LU-12624 lod: alloc dir stripes by QoS

[fs/lustre-release.git] / lustre / lod / lod_qos.c

/*
 * GPL HEADER START
 *
 * 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 COPYING file that accompanied this code.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 * GPL HEADER END
 */
/*
 * Copyright  2009 Sun Microsystems, Inc. All rights reserved
 * Use is subject to license terms.
 *
 * Copyright (c) 2012, 2017, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 * Lustre is a trademark of Sun Microsystems, Inc.
 *
 * lustre/lod/lod_qos.c
 *
 * Implementation of different allocation algorithm used
 * to distribute objects and data among OSTs.
 */

#define DEBUG_SUBSYSTEM S_LOV

#include <asm/div64.h>
#include <linux/random.h>

#include <libcfs/libcfs.h>
#include <uapi/linux/lustre/lustre_idl.h>
#include <lustre_swab.h>
#include <obd_class.h>

#include "lod_internal.h"

/*
 * force QoS policy (not RR) to be used for testing purposes
 */
#define FORCE_QOS_

#define D_QOS   D_OTHER

#define QOS_DEBUG(fmt, ...)     CDEBUG(D_QOS, fmt, ## __VA_ARGS__)
#define QOS_CONSOLE(fmt, ...)   LCONSOLE(D_QOS, fmt, ## __VA_ARGS__)

#define TGT_BAVAIL(i) (OST_TGT(lod,i)->ltd_statfs.os_bavail * \
                       OST_TGT(lod,i)->ltd_statfs.os_bsize)

static inline int lod_statfs_check(struct lu_tgt_descs *ltd,
                                   struct lu_tgt_desc *tgt)
{
        struct obd_statfs *sfs = &tgt->ltd_statfs;

        if (((sfs->os_state & OS_STATE_ENOSPC) ||
            (!ltd->ltd_is_mdt && sfs->os_state & OS_STATE_ENOINO &&
             sfs->os_fprecreated == 0)))
                return -ENOSPC;

        /* If the OST is readonly then we can't allocate objects there */
        if (sfs->os_state & OS_STATE_READONLY)
                return -EROFS;

        /* object precreation is skipped on the OST with max_create_count=0 */
        if (!ltd->ltd_is_mdt && sfs->os_state & OS_STATE_NOPRECREATE)
                return -ENOBUFS;

        return 0;
}

/**
 * Check whether the target is available for new objects.
 *
 * Request statfs data from the given target and verify it's active and not
 * read-only. If so, then it can be used to place new objects. This
 * function also maintains the number of active/inactive targets and sets
 * dirty flags if those numbers change so others can run re-balance procedures.
 * No external locking is required.
 *
 * \param[in] env       execution environment for this thread
 * \param[in] d         LOD device
 * \param[in] ltd       target table
 * \param[in] tgt       target
 *
 * \retval 0            if the target is good
 * \retval negative     negated errno on error
 */
static int lod_statfs_and_check(const struct lu_env *env, struct lod_device *d,
                                struct lu_tgt_descs *ltd,
                                struct lu_tgt_desc *tgt)
{
        struct lov_desc *desc = &ltd->ltd_lov_desc;
        int rc;

        LASSERT(d);
        LASSERT(tgt);

        rc = dt_statfs(env, tgt->ltd_tgt, &tgt->ltd_statfs);
        if (rc && rc != -ENOTCONN)
                CERROR("%s: statfs: rc = %d\n", lod2obd(d)->obd_name, rc);

        if (!rc) {
                rc = lod_statfs_check(ltd, tgt);
                if (rc == -ENOSPC)
                        return rc;
        }

        /* check whether device has changed state (active, inactive) */
        if (rc != 0 && tgt->ltd_active) {
                /* turned inactive? */
                spin_lock(&d->lod_lock);
                if (tgt->ltd_active) {
                        tgt->ltd_active = 0;
                        if (rc == -ENOTCONN)
                                tgt->ltd_connecting = 1;

                        LASSERT(desc->ld_active_tgt_count > 0);
                        desc->ld_active_tgt_count--;
                        ltd->ltd_qos.lq_dirty = 1;
                        ltd->ltd_qos.lq_rr.lqr_dirty = 1;
                        CDEBUG(D_CONFIG, "%s: turns inactive\n",
                               tgt->ltd_exp->exp_obd->obd_name);
                }
                spin_unlock(&d->lod_lock);
        } else if (rc == 0 && tgt->ltd_active == 0) {
                /* turned active? */
                LASSERTF(desc->ld_active_tgt_count < desc->ld_tgt_count,
                         "active tgt count %d, tgt nr %d\n",
                         desc->ld_active_tgt_count, desc->ld_tgt_count);
                spin_lock(&d->lod_lock);
                if (tgt->ltd_active == 0) {
                        tgt->ltd_active = 1;
                        tgt->ltd_connecting = 0;
                        desc->ld_active_tgt_count++;
                        ltd->ltd_qos.lq_dirty = 1;
                        ltd->ltd_qos.lq_rr.lqr_dirty = 1;
                        CDEBUG(D_CONFIG, "%s: turns active\n",
                               tgt->ltd_exp->exp_obd->obd_name);
                }
                spin_unlock(&d->lod_lock);
        }

        return rc;
}

static int lod_is_tgt_usable(struct lu_tgt_descs *ltd, struct lu_tgt_desc *tgt)
{
        int rc;

        rc = lod_statfs_check(ltd, tgt);
        if (rc)
                return rc;

        if (!tgt->ltd_active)
                return -ENOTCONN;

        return 0;
}

/**
 * Maintain per-target statfs data.
 *
 * The function refreshes statfs data for all the targets every N seconds.
 * The actual N is controlled via procfs and set to LOV_DESC_QOS_MAXAGE_DEFAULT
 * initially.
 *
 * \param[in] env       execution environment for this thread
 * \param[in] lod       LOD device
 * \param[in] ltd       tgt table
 */
void lod_qos_statfs_update(const struct lu_env *env, struct lod_device *lod,
                           struct lu_tgt_descs *ltd)
{
        struct obd_device *obd = lod2obd(lod);
        struct lu_tgt_desc *tgt;
        time64_t max_age;
        u64 avail;
        ENTRY;

        max_age = ktime_get_seconds() - 2 * ltd->ltd_lov_desc.ld_qos_maxage;

        if (obd->obd_osfs_age > max_age)
                /* statfs data are quite recent, don't need to refresh it */
                RETURN_EXIT;

        down_write(&ltd->ltd_qos.lq_rw_sem);

        if (obd->obd_osfs_age > max_age)
                goto out;

        ltd_foreach_tgt(ltd, tgt) {
                avail = tgt->ltd_statfs.os_bavail;
                if (lod_statfs_and_check(env, lod, ltd, tgt))
                        continue;

                if (tgt->ltd_statfs.os_bavail != avail)
                        /* recalculate weigths */
                        ltd->ltd_qos.lq_dirty = 1;
        }
        obd->obd_osfs_age = ktime_get_seconds();

out:
        up_write(&ltd->ltd_qos.lq_rw_sem);
        EXIT;
}

#define LOV_QOS_EMPTY ((__u32)-1)

/**
 * Calculate optimal round-robin order with regard to OSSes.
 *
 * Place all the OSTs from pool \a src_pool in a special array to be used for
 * round-robin (RR) stripe allocation.  The placement algorithm interleaves
 * OSTs from the different OSSs so that RR allocation can balance OSSs evenly.
 * Resorts the targets when the number of active targets changes (because of
 * a new target or activation/deactivation).
 *
 * \param[in] lod       LOD device
 * \param[in] ltd       tgt table
 * \param[in] src_pool  tgt pool
 * \param[in] lqr       round-robin list
 *
 * \retval 0            on success
 * \retval -ENOMEM      fails to allocate the array
 */
static int lod_qos_calc_rr(struct lod_device *lod, struct lu_tgt_descs *ltd,
                           const struct lu_tgt_pool *src_pool,
                           struct lu_qos_rr *lqr)
{
        struct lu_svr_qos  *svr;
        struct lu_tgt_desc *tgt;
        unsigned placed, real_count;
        unsigned int i;
        int rc;
        ENTRY;

        if (!lqr->lqr_dirty) {
                LASSERT(lqr->lqr_pool.op_size);
                RETURN(0);
        }

        /* Do actual allocation. */
        down_write(&ltd->ltd_qos.lq_rw_sem);

        /*
         * Check again. While we were sleeping on @lq_rw_sem something could
         * change.
         */
        if (!lqr->lqr_dirty) {
                LASSERT(lqr->lqr_pool.op_size);
                up_write(&ltd->ltd_qos.lq_rw_sem);
                RETURN(0);
        }

        real_count = src_pool->op_count;

        /* Zero the pool array */
        /* alloc_rr is holding a read lock on the pool, so nobody is adding/
           deleting from the pool. The lq_rw_sem insures that nobody else
           is reading. */
        lqr->lqr_pool.op_count = real_count;
        rc = lod_tgt_pool_extend(&lqr->lqr_pool, real_count);
        if (rc) {
                up_write(&ltd->ltd_qos.lq_rw_sem);
                RETURN(rc);
        }
        for (i = 0; i < lqr->lqr_pool.op_count; i++)
                lqr->lqr_pool.op_array[i] = LOV_QOS_EMPTY;

        /* Place all the tgts from 1 svr at the same time. */
        placed = 0;
        list_for_each_entry(svr, &ltd->ltd_qos.lq_svr_list, lsq_svr_list) {
                int j = 0;

                for (i = 0; i < lqr->lqr_pool.op_count; i++) {
                        int next;

                        if (!cfs_bitmap_check(ltd->ltd_tgt_bitmap,
                                              src_pool->op_array[i]))
                                continue;

                        tgt = LTD_TGT(ltd, src_pool->op_array[i]);
                        LASSERT(tgt && tgt->ltd_tgt);
                        if (tgt->ltd_qos.ltq_svr != svr)
                                continue;

                        /* Evenly space these tgts across arrayspace */
                        next = j * lqr->lqr_pool.op_count / svr->lsq_tgt_count;
                        while (lqr->lqr_pool.op_array[next] != LOV_QOS_EMPTY)
                                next = (next + 1) % lqr->lqr_pool.op_count;

                        lqr->lqr_pool.op_array[next] = src_pool->op_array[i];
                        j++;
                        placed++;
                }
        }

        lqr->lqr_dirty = 0;
        up_write(&ltd->ltd_qos.lq_rw_sem);

        if (placed != real_count) {
                /* This should never happen */
                LCONSOLE_ERROR_MSG(0x14e, "Failed to place all tgts in the "
                                   "round-robin list (%d of %d).\n",
                                   placed, real_count);
                for (i = 0; i < lqr->lqr_pool.op_count; i++) {
                        LCONSOLE(D_WARNING, "rr #%d tgt idx=%d\n", i,
                                 lqr->lqr_pool.op_array[i]);
                }
                lqr->lqr_dirty = 1;
                RETURN(-EAGAIN);
        }

