// SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright (C) 2016 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_alloc.h"
#include "xfs_errortag.h"
#include "xfs_error.h"
#include "xfs_trace.h"
#include "xfs_trans.h"
#include "xfs_rmap_btree.h"
#include "xfs_btree.h"
#include "xfs_refcount_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_ag.h"
#include "xfs_ag_resv.h"

/*
 * Per-AG Block Reservations
 *
 * For some kinds of allocation group metadata structures, it is advantageous
 * to reserve a small number of blocks in each AG so that future expansions of
 * that data structure do not encounter ENOSPC because errors during a btree
 * split cause the filesystem to go offline.
 *
 * Prior to the introduction of reflink, this wasn't an issue because the free
 * space btrees maintain a reserve of space (the AGFL) to handle any expansion
 * that may be necessary; and allocations of other metadata (inodes, BMBT,
 * dir/attr) aren't restricted to a single AG.  However, with reflink it is
 * possible to allocate all the space in an AG, have subsequent reflink/CoW
 * activity expand the refcount btree, and discover that there's no space left
 * to handle that expansion.  Since we can calculate the maximum size of the
 * refcount btree, we can reserve space for it and avoid ENOSPC.
 *
 * Handling per-AG reservations consists of three changes to the allocator's
 * behavior:  First, because these reservations are always needed, we decrease
 * the ag_max_usable counter to reflect the size of the AG after the reserved
 * blocks are taken.  Second, the reservations must be reflected in the
 * fdblocks count to maintain proper accounting.  Third, each AG must maintain
 * its own reserved block counter so that we can calculate the amount of space
 * that must remain free to maintain the reservations.  Fourth, the "remaining
 * reserved blocks" count must be used when calculating the length of the
 * longest free extent in an AG and to clamp maxlen in the per-AG allocation
 * functions.  In other words, we maintain a virtual allocation via in-core
 * accounting tricks so that we don't have to clean up after a crash. :)
 *
 * Reserved blocks can be managed by passing one of the enum xfs_ag_resv_type
 * values via struct xfs_alloc_arg or directly to the xfs_free_extent
 * function.  It might seem a little funny to maintain a reservoir of blocks
 * to feed another reservoir, but the AGFL only holds enough blocks to get
 * through the next transaction.  The per-AG reservation is to ensure (we
 * hope) that each AG never runs out of blocks.  Each data structure wanting
 * to use the reservation system should update ask/used in xfs_ag_resv_init.
 */

/*
 * Are we critically low on blocks?  For now we'll define that as the number
 * of blocks we can get our hands on being less than 10% of what we reserved
 * or less than some arbitrary number (maximum btree height).
 */
bool
xfs_ag_resv_critical(
        struct xfs_perag                *pag,
        enum xfs_ag_resv_type           type)
{
        xfs_extlen_t                    avail;
        xfs_extlen_t                    orig;

        switch (type) {
        case XFS_AG_RESV_METADATA:
                avail = pag->pagf_freeblks - pag->pag_rmapbt_resv.ar_reserved;
                orig = pag->pag_meta_resv.ar_asked;
                break;
        case XFS_AG_RESV_RMAPBT:
                avail = pag->pagf_freeblks + pag->pagf_flcount -
                        pag->pag_meta_resv.ar_reserved;
                orig = pag->pag_rmapbt_resv.ar_asked;
                break;
        default:
                ASSERT(0);
                return false;
        }

        trace_xfs_ag_resv_critical(pag, type, avail);

        /* Critically low if less than 10% or max btree height remains. */
        return XFS_TEST_ERROR(avail < orig / 10 ||
                              avail < pag->pag_mount->m_agbtree_maxlevels,
                        pag->pag_mount, XFS_ERRTAG_AG_RESV_CRITICAL);
}

/*
 * How many blocks are reserved but not used, and therefore must not be
 * allocated away?
 */
xfs_extlen_t
xfs_ag_resv_needed(
        struct xfs_perag                *pag,
        enum xfs_ag_resv_type           type)
{
        xfs_extlen_t                    len;

        len = pag->pag_meta_resv.ar_reserved + pag->pag_rmapbt_resv.ar_reserved;
        switch (type) {
        case XFS_AG_RESV_METADATA:
        case XFS_AG_RESV_RMAPBT:
                len -= xfs_perag_resv(pag, type)->ar_reserved;
                break;
        case XFS_AG_RESV_NONE:
                /* empty */
                break;
        default:
                ASSERT(0);
        }

        trace_xfs_ag_resv_needed(pag, type, len);

        return len;
}

/* Clean out a reservation */
static int
__xfs_ag_resv_free(
        struct xfs_perag                *pag,
        enum xfs_ag_resv_type           type)
{
        struct xfs_ag_resv              *resv;
        xfs_extlen_t                    oldresv;
        int                             error;

