LU-8895 target: limit grant allocation

[fs/lustre-release.git] / lustre / target / tgt_grant.c

/*
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 *
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 only,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License version 2 for more details (a copy is included
 * in the LICENSE file that accompanied this code).
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; If not, see
 * http://www.gnu.org/licenses/gpl-2.0.html
 *
 * GPL HEADER END
 */
/*
 * Copyright (c) 2009, 2010, Oracle and/or its affiliates. All rights reserved.
 * Use is subject to license terms.
 *
 * Copyright (c) 2012, 2016, Intel Corporation.
 */
/*
 * lustre/target/tgt_grant.c
 *
 * This file provides code related to grant space management on Lustre Targets
 * (OSTs and MDTs). Grant is a mechanism used by client nodes to reserve disk
 * space on a target for the data writeback cache. The Lustre client is thus
 * assured that enough space will be available when flushing dirty pages
 * asynchronously. Each client node is granted an initial amount of reserved
 * space at connect time and gets additional space back from target in bulk
 * write reply.
 *
 * We actually support three different cases:
 * - The client supports the new grant parameters (i.e. OBD_CONNECT_GRANT_PARAM)
 *   which means that all grant overhead calculation happens on the client side.
 *   The server reports at connect time the backend filesystem block size, the
 *   maximum extent size as well as the extent insertion cost and it is then up
 *   to the osc layer to the track dirty extents and consume grant accordingly
 *   (see osc_cache.c). In each bulk write request, the client provides how much
 *   grant space was consumed for this RPC.
 * - The client does not support OBD_CONNECT_GRANT_PARAM and always assumes a
 *   a backend file system block size of 4KB. We then have two cases:
 *   - If the block size is really 4KB, then the client can deal with grant
 *     allocation for partial block writes, but won't take extent insertion cost
 *     into account. For such clients, we inflate grant by 100% on the server
 *     side. It means that when 32MB of grant is hold by the client, 64MB of
 *     grant space is actually reserved on the server. All grant counters
 *     provided by such a client are inflated by 100%.
 *   - The backend filesystem block size is bigger than 4KB, which isn't
 *     supported by the client. In this case, we emulate a 4KB block size and
 *     consume one block size on the server for each 4KB of grant returned to
 *     client. With a 128KB blocksize, it means that 32MB dirty pages of 4KB
 *     on the client will actually consume 1GB of grant on the server.
 *     All grant counters provided by such a client are inflated by the block
 *     size ratio.
 *
 * This file handles the core logic for:
 * - grant allocation strategy
 * - maintaining per-client as well as global grant space accounting
 * - processing grant information packed in incoming requests
 * - allocating server-side grant space for synchronous write RPCs which did not
 *   consume grant on the client side (OBD_BRW_FROM_GRANT flag not set). If not
 *   enough space is available, such RPCs fail with ENOSPC
 *
 * Author: Johann Lombardi <johann.lombardi@intel.com>
 */

#define DEBUG_SUBSYSTEM S_FILTER

#include <obd.h>
#include <obd_class.h>

#include "tgt_internal.h"

/* Clients typically hold 2x their max_rpcs_in_flight of grant space */
#define TGT_GRANT_SHRINK_LIMIT(exp)     (2ULL * 8 * exp_max_brw_size(exp))

/* Helpers to inflate/deflate grants for clients that do not support the grant
 * parameters */
static inline u64 tgt_grant_inflate(struct tg_grants_data *tgd, u64 val)
{
        if (tgd->tgd_blockbits > COMPAT_BSIZE_SHIFT)
                /* Client does not support such large block size, grant
                 * is thus inflated. We already significantly overestimate
                 * overhead, no need to add the extent tax in this case */
                return val << (tgd->tgd_blockbits - COMPAT_BSIZE_SHIFT);
        return val;
}

/* Companion of tgt_grant_inflate() */
static inline u64 tgt_grant_deflate(struct tg_grants_data *tgd, u64 val)
{
        if (tgd->tgd_blockbits > COMPAT_BSIZE_SHIFT)
                return val >> (tgd->tgd_blockbits - COMPAT_BSIZE_SHIFT);
        return val;
}

/* Grant chunk is used as a unit for grant allocation. It should be inflated
 * if the client does not support the grant paramaters.
 * Check connection flag against \a data if not NULL. This is used during
 * connection creation where exp->exp_connect_data isn't populated yet */
static inline u64 tgt_grant_chunk(struct obd_export *exp,
                                  struct lu_target *lut,
                                  struct obd_connect_data *data)
{
        struct tg_grants_data *tgd = &lut->lut_tgd;
        u64 chunk = exp_max_brw_size(exp);
        u64 tax;

        if (exp->exp_obd->obd_self_export == exp)
                /* Grant enough space to handle a big precreate request */
                return OST_MAX_PRECREATE * lut->lut_dt_conf.ddp_inodespace / 2;

        if ((data == NULL && !(exp_grant_param_supp(exp))) ||
            (data != NULL && !OCD_HAS_FLAG(data, GRANT_PARAM)))
                /* Try to grant enough space to send 2 full-size RPCs */
                return tgt_grant_inflate(tgd, chunk) << 1;

        /* Try to return enough to send two full-size RPCs
         * = 2 * (BRW_size + #extents_in_BRW * grant_tax) */
        tax = 1ULL << tgd->tgd_blockbits;            /* block size */
        tax *= lut->lut_dt_conf.ddp_max_extent_blks; /* max extent size */
        tax = (chunk + tax - 1) / tax;               /* #extents in a RPC */
        tax *= lut->lut_dt_conf.ddp_extent_tax;      /* extent tax for a RPC */
        chunk = (chunk + tax) * 2;                   /* we said two full RPCs */
        return chunk;
}

static int tgt_check_export_grants(struct obd_export *exp, u64 *dirty,
                                   u64 *pending, u64 *granted, u64 maxsize)
{
        struct tg_export_data *ted = &exp->exp_target_data;
        int level = D_CACHE;

        if (ted->ted_grant < 0 || ted->ted_pending < 0 || ted->ted_dirty < 0)
                level = D_ERROR;
        CDEBUG_LIMIT(level, "%s: cli %s/%p dirty %ld pend %ld grant %ld\n",
                     exp->exp_obd->obd_name, exp->exp_client_uuid.uuid, exp,
                     ted->ted_dirty, ted->ted_pending, ted->ted_grant);

        if (ted->ted_grant + ted->ted_pending > maxsize) {
                CERROR("%s: cli %s/%p ted_grant(%ld) + ted_pending(%ld)"
                        " > maxsize(%llu)\n", exp->exp_obd->obd_name,
                        exp->exp_client_uuid.uuid, exp, ted->ted_grant,
                        ted->ted_pending, maxsize);
                return -EFAULT;
        }
        if (ted->ted_dirty > maxsize) {
                CERROR("%s: cli %s/%p ted_dirty(%ld) > maxsize(%llu)\n",
                        exp->exp_obd->obd_name, exp->exp_client_uuid.uuid,
                        exp, ted->ted_dirty, maxsize);
                return -EFAULT;
        }
        *granted += ted->ted_grant + ted->ted_pending;
        *pending += ted->ted_pending;
        *dirty += ted->ted_dirty;
        return 0;
}

/**
 * Perform extra sanity checks for grant accounting.
 *
 * This function scans the export list, sanity checks per-export grant counters
 * and verifies accuracy of global grant accounting. If an inconsistency is
 * found, a CERROR is printed with the function name \func that was passed as
 * argument. LBUG is only called in case of serious counter corruption (i.e.
 * value larger than the device size).
 * Those sanity checks can be pretty expensive and are disabled if the OBD
 * device has more than 100 connected exports.
 *
 * \param[in] obd       OBD device for which grant accounting should be
 *                      verified
 * \param[in] func      caller's function name
 */
void tgt_grant_sanity_check(struct obd_device *obd, const char *func)
{
        struct lu_target *lut = obd->u.obt.obt_lut;
        struct tg_grants_data *tgd = &lut->lut_tgd;
        struct obd_export *exp;
        struct tg_export_data *ted;
        u64                maxsize;
        u64                tot_dirty = 0;
        u64                tot_pending = 0;
        u64                tot_granted = 0;
        u64                fo_tot_granted;
        u64                fo_tot_pending;
        u64                fo_tot_dirty;
        int                error;

        if (list_empty(&obd->obd_exports))
                return;