#if 0
        for (i = 0; i < lqr->lqr_pool.op_count; i++)
                QOS_CONSOLE("rr #%d ost idx=%d\n", i, lqr->lqr_pool.op_array[i]);
#endif

        RETURN(0);
}

/**
 * Instantiate and declare creation of a new object.
 *
 * The function instantiates LU representation for a new object on the
 * specified device. Also it declares an intention to create that
 * object on the storage target.
 *
 * Note lu_object_anon() is used which is a trick with regard to LU/OSD
 * infrastructure - in the existing precreation framework we can't assign FID
 * at this moment, we do this later once a transaction is started. So the
 * special method instantiates FID-less object in the cache and later it
 * will get a FID and proper placement in LU cache.
 *
 * \param[in] env       execution environment for this thread
 * \param[in] d         LOD device
 * \param[in] ost_idx   OST target index where the object is being created
 * \param[in] th        transaction handle
 *
 * \retval              object ptr on success, ERR_PTR() otherwise
 */
static struct dt_object *lod_qos_declare_object_on(const struct lu_env *env,
                                                   struct lod_device *d,
                                                   __u32 ost_idx,
                                                   struct thandle *th)
{
        struct lod_tgt_desc *ost;
        struct lu_object *o, *n;
        struct lu_device *nd;
        struct dt_object *dt;
        int               rc;
        ENTRY;

        LASSERT(d);
        LASSERT(ost_idx < d->lod_ost_descs.ltd_tgts_size);
        ost = OST_TGT(d,ost_idx);
        LASSERT(ost);
        LASSERT(ost->ltd_tgt);

        nd = &ost->ltd_tgt->dd_lu_dev;

        /*
         * allocate anonymous object with zero fid, real fid
         * will be assigned by OSP within transaction
         * XXX: to be fixed with fully-functional OST fids
         */
        o = lu_object_anon(env, nd, NULL);
        if (IS_ERR(o))
                GOTO(out, dt = ERR_PTR(PTR_ERR(o)));

        n = lu_object_locate(o->lo_header, nd->ld_type);
        if (unlikely(n == NULL)) {
                CERROR("can't find slice\n");
                lu_object_put(env, o);
                GOTO(out, dt = ERR_PTR(-EINVAL));
        }

        dt = container_of(n, struct dt_object, do_lu);

        rc = lod_sub_declare_create(env, dt, NULL, NULL, NULL, th);
        if (rc < 0) {
                CDEBUG(D_OTHER, "can't declare creation on #%u: %d\n",
                       ost_idx, rc);
                lu_object_put(env, o);
                dt = ERR_PTR(rc);
        }

out:
        RETURN(dt);
}

/**
 * Calculate a minimum acceptable stripe count.
 *
 * Return an acceptable stripe count depending on flag LOV_USES_DEFAULT_STRIPE:
 * all stripes or 3/4 of stripes.
 *
 * \param[in] stripe_count      number of stripes requested
 * \param[in] flags             0 or LOV_USES_DEFAULT_STRIPE
 *
 * \retval                      acceptable stripecount
 */
static int min_stripe_count(__u32 stripe_count, int flags)
{
        return (flags & LOV_USES_DEFAULT_STRIPE ?
                stripe_count - (stripe_count / 4) : stripe_count);
}

#define LOV_CREATE_RESEED_MULT 30
#define LOV_CREATE_RESEED_MIN  2000

/**
 * Initialize temporary tgt-in-use array.
 *
 * Allocate or extend the array used to mark targets already assigned to a new
 * striping so they are not used more than once.
 *
 * \param[in] env       execution environment for this thread
 * \param[in] stripes   number of items needed in the array
 *
 * \retval 0            on success
 * \retval -ENOMEM      on error
 */
static inline int lod_qos_tgt_in_use_clear(const struct lu_env *env,
                                           __u32 stripes)
{
        struct lod_thread_info *info = lod_env_info(env);

        if (info->lti_ea_store_size < sizeof(int) * stripes)
                lod_ea_store_resize(info, stripes * sizeof(int));
        if (info->lti_ea_store_size < sizeof(int) * stripes) {
                CERROR("can't allocate memory for ost-in-use array\n");
                return -ENOMEM;
        }
        memset(info->lti_ea_store, -1, sizeof(int) * stripes);
        return 0;
}

/**
 * Remember a target in the array of used targets.
 *
 * Mark the given target as used for a new striping being created. The status
 * of an tgt in a striping can be checked with lod_qos_is_tgt_used().
 *
 * \param[in] env       execution environment for this thread
 * \param[in] idx       index in the array
 * \param[in] tgt_idx   target index to mark as used
 */
static inline void lod_qos_tgt_in_use(const struct lu_env *env,
                                      int idx, int tgt_idx)
{
        struct lod_thread_info *info = lod_env_info(env);
        int *tgts = info->lti_ea_store;

        LASSERT(info->lti_ea_store_size >= idx * sizeof(int));
        tgts[idx] = tgt_idx;
}

/**
 * Check is tgt used in a striping.
 *
 * Checks whether tgt with the given index is marked as used in the temporary
 * array (see lod_qos_tgt_in_use()).
 *
 * \param[in] env       execution environment for this thread
 * \param[in] tgt_idx   target index to check
 * \param[in] stripes   the number of items used in the array already
 *
 * \retval 0            not used
 * \retval 1            used
 */
static int lod_qos_is_tgt_used(const struct lu_env *env, int tgt_idx,
                               __u32 stripes)
{
        struct lod_thread_info *info = lod_env_info(env);
        int *tgts = info->lti_ea_store;
        __u32 j;

        for (j = 0; j < stripes; j++) {
                if (tgts[j] == tgt_idx)
                        return 1;
        }
        return 0;
}

static inline bool
lod_obj_is_ost_use_skip_cb(const struct lu_env *env, struct lod_object *lo,
                           int comp_idx, struct lod_obj_stripe_cb_data *data)
{
        struct lod_layout_component *comp = &lo->ldo_comp_entries[comp_idx];

        return comp->llc_ost_indices == NULL;
}

static inline int
lod_obj_is_ost_use_cb(const struct lu_env *env, struct lod_object *lo,
                      int comp_idx, struct lod_obj_stripe_cb_data *data)
{
        struct lod_layout_component *comp = &lo->ldo_comp_entries[comp_idx];
        int i;

        for (i = 0; i < comp->llc_stripe_count; i++) {
                if (comp->llc_ost_indices[i] == data->locd_ost_index) {
                        data->locd_ost_index = -1;
                        return -EEXIST;
                }
        }

        return 0;
}

/**
 * Check is OST used in a composite layout
 *
 * \param[in] lo        lod object
 * \param[in] ost       OST target index to check
 *
 * \retval false        not used
 * \retval true         used
 */
static inline bool lod_comp_is_ost_used(const struct lu_env *env,
                                       struct lod_object *lo, int ost)
{
        struct lod_obj_stripe_cb_data data = { { 0 } };

        data.locd_ost_index = ost;
        data.locd_comp_skip_cb = lod_obj_is_ost_use_skip_cb;
        data.locd_comp_cb = lod_obj_is_ost_use_cb;

        (void)lod_obj_for_each_stripe(env, lo, NULL, &data);

        return data.locd_ost_index == -1;
}

static inline void lod_avoid_update(struct lod_object *lo,
                                    struct lod_avoid_guide *lag)
{
        if (!lod_is_flr(lo))
                return;

        lag->lag_ost_avail--;
}

static inline bool lod_should_avoid_ost(struct lod_object *lo,
                                        struct lod_avoid_guide *lag,
                                        __u32 index)
{
        struct lod_device *lod = lu2lod_dev(lo->ldo_obj.do_lu.lo_dev);
        struct lod_tgt_desc *ost = OST_TGT(lod, index);
        struct lu_svr_qos *lsq = ost->ltd_qos.ltq_svr;
        bool used = false;
        int i;

        if (!cfs_bitmap_check(lod->lod_ost_bitmap, index)) {
                QOS_DEBUG("OST%d: been used in conflicting mirror component\n",
                          index);
                return true;
        }

        /**
         * we've tried our best, all available OSTs have been used in
         * overlapped components in the other mirror
         */
        if (lag->lag_ost_avail == 0)
                return false;

        /* check OSS use */
        for (i = 0; i < lag->lag_oaa_count; i++) {
                if (lag->lag_oss_avoid_array[i] == lsq->lsq_id) {
                        used = true;
                        break;
                }
        }
        /**
         * if the OSS which OST[index] resides has not been used, we'd like to
         * use it
         */
        if (!used)
                return false;

        /* if the OSS has been used, check whether the OST has been used */
        if (!cfs_bitmap_check(lag->lag_ost_avoid_bitmap, index))
                used = false;
        else
                QOS_DEBUG("OST%d: been used in conflicting mirror component\n",
                          index);
        return used;
}

static int lod_check_and_reserve_ost(const struct lu_env *env,
                                     struct lod_object *lo,
                                     struct lod_layout_component *lod_comp,
                                     __u32 ost_idx, __u32 speed, __u32 *s_idx,
                                     struct dt_object **stripe,
                                     __u32 *ost_indices,
                                     struct thandle *th,
                                     bool *overstriped)
{
        struct lod_device *lod = lu2lod_dev(lo->ldo_obj.do_lu.lo_dev);
        struct lod_avoid_guide *lag = &lod_env_info(env)->lti_avoid;
        struct lu_tgt_desc *ost = OST_TGT(lod, ost_idx);
        struct dt_object   *o;
        __u32 stripe_idx = *s_idx;
        int rc;

        ENTRY;

        rc = lod_statfs_and_check(env, lod, &lod->lod_ost_descs, ost);
        if (rc)
                RETURN(rc);

        /*
         * We expect number of precreated objects in f_ffree at
         * the first iteration, skip OSPs with no objects ready
         */
        if (ost->ltd_statfs.os_fprecreated == 0 && speed == 0) {
                QOS_DEBUG("#%d: precreation is empty\n", ost_idx);
                RETURN(rc);
        }

        /*
         * try to use another OSP if this one is degraded
         */
        if (ost->ltd_statfs.os_state & OS_STATE_DEGRADED && speed < 2) {
                QOS_DEBUG("#%d: degraded\n", ost_idx);
                RETURN(rc);
        }

        /*
         * try not allocate on OST which has been used by other
         * component
         */
        if (speed == 0 && lod_comp_is_ost_used(env, lo, ost_idx)) {
                QOS_DEBUG("iter %d: OST%d used by other component\n",
                          speed, ost_idx);
                RETURN(rc);
        }

        /**
         * try not allocate OSTs used by conflicting component of other mirrors
         * for the first and second time.
         */
        if (speed < 2 && lod_should_avoid_ost(lo, lag, ost_idx)) {
                QOS_DEBUG("iter %d: OST%d used by conflicting mirror component\n",
                          speed, ost_idx);
                RETURN(rc);
        }

