// SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright (C) 2017 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_btree.h"
#include "xfs_rmap.h"
#include "xfs_refcount.h"
#include "scrub/scrub.h"
#include "scrub/common.h"
#include "scrub/btree.h"
#include "xfs_ag.h"

/*
 * Set us up to scrub reference count btrees.
 */
int
xchk_setup_ag_refcountbt(
        struct xfs_scrub        *sc)
{
        return xchk_setup_ag_btree(sc, false);
}

/* Reference count btree scrubber. */

/*
 * Confirming Reference Counts via Reverse Mappings
 *
 * We want to count the reverse mappings overlapping a refcount record
 * (bno, len, refcount), allowing for the possibility that some of the
 * overlap may come from smaller adjoining reverse mappings, while some
 * comes from single extents which overlap the range entirely.  The
 * outer loop is as follows:
 *
 * 1. For all reverse mappings overlapping the refcount extent,
 *    a. If a given rmap completely overlaps, mark it as seen.
 *    b. Otherwise, record the fragment (in agbno order) for later
 *       processing.
 *
 * Once we've seen all the rmaps, we know that for all blocks in the
 * refcount record we want to find $refcount owners and we've already
 * visited $seen extents that overlap all the blocks.  Therefore, we
 * need to find ($refcount - $seen) owners for every block in the
 * extent; call that quantity $target_nr.  Proceed as follows:
 *
 * 2. Pull the first $target_nr fragments from the list; all of them
 *    should start at or before the start of the extent.
 *    Call this subset of fragments the working set.
 * 3. Until there are no more unprocessed fragments,
 *    a. Find the shortest fragments in the set and remove them.
 *    b. Note the block number of the end of these fragments.
 *    c. Pull the same number of fragments from the list.  All of these
 *       fragments should start at the block number recorded in the
 *       previous step.
 *    d. Put those fragments in the set.
 * 4. Check that there are $target_nr fragments remaining in the list,
 *    and that they all end at or beyond the end of the refcount extent.
 *
 * If the refcount is correct, all the check conditions in the algorithm
 * should always hold true.  If not, the refcount is incorrect.
 */
struct xchk_refcnt_frag {
        struct list_head        list;
        struct xfs_rmap_irec    rm;
};

struct xchk_refcnt_check {
        struct xfs_scrub        *sc;
        struct list_head        fragments;

        /* refcount extent we're examining */
        xfs_agblock_t           bno;
        xfs_extlen_t            len;
        xfs_nlink_t             refcount;

        /* number of owners seen */
        xfs_nlink_t             seen;
};

/*
 * Decide if the given rmap is large enough that we can redeem it
 * towards refcount verification now, or if it's a fragment, in
 * which case we'll hang onto it in the hopes that we'll later
 * discover that we've collected exactly the correct number of
 * fragments as the refcountbt says we should have.
 */
STATIC int
xchk_refcountbt_rmap_check(
        struct xfs_btree_cur            *cur,
        const struct xfs_rmap_irec      *rec,
        void                            *priv)
{
        struct xchk_refcnt_check        *refchk = priv;
        struct xchk_refcnt_frag         *frag;
        xfs_agblock_t                   rm_last;
        xfs_agblock_t                   rc_last;
        int                             error = 0;

        if (xchk_should_terminate(refchk->sc, &error))
                return error;

        rm_last = rec->rm_startblock + rec->rm_blockcount - 1;
        rc_last = refchk->bno + refchk->len - 1;

        /* Confirm that a single-owner refc extent is a CoW stage. */
        if (refchk->refcount == 1 && rec->rm_owner != XFS_RMAP_OWN_COW) {
                xchk_btree_xref_set_corrupt(refchk->sc, cur, 0);
                return 0;
        }

        if (rec->rm_startblock <= refchk->bno && rm_last >= rc_last) {
                /*
                 * The rmap overlaps the refcount record, so we can confirm
                 * one refcount owner seen.
                 */
                refchk->seen++;
        } else {
                /*
                 * This rmap covers only part of the refcount record, so
                 * save the fragment for later processing.  If the rmapbt
                 * is healthy each rmap_irec we see will be in agbno order
                 * so we don't need insertion sort here.
                 */
                frag = kmem_alloc(sizeof(struct xchk_refcnt_frag),
                                KM_MAYFAIL);
                if (!frag)
                        return -ENOMEM;
                memcpy(&frag->rm, rec, sizeof(frag->rm));
                list_add_tail(&frag->list, &refchk->fragments);
        }