        /* We don't want to do this for large machines that do lots of
         * mounts or unmounts.  It burns... */
        if (obd->obd_num_exports > 100)
                return;

        maxsize = tgd->tgd_osfs.os_blocks << tgd->tgd_blockbits;

        spin_lock(&obd->obd_dev_lock);
        spin_lock(&tgd->tgd_grant_lock);
        exp = obd->obd_self_export;
        ted = &exp->exp_target_data;
        CDEBUG(D_CACHE, "%s: processing self export: %ld %ld "
               "%ld\n", obd->obd_name, ted->ted_grant,
               ted->ted_pending, ted->ted_dirty);
        tot_granted += ted->ted_grant + ted->ted_pending;
        tot_pending += ted->ted_pending;
        tot_dirty += ted->ted_dirty;

        list_for_each_entry(exp, &obd->obd_exports, exp_obd_chain) {
                error = tgt_check_export_grants(exp, &tot_dirty, &tot_pending,
                                                &tot_granted, maxsize);
                if (error < 0) {
                        spin_unlock(&obd->obd_dev_lock);
                        spin_unlock(&tgd->tgd_grant_lock);
                        LBUG();
                }
        }

        /* exports about to be unlinked should also be taken into account since
         * they might still hold pending grant space to be released at
         * commit time */
        list_for_each_entry(exp, &obd->obd_unlinked_exports, exp_obd_chain) {
                error = tgt_check_export_grants(exp, &tot_dirty, &tot_pending,
                                                &tot_granted, maxsize);
                if (error < 0) {
                        spin_unlock(&obd->obd_dev_lock);
                        spin_unlock(&tgd->tgd_grant_lock);
                        LBUG();
                }
        }

        fo_tot_granted = tgd->tgd_tot_granted;
        fo_tot_pending = tgd->tgd_tot_pending;
        fo_tot_dirty = tgd->tgd_tot_dirty;
        spin_unlock(&obd->obd_dev_lock);
        spin_unlock(&tgd->tgd_grant_lock);

        if (tot_granted != fo_tot_granted)
                CERROR("%s: tot_granted %llu != fo_tot_granted %llu\n",
                       func, tot_granted, fo_tot_granted);
        if (tot_pending != fo_tot_pending)
                CERROR("%s: tot_pending %llu != fo_tot_pending %llu\n",
                       func, tot_pending, fo_tot_pending);
        if (tot_dirty != fo_tot_dirty)
                CERROR("%s: tot_dirty %llu != fo_tot_dirty %llu\n",
                       func, tot_dirty, fo_tot_dirty);
        if (tot_pending > tot_granted)
                CERROR("%s: tot_pending %llu > tot_granted %llu\n",
                       func, tot_pending, tot_granted);
        if (tot_granted > maxsize)
                CERROR("%s: tot_granted %llu > maxsize %llu\n",
                       func, tot_granted, maxsize);
        if (tot_dirty > maxsize)
                CERROR("%s: tot_dirty %llu > maxsize %llu\n",
                       func, tot_dirty, maxsize);
}
EXPORT_SYMBOL(tgt_grant_sanity_check);

/**
 * Get file system statistics of target.
 *
 * Helper function for statfs(), also used by grant code.
 * Implements caching for statistics to avoid calling OSD device each time.
 *
 * \param[in]  env        execution environment
 * \param[in]  lut        LU target
 * \param[out] osfs       statistic data to return
 * \param[in]  max_age    maximum age for cached data
 * \param[in]  from_cache show that data was get from cache or not
 *
 * \retval              0 if successful
 * \retval              negative value on error
 */
int tgt_statfs_internal(const struct lu_env *env, struct lu_target *lut,
                        struct obd_statfs *osfs, __u64 max_age, int *from_cache)
{
        struct tg_grants_data *tgd = &lut->lut_tgd;
        int rc = 0;
        ENTRY;

        spin_lock(&tgd->tgd_osfs_lock);
        if (cfs_time_before_64(tgd->tgd_osfs_age, max_age) || max_age == 0) {
                u64 unstable;

                /* statfs data are too old, get up-to-date one.
                 * we must be cautious here since multiple threads might be
                 * willing to update statfs data concurrently and we must
                 * grant that cached statfs data are always consistent */

                if (tgd->tgd_statfs_inflight == 0)
                        /* clear inflight counter if no users, although it would
                         * take a while to overflow this 64-bit counter ... */
                        tgd->tgd_osfs_inflight = 0;
                /* notify tgt_grant_commit() that we want to track writes
                 * completed as of now */
                tgd->tgd_statfs_inflight++;
                /* record value of inflight counter before running statfs to
                 * compute the diff once statfs is completed */
                unstable = tgd->tgd_osfs_inflight;
                spin_unlock(&tgd->tgd_osfs_lock);

                /* statfs can sleep ... hopefully not for too long since we can
                 * call it fairly often as space fills up */
                rc = dt_statfs(env, lut->lut_bottom, osfs);
                if (unlikely(rc))
                        GOTO(out, rc);

                osfs->os_namelen = min_t(__u32, osfs->os_namelen, NAME_MAX);

                spin_lock(&tgd->tgd_grant_lock);
                spin_lock(&tgd->tgd_osfs_lock);
                /* calculate how much space was written while we released the
                 * tgd_osfs_lock */
                unstable = tgd->tgd_osfs_inflight - unstable;
                tgd->tgd_osfs_unstable = 0;
                if (unstable) {
                        /* some writes committed while we were running statfs
                         * w/o the tgd_osfs_lock. Those ones got added to
                         * the cached statfs data that we are about to crunch.
                         * Take them into account in the new statfs data */
                        osfs->os_bavail -= min_t(u64, osfs->os_bavail,
                                               unstable >> tgd->tgd_blockbits);
                        /* However, we don't really know if those writes got
                         * accounted in the statfs call, so tell
                         * tgt_grant_space_left() there is some uncertainty
                         * on the accounting of those writes.
                         * The purpose is to prevent spurious error messages in
                         * tgt_grant_space_left() since those writes might be
                         * accounted twice. */
                        tgd->tgd_osfs_unstable += unstable;
                }
                /* similarly, there is some uncertainty on write requests
                 * between prepare & commit */
                tgd->tgd_osfs_unstable += tgd->tgd_tot_pending;
                spin_unlock(&tgd->tgd_grant_lock);

                /* finally udpate cached statfs data */
                tgd->tgd_osfs = *osfs;
                tgd->tgd_osfs_age = cfs_time_current_64();

                tgd->tgd_statfs_inflight--; /* stop tracking */
                if (tgd->tgd_statfs_inflight == 0)
                        tgd->tgd_osfs_inflight = 0;
                spin_unlock(&tgd->tgd_osfs_lock);

                if (from_cache)
                        *from_cache = 0;
        } else {
                /* use cached statfs data */
                *osfs = tgd->tgd_osfs;
                spin_unlock(&tgd->tgd_osfs_lock);
                if (from_cache)
                        *from_cache = 1;
        }
        GOTO(out, rc);

out:
        return rc;
}
EXPORT_SYMBOL(tgt_statfs_internal);

/**
 * Update cached statfs information from the OSD layer
 *
 * Refresh statfs information cached in tgd::tgd_osfs if the cache is older
 * than 1s or if force is set. The OSD layer is in charge of estimating data &
 * metadata overhead.
 * This function can sleep so it should not be called with any spinlock held.
 *
 * \param[in] env               LU environment passed by the caller
 * \param[in] exp               export used to print client info in debug
 *                              messages
 * \param[in] force             force a refresh of statfs information
 * \param[out] from_cache       returns whether the statfs information are
 *                              taken from cache
 */
static void tgt_grant_statfs(const struct lu_env *env, struct obd_export *exp,
                             int force, int *from_cache)
{
        struct obd_device       *obd = exp->exp_obd;
        struct lu_target        *lut = obd->u.obt.obt_lut;
        struct tg_grants_data   *tgd = &lut->lut_tgd;
        struct tgt_thread_info  *tti;
        struct obd_statfs       *osfs;
        __u64                    max_age;
        int                      rc;

        if (force)
                max_age = 0; /* get fresh statfs data */
        else
                max_age = cfs_time_shift_64(-OBD_STATFS_CACHE_SECONDS);

        tti = tgt_th_info(env);
        osfs = &tti->tti_u.osfs;
        rc = tgt_statfs_internal(env, lut, osfs, max_age, from_cache);
        if (unlikely(rc)) {
                if (from_cache)
                        *from_cache = 0;
                return;
        }