        /* do not put >1 objects on a single OST, except for overstriping */
        if (lod_qos_is_tgt_used(env, ost_idx, stripe_idx)) {
                if (lod_comp->llc_pattern & LOV_PATTERN_OVERSTRIPING)
                        *overstriped = true;
                else
                        RETURN(rc);
        }

        o = lod_qos_declare_object_on(env, lod, ost_idx, th);
        if (IS_ERR(o)) {
                CDEBUG(D_OTHER, "can't declare new object on #%u: %d\n",
                       ost_idx, (int) PTR_ERR(o));
                rc = PTR_ERR(o);
                RETURN(rc);
        }

        /*
         * We've successfully declared (reserved) an object
         */
        lod_avoid_update(lo, lag);
        lod_qos_tgt_in_use(env, stripe_idx, ost_idx);
        stripe[stripe_idx] = o;
        ost_indices[stripe_idx] = ost_idx;
        OBD_FAIL_TIMEOUT(OBD_FAIL_MDS_LOV_CREATE_RACE, 2);
        stripe_idx++;
        *s_idx = stripe_idx;

        RETURN(rc);
}

/**
 * Allocate a striping using round-robin algorithm.
 *
 * Allocates a new striping using round-robin algorithm. The function refreshes
 * all the internal structures (statfs cache, array of available OSTs sorted
 * with regard to OSS, etc). The number of stripes required is taken from the
 * object (must be prepared by the caller), but can change if the flag
 * LOV_USES_DEFAULT_STRIPE is supplied. The caller should ensure nobody else
 * is trying to create a striping on the object in parallel. All the internal
 * structures (like pools, etc) are protected and no additional locking is
 * required. The function succeeds even if a single stripe is allocated. To save
 * time we give priority to targets which already have objects precreated.
 * Full OSTs are skipped (see lod_qos_dev_is_full() for the details).
 *
 * \param[in] env               execution environment for this thread
 * \param[in] lo                LOD object
 * \param[out] stripe           striping created
 * \param[out] ost_indices      ost indices of striping created
 * \param[in] flags             allocation flags (0 or LOV_USES_DEFAULT_STRIPE)
 * \param[in] th                transaction handle
 * \param[in] comp_idx          index of ldo_comp_entries
 *
 * \retval 0            on success
 * \retval -ENOSPC      if not enough OSTs are found
 * \retval negative     negated errno for other failures
 */
static int lod_ost_alloc_rr(const struct lu_env *env, struct lod_object *lo,
                            struct dt_object **stripe, __u32 *ost_indices,
                            int flags, struct thandle *th, int comp_idx)
{
        struct lod_layout_component *lod_comp;
        struct lod_device *m = lu2lod_dev(lo->ldo_obj.do_lu.lo_dev);
        struct pool_desc  *pool = NULL;
        struct lu_tgt_pool *osts;
        struct lu_qos_rr *lqr;
        unsigned int i, array_idx;
        __u32 ost_start_idx_temp;
        __u32 stripe_idx = 0;
        __u32 stripe_count, stripe_count_min, ost_idx;
        int rc, speed = 0, ost_connecting = 0;
        int stripes_per_ost = 1;
        bool overstriped = false;
        ENTRY;

        LASSERT(lo->ldo_comp_cnt > comp_idx && lo->ldo_comp_entries != NULL);
        lod_comp = &lo->ldo_comp_entries[comp_idx];
        stripe_count = lod_comp->llc_stripe_count;
        stripe_count_min = min_stripe_count(stripe_count, flags);

        if (lod_comp->llc_pool != NULL)
                pool = lod_find_pool(m, lod_comp->llc_pool);

        if (pool != NULL) {
                down_read(&pool_tgt_rw_sem(pool));
                osts = &(pool->pool_obds);
                lqr = &(pool->pool_rr);
        } else {
                osts = &m->lod_ost_descs.ltd_tgt_pool;
                lqr = &(m->lod_ost_descs.ltd_qos.lq_rr);
        }

        rc = lod_qos_calc_rr(m, &m->lod_ost_descs, osts, lqr);
        if (rc)
                GOTO(out, rc);

        rc = lod_qos_tgt_in_use_clear(env, stripe_count);
        if (rc)
                GOTO(out, rc);

        down_read(&m->lod_ost_descs.ltd_qos.lq_rw_sem);
        spin_lock(&lqr->lqr_alloc);
        if (--lqr->lqr_start_count <= 0) {
                lqr->lqr_start_idx = prandom_u32_max(osts->op_count);
                lqr->lqr_start_count =
                        (LOV_CREATE_RESEED_MIN / max(osts->op_count, 1U) +
                         LOV_CREATE_RESEED_MULT) * max(osts->op_count, 1U);
        } else if (stripe_count_min >= osts->op_count ||
                        lqr->lqr_start_idx > osts->op_count) {
                /* If we have allocated from all of the OSTs, slowly
                 * precess the next start if the OST/stripe count isn't
                 * already doing this for us. */
                lqr->lqr_start_idx %= osts->op_count;
                if (stripe_count > 1 && (osts->op_count % stripe_count) != 1)
                        ++lqr->lqr_offset_idx;
        }
        ost_start_idx_temp = lqr->lqr_start_idx;

repeat_find:

        QOS_DEBUG("pool '%s' want %d start_idx %d start_count %d offset %d "
                  "active %d count %d\n",
                  lod_comp->llc_pool ? lod_comp->llc_pool : "",
                  stripe_count, lqr->lqr_start_idx, lqr->lqr_start_count,
                  lqr->lqr_offset_idx, osts->op_count, osts->op_count);

        if (lod_comp->llc_pattern & LOV_PATTERN_OVERSTRIPING)
                stripes_per_ost =
                        (lod_comp->llc_stripe_count - 1)/osts->op_count + 1;

        for (i = 0; i < osts->op_count * stripes_per_ost
             && stripe_idx < stripe_count; i++) {
                array_idx = (lqr->lqr_start_idx + lqr->lqr_offset_idx) %
                                osts->op_count;
                ++lqr->lqr_start_idx;
                ost_idx = lqr->lqr_pool.op_array[array_idx];

                QOS_DEBUG("#%d strt %d act %d strp %d ary %d idx %d\n",
                          i, lqr->lqr_start_idx, /* XXX: active*/ 0,
                          stripe_idx, array_idx, ost_idx);

                if ((ost_idx == LOV_QOS_EMPTY) ||
                    !cfs_bitmap_check(m->lod_ost_bitmap, ost_idx))
                        continue;

                /* Fail Check before osc_precreate() is called
                   so we can only 'fail' single OSC. */
                if (OBD_FAIL_CHECK(OBD_FAIL_MDS_OSC_PRECREATE) && ost_idx == 0)
                        continue;

                spin_unlock(&lqr->lqr_alloc);
                rc = lod_check_and_reserve_ost(env, lo, lod_comp, ost_idx,
                                               speed, &stripe_idx, stripe,
                                               ost_indices, th, &overstriped);
                spin_lock(&lqr->lqr_alloc);

                if (rc != 0 && OST_TGT(m, ost_idx)->ltd_connecting)
                        ost_connecting = 1;
        }
        if ((speed < 2) && (stripe_idx < stripe_count_min)) {
                /* Try again, allowing slower OSCs */
                speed++;
                lqr->lqr_start_idx = ost_start_idx_temp;

                ost_connecting = 0;
                goto repeat_find;
        }

        spin_unlock(&lqr->lqr_alloc);
        up_read(&m->lod_ost_descs.ltd_qos.lq_rw_sem);

        /* If there are enough OSTs, a component with overstriping requested
         * will not actually end up overstriped.  The comp should reflect this.
         */
        if (!overstriped)
                lod_comp->llc_pattern &= ~LOV_PATTERN_OVERSTRIPING;

        if (stripe_idx) {
                lod_comp->llc_stripe_count = stripe_idx;
                /* at least one stripe is allocated */
                rc = 0;
        } else {
                /* nobody provided us with a single object */
                if (ost_connecting)
                        rc = -EINPROGRESS;
                else
                        rc = -ENOSPC;
        }

out:
        if (pool != NULL) {
                up_read(&pool_tgt_rw_sem(pool));
                /* put back ref got by lod_find_pool() */
                lod_pool_putref(pool);
        }

        RETURN(rc);
}

/**
 * Allocate a striping using round-robin algorithm.
 *
 * Allocates a new striping using round-robin algorithm. The function refreshes
 * all the internal structures (statfs cache, array of available remote MDTs
 * sorted with regard to MDS, etc). The number of stripes required is taken from
 * the object (must be prepared by the caller). The caller should ensure nobody
 * else is trying to create a striping on the object in parallel. All the
 * internal structures (like pools, etc) are protected and no additional locking
 * is required. The function succeeds even if a single stripe is allocated.
 *
 * \param[in] env               execution environment for this thread
 * \param[in] lo                LOD object
 * \param[out] stripe           striping created
 *
 * \retval positive     stripe objects allocated, including the first stripe
 *                      allocated outside
 * \retval -ENOSPC      if not enough MDTs are found
 * \retval negative     negated errno for other failures
 */
int lod_mdt_alloc_rr(const struct lu_env *env, struct lod_object *lo,
                     struct dt_object **stripe)
{
        struct lod_device *lod = lu2lod_dev(lo->ldo_obj.do_lu.lo_dev);
        struct lu_tgt_descs *ltd = &lod->lod_mdt_descs;
        struct lu_tgt_pool *pool;
        struct lu_qos_rr *lqr;
        struct lu_tgt_desc *mdt;
        struct lu_object_conf conf = { .loc_flags = LOC_F_NEW };
        struct lu_fid fid = { 0 };
        struct dt_object *dto;
        unsigned int pool_idx;
        unsigned int i;
        u32 start_idx_temp;
        u32 stripe_count = lo->ldo_dir_stripe_count;
        u32 stripe_idx = 1;
        u32 mdt_idx;
        bool use_degraded = false;
        int tgt_connecting = 0;
        int rc;

