
                        break;
        }
        if (pag)
                xfs_perag_put(pag);
        if (polled)
                xfs_pwork_poll(&pctl);
        return xfs_pwork_destroy(&pctl);
}

/*
 * Allow callers to cache up to a page's worth of inobt records.  This reflects
 * the existing inumbers prefetching behavior.  Since the inobt walk does not
 * itself do anything with the inobt records, we can set a fairly high limit
 * here.
 */
#define MAX_INOBT_WALK_PREFETCH \
        (PAGE_SIZE / sizeof(struct xfs_inobt_rec_incore))

/*
 * Given the number of records that the user wanted, set the number of inobt
 * records that we buffer in memory.  Set the maximum if @inobt_records == 0.
 */
static inline unsigned int
xfs_inobt_walk_prefetch(
        unsigned int            inobt_records)
{
        /*
         * If the caller didn't tell us the number of inobt records they
         * wanted, assume the maximum prefetch possible for best performance.
         */
        if (inobt_records == 0)
                inobt_records = MAX_INOBT_WALK_PREFETCH;

        /*
         * Allocate enough space to prefetch at least two inobt records so that
         * we can cache both the record where the iwalk started and the next
         * record.  This simplifies the AG inode walk loop setup code.
         */
        inobt_records = max(inobt_records, 2U);

        /*
         * Cap prefetch at that maximum so that we don't use an absurd amount
         * of memory.
         */
        return min_t(unsigned int, inobt_records, MAX_INOBT_WALK_PREFETCH);
}

/*
 * Walk all inode btree records in the filesystem starting from @startino.  The
 * @inobt_walk_fn will be called for each btree record, being passed the incore
 * record and @data.  @max_prefetch controls how many inobt records we try to
 * cache ahead of time.
 */
int
xfs_inobt_walk(
        struct xfs_mount        *mp,
        struct xfs_trans        *tp,
        xfs_ino_t               startino,
        unsigned int            flags,
        xfs_inobt_walk_fn       inobt_walk_fn,
        unsigned int            inobt_records,
        void                    *data)
{
        struct xfs_iwalk_ag     iwag = {
                .mp             = mp,
                .tp             = tp,
                .inobt_walk_fn  = inobt_walk_fn,
                .data           = data,
                .startino       = startino,
                .sz_recs        = xfs_inobt_walk_prefetch(inobt_records),
                .pwork          = XFS_PWORK_SINGLE_THREADED,
                .lastino        = NULLFSINO,
        };
        struct xfs_perag        *pag;
        xfs_agnumber_t          agno = XFS_INO_TO_AGNO(mp, startino);
        int                     error;

        ASSERT(agno < mp->m_sb.sb_agcount);
        ASSERT(!(flags & ~XFS_INOBT_WALK_FLAGS_ALL));

        error = xfs_iwalk_alloc(&iwag);
        if (error)
                return error;

        for_each_perag_from(mp, agno, pag) {
                iwag.pag = pag;
                error = xfs_iwalk_ag(&iwag);
                if (error)
                        break;
                iwag.startino = XFS_AGINO_TO_INO(mp, pag->pag_agno + 1, 0);
                if (flags & XFS_INOBT_WALK_SAME_AG)
                        break;
                iwag.pag = NULL;
        }

        if (iwag.pag)
                xfs_perag_put(pag);
        xfs_iwalk_free(&iwag);
        return error;
}