        CDEBUG(D_CACHE, "%s: cli %s/%p free: %llu avail: %llu\n",
               obd->obd_name, exp->exp_client_uuid.uuid, exp,
               osfs->os_bfree << tgd->tgd_blockbits,
               osfs->os_bavail << tgd->tgd_blockbits);
}

/**
 * Figure out how much space is available on the backend filesystem after
 * removing grant space already booked by clients.
 *
 * This is done by accessing cached statfs data previously populated by
 * tgt_grant_statfs(), from which we withdraw the space already granted to
 * clients and the reserved space.
 * Caller must hold tgd_grant_lock spinlock.
 *
 * \param[in] exp       export associated with the device for which the amount
 *                      of available space is requested
 * \retval              amount of non-allocated space, in bytes
 */
static u64 tgt_grant_space_left(struct obd_export *exp)
{
        struct obd_device       *obd = exp->exp_obd;
        struct lu_target        *lut = obd->u.obt.obt_lut;
        struct tg_grants_data   *tgd = &lut->lut_tgd;
        u64                      tot_granted;
        u64                      left;
        u64                      avail;
        u64                      unstable;
        u64                      reserved;

        ENTRY;
        assert_spin_locked(&tgd->tgd_grant_lock);

        spin_lock(&tgd->tgd_osfs_lock);
        /* get available space from cached statfs data */
        left = tgd->tgd_osfs.os_bavail << tgd->tgd_blockbits;
        unstable = tgd->tgd_osfs_unstable; /* those might be accounted twice */
        spin_unlock(&tgd->tgd_osfs_lock);

        reserved = left * tgd->tgd_reserved_pcnt / 100;
        tot_granted = tgd->tgd_tot_granted + reserved;

        if (left < tot_granted) {
                int mask = (left + unstable <
                            tot_granted - tgd->tgd_tot_pending) ?
                            D_ERROR : D_CACHE;

                CDEBUG_LIMIT(mask, "%s: cli %s/%p left %llu < tot_grant "
                             "%llu unstable %llu pending %llu "
                             "dirty %llu\n",
                             obd->obd_name, exp->exp_client_uuid.uuid, exp,
                             left, tot_granted, unstable,
                             tgd->tgd_tot_pending,
                             tgd->tgd_tot_dirty);
                RETURN(0);
        }

        avail = left;
        /* Withdraw space already granted to clients */
        left -= tot_granted;

        /* Align left on block size */
        left &= ~((1ULL << tgd->tgd_blockbits) - 1);

        CDEBUG(D_CACHE, "%s: cli %s/%p avail %llu left %llu unstable "
               "%llu tot_grant %llu pending %llu\n", obd->obd_name,
               exp->exp_client_uuid.uuid, exp, avail, left, unstable,
               tot_granted, tgd->tgd_tot_pending);

        RETURN(left);
}

/**
 * Process grant information from obdo structure packed in incoming BRW
 * and inflate grant counters if required.
 *
 * Grab the dirty and seen grant announcements from the incoming obdo and
 * inflate all grant counters passed in the request if the client does not
 * support the grant parameters.
 * We will later calculate the client's new grant and return it.
 * Caller must hold tgd_grant_lock spinlock.
 *
 * \param[in] env       LU environment supplying osfs storage
 * \param[in] exp       export for which we received the request
 * \param[in,out] oa    incoming obdo sent by the client
 */
static void tgt_grant_incoming(const struct lu_env *env, struct obd_export *exp,
                               struct obdo *oa, long chunk)
{
        struct tg_export_data   *ted = &exp->exp_target_data;
        struct obd_device       *obd = exp->exp_obd;
        struct tg_grants_data   *tgd = &obd->u.obt.obt_lut->lut_tgd;
        long                     dirty;
        long                     dropped;
        ENTRY;

        assert_spin_locked(&tgd->tgd_grant_lock);

        if ((oa->o_valid & (OBD_MD_FLBLOCKS|OBD_MD_FLGRANT)) !=
                                        (OBD_MD_FLBLOCKS|OBD_MD_FLGRANT)) {
                oa->o_valid &= ~OBD_MD_FLGRANT;
                RETURN_EXIT;
        }

        /* Add some margin, since there is a small race if other RPCs arrive
         * out-or-order and have already consumed some grant.  We want to
         * leave this here in case there is a large error in accounting. */
        CDEBUG(D_CACHE,
               "%s: cli %s/%p reports grant %llu dropped %u, local %lu\n",
               obd->obd_name, exp->exp_client_uuid.uuid, exp, oa->o_grant,
               oa->o_dropped, ted->ted_grant);

        if ((long long)oa->o_dirty < 0)
                oa->o_dirty = 0;

        /* inflate grant counters if required */
        if (!exp_grant_param_supp(exp)) {
                oa->o_grant     = tgt_grant_inflate(tgd, oa->o_grant);
                oa->o_dirty     = tgt_grant_inflate(tgd, oa->o_dirty);
                oa->o_dropped   = tgt_grant_inflate(tgd, (u64)oa->o_dropped);
                oa->o_undirty   = tgt_grant_inflate(tgd, oa->o_undirty);
        }

        dirty = oa->o_dirty;
        dropped = oa->o_dropped;

        /* Update our accounting now so that statfs takes it into account.
         * Note that ted_dirty is only approximate and can become incorrect
         * if RPCs arrive out-of-order.  No important calculations depend
         * on ted_dirty however, but we must check sanity to not assert. */
        if (dirty > ted->ted_grant + 4 * chunk)
                dirty = ted->ted_grant + 4 * chunk;
        tgd->tgd_tot_dirty += dirty - ted->ted_dirty;
        if (ted->ted_grant < dropped) {
                CDEBUG(D_CACHE,
                       "%s: cli %s/%p reports %lu dropped > grant %lu\n",
                       obd->obd_name, exp->exp_client_uuid.uuid, exp, dropped,
                       ted->ted_grant);
                dropped = 0;
        }
        if (tgd->tgd_tot_granted < dropped) {
                CERROR("%s: cli %s/%p reports %lu dropped > tot_grant %llu\n",
                       obd->obd_name, exp->exp_client_uuid.uuid, exp,
                       dropped, tgd->tgd_tot_granted);
                dropped = 0;
        }
        tgd->tgd_tot_granted -= dropped;
        ted->ted_grant -= dropped;
        ted->ted_dirty = dirty;

        if (ted->ted_dirty < 0 || ted->ted_grant < 0 || ted->ted_pending < 0) {
                CERROR("%s: cli %s/%p dirty %ld pend %ld grant %ld\n",
                       obd->obd_name, exp->exp_client_uuid.uuid, exp,
                       ted->ted_dirty, ted->ted_pending, ted->ted_grant);
                spin_unlock(&tgd->tgd_grant_lock);
                LBUG();
        }
        EXIT;
}

/**
 * Grant shrink request handler.
 *
 * Client nodes can explicitly release grant space (i.e. process called grant
 * shrinking). This function proceeds with the shrink request when there is
 * less ungranted space remaining than the amount all of the connected clients
 * would consume if they used their full grant.
 * Caller must hold tgd_grant_lock spinlock.
 *
 * \param[in] exp               export releasing grant space
 * \param[in,out] oa            incoming obdo sent by the client
 * \param[in] left_space        remaining free space with space already granted
 *                              taken out
 */
static void tgt_grant_shrink(struct obd_export *exp, struct obdo *oa,
                             u64 left_space)
{
        struct tg_export_data   *ted = &exp->exp_target_data;
        struct obd_device       *obd = exp->exp_obd;
        struct tg_grants_data   *tgd = &obd->u.obt.obt_lut->lut_tgd;
        long                     grant_shrink;

        assert_spin_locked(&tgd->tgd_grant_lock);
        LASSERT(exp);
        if (left_space >= tgd->tgd_tot_granted_clients *
                          TGT_GRANT_SHRINK_LIMIT(exp))
                return;

        grant_shrink = oa->o_grant;

        ted->ted_grant -= grant_shrink;
        tgd->tgd_tot_granted -= grant_shrink;