        ENTRY;

        pool = &ltd->ltd_tgt_pool;
        lqr = &ltd->ltd_qos.lq_rr;
        rc = lod_qos_calc_rr(lod, ltd, pool, lqr);
        if (rc)
                RETURN(rc);

        rc = lod_qos_tgt_in_use_clear(env, stripe_count);
        if (rc)
                RETURN(rc);

        down_read(&ltd->ltd_qos.lq_rw_sem);
        spin_lock(&lqr->lqr_alloc);
        if (--lqr->lqr_start_count <= 0) {
                lqr->lqr_start_idx = prandom_u32_max(pool->op_count);
                lqr->lqr_start_count =
                        (LOV_CREATE_RESEED_MIN / max(pool->op_count, 1U) +
                         LOV_CREATE_RESEED_MULT) * max(pool->op_count, 1U);
        } else if (stripe_count - 1 >= pool->op_count ||
                   lqr->lqr_start_idx > pool->op_count) {
                /* If we have allocated from all of the tgts, slowly
                 * precess the next start if the tgt/stripe count isn't
                 * already doing this for us. */
                lqr->lqr_start_idx %= pool->op_count;
                if (stripe_count - 1 > 1 &&
                    (pool->op_count % (stripe_count - 1)) != 1)
                        ++lqr->lqr_offset_idx;
        }
        start_idx_temp = lqr->lqr_start_idx;

repeat_find:
        QOS_DEBUG("want %d start_idx %d start_count %d offset %d active %d count %d\n",
                  stripe_count - 1, lqr->lqr_start_idx, lqr->lqr_start_count,
                  lqr->lqr_offset_idx, pool->op_count, pool->op_count);

        for (i = 0; i < pool->op_count && stripe_idx < stripe_count; i++) {
                pool_idx = (lqr->lqr_start_idx + lqr->lqr_offset_idx) %
                            pool->op_count;
                ++lqr->lqr_start_idx;
                mdt_idx = lqr->lqr_pool.op_array[pool_idx];
                mdt = LTD_TGT(ltd, mdt_idx);

                QOS_DEBUG("#%d strt %d act %d strp %d ary %d idx %d\n",
                          i, lqr->lqr_start_idx, /* XXX: active*/ 0,
                          stripe_idx, pool_idx, mdt_idx);

                if (mdt_idx == LOV_QOS_EMPTY ||
                    !cfs_bitmap_check(ltd->ltd_tgt_bitmap, mdt_idx))
                        continue;

                /* do not put >1 objects on one MDT */
                if (lod_qos_is_tgt_used(env, mdt_idx, stripe_idx))
                        continue;

                rc = lod_is_tgt_usable(ltd, mdt);
                if (rc) {
                        if (mdt->ltd_connecting)
                                tgt_connecting = 1;
                        continue;
                }

                /* try to use another OSP if this one is degraded */
                if (mdt->ltd_statfs.os_state & OS_STATE_DEGRADED &&
                    !use_degraded) {
                        QOS_DEBUG("#%d: degraded\n", mdt_idx);
                        continue;
                }
                spin_unlock(&lqr->lqr_alloc);

                rc = obd_fid_alloc(env, mdt->ltd_exp, &fid, NULL);
                if (rc) {
                        QOS_DEBUG("#%d: alloc FID failed: %dl\n", mdt_idx, rc);
                        spin_lock(&lqr->lqr_alloc);
                        continue;
                }

                dto = dt_locate_at(env, mdt->ltd_tgt, &fid,
                                lo->ldo_obj.do_lu.lo_dev->ld_site->ls_top_dev,
                                &conf);

                spin_lock(&lqr->lqr_alloc);
                if (IS_ERR(dto)) {
                        QOS_DEBUG("can't alloc stripe on #%u: %d\n",
                                  mdt->ltd_index, (int) PTR_ERR(dto));

                        if (mdt->ltd_connecting)
                                tgt_connecting = 1;
                        continue;
                }

                lod_qos_tgt_in_use(env, stripe_idx, mdt_idx);
                stripe[stripe_idx] = dto;
                stripe_idx++;
        }

        if (!use_degraded && stripe_idx < stripe_count) {
                /* Try again, allowing slower OSCs */
                use_degraded = true;
                lqr->lqr_start_idx = start_idx_temp;

                tgt_connecting = 0;
                goto repeat_find;
        }
        spin_unlock(&lqr->lqr_alloc);
        up_read(&ltd->ltd_qos.lq_rw_sem);

        if (stripe_idx > 1)
                /* at least one stripe is allocated */
                RETURN(stripe_idx);

        /* nobody provided us with a single object */
        if (tgt_connecting)
                RETURN(-EINPROGRESS);

        RETURN(-ENOSPC);
}

/**
 * Allocate a specific striping layout on a user defined set of OSTs.
 *
 * Allocates new striping using the OST index range provided by the data from
 * the lmm_obejcts contained in the lov_user_md passed to this method. Full
 * OSTs are not considered. The exact order of OSTs requested by the user
 * is respected as much as possible depending on OST status. The number of
 * stripes needed and stripe offset are taken from the object. If that number
 * can not be met, then the function returns a failure and then it's the
 * caller's responsibility to release the stripes allocated. All the internal
 * structures are protected, but no concurrent allocation is allowed on the
 * same objects.
 *
 * \param[in] env               execution environment for this thread
 * \param[in] lo                LOD object
 * \param[out] stripe           striping created
 * \param[out] ost_indices      ost indices of striping created
 * \param[in] th                transaction handle
 * \param[in] comp_idx          index of ldo_comp_entries
 *
 * \retval 0            on success
 * \retval -ENODEV      OST index does not exist on file system
 * \retval -EINVAL      requested OST index is invalid
 * \retval negative     negated errno on error
 */
static int lod_alloc_ost_list(const struct lu_env *env, struct lod_object *lo,
                              struct dt_object **stripe, __u32 *ost_indices,
                              struct thandle *th, int comp_idx)
{
        struct lod_layout_component *lod_comp;
        struct lod_device       *m = lu2lod_dev(lo->ldo_obj.do_lu.lo_dev);
        struct dt_object        *o;
        unsigned int            array_idx = 0;
        int                     stripe_count = 0;
        int                     i;
        int                     rc = -EINVAL;
        ENTRY;

        /* for specific OSTs layout */
        LASSERT(lo->ldo_comp_cnt > comp_idx && lo->ldo_comp_entries != NULL);
        lod_comp = &lo->ldo_comp_entries[comp_idx];
        LASSERT(lod_comp->llc_ostlist.op_array);
        LASSERT(lod_comp->llc_ostlist.op_count);

        rc = lod_qos_tgt_in_use_clear(env, lod_comp->llc_stripe_count);
        if (rc < 0)
                RETURN(rc);

        if (lod_comp->llc_stripe_offset == LOV_OFFSET_DEFAULT)
                lod_comp->llc_stripe_offset =
                                lod_comp->llc_ostlist.op_array[0];

        for (i = 0; i < lod_comp->llc_stripe_count; i++) {
                if (lod_comp->llc_ostlist.op_array[i] ==
                    lod_comp->llc_stripe_offset) {
                        array_idx = i;
                        break;
                }
        }
        if (i == lod_comp->llc_stripe_count) {
                CDEBUG(D_OTHER,
                       "%s: start index %d not in the specified list of OSTs\n",
                       lod2obd(m)->obd_name, lod_comp->llc_stripe_offset);
                RETURN(-EINVAL);
        }

        for (i = 0; i < lod_comp->llc_stripe_count;
             i++, array_idx = (array_idx + 1) % lod_comp->llc_stripe_count) {
                __u32 ost_idx = lod_comp->llc_ostlist.op_array[array_idx];

                if (!cfs_bitmap_check(m->lod_ost_bitmap, ost_idx)) {
                        rc = -ENODEV;
                        break;
                }

                /* do not put >1 objects on a single OST, except for
                 * overstriping
                 */
                if (lod_qos_is_tgt_used(env, ost_idx, stripe_count) &&
                    !(lod_comp->llc_pattern & LOV_PATTERN_OVERSTRIPING)) {
                        rc = -EINVAL;
                        break;
                }

                rc = lod_statfs_and_check(env, m, &m->lod_ost_descs,
                                          LTD_TGT(&m->lod_ost_descs, ost_idx));
                if (rc < 0) /* this OSP doesn't feel well */
                        break;

                o = lod_qos_declare_object_on(env, m, ost_idx, th);
                if (IS_ERR(o)) {
                        rc = PTR_ERR(o);
                        CDEBUG(D_OTHER,
                               "%s: can't declare new object on #%u: %d\n",
                               lod2obd(m)->obd_name, ost_idx, rc);
                        break;
                }

                /*
                 * We've successfully declared (reserved) an object
                 */
                lod_qos_tgt_in_use(env, stripe_count, ost_idx);
                stripe[stripe_count] = o;
                ost_indices[stripe_count] = ost_idx;
                stripe_count++;
        }

        RETURN(rc);
}

/**
 * Allocate a striping on a predefined set of OSTs.
 *
 * Allocates new layout starting from OST index in lo->ldo_stripe_offset.
 * Full OSTs are not considered. The exact order of OSTs is not important and
 * varies depending on OST status. The allocation procedure prefers the targets
 * with precreated objects ready. The number of stripes needed and stripe
 * offset are taken from the object. If that number cannot be met, then the
 * function returns an error and then it's the caller's responsibility to
 * release the stripes allocated. All the internal structures are protected,
 * but no concurrent allocation is allowed on the same objects.
 *
 * \param[in] env               execution environment for this thread
 * \param[in] lo                LOD object
 * \param[out] stripe           striping created
 * \param[out] ost_indices      ost indices of striping created
 * \param[in] flags             not used
 * \param[in] th                transaction handle
 * \param[in] comp_idx          index of ldo_comp_entries
 *
 * \retval 0            on success
 * \retval -ENOSPC      if no OST objects are available at all
 * \retval -EFBIG       if not enough OST objects are found
 * \retval -EINVAL      requested offset is invalid
 * \retval negative     errno on failure
 */
static int lod_ost_alloc_specific(const struct lu_env *env,
                                  struct lod_object *lo,
                                  struct dt_object **stripe, __u32 *ost_indices,
                                  int flags, struct thandle *th, int comp_idx)
{
        struct lod_layout_component *lod_comp;
        struct lod_device *m = lu2lod_dev(lo->ldo_obj.do_lu.lo_dev);
        struct dt_object *o;
        struct lu_tgt_desc *tgt;
        __u32 ost_idx;
        unsigned int i, array_idx, ost_count;
        int rc, stripe_num = 0;
        int speed = 0;
        struct pool_desc *pool = NULL;
        struct lu_tgt_pool *osts;
        int stripes_per_ost = 1;
        bool overstriped = false;
        ENTRY;

        LASSERT(lo->ldo_comp_cnt > comp_idx && lo->ldo_comp_entries != NULL);
        lod_comp = &lo->ldo_comp_entries[comp_idx];

        rc = lod_qos_tgt_in_use_clear(env, lod_comp->llc_stripe_count);
        if (rc)
                GOTO(out, rc);

        if (lod_comp->llc_pool != NULL)
                pool = lod_find_pool(m, lod_comp->llc_pool);

        if (pool != NULL) {
                down_read(&pool_tgt_rw_sem(pool));
                osts = &(pool->pool_obds);
        } else {
                osts = &m->lod_ost_descs.ltd_tgt_pool;
        }

        ost_count = osts->op_count;

repeat_find:
        /* search loi_ost_idx in ost array */
        array_idx = 0;
        for (i = 0; i < ost_count; i++) {
                if (osts->op_array[i] == lod_comp->llc_stripe_offset) {
                        array_idx = i;
                        break;
                }
        }
        if (i == ost_count) {
                CERROR("Start index %d not found in pool '%s'\n",
                       lod_comp->llc_stripe_offset,
                       lod_comp->llc_pool ? lod_comp->llc_pool : "");
                GOTO(out, rc = -EINVAL);
        }

        if (lod_comp->llc_pattern & LOV_PATTERN_OVERSTRIPING)
                stripes_per_ost =
                        (lod_comp->llc_stripe_count - 1)/ost_count + 1;

        for (i = 0; i < ost_count * stripes_per_ost;
                        i++, array_idx = (array_idx + 1) % ost_count) {
                ost_idx = osts->op_array[array_idx];

                if (!cfs_bitmap_check(m->lod_ost_bitmap, ost_idx))
                        continue;