        trace_xfs_ag_resv_free(pag, type, 0);

        resv = xfs_perag_resv(pag, type);
        if (pag->pag_agno == 0)
                pag->pag_mount->m_ag_max_usable += resv->ar_asked;
        /*
         * RMAPBT blocks come from the AGFL and AGFL blocks are always
         * considered "free", so whatever was reserved at mount time must be
         * given back at umount.
         */
        if (type == XFS_AG_RESV_RMAPBT)
                oldresv = resv->ar_orig_reserved;
        else
                oldresv = resv->ar_reserved;
        error = xfs_mod_fdblocks(pag->pag_mount, oldresv, true);
        resv->ar_reserved = 0;
        resv->ar_asked = 0;
        resv->ar_orig_reserved = 0;

        if (error)
                trace_xfs_ag_resv_free_error(pag->pag_mount, pag->pag_agno,
                                error, _RET_IP_);
        return error;
}

/* Free a per-AG reservation. */
int
xfs_ag_resv_free(
        struct xfs_perag                *pag)
{
        int                             error;
        int                             err2;

        error = __xfs_ag_resv_free(pag, XFS_AG_RESV_RMAPBT);
        err2 = __xfs_ag_resv_free(pag, XFS_AG_RESV_METADATA);
        if (err2 && !error)
                error = err2;
        return error;
}

static int
__xfs_ag_resv_init(
        struct xfs_perag                *pag,
        enum xfs_ag_resv_type           type,
        xfs_extlen_t                    ask,
        xfs_extlen_t                    used)
{
        struct xfs_mount                *mp = pag->pag_mount;
        struct xfs_ag_resv              *resv;
        int                             error;
        xfs_extlen_t                    hidden_space;

        if (used > ask)
                ask = used;

        switch (type) {
        case XFS_AG_RESV_RMAPBT:
                /*
                 * Space taken by the rmapbt is not subtracted from fdblocks
                 * because the rmapbt lives in the free space.  Here we must
                 * subtract the entire reservation from fdblocks so that we
                 * always have blocks available for rmapbt expansion.
                 */
                hidden_space = ask;
                break;
        case XFS_AG_RESV_METADATA:
                /*
                 * Space taken by all other metadata btrees are accounted
                 * on-disk as used space.  We therefore only hide the space
                 * that is reserved but not used by the trees.
                 */
                hidden_space = ask - used;
                break;
        default:
                ASSERT(0);
                return -EINVAL;
        }

        if (XFS_TEST_ERROR(false, mp, XFS_ERRTAG_AG_RESV_FAIL))
                error = -ENOSPC;
        else
                error = xfs_mod_fdblocks(mp, -(int64_t)hidden_space, true);
        if (error) {
                trace_xfs_ag_resv_init_error(pag->pag_mount, pag->pag_agno,
                                error, _RET_IP_);
                xfs_warn(mp,
"Per-AG reservation for AG %u failed.  Filesystem may run out of space.",
                                pag->pag_agno);
                return error;
        }

        /*
         * Reduce the maximum per-AG allocation length by however much we're
         * trying to reserve for an AG.  Since this is a filesystem-wide
         * counter, we only make the adjustment for AG 0.  This assumes that
         * there aren't any AGs hungrier for per-AG reservation than AG 0.
         */
        if (pag->pag_agno == 0)
                mp->m_ag_max_usable -= ask;

        resv = xfs_perag_resv(pag, type);
        resv->ar_asked = ask;
        resv->ar_orig_reserved = hidden_space;
        resv->ar_reserved = ask - used;

        trace_xfs_ag_resv_init(pag, type, ask);
        return 0;
}

/* Create a per-AG block reservation. */
int
xfs_ag_resv_init(
        struct xfs_perag                *pag,
        struct xfs_trans                *tp)
{
        struct xfs_mount                *mp = pag->pag_mount;
        xfs_extlen_t                    ask;
        xfs_extlen_t                    used;
        int                             error = 0, error2;
        bool                            has_resv = false;

        /* Create the metadata reservation. */
        if (pag->pag_meta_resv.ar_asked == 0) {
                ask = used = 0;

                error = xfs_refcountbt_calc_reserves(mp, tp, pag, &ask, &used);
                if (error)
                        goto out;

                error = xfs_finobt_calc_reserves(mp, tp, pag, &ask, &used);
                if (error)
                        goto out;

                error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
                                ask, used);
                if (error) {
                        /*
                         * Because we didn't have per-AG reservations when the
                         * finobt feature was added we might not be able to
                         * reserve all needed blocks.  Warn and fall back to the
                         * old and potentially buggy code in that case, but
                         * ensure we do have the reservation for the refcountbt.
                         */
                        ask = used = 0;