        CDEBUG(D_CACHE, "%s: cli %s/%p shrink %ld ted_grant %ld total %llu\n",
               obd->obd_name, exp->exp_client_uuid.uuid, exp, grant_shrink,
               ted->ted_grant, tgd->tgd_tot_granted);

        /* client has just released some grant, don't grant any space back */
        oa->o_grant = 0;
}

/**
 * Calculate how much space is required to write a given network buffer
 *
 * This function takes block alignment into account to estimate how much on-disk
 * space will be required to successfully write the whole niobuf.
 * Estimated space is inflated if the export does not support
 * OBD_CONNECT_GRANT_PARAM and if the backend filesystem has a block size
 * larger than the minimal supported page size (i.e. 4KB).
 *
 * \param[in] exp       export associated which the write request
 *                      if NULL, then size estimate is done for server-side
 *                      grant allocation.
 * \param[in] lut       LU target handling the request
 * \param[in] rnb       network buffer to estimate size of
 *
 * \retval              space (in bytes) that will be consumed to write the
 *                      network buffer
 */
static inline u64 tgt_grant_rnb_size(struct obd_export *exp,
                                     struct lu_target *lut,
                                     struct niobuf_remote *rnb)
{
        struct tg_grants_data *tgd = &lut->lut_tgd;
        u64 blksize;
        u64 bytes;
        u64 end;

        if (exp && !exp_grant_param_supp(exp) &&
            tgd->tgd_blockbits > COMPAT_BSIZE_SHIFT)
                blksize = 1ULL << COMPAT_BSIZE_SHIFT;
        else
                blksize = 1ULL << tgd->tgd_blockbits;

        /* The network buffer might span several blocks, align it on block
         * boundaries */
        bytes  = rnb->rnb_offset & (blksize - 1);
        bytes += rnb->rnb_len;
        end    = bytes & (blksize - 1);
        if (end)
                bytes += blksize - end;

        if (exp == NULL || exp_grant_param_supp(exp)) {
                /* add per-extent insertion cost */
                u64 max_ext;
                int nr_ext;

                max_ext = blksize * lut->lut_dt_conf.ddp_max_extent_blks;
                nr_ext = (bytes + max_ext - 1) / max_ext;
                bytes += nr_ext * lut->lut_dt_conf.ddp_extent_tax;
        } else {
                /* Inflate grant space if client does not support extent-based
                 * grant allocation */
                bytes = tgt_grant_inflate(tgd, (u64)bytes);
        }

        return bytes;
}

/**
 * Validate grant accounting for each incoming remote network buffer.
 *
 * When clients have dirtied as much space as they've been granted they
 * fall through to sync writes. These sync writes haven't been expressed
 * in grants and need to error with ENOSPC when there isn't room in the
 * filesystem for them after grants are taken into account. However,
 * writeback of the dirty data that was already granted space can write
 * right on through.
 * The OBD_BRW_GRANTED flag will be set in the rnb_flags of each network
 * buffer which has been granted enough space to proceed. Buffers without
 * this flag will fail to be written with -ENOSPC (see tgt_preprw_write().
 * Caller must hold tgd_grant_lock spinlock.
 *
 * \param[in] env       LU environment passed by the caller
 * \param[in] exp       export identifying the client which sent the RPC
 * \param[in] oa        incoming obdo in which we should return the pack the
 *                      additional grant
 * \param[in,out] rnb   the list of network buffers
 * \param[in] niocount  the number of network buffers in the list
 * \param[in] left      the remaining free space with space already granted
 *                      taken out
 */
static void tgt_grant_check(const struct lu_env *env, struct obd_export *exp,
                            struct obdo *oa, struct niobuf_remote *rnb,
                            int niocount, u64 *left)
{
        struct tg_export_data   *ted = &exp->exp_target_data;
        struct obd_device       *obd = exp->exp_obd;
        struct lu_target        *lut = obd->u.obt.obt_lut;
        struct tg_grants_data   *tgd = &lut->lut_tgd;
        unsigned long            ungranted = 0;
        unsigned long            granted = 0;
        int                      i;
        bool                     skip = false;

        ENTRY;

        assert_spin_locked(&tgd->tgd_grant_lock);

        if (obd->obd_recovering) {
                /* Replaying write. Grant info have been processed already so no
                 * need to do any enforcement here. It is worth noting that only
                 * bulk writes with all rnbs having OBD_BRW_FROM_GRANT can be
                 * replayed. If one page hasn't OBD_BRW_FROM_GRANT set, then
                 * the whole bulk is written synchronously */
                skip = true;
                CDEBUG(D_CACHE, "Replaying write, skipping accounting\n");
        } else if ((oa->o_valid & OBD_MD_FLFLAGS) &&
                   (oa->o_flags & OBD_FL_RECOV_RESEND)) {
                /* Recoverable resend, grant info have already been processed as
                 * well */
                skip = true;
                CDEBUG(D_CACHE, "Recoverable resend arrived, skipping "
                                "accounting\n");
        } else if (exp_grant_param_supp(exp) && oa->o_grant_used > 0) {
                /* Client supports the new grant parameters and is telling us
                 * how much grant space it consumed for this bulk write.
                 * Although all rnbs are supposed to have the OBD_BRW_FROM_GRANT
                 * flag set, we will scan the rnb list and looks for non-cache
                 * I/O in case it changes in the future */
                if (ted->ted_grant >= oa->o_grant_used) {
                        /* skip grant accounting for rnbs with
                         * OBD_BRW_FROM_GRANT and just used grant consumption
                         * claimed in the request */
                        granted = oa->o_grant_used;
                        skip = true;
                } else {
                        /* client has used more grants for this request that
                         * it owns ... */
                        CERROR("%s: cli %s claims %lu GRANT, real grant %lu\n",
                               exp->exp_obd->obd_name,
                               exp->exp_client_uuid.uuid,
                               (unsigned long)oa->o_grant_used, ted->ted_grant);

                        /* check whether we can fill the gap with unallocated
                         * grant */
                        if (*left > (oa->o_grant_used - ted->ted_grant)) {
                                /* ouf .. we are safe for now */
                                granted = ted->ted_grant;
                                ungranted = oa->o_grant_used - granted;
                                *left -= ungranted;
                                skip = true;
                        }
                        /* too bad, but we cannot afford to blow up our grant
                         * accounting. The loop below will handle each rnb in
                         * case by case. */
                }
        }

        for (i = 0; i < niocount; i++) {
                int bytes;

                if ((rnb[i].rnb_flags & OBD_BRW_FROM_GRANT)) {
                        if (skip) {
                                rnb[i].rnb_flags |= OBD_BRW_GRANTED;
                                continue;
                        }

                        /* compute how much grant space is actually needed for
                         * this rnb, inflate grant if required */
                        bytes = tgt_grant_rnb_size(exp, lut, &rnb[i]);
                        if (ted->ted_grant >= granted + bytes) {
                                granted += bytes;
                                rnb[i].rnb_flags |= OBD_BRW_GRANTED;
                                continue;
                        }

                        CDEBUG(D_CACHE, "%s: cli %s/%p claims %ld+%d GRANT, "
                               "real grant %lu idx %d\n", obd->obd_name,
                               exp->exp_client_uuid.uuid, exp, granted, bytes,
                               ted->ted_grant, i);
                }

                if (obd->obd_recovering)
                        CERROR("%s: cli %s is replaying OST_WRITE while one rnb"
                               " hasn't OBD_BRW_FROM_GRANT set (0x%x)\n",
                               obd->obd_name, exp->exp_client_uuid.uuid,
                               rnb[i].rnb_flags);

                /* Consume grant space on the server.
                 * Unlike above, tgt_grant_rnb_size() is called with exp = NULL
                 * so that the required grant space isn't inflated. This is
                 * done on purpose since the server can deal with large block
                 * size, unlike some clients */
                bytes = tgt_grant_rnb_size(NULL, lut, &rnb[i]);
                if (*left > bytes) {
                        /* if enough space, pretend it was granted */
                        ungranted += bytes;
                        *left -= bytes;
                        rnb[i].rnb_flags |= OBD_BRW_GRANTED;
                        continue;
                }