                /* Fail Check before osc_precreate() is called
                   so we can only 'fail' single OSC. */
                if (OBD_FAIL_CHECK(OBD_FAIL_MDS_OSC_PRECREATE) && ost_idx == 0)
                        continue;

                /*
                 * do not put >1 objects on a single OST, except for
                 * overstriping, where it is intended
                 */
                if (lod_qos_is_tgt_used(env, ost_idx, stripe_num)) {
                        if (lod_comp->llc_pattern & LOV_PATTERN_OVERSTRIPING)
                                overstriped = true;
                        else
                                continue;
                }

                /*
                 * try not allocate on the OST used by other component
                 */
                if (speed == 0 && i != 0 &&
                    lod_comp_is_ost_used(env, lo, ost_idx))
                        continue;

                tgt = LTD_TGT(&m->lod_ost_descs, ost_idx);

                /* Drop slow OSCs if we can, but not for requested start idx.
                 *
                 * This means "if OSC is slow and it is not the requested
                 * start OST, then it can be skipped, otherwise skip it only
                 * if it is inactive/recovering/out-of-space." */

                rc = lod_statfs_and_check(env, m, &m->lod_ost_descs, tgt);
                if (rc) {
                        /* this OSP doesn't feel well */
                        continue;
                }

                /*
                 * We expect number of precreated objects at the first
                 * iteration.  Skip OSPs with no objects ready.  Don't apply
                 * this logic to OST specified with stripe_offset.
                 */
                if (i && !tgt->ltd_statfs.os_fprecreated && !speed)
                        continue;

                o = lod_qos_declare_object_on(env, m, ost_idx, th);
                if (IS_ERR(o)) {
                        CDEBUG(D_OTHER, "can't declare new object on #%u: %d\n",
                               ost_idx, (int) PTR_ERR(o));
                        continue;
                }

                /*
                 * We've successfully declared (reserved) an object
                 */
                lod_qos_tgt_in_use(env, stripe_num, ost_idx);
                stripe[stripe_num] = o;
                ost_indices[stripe_num] = ost_idx;
                stripe_num++;

                /* We have enough stripes */
                if (stripe_num == lod_comp->llc_stripe_count)
                        GOTO(out, rc = 0);
        }
        if (speed < 2) {
                /* Try again, allowing slower OSCs */
                speed++;
                goto repeat_find;
        }

        /* If we were passed specific striping params, then a failure to
         * meet those requirements is an error, since we can't reallocate
         * that memory (it might be part of a larger array or something).
         */
        CERROR("can't lstripe objid "DFID": have %d want %u\n",
               PFID(lu_object_fid(lod2lu_obj(lo))), stripe_num,
               lod_comp->llc_stripe_count);
        rc = stripe_num == 0 ? -ENOSPC : -EFBIG;

        /* If there are enough OSTs, a component with overstriping requessted
         * will not actually end up overstriped.  The comp should reflect this.
         */
        if (rc == 0 && !overstriped)
                lod_comp->llc_pattern &= ~LOV_PATTERN_OVERSTRIPING;

out:
        if (pool != NULL) {
                up_read(&pool_tgt_rw_sem(pool));
                /* put back ref got by lod_find_pool() */
                lod_pool_putref(pool);
        }

        RETURN(rc);
}

/**
 * Allocate a striping using an algorithm with weights.
 *
 * The function allocates OST objects to create a striping. The algorithm
 * used is based on weights (currently only using the free space), and it's
 * trying to ensure the space is used evenly by OSTs and OSSs. The striping
 * configuration (# of stripes, offset, pool) is taken from the object and
 * is prepared by the caller.
 *
 * If LOV_USES_DEFAULT_STRIPE is not passed and prepared configuration can't
 * be met due to too few OSTs, then allocation fails. If the flag is passed
 * fewer than 3/4 of the requested number of stripes can be allocated, then
 * allocation fails.
 *
 * No concurrent allocation is allowed on the object and this must be ensured
 * by the caller. All the internal structures are protected by the function.
 *
 * The algorithm has two steps: find available OSTs and calculate their
 * weights, then select the OSTs with their weights used as the probability.
 * An OST with a higher weight is proportionately more likely to be selected
 * than one with a lower weight.
 *
 * \param[in] env               execution environment for this thread
 * \param[in] lo                LOD object
 * \param[out] stripe           striping created
 * \param[out] ost_indices      ost indices of striping created
 * \param[in] flags             0 or LOV_USES_DEFAULT_STRIPE
 * \param[in] th                transaction handle
 * \param[in] comp_idx          index of ldo_comp_entries
 *
 * \retval 0            on success
 * \retval -EAGAIN      not enough OSTs are found for specified stripe count
 * \retval -EINVAL      requested OST index is invalid
 * \retval negative     errno on failure
 */
static int lod_ost_alloc_qos(const struct lu_env *env, struct lod_object *lo,
                             struct dt_object **stripe, __u32 *ost_indices,
                             int flags, struct thandle *th, int comp_idx)
{
        struct lod_layout_component *lod_comp;
        struct lod_device *lod = lu2lod_dev(lo->ldo_obj.do_lu.lo_dev);
        struct lod_avoid_guide *lag = &lod_env_info(env)->lti_avoid;
        struct lod_tgt_desc *ost;
        struct dt_object *o;
        __u64 total_weight = 0;
        struct pool_desc *pool = NULL;
        struct lu_tgt_pool *osts;
        unsigned int i;
        __u32 nfound, good_osts, stripe_count, stripe_count_min;
        bool overstriped = false;
        int stripes_per_ost = 1;
        int rc = 0;
        ENTRY;

        LASSERT(lo->ldo_comp_cnt > comp_idx && lo->ldo_comp_entries != NULL);
        lod_comp = &lo->ldo_comp_entries[comp_idx];
        stripe_count = lod_comp->llc_stripe_count;
        stripe_count_min = min_stripe_count(stripe_count, flags);
        if (stripe_count_min < 1)
                RETURN(-EINVAL);

        if (lod_comp->llc_pool != NULL)
                pool = lod_find_pool(lod, lod_comp->llc_pool);

        if (pool != NULL) {
                down_read(&pool_tgt_rw_sem(pool));
                osts = &(pool->pool_obds);
        } else {
                osts = &lod->lod_ost_descs.ltd_tgt_pool;
        }

        /* Detect -EAGAIN early, before expensive lock is taken. */
        if (!ltd_qos_is_usable(&lod->lod_ost_descs))
                GOTO(out_nolock, rc = -EAGAIN);

        if (lod_comp->llc_pattern & LOV_PATTERN_OVERSTRIPING)
                stripes_per_ost =
                        (lod_comp->llc_stripe_count - 1)/osts->op_count + 1;

        /* Do actual allocation, use write lock here. */
        down_write(&lod->lod_ost_descs.ltd_qos.lq_rw_sem);

        /*
         * Check again, while we were sleeping on @lq_rw_sem things could
         * change.
         */
        if (!ltd_qos_is_usable(&lod->lod_ost_descs))
                GOTO(out, rc = -EAGAIN);

        rc = ltd_qos_penalties_calc(&lod->lod_ost_descs);
        if (rc)
                GOTO(out, rc);

        rc = lod_qos_tgt_in_use_clear(env, lod_comp->llc_stripe_count);
        if (rc)
                GOTO(out, rc);

        good_osts = 0;
        /* Find all the OSTs that are valid stripe candidates */
        for (i = 0; i < osts->op_count; i++) {
                if (!cfs_bitmap_check(lod->lod_ost_bitmap, osts->op_array[i]))
                        continue;

                ost = OST_TGT(lod, osts->op_array[i]);
                ost->ltd_qos.ltq_usable = 0;

                rc = lod_statfs_and_check(env, lod, &lod->lod_ost_descs, ost);
                if (rc) {
                        /* this OSP doesn't feel well */
                        continue;
                }

                if (ost->ltd_statfs.os_state & OS_STATE_DEGRADED)
                        continue;

                /* Fail Check before osc_precreate() is called
                 * so we can only 'fail' single OSC.
                 */
                if (OBD_FAIL_CHECK(OBD_FAIL_MDS_OSC_PRECREATE) &&
                                   osts->op_array[i] == 0)
                        continue;

                ost->ltd_qos.ltq_usable = 1;
                lu_tgt_qos_weight_calc(ost);
                total_weight += ost->ltd_qos.ltq_weight;

                good_osts++;
        }

        QOS_DEBUG("found %d good osts\n", good_osts);

        if (good_osts < stripe_count_min)
                GOTO(out, rc = -EAGAIN);

        /* If we do not have enough OSTs for the requested stripe count, do not
         * put more stripes per OST than requested.
         */
        if (stripe_count / stripes_per_ost > good_osts)
                stripe_count = good_osts * stripes_per_ost;

        /* Find enough OSTs with weighted random allocation. */
        nfound = 0;
        while (nfound < stripe_count) {
                u64 rand, cur_weight;

                cur_weight = 0;
                rc = -ENOSPC;

                rand = lu_prandom_u64_max(total_weight);

                /* On average, this will hit larger-weighted OSTs more often.
                 * 0-weight OSTs will always get used last (only when rand=0)
                 */
                for (i = 0; i < osts->op_count; i++) {
                        __u32 idx = osts->op_array[i];

                        if (lod_should_avoid_ost(lo, lag, idx))
                                continue;

                        ost = OST_TGT(lod, idx);

                        if (!ost->ltd_qos.ltq_usable)
                                continue;

                        cur_weight += ost->ltd_qos.ltq_weight;
                        QOS_DEBUG("stripe_count=%d nfound=%d cur_weight=%llu "
                                  "rand=%llu total_weight=%llu\n",
                                  stripe_count, nfound, cur_weight, rand,
                                  total_weight);

                        if (cur_weight < rand)
                                continue;

                        QOS_DEBUG("stripe=%d to idx=%d\n", nfound, idx);
                        /*
                         * do not put >1 objects on a single OST, except for
                         * overstriping
                         */
                        if ((lod_comp_is_ost_used(env, lo, idx)) &&
                            !(lod_comp->llc_pattern & LOV_PATTERN_OVERSTRIPING))
                                continue;

                        if (lod_qos_is_tgt_used(env, idx, nfound)) {
                                if (lod_comp->llc_pattern &
                                    LOV_PATTERN_OVERSTRIPING)
                                        overstriped = true;
                                else
                                        continue;
                        }