                        mp->m_finobt_nores = true;

                        error = xfs_refcountbt_calc_reserves(mp, tp, pag, &ask,
                                        &used);
                        if (error)
                                goto out;

                        error = __xfs_ag_resv_init(pag, XFS_AG_RESV_METADATA,
                                        ask, used);
                        if (error)
                                goto out;
                }
                if (ask)
                        has_resv = true;
        }

        /* Create the RMAPBT metadata reservation */
        if (pag->pag_rmapbt_resv.ar_asked == 0) {
                ask = used = 0;

                error = xfs_rmapbt_calc_reserves(mp, tp, pag, &ask, &used);
                if (error)
                        goto out;

                error = __xfs_ag_resv_init(pag, XFS_AG_RESV_RMAPBT, ask, used);
                if (error)
                        goto out;
                if (ask)
                        has_resv = true;
        }

out:
        /*
         * Initialize the pagf if we have at least one active reservation on the
         * AG. This may have occurred already via reservation calculation, but
         * fall back to an explicit init to ensure the in-core allocbt usage
         * counters are initialized as soon as possible. This is important
         * because filesystems with large perag reservations are susceptible to
         * free space reservation problems that the allocbt counter is used to
         * address.
         */
        if (has_resv) {
                error2 = xfs_alloc_pagf_init(mp, tp, pag->pag_agno, 0);
                if (error2)
                        return error2;

                /*
                 * If there isn't enough space in the AG to satisfy the
                 * reservation, let the caller know that there wasn't enough
                 * space.  Callers are responsible for deciding what to do
                 * next, since (in theory) we can stumble along with
                 * insufficient reservation if data blocks are being freed to
                 * replenish the AG's free space.
                 */
                if (!error &&
                    xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved +
                    xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved >
                    pag->pagf_freeblks + pag->pagf_flcount)
                        error = -ENOSPC;
        }

        return error;
}

/* Allocate a block from the reservation. */
void
xfs_ag_resv_alloc_extent(
        struct xfs_perag                *pag,
        enum xfs_ag_resv_type           type,
        struct xfs_alloc_arg            *args)
{
        struct xfs_ag_resv              *resv;
        xfs_extlen_t                    len;
        uint                            field;

        trace_xfs_ag_resv_alloc_extent(pag, type, args->len);

        switch (type) {
        case XFS_AG_RESV_AGFL:
                return;
        case XFS_AG_RESV_METADATA:
        case XFS_AG_RESV_RMAPBT:
                resv = xfs_perag_resv(pag, type);
                break;
        default:
                ASSERT(0);
                fallthrough;
        case XFS_AG_RESV_NONE:
                field = args->wasdel ? XFS_TRANS_SB_RES_FDBLOCKS :
                                       XFS_TRANS_SB_FDBLOCKS;
                xfs_trans_mod_sb(args->tp, field, -(int64_t)args->len);
                return;
        }

        len = min_t(xfs_extlen_t, args->len, resv->ar_reserved);
        resv->ar_reserved -= len;
        if (type == XFS_AG_RESV_RMAPBT)
                return;
        /* Allocations of reserved blocks only need on-disk sb updates... */
        xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_RES_FDBLOCKS, -(int64_t)len);
        /* ...but non-reserved blocks need in-core and on-disk updates. */
        if (args->len > len)
                xfs_trans_mod_sb(args->tp, XFS_TRANS_SB_FDBLOCKS,
                                -((int64_t)args->len - len));
}

/* Free a block to the reservation. */
void
xfs_ag_resv_free_extent(
        struct xfs_perag                *pag,
        enum xfs_ag_resv_type           type,
        struct xfs_trans                *tp,
        xfs_extlen_t                    len)
{
        xfs_extlen_t                    leftover;
        struct xfs_ag_resv              *resv;

        trace_xfs_ag_resv_free_extent(pag, type, len);

        switch (type) {
        case XFS_AG_RESV_AGFL:
                return;
        case XFS_AG_RESV_METADATA:
        case XFS_AG_RESV_RMAPBT:
                resv = xfs_perag_resv(pag, type);
                break;
        default:
                ASSERT(0);
                fallthrough;
        case XFS_AG_RESV_NONE:
                xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, (int64_t)len);
                return;
        }

        leftover = min_t(xfs_extlen_t, len, resv->ar_asked - resv->ar_reserved);
        resv->ar_reserved += leftover;
        if (type == XFS_AG_RESV_RMAPBT)
                return;
        /* Freeing into the reserved pool only requires on-disk update... */
        xfs_trans_mod_sb(tp, XFS_TRANS_SB_RES_FDBLOCKS, len);
        /* ...but freeing beyond that requires in-core and on-disk update. */
        if (len > leftover)
                xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, len - leftover);
}