                /* We can't check for already-mapped blocks here (make sense
                 * when backend filesystem does not use COW) as it requires
                 * dropping the grant lock.
                 * Instead, we clear OBD_BRW_GRANTED and in that case we need
                 * to go through and verify if all of the blocks not marked
                 *  BRW_GRANTED are already mapped and we can ignore this error.
                 */
                rnb[i].rnb_flags &= ~OBD_BRW_GRANTED;
                CDEBUG(D_CACHE, "%s: cli %s/%p idx %d no space for %d\n",
                       obd->obd_name, exp->exp_client_uuid.uuid, exp, i, bytes);
        }

        /* record in o_grant_used the actual space reserved for the I/O, will be
         * used later in tgt_grant_commmit() */
        oa->o_grant_used = granted + ungranted;

        /* record space used for the I/O, will be used in tgt_grant_commmit() */
        /* Now substract what the clients has used already.  We don't subtract
         * this from the tot_granted yet, so that other client's can't grab
         * that space before we have actually allocated our blocks. That
         * happens in tgt_grant_commit() after the writes are done. */
        ted->ted_grant -= granted;
        ted->ted_pending += oa->o_grant_used;
        tgd->tgd_tot_granted += ungranted;
        tgd->tgd_tot_pending += oa->o_grant_used;

        CDEBUG(D_CACHE,
               "%s: cli %s/%p granted: %lu ungranted: %lu grant: %lu dirty: %lu"
               "\n", obd->obd_name, exp->exp_client_uuid.uuid, exp,
               granted, ungranted, ted->ted_grant, ted->ted_dirty);

        if (obd->obd_recovering || (oa->o_valid & OBD_MD_FLGRANT) == 0)
                /* don't update dirty accounting during recovery or
                 * if grant information got discarded (e.g. during resend) */
                RETURN_EXIT;

        if (ted->ted_dirty < granted) {
                CWARN("%s: cli %s/%p claims granted %lu > ted_dirty %lu\n",
                       obd->obd_name, exp->exp_client_uuid.uuid, exp,
                       granted, ted->ted_dirty);
                granted = ted->ted_dirty;
        }
        tgd->tgd_tot_dirty -= granted;
        ted->ted_dirty -= granted;

        if (ted->ted_dirty < 0 || ted->ted_grant < 0 || ted->ted_pending < 0) {
                CERROR("%s: cli %s/%p dirty %ld pend %ld grant %ld\n",
                       obd->obd_name, exp->exp_client_uuid.uuid, exp,
                       ted->ted_dirty, ted->ted_pending, ted->ted_grant);
                spin_unlock(&tgd->tgd_grant_lock);
                LBUG();
        }
        EXIT;
}

/**
 * Allocate additional grant space to a client
 *
 * Calculate how much grant space to return to client, based on how much space
 * is currently free and how much of that is already granted.
 * Caller must hold tgd_grant_lock spinlock.
 *
 * \param[in] exp               export of the client which sent the request
 * \param[in] curgrant          current grant claimed by the client
 * \param[in] want              how much grant space the client would like to
 *                              have
 * \param[in] left              remaining free space with granted space taken
 *                              out
 * \param[in] conservative      if set to true, the server should be cautious
 *                              and limit how much space is granted back to the
 *                              client. Otherwise, the server should try hard to
 *                              satisfy the client request.
 *
 * \retval                      amount of grant space allocated
 */
static long tgt_grant_alloc(struct obd_export *exp, u64 curgrant,
                            u64 want, u64 left, long chunk,
                            bool conservative)
{
        struct obd_device       *obd = exp->exp_obd;
        struct tg_grants_data   *tgd = &obd->u.obt.obt_lut->lut_tgd;
        struct tg_export_data   *ted = &exp->exp_target_data;
        u64                      grant;

        ENTRY;

        /* When tgd_grant_compat_disable is set, we don't grant any space to
         * clients not supporting OBD_CONNECT_GRANT_PARAM.
         * Otherwise, space granted to such a client is inflated since it
         * consumes PAGE_SIZE of grant space per block */
        if ((obd->obd_self_export != exp && !exp_grant_param_supp(exp) &&
             tgd->tgd_grant_compat_disable) || left == 0 || exp->exp_failed)
                RETURN(0);

        if (want > 0x7fffffff) {
                CERROR("%s: client %s/%p requesting > 2GB grant %llu\n",
                       obd->obd_name, exp->exp_client_uuid.uuid, exp, want);
                RETURN(0);
        }

        /* Grant some fraction of the client's requested grant space so that
         * they are not always waiting for write credits (not all of it to
         * avoid overgranting in face of multiple RPCs in flight).  This
         * essentially will be able to control the OSC_MAX_RIF for a client.
         *
         * If we do have a large disparity between what the client thinks it
         * has and what we think it has, don't grant very much and let the
         * client consume its grant first.  Either it just has lots of RPCs
         * in flight, or it was evicted and its grants will soon be used up. */
        if (curgrant >= want || curgrant >= ted->ted_grant + chunk)
                RETURN(0);

        if (obd->obd_recovering)
                conservative = false;

        if (conservative)
                /* don't grant more than 1/8th of the remaining free space in
                 * one chunk */
                left >>= 3;
        grant = min(want - curgrant, left);
        /* round grant up to the next block size */
        grant = (grant + (1 << tgd->tgd_blockbits) - 1) &
                ~((1ULL << tgd->tgd_blockbits) - 1);

        if (!grant)
                RETURN(0);

        /* Limit to grant_chunk if not reconnect/recovery */
        if ((grant > chunk) && conservative)
                grant = chunk;

        /*
         * Limit grant so that export' grant does not exceed what the
         * client would like to have by more than grants for 2 full
         * RPCs
         */
        if (ted->ted_grant + grant > want + chunk)
                grant = want + chunk - ted->ted_grant;

        tgd->tgd_tot_granted += grant;
        ted->ted_grant += grant;

        if (ted->ted_grant < 0) {
                CERROR("%s: cli %s/%p grant %ld want %llu current %llu\n",
                       obd->obd_name, exp->exp_client_uuid.uuid, exp,
                       ted->ted_grant, want, curgrant);
                spin_unlock(&tgd->tgd_grant_lock);
                LBUG();
        }

        CDEBUG(D_CACHE,
               "%s: cli %s/%p wants: %llu current grant %llu"
               " granting: %llu\n", obd->obd_name, exp->exp_client_uuid.uuid,
               exp, want, curgrant, grant);
        CDEBUG(D_CACHE,
               "%s: cli %s/%p tot cached:%llu granted:%llu"
               " num_exports: %d\n", obd->obd_name, exp->exp_client_uuid.uuid,
               exp, tgd->tgd_tot_dirty, tgd->tgd_tot_granted,
               obd->obd_num_exports);

        RETURN(grant);
}

/**
 * Handle grant space allocation on client connection & reconnection.
 *
 * A new non-readonly connection gets an initial grant allocation equals to
 * tgt_grant_chunk() (i.e. twice the max BRW size in most of the cases).
 * On reconnection, grant counters between client & target are resynchronized
 * and additional space might be granted back if possible.
 *
 * \param[in] env       LU environment provided by the caller
 * \param[in] exp       client's export which is (re)connecting
 * \param[in,out] data  obd_connect_data structure sent by the client in the
 *                      connect request
 * \param[in] new_conn  must set to true if this is a new connection and false
 *                      for a reconnection
 */
void tgt_grant_connect(const struct lu_env *env, struct obd_export *exp,
                       struct obd_connect_data *data, bool new_conn)
{
        struct lu_target        *lut = exp->exp_obd->u.obt.obt_lut;
        struct tg_grants_data   *tgd = &lut->lut_tgd;
        struct tg_export_data   *ted = &exp->exp_target_data;
        u64                      left = 0;
        u64                      want;
        long                     chunk;
        int                      from_cache;
        int                      force = 0; /* can use cached data */