                        o = lod_qos_declare_object_on(env, lod, idx, th);
                        if (IS_ERR(o)) {
                                QOS_DEBUG("can't declare object on #%u: %d\n",
                                          idx, (int) PTR_ERR(o));
                                continue;
                        }

                        lod_avoid_update(lo, lag);
                        lod_qos_tgt_in_use(env, nfound, idx);
                        stripe[nfound] = o;
                        ost_indices[nfound] = idx;
                        ltd_qos_update(&lod->lod_ost_descs, ost, &total_weight);
                        nfound++;
                        rc = 0;
                        break;
                }

                if (rc) {
                        /* no OST found on this iteration, give up */
                        break;
                }
        }

        if (unlikely(nfound != stripe_count)) {
                /*
                 * when the decision to use weighted algorithm was made
                 * we had enough appropriate OSPs, but this state can
                 * change anytime (no space on OST, broken connection, etc)
                 * so it's possible OSP won't be able to provide us with
                 * an object due to just changed state
                 */
                QOS_DEBUG("%s: wanted %d objects, found only %d\n",
                          lod2obd(lod)->obd_name, stripe_count, nfound);
                for (i = 0; i < nfound; i++) {
                        LASSERT(stripe[i] != NULL);
                        dt_object_put(env, stripe[i]);
                        stripe[i] = NULL;
                }

                /* makes sense to rebalance next time */
                lod->lod_ost_descs.ltd_qos.lq_dirty = 1;
                lod->lod_ost_descs.ltd_qos.lq_same_space = 0;

                rc = -EAGAIN;
        }

        /* If there are enough OSTs, a component with overstriping requessted
         * will not actually end up overstriped.  The comp should reflect this.
         */
        if (rc == 0 && !overstriped)
                lod_comp->llc_pattern &= ~LOV_PATTERN_OVERSTRIPING;

out:
        up_write(&lod->lod_ost_descs.ltd_qos.lq_rw_sem);

out_nolock:
        if (pool != NULL) {
                up_read(&pool_tgt_rw_sem(pool));
                /* put back ref got by lod_find_pool() */
                lod_pool_putref(pool);
        }

        RETURN(rc);
}

/**
 * Allocate a striping using an algorithm with weights.
 *
 * The function allocates remote MDT objects to create a striping, the first
 * object was already allocated on current MDT to ensure master object and
 * the first object are on the same MDT. The algorithm used is based on weights
 * (both free space and inodes), and it's trying to ensure the space/inodes are
 * used evenly by MDTs and MDSs. The striping configuration (# of stripes,
 * offset, pool) is taken from the object and is prepared by the caller.
 *
 * If prepared configuration can't be met due to too few MDTs, then allocation
 * fails.
 *
 * No concurrent allocation is allowed on the object and this must be ensured
 * by the caller. All the internal structures are protected by the function.
 *
 * The algorithm has two steps: find available MDTs and calculate their
 * weights, then select the MDTs with their weights used as the probability.
 * An MDT with a higher weight is proportionately more likely to be selected
 * than one with a lower weight.
 *
 * \param[in] env               execution environment for this thread
 * \param[in] lo                LOD object
 * \param[out] stripes          striping created
 *
 * \retval positive     stripes allocated, and it should be equal to
 *                      lo->ldo_dir_stripe_count
 * \retval -EAGAIN      not enough tgts are found for specified stripe count
 * \retval -EINVAL      requested MDT index is invalid
 * \retval negative     errno on failure
 */
int lod_mdt_alloc_qos(const struct lu_env *env, struct lod_object *lo,
                      struct dt_object **stripes)
{
        struct lod_device *lod = lu2lod_dev(lo->ldo_obj.do_lu.lo_dev);
        struct lu_tgt_descs *ltd = &lod->lod_mdt_descs;
        struct lu_object_conf conf = { .loc_flags = LOC_F_NEW };
        struct lu_fid fid = { 0 };
        const struct lu_tgt_pool *pool;
        struct lu_tgt_desc *mdt;
        struct dt_object *dto;
        u64 total_weight = 0;
        u32 stripe_count = lo->ldo_dir_stripe_count;
        unsigned int nfound;
        unsigned int good_mdts;
        unsigned int i;
        int rc = 0;

        ENTRY;

        if (stripe_count == 1)
                RETURN(1);

        pool = &ltd->ltd_tgt_pool;

        /* Detect -EAGAIN early, before expensive lock is taken. */
        if (!ltd_qos_is_usable(ltd))
                RETURN(-EAGAIN);

        /* Do actual allocation, use write lock here. */
        down_write(&ltd->ltd_qos.lq_rw_sem);

        /*
         * Check again, while we were sleeping on @lq_rw_sem things could
         * change.
         */
        if (!ltd_qos_is_usable(ltd))
                GOTO(unlock, rc = -EAGAIN);

        rc = ltd_qos_penalties_calc(ltd);
        if (rc)
                GOTO(unlock, rc);

        rc = lod_qos_tgt_in_use_clear(env, stripe_count);
        if (rc)
                GOTO(unlock, rc);

        good_mdts = 0;
        /* Find all the tgts that are valid stripe candidates */
        for (i = 0; i < pool->op_count; i++) {
                if (!cfs_bitmap_check(ltd->ltd_tgt_bitmap, pool->op_array[i]))
                        continue;

                mdt = LTD_TGT(ltd, pool->op_array[i]);
                mdt->ltd_qos.ltq_usable = 0;

                rc = lod_is_tgt_usable(ltd, mdt);
                if (rc)
                        continue;

                if (mdt->ltd_statfs.os_state & OS_STATE_DEGRADED)
                        continue;

                mdt->ltd_qos.ltq_usable = 1;
                lu_tgt_qos_weight_calc(mdt);
                total_weight += mdt->ltd_qos.ltq_weight;

                good_mdts++;
        }

        QOS_DEBUG("found %d good tgts\n", good_mdts);

        if (good_mdts < stripe_count - 1)
                GOTO(unlock, rc = -EAGAIN);

        /* Find enough tgts with weighted random allocation. */
        nfound = 1;
        while (nfound < stripe_count) {
                u64 rand, cur_weight;

                cur_weight = 0;
                rc = -ENOSPC;

                rand = lu_prandom_u64_max(total_weight);

                /* On average, this will hit larger-weighted tgts more often.
                 * 0-weight tgts will always get used last (only when rand=0) */
                for (i = 0; i < pool->op_count; i++) {
                        __u32 idx = pool->op_array[i];
                        int rc2;

                        mdt = LTD_TGT(ltd, idx);

                        if (!mdt->ltd_qos.ltq_usable)
                                continue;

                        cur_weight += mdt->ltd_qos.ltq_weight;

                        QOS_DEBUG("idx=%d nfound=%d cur_weight=%llu rand=%llu total_weight=%llu\n",
                                  idx, nfound, cur_weight, rand,
                                  total_weight);

                        if (cur_weight < rand)
                                continue;

                        QOS_DEBUG("stripe=%d to idx=%d\n", nfound, idx);

                        if (lod_qos_is_tgt_used(env, idx, nfound))
                                continue;

                        rc2 = obd_fid_alloc(env, mdt->ltd_exp, &fid, NULL);
                        if (rc2) {
                                QOS_DEBUG("can't alloc FID on #%u: %d\n",
                                          idx, rc2);
                                continue;
                        }

                        conf.loc_flags = LOC_F_NEW;
                        dto = dt_locate_at(env, mdt->ltd_tgt, &fid,
                                lo->ldo_obj.do_lu.lo_dev->ld_site->ls_top_dev,
                                &conf);
                        if (IS_ERR(dto)) {
                                QOS_DEBUG("can't alloc stripe on #%u: %d\n",
                                          idx, (int) PTR_ERR(dto));
                                continue;
                        }

                        lod_qos_tgt_in_use(env, nfound, idx);
                        stripes[nfound] = dto;
                        ltd_qos_update(ltd, mdt, &total_weight);
                        nfound++;
                        rc = 0;
                        break;
                }

                /* no MDT found on this iteration, give up */
                if (rc)
                        break;
        }

        if (unlikely(nfound != stripe_count)) {
                /*
                 * when the decision to use weighted algorithm was made
                 * we had enough appropriate OSPs, but this state can
                 * change anytime (no space on MDT, broken connection, etc)
                 * so it's possible OSP won't be able to provide us with
                 * an object due to just changed state
                 */
                QOS_DEBUG("%s: wanted %d objects, found only %d\n",
                          lod2obd(lod)->obd_name, stripe_count, nfound);
                for (i = 1; i < nfound; i++) {
                        LASSERT(stripes[i] != NULL);
                        dt_object_put(env, stripes[i]);
                        stripes[i] = NULL;
                }

                /* makes sense to rebalance next time */
                ltd->ltd_qos.lq_dirty = 1;
                ltd->ltd_qos.lq_same_space = 0;

                rc = -EAGAIN;
        } else {
                rc = nfound;
        }

unlock:
        up_write(&ltd->ltd_qos.lq_rw_sem);

        RETURN(rc);
}

/**
 * Check stripe count the caller can use.
 *
 * For new layouts (no initialized components), check the total size of the
 * layout against the maximum EA size from the backing file system.  This
 * stops us from creating a layout which will be too large once initialized.
 *
 * For existing layouts (with initialized components):
 * Find the maximal possible stripe count not greater than \a stripe_count.
 * If the provided stripe count is 0, then the filesystem's default is used.
 *
 * \param[in] lod       LOD device
 * \param[in] lo        The lod_object
 * \param[in] stripe_count      count the caller would like to use
 *
 * \retval              the maximum usable stripe count
 */
__u16 lod_get_stripe_count(struct lod_device *lod, struct lod_object *lo,
                           __u16 stripe_count, bool overstriping)
{
        __u32 max_stripes = LOV_MAX_STRIPE_COUNT_OLD;
        /* max stripe count is based on OSD ea size */
        unsigned int easize = lod->lod_osd_max_easize;
        int i;


        if (!stripe_count)
                stripe_count =
                        lod->lod_ost_descs.ltd_lov_desc.ld_default_stripe_count;
        if (!stripe_count)
                stripe_count = 1;
        /* Overstriping allows more stripes than targets */
        if (stripe_count >
                lod->lod_ost_descs.ltd_lov_desc.ld_active_tgt_count &&
            !overstriping)
                stripe_count =
                        lod->lod_ost_descs.ltd_lov_desc.ld_active_tgt_count;

        if (lo->ldo_is_composite) {
                struct lod_layout_component *lod_comp;
                unsigned int header_sz = sizeof(struct lov_comp_md_v1);
                unsigned int init_comp_sz = 0;
                unsigned int total_comp_sz = 0;
                unsigned int comp_sz;

                header_sz += sizeof(struct lov_comp_md_entry_v1) *
                                lo->ldo_comp_cnt;