        return 0;
}

/*
 * Given a bunch of rmap fragments, iterate through them, keeping
 * a running tally of the refcount.  If this ever deviates from
 * what we expect (which is the refcountbt's refcount minus the
 * number of extents that totally covered the refcountbt extent),
 * we have a refcountbt error.
 */
STATIC void
xchk_refcountbt_process_rmap_fragments(
        struct xchk_refcnt_check        *refchk)
{
        struct list_head                worklist;
        struct xchk_refcnt_frag         *frag;
        struct xchk_refcnt_frag         *n;
        xfs_agblock_t                   bno;
        xfs_agblock_t                   rbno;
        xfs_agblock_t                   next_rbno;
        xfs_nlink_t                     nr;
        xfs_nlink_t                     target_nr;

        target_nr = refchk->refcount - refchk->seen;
        if (target_nr == 0)
                return;

        /*
         * There are (refchk->rc.rc_refcount - refchk->nr refcount)
         * references we haven't found yet.  Pull that many off the
         * fragment list and figure out where the smallest rmap ends
         * (and therefore the next rmap should start).  All the rmaps
         * we pull off should start at or before the beginning of the
         * refcount record's range.
         */
        INIT_LIST_HEAD(&worklist);
        rbno = NULLAGBLOCK;

        /* Make sure the fragments actually /are/ in agbno order. */
        bno = 0;
        list_for_each_entry(frag, &refchk->fragments, list) {
                if (frag->rm.rm_startblock < bno)
                        goto done;
                bno = frag->rm.rm_startblock;
        }

        /*
         * Find all the rmaps that start at or before the refc extent,
         * and put them on the worklist.
         */
        nr = 0;
        list_for_each_entry_safe(frag, n, &refchk->fragments, list) {
                if (frag->rm.rm_startblock > refchk->bno || nr > target_nr)
                        break;
                bno = frag->rm.rm_startblock + frag->rm.rm_blockcount;
                if (bno < rbno)
                        rbno = bno;
                list_move_tail(&frag->list, &worklist);
                nr++;
        }

        /*
         * We should have found exactly $target_nr rmap fragments starting
         * at or before the refcount extent.
         */
        if (nr != target_nr)
                goto done;

        while (!list_empty(&refchk->fragments)) {
                /* Discard any fragments ending at rbno from the worklist. */
                nr = 0;
                next_rbno = NULLAGBLOCK;
                list_for_each_entry_safe(frag, n, &worklist, list) {
                        bno = frag->rm.rm_startblock + frag->rm.rm_blockcount;
                        if (bno != rbno) {
                                if (bno < next_rbno)
                                        next_rbno = bno;
                                continue;
                        }
                        list_del(&frag->list);
                        kmem_free(frag);
                        nr++;
                }

                /* Try to add nr rmaps starting at rbno to the worklist. */
                list_for_each_entry_safe(frag, n, &refchk->fragments, list) {
                        bno = frag->rm.rm_startblock + frag->rm.rm_blockcount;
                        if (frag->rm.rm_startblock != rbno)
                                goto done;
                        list_move_tail(&frag->list, &worklist);
                        if (next_rbno > bno)
                                next_rbno = bno;
                        nr--;
                        if (nr == 0)
                                break;
                }

                /*
                 * If we get here and nr > 0, this means that we added fewer
                 * items to the worklist than we discarded because the fragment
                 * list ran out of items.  Therefore, we cannot maintain the
                 * required refcount.  Something is wrong, so we're done.
                 */
                if (nr)
                        goto done;

                rbno = next_rbno;
        }

        /*
         * Make sure the last extent we processed ends at or beyond
         * the end of the refcount extent.
         */
        if (rbno < refchk->bno + refchk->len)
                goto done;