        /* don't grant space to client with read-only access */
        if (OCD_HAS_FLAG(data, RDONLY) ||
            (!OCD_HAS_FLAG(data, GRANT_PARAM) &&
             tgd->tgd_grant_compat_disable)) {
                data->ocd_grant = 0;
                data->ocd_connect_flags &= ~(OBD_CONNECT_GRANT |
                                             OBD_CONNECT_GRANT_PARAM);
                RETURN_EXIT;
        }

        if (OCD_HAS_FLAG(data, GRANT_PARAM))
                want = data->ocd_grant;
        else
                want = tgt_grant_inflate(tgd, data->ocd_grant);
        chunk = tgt_grant_chunk(exp, lut, data);
refresh:
        tgt_grant_statfs(env, exp, force, &from_cache);

        spin_lock(&tgd->tgd_grant_lock);

        /* Grab free space from cached info and take out space already granted
         * to clients as well as reserved space */
        left = tgt_grant_space_left(exp);

        /* get fresh statfs data if we are short in ungranted space */
        if (from_cache && left < 32 * chunk) {
                spin_unlock(&tgd->tgd_grant_lock);
                CDEBUG(D_CACHE, "fs has no space left and statfs too old\n");
                force = 1;
                goto refresh;
        }

        tgt_grant_alloc(exp, (u64)ted->ted_grant, want, left, chunk, new_conn);

        /* return to client its current grant */
        if (OCD_HAS_FLAG(data, GRANT_PARAM))
                data->ocd_grant = ted->ted_grant;
        else
                /* deflate grant */
                data->ocd_grant = tgt_grant_deflate(tgd, (u64)ted->ted_grant);

        /* reset dirty accounting */
        tgd->tgd_tot_dirty -= ted->ted_dirty;
        ted->ted_dirty = 0;

        if (new_conn && OCD_HAS_FLAG(data, GRANT))
                tgd->tgd_tot_granted_clients++;

        spin_unlock(&tgd->tgd_grant_lock);

        CDEBUG(D_CACHE, "%s: cli %s/%p ocd_grant: %d want: %llu left: %llu\n",
               exp->exp_obd->obd_name, exp->exp_client_uuid.uuid,
               exp, data->ocd_grant, want, left);

        EXIT;
}
EXPORT_SYMBOL(tgt_grant_connect);

/**
 * Release all grant space attached to a given export.
 *
 * Remove a client from the grant accounting totals.  We also remove
 * the export from the obd device under the osfs and dev locks to ensure
 * that the tgt_grant_sanity_check() calculations are always valid.
 * The client should do something similar when it invalidates its import.
 *
 * \param[in] exp       client's export to remove from grant accounting
 */
void tgt_grant_discard(struct obd_export *exp)
{
        struct obd_device       *obd = exp->exp_obd;
        struct tg_grants_data   *tgd = &obd->u.obt.obt_lut->lut_tgd;
        struct tg_export_data   *ted = &exp->exp_target_data;

        spin_lock(&tgd->tgd_grant_lock);
        LASSERTF(tgd->tgd_tot_granted >= ted->ted_grant,
                 "%s: tot_granted %llu cli %s/%p ted_grant %ld\n",
                 obd->obd_name, tgd->tgd_tot_granted,
                 exp->exp_client_uuid.uuid, exp, ted->ted_grant);
        tgd->tgd_tot_granted -= ted->ted_grant;
        ted->ted_grant = 0;
        LASSERTF(tgd->tgd_tot_pending >= ted->ted_pending,
                 "%s: tot_pending %llu cli %s/%p ted_pending %ld\n",
                 obd->obd_name, tgd->tgd_tot_pending,
                 exp->exp_client_uuid.uuid, exp, ted->ted_pending);
        /* tgd_tot_pending is handled in tgt_grant_commit as bulk
         * commmits */
        LASSERTF(tgd->tgd_tot_dirty >= ted->ted_dirty,
                 "%s: tot_dirty %llu cli %s/%p ted_dirty %ld\n",
                 obd->obd_name, tgd->tgd_tot_dirty,
                 exp->exp_client_uuid.uuid, exp, ted->ted_dirty);
        tgd->tgd_tot_dirty -= ted->ted_dirty;
        ted->ted_dirty = 0;
        spin_unlock(&tgd->tgd_grant_lock);
}
EXPORT_SYMBOL(tgt_grant_discard);

/**
 * Process grant information from incoming bulk read request.
 *
 * Extract grant information packed in obdo structure (OBD_MD_FLGRANT set in
 * o_valid). Bulk reads usually comes with grant announcements (number of dirty
 * blocks, remaining amount of grant space, ...) and could also include a grant
 * shrink request. Unlike bulk write, no additional grant space is returned on
 * bulk read request.
 *
 * \param[in] env       is the lu environment provided by the caller
 * \param[in] exp       is the export of the client which sent the request
 * \param[in,out] oa    is the incoming obdo sent by the client
 */
void tgt_grant_prepare_read(const struct lu_env *env,
                            struct obd_export *exp, struct obdo *oa)
{
        struct lu_target        *lut = exp->exp_obd->u.obt.obt_lut;
        struct tg_grants_data   *tgd = &lut->lut_tgd;
        int                      do_shrink;
        u64                      left = 0;

        ENTRY;

        if (!oa)
                RETURN_EXIT;

        if ((oa->o_valid & OBD_MD_FLGRANT) == 0)
                /* The read request does not contain any grant
                 * information */
                RETURN_EXIT;

        if ((oa->o_valid & OBD_MD_FLFLAGS) &&
            (oa->o_flags & OBD_FL_SHRINK_GRANT)) {
                /* To process grant shrink request, we need to know how much
                 * available space remains on the backend filesystem.
                 * Shrink requests are not so common, we always get fresh
                 * statfs information. */
                tgt_grant_statfs(env, exp, 1, NULL);

                /* protect all grant counters */
                spin_lock(&tgd->tgd_grant_lock);

                /* Grab free space from cached statfs data and take out space
                 * already granted to clients as well as reserved space */
                left = tgt_grant_space_left(exp);

                /* all set now to proceed with shrinking */
                do_shrink = 1;
        } else {
                /* no grant shrinking request packed in the obdo and
                 * since we don't grant space back on reads, no point
                 * in running statfs, so just skip it and process
                 * incoming grant data directly. */
                spin_lock(&tgd->tgd_grant_lock);
                do_shrink = 0;
        }

        /* extract incoming grant information provided by the client and
         * inflate grant counters if required */
        tgt_grant_incoming(env, exp, oa, tgt_grant_chunk(exp, lut, NULL));

        /* unlike writes, we don't return grants back on reads unless a grant
         * shrink request was packed and we decided to turn it down. */
        if (do_shrink)
                tgt_grant_shrink(exp, oa, left);
        else
                oa->o_grant = 0;

        if (!exp_grant_param_supp(exp))
                oa->o_grant = tgt_grant_deflate(tgd, oa->o_grant);
        spin_unlock(&tgd->tgd_grant_lock);
        EXIT;
}
EXPORT_SYMBOL(tgt_grant_prepare_read);

/**
 * Process grant information from incoming bulk write request.
 *
 * This function extracts client's grant announcements from incoming bulk write
 * request and attempts to allocate grant space for network buffers that need it
 * (i.e. OBD_BRW_FROM_GRANT not set in rnb_fags).
 * Network buffers which aren't granted the OBD_BRW_GRANTED flag should not
 * proceed further and should fail with -ENOSPC.
 * Whenever possible, additional grant space will be returned to the client
 * in the bulk write reply.
 * tgt_grant_prepare_write() must be called before writting any buffers to
 * the backend storage. This function works in pair with tgt_grant_commit()
 * which must be invoked once all buffers have been written to disk in order
 * to release space from the pending grant counter.
 *
 * \param[in] env       LU environment provided by the caller
 * \param[in] exp       export of the client which sent the request
 * \param[in] oa        incoming obdo sent by the client
 * \param[in] rnb       list of network buffers
 * \param[in] niocount  number of network buffers in the list
 */
void tgt_grant_prepare_write(const struct lu_env *env,
                             struct obd_export *exp, struct obdo *oa,
                             struct niobuf_remote *rnb, int niocount)
{
        struct obd_device       *obd = exp->exp_obd;
        struct lu_target        *lut = obd->u.obt.obt_lut;
        struct tg_grants_data   *tgd = &lut->lut_tgd;
        u64                      left;
        int                      from_cache;
        int                      force = 0; /* can use cached data intially */
        long                     chunk = tgt_grant_chunk(exp, lut, NULL);