                for (i = 0; i < lo->ldo_comp_cnt; i++) {
                        lod_comp = &lo->ldo_comp_entries[i];
                        comp_sz = lov_mds_md_size(lod_comp->llc_stripe_count,
                                                  LOV_MAGIC_V3);
                        total_comp_sz += comp_sz;
                        if (lod_comp->llc_flags & LCME_FL_INIT)
                                init_comp_sz += comp_sz;
                }

                if (init_comp_sz > 0)
                        total_comp_sz = init_comp_sz;

                header_sz += total_comp_sz;

                if (easize > header_sz)
                        easize -= header_sz;
                else
                        easize = 0;
        }

        max_stripes = lov_mds_md_max_stripe_count(easize, LOV_MAGIC_V3);

        return (stripe_count < max_stripes) ? stripe_count : max_stripes;
}

/**
 * Create in-core respresentation for a fully-defined striping
 *
 * When the caller passes a fully-defined striping (i.e. everything including
 * OST object FIDs are defined), then we still need to instantiate LU-cache
 * with the objects representing the stripes defined. This function completes
 * that task.
 *
 * \param[in] env       execution environment for this thread
 * \param[in] mo        LOD object
 * \param[in] buf       buffer containing the striping
 *
 * \retval 0            on success
 * \retval negative     negated errno on error
 */
int lod_use_defined_striping(const struct lu_env *env,
                             struct lod_object *mo,
                             const struct lu_buf *buf)
{
        struct lod_layout_component *lod_comp;
        struct lov_mds_md_v1   *v1 = buf->lb_buf;
        struct lov_mds_md_v3   *v3 = buf->lb_buf;
        struct lov_comp_md_v1  *comp_v1 = NULL;
        struct lov_ost_data_v1 *objs;
        __u32   magic;
        __u16   comp_cnt;
        __u16   mirror_cnt;
        int     rc = 0, i;
        ENTRY;

        mutex_lock(&mo->ldo_layout_mutex);
        lod_striping_free_nolock(env, mo);

        magic = le32_to_cpu(v1->lmm_magic) & ~LOV_MAGIC_DEFINED;

        if (magic != LOV_MAGIC_V1 && magic != LOV_MAGIC_V3 &&
            magic != LOV_MAGIC_COMP_V1 && magic != LOV_MAGIC_FOREIGN)
                GOTO(unlock, rc = -EINVAL);

        if (magic == LOV_MAGIC_COMP_V1) {
                comp_v1 = buf->lb_buf;
                comp_cnt = le16_to_cpu(comp_v1->lcm_entry_count);
                if (comp_cnt == 0)
                        GOTO(unlock, rc = -EINVAL);
                mirror_cnt = le16_to_cpu(comp_v1->lcm_mirror_count) + 1;
                mo->ldo_flr_state = le16_to_cpu(comp_v1->lcm_flags) &
                                        LCM_FL_FLR_MASK;
                mo->ldo_is_composite = 1;
        } else if (magic == LOV_MAGIC_FOREIGN) {
                struct lov_foreign_md *foreign;
                size_t length;

                if (buf->lb_len < offsetof(typeof(*foreign), lfm_value)) {
                        CDEBUG(D_LAYOUT,
                               "buf len %zu < min lov_foreign_md size (%zu)\n",
                               buf->lb_len,
                               offsetof(typeof(*foreign), lfm_value));
                        GOTO(out, rc = -EINVAL);
                }
                foreign = (struct lov_foreign_md *)buf->lb_buf;
                length = foreign_size_le(foreign);
                if (buf->lb_len < length) {
                        CDEBUG(D_LAYOUT,
                               "buf len %zu < this lov_foreign_md size (%zu)\n",
                               buf->lb_len, length);
                        GOTO(out, rc = -EINVAL);
                }

                /* just cache foreign LOV EA raw */
                rc = lod_alloc_foreign_lov(mo, length);
                if (rc)
                        GOTO(out, rc);
                memcpy(mo->ldo_foreign_lov, buf->lb_buf, length);
                GOTO(out, rc);
        } else {
                mo->ldo_is_composite = 0;
                comp_cnt = 1;
                mirror_cnt = 0;
        }
        mo->ldo_layout_gen = le16_to_cpu(v1->lmm_layout_gen);

        rc = lod_alloc_comp_entries(mo, mirror_cnt, comp_cnt);
        if (rc)
                GOTO(unlock, rc);

        for (i = 0; i < comp_cnt; i++) {
                struct lu_extent *ext;
                char    *pool_name;
                __u32   offs;

                lod_comp = &mo->ldo_comp_entries[i];

                if (mo->ldo_is_composite) {
                        offs = le32_to_cpu(comp_v1->lcm_entries[i].lcme_offset);
                        v1 = (struct lov_mds_md_v1 *)((char *)comp_v1 + offs);
                        v3 = (struct lov_mds_md_v3 *)v1;
                        magic = le32_to_cpu(v1->lmm_magic);

                        ext = &comp_v1->lcm_entries[i].lcme_extent;
                        lod_comp->llc_extent.e_start =
                                le64_to_cpu(ext->e_start);
                        lod_comp->llc_extent.e_end = le64_to_cpu(ext->e_end);
                        lod_comp->llc_flags =
                                le32_to_cpu(comp_v1->lcm_entries[i].lcme_flags);
                        if (lod_comp->llc_flags & LCME_FL_NOSYNC)
                                lod_comp->llc_timestamp = le64_to_cpu(
                                        comp_v1->lcm_entries[i].lcme_timestamp);
                        lod_comp->llc_id =
                                le32_to_cpu(comp_v1->lcm_entries[i].lcme_id);
                        if (lod_comp->llc_id == LCME_ID_INVAL)
                                GOTO(out, rc = -EINVAL);
                }

                pool_name = NULL;
                if (magic == LOV_MAGIC_V1) {
                        objs = &v1->lmm_objects[0];
                } else if (magic == LOV_MAGIC_V3) {
                        objs = &v3->lmm_objects[0];
                        if (v3->lmm_pool_name[0] != '\0')
                                pool_name = v3->lmm_pool_name;
                } else {
                        CDEBUG(D_LAYOUT, "Invalid magic %x\n", magic);
                        GOTO(out, rc = -EINVAL);
                }

                lod_comp->llc_pattern = le32_to_cpu(v1->lmm_pattern);
                lod_comp->llc_stripe_size = le32_to_cpu(v1->lmm_stripe_size);
                lod_comp->llc_stripe_count = le16_to_cpu(v1->lmm_stripe_count);
                lod_comp->llc_layout_gen = le16_to_cpu(v1->lmm_layout_gen);
                /**
                 * The stripe_offset of an uninit-ed component is stored in
                 * the lmm_layout_gen
                 */
                if (mo->ldo_is_composite && !lod_comp_inited(lod_comp))
                        lod_comp->llc_stripe_offset = lod_comp->llc_layout_gen;
                lod_obj_set_pool(mo, i, pool_name);

                if ((!mo->ldo_is_composite || lod_comp_inited(lod_comp)) &&
                    !(lod_comp->llc_pattern & LOV_PATTERN_F_RELEASED) &&
                    !(lod_comp->llc_pattern & LOV_PATTERN_MDT)) {
                        rc = lod_initialize_objects(env, mo, objs, i);
                        if (rc)
                                GOTO(out, rc);
                }
        }

        rc = lod_fill_mirrors(mo);
        GOTO(out, rc);
out:
        if (rc)
                lod_striping_free_nolock(env, mo);
unlock:
        mutex_unlock(&mo->ldo_layout_mutex);

        RETURN(rc);
}

/**
 * Parse suggested striping configuration.
 *
 * The caller gets a suggested striping configuration from a number of sources
 * including per-directory default and applications. Then it needs to verify
 * the suggested striping is valid, apply missing bits and store the resulting
 * configuration in the object to be used by the allocator later. Must not be
 * called concurrently against the same object. It's OK to provide a
 * fully-defined striping.
 *
 * \param[in] env       execution environment for this thread
 * \param[in] lo        LOD object
 * \param[in] buf       buffer containing the striping
 *
 * \retval 0            on success
 * \retval negative     negated errno on error
 */
int lod_qos_parse_config(const struct lu_env *env, struct lod_object *lo,
                         const struct lu_buf *buf)
{
        struct lod_layout_component *lod_comp;
        struct lod_device *d = lu2lod_dev(lod2lu_obj(lo)->lo_dev);
        struct lov_desc *desc = &d->lod_ost_descs.ltd_lov_desc;
        struct lov_user_md_v1 *v1 = NULL;
        struct lov_user_md_v3 *v3 = NULL;
        struct lov_comp_md_v1 *comp_v1 = NULL;
        struct lov_foreign_md *lfm = NULL;
        char def_pool[LOV_MAXPOOLNAME + 1];
        __u32 magic;
        __u16 comp_cnt;
        __u16 mirror_cnt;
        int i, rc;
        ENTRY;

        if (buf == NULL || buf->lb_buf == NULL || buf->lb_len == 0)
                RETURN(0);

        memset(def_pool, 0, sizeof(def_pool));
        if (lo->ldo_comp_entries != NULL)
                lod_layout_get_pool(lo->ldo_comp_entries, lo->ldo_comp_cnt,
                                    def_pool, sizeof(def_pool));

        /* free default striping info */
        if (lo->ldo_is_foreign)
                lod_free_foreign_lov(lo);
        else
                lod_free_comp_entries(lo);

        rc = lod_verify_striping(d, lo, buf, false);
        if (rc)
                RETURN(-EINVAL);

        v3 = buf->lb_buf;
        v1 = buf->lb_buf;
        comp_v1 = buf->lb_buf;
        /* {lmm,lfm}_magic position/length work for all LOV formats */
        magic = v1->lmm_magic;

        if (unlikely(le32_to_cpu(magic) & LOV_MAGIC_DEFINED)) {
                /* try to use as fully defined striping */
                rc = lod_use_defined_striping(env, lo, buf);
                RETURN(rc);
        }