        /* Actually record us having seen the remaining refcount. */
        refchk->seen = refchk->refcount;
done:
        /* Delete fragments and work list. */
        list_for_each_entry_safe(frag, n, &worklist, list) {
                list_del(&frag->list);
                kmem_free(frag);
        }
        list_for_each_entry_safe(frag, n, &refchk->fragments, list) {
                list_del(&frag->list);
                kmem_free(frag);
        }
}

/* Use the rmap entries covering this extent to verify the refcount. */
STATIC void
xchk_refcountbt_xref_rmap(
        struct xfs_scrub                *sc,
        xfs_agblock_t                   bno,
        xfs_extlen_t                    len,
        xfs_nlink_t                     refcount)
{
        struct xchk_refcnt_check        refchk = {
                .sc = sc,
                .bno = bno,
                .len = len,
                .refcount = refcount,
                .seen = 0,
        };
        struct xfs_rmap_irec            low;
        struct xfs_rmap_irec            high;
        struct xchk_refcnt_frag         *frag;
        struct xchk_refcnt_frag         *n;
        int                             error;

        if (!sc->sa.rmap_cur || xchk_skip_xref(sc->sm))
                return;

        /* Cross-reference with the rmapbt to confirm the refcount. */
        memset(&low, 0, sizeof(low));
        low.rm_startblock = bno;
        memset(&high, 0xFF, sizeof(high));
        high.rm_startblock = bno + len - 1;

        INIT_LIST_HEAD(&refchk.fragments);
        error = xfs_rmap_query_range(sc->sa.rmap_cur, &low, &high,
                        &xchk_refcountbt_rmap_check, &refchk);
        if (!xchk_should_check_xref(sc, &error, &sc->sa.rmap_cur))
                goto out_free;

        xchk_refcountbt_process_rmap_fragments(&refchk);
        if (refcount != refchk.seen)
                xchk_btree_xref_set_corrupt(sc, sc->sa.rmap_cur, 0);

out_free:
        list_for_each_entry_safe(frag, n, &refchk.fragments, list) {
                list_del(&frag->list);
                kmem_free(frag);
        }
}

/* Cross-reference with the other btrees. */
STATIC void
xchk_refcountbt_xref(
        struct xfs_scrub        *sc,
        xfs_agblock_t           agbno,
        xfs_extlen_t            len,
        xfs_nlink_t             refcount)
{
        if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
                return;

        xchk_xref_is_used_space(sc, agbno, len);
        xchk_xref_is_not_inode_chunk(sc, agbno, len);
        xchk_refcountbt_xref_rmap(sc, agbno, len, refcount);
}

/* Scrub a refcountbt record. */
STATIC int
xchk_refcountbt_rec(
        struct xchk_btree       *bs,
        const union xfs_btree_rec *rec)
{
        struct xfs_mount        *mp = bs->cur->bc_mp;
        xfs_agblock_t           *cow_blocks = bs->private;
        xfs_agnumber_t          agno = bs->cur->bc_ag.pag->pag_agno;
        xfs_agblock_t           bno;
        xfs_extlen_t            len;
        xfs_nlink_t             refcount;
        bool                    has_cowflag;

        bno = be32_to_cpu(rec->refc.rc_startblock);
        len = be32_to_cpu(rec->refc.rc_blockcount);
        refcount = be32_to_cpu(rec->refc.rc_refcount);

        /* Only CoW records can have refcount == 1. */
        has_cowflag = (bno & XFS_REFC_COW_START);
        if ((refcount == 1 && !has_cowflag) || (refcount != 1 && has_cowflag))
                xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
        if (has_cowflag)
                (*cow_blocks) += len;

        /* Check the extent. */
        bno &= ~XFS_REFC_COW_START;
        if (bno + len <= bno ||
            !xfs_verify_agbno(mp, agno, bno) ||
            !xfs_verify_agbno(mp, agno, bno + len - 1))
                xchk_btree_set_corrupt(bs->sc, bs->cur, 0);

        if (refcount == 0)
                xchk_btree_set_corrupt(bs->sc, bs->cur, 0);

        xchk_refcountbt_xref(bs->sc, bno, len, refcount);

        return 0;
}

/* Make sure we have as many refc blocks as the rmap says. */
STATIC void
xchk_refcount_xref_rmap(
        struct xfs_scrub        *sc,
        xfs_filblks_t           cow_blocks)
{
        xfs_extlen_t            refcbt_blocks = 0;
        xfs_filblks_t           blocks;
        int                     error;

        if (!sc->sa.rmap_cur || xchk_skip_xref(sc->sm))
                return;