        ENTRY;

refresh:
        /* get statfs information from OSD layer */
        tgt_grant_statfs(env, exp, force, &from_cache);

        spin_lock(&tgd->tgd_grant_lock); /* protect all grant counters */

        /* Grab free space from cached statfs data and take out space already
         * granted to clients as well as reserved space */
        left = tgt_grant_space_left(exp);

        /* Get fresh statfs data if we are short in ungranted space */
        if (from_cache && left < 32 * chunk) {
                spin_unlock(&tgd->tgd_grant_lock);
                CDEBUG(D_CACHE, "%s: fs has no space left and statfs too old\n",
                       obd->obd_name);
                force = 1;
                goto refresh;
        }

        /* When close to free space exhaustion, trigger a sync to force
         * writeback cache to consume required space immediately and release as
         * much space as possible. */
        if (!obd->obd_recovering && force != 2 && left < chunk) {
                bool from_grant = true;
                int  i;

                /* That said, it is worth running a sync only if some pages did
                 * not consume grant space on the client and could thus fail
                 * with ENOSPC later in tgt_grant_check() */
                for (i = 0; i < niocount; i++)
                        if (!(rnb[i].rnb_flags & OBD_BRW_FROM_GRANT))
                                from_grant = false;

                if (!from_grant) {
                        /* at least one network buffer requires acquiring grant
                         * space on the server */
                        spin_unlock(&tgd->tgd_grant_lock);
                        /* discard errors, at least we tried ... */
                        dt_sync(env, lut->lut_bottom);
                        force = 2;
                        goto refresh;
                }
        }

        /* extract incoming grant information provided by the client,
         * and inflate grant counters if required */
        tgt_grant_incoming(env, exp, oa, chunk);

        /* check limit */
        tgt_grant_check(env, exp, oa, rnb, niocount, &left);

        if (!(oa->o_valid & OBD_MD_FLGRANT)) {
                spin_unlock(&tgd->tgd_grant_lock);
                RETURN_EXIT;
        }

        /* if OBD_FL_SHRINK_GRANT is set, the client is willing to release some
         * grant space. */
        if ((oa->o_valid & OBD_MD_FLFLAGS) &&
            (oa->o_flags & OBD_FL_SHRINK_GRANT))
                tgt_grant_shrink(exp, oa, left);
        else
                /* grant more space back to the client if possible */
                oa->o_grant = tgt_grant_alloc(exp, oa->o_grant, oa->o_undirty,
                                              left, chunk, true);

        if (!exp_grant_param_supp(exp))
                oa->o_grant = tgt_grant_deflate(tgd, oa->o_grant);
        spin_unlock(&tgd->tgd_grant_lock);
        EXIT;
}
EXPORT_SYMBOL(tgt_grant_prepare_write);

/**
 * Consume grant space reserved for object creation.
 *
 * Grant space is allocated to the local self export for object precreation.
 * This is required to prevent object precreation from consuming grant space
 * allocated to client nodes for the data writeback cache.
 * This function consumes enough space to create \a nr objects and allocates
 * more grant space to the self export for future precreation requests, if
 * possible.
 *
 * \param[in] env       LU environment provided by the caller
 * \param[in] exp       export holding the grant space for precreation (= self
 *                      export currently)
 * \param[in] nr        number of objects to be created
 *
 * \retval >= 0         amount of grant space allocated to the precreate request
 * \retval -ENOSPC      on failure
 */
long tgt_grant_create(const struct lu_env *env, struct obd_export *exp, s64 *nr)
{
        struct lu_target        *lut = exp->exp_obd->u.obt.obt_lut;
        struct tg_grants_data   *tgd = &lut->lut_tgd;
        struct tg_export_data   *ted = &exp->exp_target_data;
        u64                      left = 0;
        unsigned long            wanted;
        unsigned long            granted;
        ENTRY;

        if (exp->exp_obd->obd_recovering ||
            lut->lut_dt_conf.ddp_inodespace == 0)
                /* don't enforce grant during recovery */
                RETURN(0);

        /* Update statfs data if required */
        tgt_grant_statfs(env, exp, 1, NULL);

        /* protect all grant counters */
        spin_lock(&tgd->tgd_grant_lock);

        /* fail precreate request if there is not enough blocks available for
         * writing */
        if (tgd->tgd_osfs.os_bavail - (ted->ted_grant >> tgd->tgd_blockbits) <
            (tgd->tgd_osfs.os_blocks >> 10)) {
                spin_unlock(&tgd->tgd_grant_lock);
                CDEBUG(D_RPCTRACE, "%s: not enough space for create %llu\n",
                       exp->exp_obd->obd_name,
                       tgd->tgd_osfs.os_bavail * tgd->tgd_osfs.os_blocks);
                RETURN(-ENOSPC);
        }

        /* Grab free space from cached statfs data and take out space
         * already granted to clients as well as reserved space */
        left = tgt_grant_space_left(exp);

        /* compute how much space is required to handle the precreation
         * request */
        wanted = *nr * lut->lut_dt_conf.ddp_inodespace;
        if (wanted > ted->ted_grant + left) {
                /* that's beyond what remains, adjust the number of objects that
                 * can be safely precreated */
                wanted = ted->ted_grant + left;
                *nr = wanted / lut->lut_dt_conf.ddp_inodespace;
                if (*nr == 0) {
                        /* we really have no space any more for precreation,
                         * fail the precreate request with ENOSPC */
                        spin_unlock(&tgd->tgd_grant_lock);
                        RETURN(-ENOSPC);
                }
                /* compute space needed for the new number of creations */
                wanted = *nr * lut->lut_dt_conf.ddp_inodespace;
        }
        LASSERT(wanted <= ted->ted_grant + left);

        if (wanted <= ted->ted_grant) {
                /* we've enough grant space to handle this precreate request */
                ted->ted_grant -= wanted;
        } else {
                /* we need to take some space from the ungranted pool */
                tgd->tgd_tot_granted += wanted - ted->ted_grant;
                left -= wanted - ted->ted_grant;
                ted->ted_grant = 0;
        }
        granted = wanted;
        ted->ted_pending += granted;
        tgd->tgd_tot_pending += granted;

        /* grant more space for precreate purpose if possible. */
        wanted = OST_MAX_PRECREATE * lut->lut_dt_conf.ddp_inodespace / 2;
        if (wanted > ted->ted_grant) {
                long chunk;

                /* always try to book enough space to handle a large precreate
                 * request */
                chunk = tgt_grant_chunk(exp, lut, NULL);
                wanted -= ted->ted_grant;
                tgt_grant_alloc(exp, ted->ted_grant, wanted, left, chunk,
                                false);
        }
        spin_unlock(&tgd->tgd_grant_lock);
        RETURN(granted);
}
EXPORT_SYMBOL(tgt_grant_create);

/**
 * Release grant space added to the pending counter by tgt_grant_prepare_write()
 *
 * Update pending grant counter once buffers have been written to the disk.
 *
 * \param[in] exp       export of the client which sent the request
 * \param[in] pending   amount of reserved space to be released
 * \param[in] rc        return code of pre-commit operations
 */
void tgt_grant_commit(struct obd_export *exp, unsigned long pending,
                      int rc)
{
        struct tg_grants_data *tgd = &exp->exp_obd->u.obt.obt_lut->lut_tgd;

        ENTRY;

        /* get space accounted in tot_pending for the I/O, set in
         * tgt_grant_check() */
        if (pending == 0)
                RETURN_EXIT;

        spin_lock(&tgd->tgd_grant_lock);
        /* Don't update statfs data for errors raised before commit (e.g.
         * bulk transfer failed, ...) since we know those writes have not been
         * processed. For other errors hit during commit, we cannot really tell
         * whether or not something was written, so we update statfs data.
         * In any case, this should not be fatal since we always get fresh
         * statfs data before failing a request with ENOSPC */
        if (rc == 0) {
                spin_lock(&tgd->tgd_osfs_lock);
                /* Take pending out of cached statfs data */
                tgd->tgd_osfs.os_bavail -= min_t(u64,
                                                 tgd->tgd_osfs.os_bavail,
                                                 pending >> tgd->tgd_blockbits);
                if (tgd->tgd_statfs_inflight)
                        /* someone is running statfs and want to be notified of
                         * writes happening meanwhile */
                        tgd->tgd_osfs_inflight += pending;
                spin_unlock(&tgd->tgd_osfs_lock);
        }

        if (exp->exp_target_data.ted_pending < pending) {
                CERROR("%s: cli %s/%p ted_pending(%lu) < grant_used(%lu)\n",
                       exp->exp_obd->obd_name, exp->exp_client_uuid.uuid, exp,
                       exp->exp_target_data.ted_pending, pending);
                spin_unlock(&tgd->tgd_grant_lock);
                LBUG();
        }
        exp->exp_target_data.ted_pending -= pending;

        if (tgd->tgd_tot_granted < pending) {
                CERROR("%s: cli %s/%p tot_granted(%llu) < grant_used(%lu)\n",
                       exp->exp_obd->obd_name, exp->exp_client_uuid.uuid, exp,
                       tgd->tgd_tot_granted, pending);
                spin_unlock(&tgd->tgd_grant_lock);
                LBUG();
        }
        tgd->tgd_tot_granted -= pending;

        if (tgd->tgd_tot_pending < pending) {
                CERROR("%s: cli %s/%p tot_pending(%llu) < grant_used(%lu)\n",
                       exp->exp_obd->obd_name, exp->exp_client_uuid.uuid, exp,
                       tgd->tgd_tot_pending, pending);
                spin_unlock(&tgd->tgd_grant_lock);
                LBUG();
        }
        tgd->tgd_tot_pending -= pending;
        spin_unlock(&tgd->tgd_grant_lock);
        EXIT;
}
EXPORT_SYMBOL(tgt_grant_commit);

struct tgt_grant_cb {
        /* commit callback structure */
        struct dt_txn_commit_cb  tgc_cb;
        /* export associated with the bulk write */
        struct obd_export       *tgc_exp;
        /* pending grant to be released */
        unsigned long            tgc_granted;
};

/**
 * Callback function for grant releasing
 *
 * Release grant space reserved by the client node.
 *
 * \param[in] env       execution environment
 * \param[in] th        transaction handle
 * \param[in] cb        callback data
 * \param[in] err       error code
 */
static void tgt_grant_commit_cb(struct lu_env *env, struct thandle *th,
                                struct dt_txn_commit_cb *cb, int err)
{
        struct tgt_grant_cb *tgc;

        tgc = container_of(cb, struct tgt_grant_cb, tgc_cb);

        tgt_grant_commit(tgc->tgc_exp, tgc->tgc_granted, err);
        class_export_cb_put(tgc->tgc_exp);
        OBD_FREE_PTR(tgc);
}

/**
 * Add callback for grant releasing
 *
 * Register a commit callback to release grant space.
 *
 * \param[in] th        transaction handle
 * \param[in] exp       OBD export of client
 * \param[in] granted   amount of grant space to be released upon commit
 *
 * \retval              0 on successful callback adding
 * \retval              negative value on error
 */
int tgt_grant_commit_cb_add(struct thandle *th, struct obd_export *exp,
                            unsigned long granted)
{
        struct tgt_grant_cb     *tgc;
        struct dt_txn_commit_cb *dcb;
        int                      rc;
        ENTRY;

        OBD_ALLOC_PTR(tgc);
        if (tgc == NULL)
                RETURN(-ENOMEM);

        tgc->tgc_exp = class_export_cb_get(exp);
        tgc->tgc_granted = granted;

        dcb = &tgc->tgc_cb;
        dcb->dcb_func = tgt_grant_commit_cb;
        INIT_LIST_HEAD(&dcb->dcb_linkage);
        strlcpy(dcb->dcb_name, "tgt_grant_commit_cb", sizeof(dcb->dcb_name));

        rc = dt_trans_cb_add(th, dcb);
        if (rc) {
                class_export_cb_put(tgc->tgc_exp);
                OBD_FREE_PTR(tgc);
        }

        RETURN(rc);
}
EXPORT_SYMBOL(tgt_grant_commit_cb_add);

/**
 * Show estimate of total amount of dirty data on clients.
 *
 * \param[in] m         seq_file handle
 * \param[in] data      unused for single entry
 *
 * \retval              0 on success
 * \retval              negative value on error
 */
int tgt_tot_dirty_seq_show(struct seq_file *m, void *data)
{
        struct obd_device *obd = m->private;
        struct tg_grants_data *tgd;

        LASSERT(obd != NULL);
        tgd = &obd->u.obt.obt_lut->lut_tgd;
        seq_printf(m, "%llu\n", tgd->tgd_tot_dirty);
        return 0;
}
EXPORT_SYMBOL(tgt_tot_dirty_seq_show);

/**
 * Show total amount of space granted to clients.
 *
 * \param[in] m         seq_file handle
 * \param[in] data      unused for single entry
 *
 * \retval              0 on success
 * \retval              negative value on error
 */
int tgt_tot_granted_seq_show(struct seq_file *m, void *data)
{
        struct obd_device *obd = m->private;
        struct tg_grants_data *tgd;

        LASSERT(obd != NULL);
        tgd = &obd->u.obt.obt_lut->lut_tgd;
        seq_printf(m, "%llu\n", tgd->tgd_tot_granted);
        return 0;
}
EXPORT_SYMBOL(tgt_tot_granted_seq_show);

/**
 * Show total amount of space used by IO in progress.
 *
 * \param[in] m         seq_file handle
 * \param[in] data      unused for single entry
 *
 * \retval              0 on success
 * \retval              negative value on error
 */
int tgt_tot_pending_seq_show(struct seq_file *m, void *data)
{
        struct obd_device *obd = m->private;
        struct tg_grants_data *tgd;

        LASSERT(obd != NULL);
        tgd = &obd->u.obt.obt_lut->lut_tgd;
        seq_printf(m, "%llu\n", tgd->tgd_tot_pending);
        return 0;
}
EXPORT_SYMBOL(tgt_tot_pending_seq_show);

/**
 * Show if grants compatibility mode is disabled.
 *
 * When tgd_grant_compat_disable is set, we don't grant any space to clients
 * not supporting OBD_CONNECT_GRANT_PARAM. Otherwise, space granted to such
 * a client is inflated since it consumes PAGE_SIZE of grant space per
 * block, (i.e. typically 4kB units), but underlaying file system might have
 * block size bigger than page size, e.g. ZFS. See LU-2049 for details.
 *
 * \param[in] m         seq_file handle
 * \param[in] data      unused for single entry
 *
 * \retval              0 on success
 * \retval              negative value on error
 */
int tgt_grant_compat_disable_seq_show(struct seq_file *m, void *data)
{
        struct obd_device *obd = m->private;
        struct tg_grants_data *tgd = &obd->u.obt.obt_lut->lut_tgd;

        seq_printf(m, "%u\n", tgd->tgd_grant_compat_disable);
        return 0;
}
EXPORT_SYMBOL(tgt_grant_compat_disable_seq_show);

/**
 * Change grant compatibility mode.
 *
 * Setting tgd_grant_compat_disable prohibit any space granting to clients
 * not supporting OBD_CONNECT_GRANT_PARAM. See details above.
 *
 * \param[in] file      proc file
 * \param[in] buffer    string which represents mode
 *                      1: disable compatibility mode
 *                      0: enable compatibility mode
 * \param[in] count     \a buffer length
 * \param[in] off       unused for single entry
 *
 * \retval              \a count on success
 * \retval              negative number on error
 */
ssize_t tgt_grant_compat_disable_seq_write(struct file *file,
                                           const char __user *buffer,
                                           size_t count, loff_t *off)
{
        struct seq_file *m = file->private_data;
        struct obd_device *obd = m->private;
        struct tg_grants_data *tgd = &obd->u.obt.obt_lut->lut_tgd;
        __s64 val;
        int rc;

        rc = lprocfs_str_to_s64(buffer, count, &val);
        if (rc)
                return rc;

        if (val < 0)
                return -EINVAL;

        tgd->tgd_grant_compat_disable = !!val;

        return count;
}
EXPORT_SYMBOL(tgt_grant_compat_disable_seq_write);