        /* Check that we saw as many refcbt blocks as the rmap knows about. */
        error = xfs_btree_count_blocks(sc->sa.refc_cur, &refcbt_blocks);
        if (!xchk_btree_process_error(sc, sc->sa.refc_cur, 0, &error))
                return;
        error = xchk_count_rmap_ownedby_ag(sc, sc->sa.rmap_cur,
                        &XFS_RMAP_OINFO_REFC, &blocks);
        if (!xchk_should_check_xref(sc, &error, &sc->sa.rmap_cur))
                return;
        if (blocks != refcbt_blocks)
                xchk_btree_xref_set_corrupt(sc, sc->sa.rmap_cur, 0);

        /* Check that we saw as many cow blocks as the rmap knows about. */
        error = xchk_count_rmap_ownedby_ag(sc, sc->sa.rmap_cur,
                        &XFS_RMAP_OINFO_COW, &blocks);
        if (!xchk_should_check_xref(sc, &error, &sc->sa.rmap_cur))
                return;
        if (blocks != cow_blocks)
                xchk_btree_xref_set_corrupt(sc, sc->sa.rmap_cur, 0);
}

/* Scrub the refcount btree for some AG. */
int
xchk_refcountbt(
        struct xfs_scrub        *sc)
{
        xfs_agblock_t           cow_blocks = 0;
        int                     error;

        error = xchk_btree(sc, sc->sa.refc_cur, xchk_refcountbt_rec,
                        &XFS_RMAP_OINFO_REFC, &cow_blocks);
        if (error)
                return error;

        xchk_refcount_xref_rmap(sc, cow_blocks);

        return 0;
}

/* xref check that a cow staging extent is marked in the refcountbt. */
void
xchk_xref_is_cow_staging(
        struct xfs_scrub                *sc,
        xfs_agblock_t                   agbno,
        xfs_extlen_t                    len)
{
        struct xfs_refcount_irec        rc;
        bool                            has_cowflag;
        int                             has_refcount;
        int                             error;

        if (!sc->sa.refc_cur || xchk_skip_xref(sc->sm))
                return;

        /* Find the CoW staging extent. */
        error = xfs_refcount_lookup_le(sc->sa.refc_cur,
                        agbno + XFS_REFC_COW_START, &has_refcount);
        if (!xchk_should_check_xref(sc, &error, &sc->sa.refc_cur))
                return;
        if (!has_refcount) {
                xchk_btree_xref_set_corrupt(sc, sc->sa.refc_cur, 0);
                return;
        }

        error = xfs_refcount_get_rec(sc->sa.refc_cur, &rc, &has_refcount);
        if (!xchk_should_check_xref(sc, &error, &sc->sa.refc_cur))
                return;
        if (!has_refcount) {
                xchk_btree_xref_set_corrupt(sc, sc->sa.refc_cur, 0);
                return;
        }

        /* CoW flag must be set, refcount must be 1. */
        has_cowflag = (rc.rc_startblock & XFS_REFC_COW_START);
        if (!has_cowflag || rc.rc_refcount != 1)
                xchk_btree_xref_set_corrupt(sc, sc->sa.refc_cur, 0);

        /* Must be at least as long as what was passed in */
        if (rc.rc_blockcount < len)
                xchk_btree_xref_set_corrupt(sc, sc->sa.refc_cur, 0);
}

/*
 * xref check that the extent is not shared.  Only file data blocks
 * can have multiple owners.
 */
void
xchk_xref_is_not_shared(
        struct xfs_scrub        *sc,
        xfs_agblock_t           agbno,
        xfs_extlen_t            len)
{
        bool                    shared;
        int                     error;

        if (!sc->sa.refc_cur || xchk_skip_xref(sc->sm))
                return;

        error = xfs_refcount_has_record(sc->sa.refc_cur, agbno, len, &shared);
        if (!xchk_should_check_xref(sc, &error, &sc->sa.refc_cur))
                return;
        if (shared)
                xchk_btree_xref_set_corrupt(sc, sc->sa.refc_cur, 0);
}