        switch (magic) {
        case __swab32(LOV_USER_MAGIC_V1):
                lustre_swab_lov_user_md_v1(v1);
                magic = v1->lmm_magic;
                /* fall through */
        case LOV_USER_MAGIC_V1:
                break;
        case __swab32(LOV_USER_MAGIC_V3):
                lustre_swab_lov_user_md_v3(v3);
                magic = v3->lmm_magic;
                /* fall through */
        case LOV_USER_MAGIC_V3:
                break;
        case __swab32(LOV_USER_MAGIC_SPECIFIC):
                lustre_swab_lov_user_md_v3(v3);
                lustre_swab_lov_user_md_objects(v3->lmm_objects,
                                                v3->lmm_stripe_count);
                magic = v3->lmm_magic;
                /* fall through */
        case LOV_USER_MAGIC_SPECIFIC:
                break;
        case __swab32(LOV_USER_MAGIC_COMP_V1):
                lustre_swab_lov_comp_md_v1(comp_v1);
                magic = comp_v1->lcm_magic;
                /* fall trhough */
        case LOV_USER_MAGIC_COMP_V1:
                break;
        case __swab32(LOV_USER_MAGIC_FOREIGN):
                lfm = buf->lb_buf;
                __swab32s(&lfm->lfm_magic);
                __swab32s(&lfm->lfm_length);
                __swab32s(&lfm->lfm_type);
                __swab32s(&lfm->lfm_flags);
                magic = lfm->lfm_magic;
                /* fall through */
        case LOV_USER_MAGIC_FOREIGN:
                if (!lfm)
                        lfm = buf->lb_buf;
                rc = lod_alloc_foreign_lov(lo, foreign_size(lfm));
                if (rc)
                        RETURN(rc);
                memcpy(lo->ldo_foreign_lov, buf->lb_buf, foreign_size(lfm));
                RETURN(0);
        default:
                CERROR("%s: unrecognized magic %X\n",
                       lod2obd(d)->obd_name, magic);
                RETURN(-EINVAL);
        }

        lustre_print_user_md(D_OTHER, v1, "parse config");

        if (magic == LOV_USER_MAGIC_COMP_V1) {
                comp_cnt = comp_v1->lcm_entry_count;
                if (comp_cnt == 0)
                        RETURN(-EINVAL);
                mirror_cnt =  comp_v1->lcm_mirror_count + 1;
                if (mirror_cnt > 1)
                        lo->ldo_flr_state = LCM_FL_RDONLY;
                lo->ldo_is_composite = 1;
        } else {
                comp_cnt = 1;
                mirror_cnt = 0;
                lo->ldo_is_composite = 0;
        }

        rc = lod_alloc_comp_entries(lo, mirror_cnt, comp_cnt);
        if (rc)
                RETURN(rc);

        LASSERT(lo->ldo_comp_entries);

        for (i = 0; i < comp_cnt; i++) {
                struct pool_desc        *pool;
                struct lu_extent        *ext;
                char    *pool_name;

                lod_comp = &lo->ldo_comp_entries[i];

                if (lo->ldo_is_composite) {
                        v1 = (struct lov_user_md *)((char *)comp_v1 +
                                        comp_v1->lcm_entries[i].lcme_offset);
                        ext = &comp_v1->lcm_entries[i].lcme_extent;
                        lod_comp->llc_extent = *ext;
                        lod_comp->llc_flags =
                                comp_v1->lcm_entries[i].lcme_flags &
                                        LCME_CL_COMP_FLAGS;
                }

                pool_name = NULL;
                if (v1->lmm_magic == LOV_USER_MAGIC_V3 ||
                    v1->lmm_magic == LOV_USER_MAGIC_SPECIFIC) {
                        v3 = (struct lov_user_md_v3 *)v1;
                        if (v3->lmm_pool_name[0] != '\0')
                                pool_name = v3->lmm_pool_name;

                        if (v3->lmm_magic == LOV_USER_MAGIC_SPECIFIC) {
                                rc = lod_comp_copy_ost_lists(lod_comp, v3);
                                if (rc)
                                        GOTO(free_comp, rc);
                        }
                }

                if (pool_name == NULL && def_pool[0] != '\0')
                        pool_name = def_pool;

                if (v1->lmm_pattern == 0)
                        v1->lmm_pattern = LOV_PATTERN_RAID0;
                if (lov_pattern(v1->lmm_pattern) != LOV_PATTERN_RAID0 &&
                    lov_pattern(v1->lmm_pattern) != LOV_PATTERN_MDT &&
                    lov_pattern(v1->lmm_pattern) !=
                        (LOV_PATTERN_RAID0 | LOV_PATTERN_OVERSTRIPING)) {
                        CDEBUG(D_LAYOUT, "%s: invalid pattern: %x\n",
                               lod2obd(d)->obd_name, v1->lmm_pattern);
                        GOTO(free_comp, rc = -EINVAL);
                }

                lod_comp->llc_pattern = v1->lmm_pattern;
                lod_comp->llc_stripe_size = desc->ld_default_stripe_size;
                if (v1->lmm_stripe_size)
                        lod_comp->llc_stripe_size = v1->lmm_stripe_size;

                lod_comp->llc_stripe_count = desc->ld_default_stripe_count;
                if (v1->lmm_stripe_count ||
                    lov_pattern(v1->lmm_pattern) == LOV_PATTERN_MDT)
                        lod_comp->llc_stripe_count = v1->lmm_stripe_count;

                lod_comp->llc_stripe_offset = v1->lmm_stripe_offset;
                lod_obj_set_pool(lo, i, pool_name);

                LASSERT(ergo(lov_pattern(lod_comp->llc_pattern) ==
                             LOV_PATTERN_MDT, lod_comp->llc_stripe_count == 0));

                if (pool_name == NULL)
                        continue;

                /* In the function below, .hs_keycmp resolves to
                 * pool_hashkey_keycmp() */
                /* coverity[overrun-buffer-val] */
                pool = lod_find_pool(d, pool_name);
                if (pool == NULL)
                        continue;

                if (lod_comp->llc_stripe_offset != LOV_OFFSET_DEFAULT) {
                        rc = lod_check_index_in_pool(
                                        lod_comp->llc_stripe_offset, pool);
                        if (rc < 0) {
                                lod_pool_putref(pool);
                                CDEBUG(D_LAYOUT, "%s: invalid offset, %u\n",
                                       lod2obd(d)->obd_name,
                                       lod_comp->llc_stripe_offset);
                                GOTO(free_comp, rc = -EINVAL);
                        }
                }

                if (lod_comp->llc_stripe_count > pool_tgt_count(pool) &&
                    !(lod_comp->llc_pattern & LOV_PATTERN_OVERSTRIPING))
                        lod_comp->llc_stripe_count = pool_tgt_count(pool);

                lod_pool_putref(pool);
        }

        RETURN(0);

free_comp:
        lod_free_comp_entries(lo);
        RETURN(rc);
}

/**
 * prepare enough OST avoidance bitmap space
 */
int lod_prepare_avoidance(const struct lu_env *env, struct lod_object *lo)
{
        struct lod_device *lod = lu2lod_dev(lo->ldo_obj.do_lu.lo_dev);
        struct lod_avoid_guide *lag = &lod_env_info(env)->lti_avoid;
        struct cfs_bitmap *bitmap = NULL;
        __u32 *new_oss = NULL;

        lag->lag_ost_avail = lod->lod_ost_count;

        /* reset OSS avoid guide array */
        lag->lag_oaa_count = 0;
        if (lag->lag_oss_avoid_array &&
            lag->lag_oaa_size < lod->lod_ost_count) {
                OBD_FREE(lag->lag_oss_avoid_array,
                         sizeof(__u32) * lag->lag_oaa_size);
                lag->lag_oss_avoid_array = NULL;
                lag->lag_oaa_size = 0;
        }

        /* init OST avoid guide bitmap */
        if (lag->lag_ost_avoid_bitmap) {
                if (lod->lod_ost_count <= lag->lag_ost_avoid_bitmap->size) {
                        CFS_RESET_BITMAP(lag->lag_ost_avoid_bitmap);
                } else {
                        CFS_FREE_BITMAP(lag->lag_ost_avoid_bitmap);
                        lag->lag_ost_avoid_bitmap = NULL;
                }
        }

        if (!lag->lag_ost_avoid_bitmap) {
                bitmap = CFS_ALLOCATE_BITMAP(lod->lod_ost_count);
                if (!bitmap)
                        return -ENOMEM;
        }

        if (!lag->lag_oss_avoid_array) {
                /**
                 * usually there are multiple OSTs in one OSS, but we don't
                 * know the exact OSS number, so we choose a safe option,
                 * using OST count to allocate the array to store the OSS
                 * id.
                 */
                OBD_ALLOC(new_oss, sizeof(*new_oss) * lod->lod_ost_count);
                if (!new_oss) {
                        CFS_FREE_BITMAP(bitmap);
                        return -ENOMEM;
                }
        }

        if (new_oss) {
                lag->lag_oss_avoid_array = new_oss;
                lag->lag_oaa_size = lod->lod_ost_count;
        }
        if (bitmap)
                lag->lag_ost_avoid_bitmap = bitmap;

        return 0;
}

/**
 * Collect information of used OSTs and OSSs in the overlapped components
 * of other mirrors
 */
void lod_collect_avoidance(struct lod_object *lo, struct lod_avoid_guide *lag,
                           int comp_idx)
{
        struct lod_device *lod = lu2lod_dev(lo->ldo_obj.do_lu.lo_dev);
        struct lod_layout_component *lod_comp = &lo->ldo_comp_entries[comp_idx];
        struct cfs_bitmap *bitmap = lag->lag_ost_avoid_bitmap;
        int i, j;

        /* iterate mirrors */
        for (i = 0; i < lo->ldo_mirror_count; i++) {
                struct lod_layout_component *comp;

                /**
                 * skip mirror containing component[comp_idx], we only
                 * collect OSTs info of conflicting component in other mirrors,
                 * so that during read, if OSTs of a mirror's component are
                 * not available, we still have other mirror with different
                 * OSTs to read the data.
                 */
                comp = &lo->ldo_comp_entries[lo->ldo_mirrors[i].lme_start];
                if (comp->llc_id != LCME_ID_INVAL &&
                    mirror_id_of(comp->llc_id) ==
                                                mirror_id_of(lod_comp->llc_id))
                        continue;

                /* iterate components of a mirror */
                lod_foreach_mirror_comp(comp, lo, i) {
                        /**
                         * skip non-overlapped or un-instantiated components,
                         * NOTE: don't use lod_comp_inited(comp) to judge
                         * whether @comp has been inited, since during
                         * declare phase, comp->llc_stripe has been allocated
                         * while it's init flag not been set until the exec
                         * phase.
                         */
                        if (!lu_extent_is_overlapped(&comp->llc_extent,
                                                     &lod_comp->llc_extent) ||
                            !comp->llc_stripe)
                                continue;

                        /**
                         * collect used OSTs index and OSS info from a
                         * component
                         */
                        for (j = 0; j < comp->llc_stripe_count; j++) {
                                struct lod_tgt_desc *ost;
                                struct lu_svr_qos *lsq;
                                int k;

                                ost = OST_TGT(lod, comp->llc_ost_indices[j]);
                                lsq = ost->ltd_qos.ltq_svr;

                                if (cfs_bitmap_check(bitmap, ost->ltd_index))
                                        continue;

                                QOS_DEBUG("OST%d used in conflicting mirror "
                                          "component\n", ost->ltd_index);
                                cfs_bitmap_set(bitmap, ost->ltd_index);
                                lag->lag_ost_avail--;

                                for (k = 0; k < lag->lag_oaa_count; k++) {
                                        if (lag->lag_oss_avoid_array[k] ==
                                            lsq->lsq_id)
                                                break;
                                }
                                if (k == lag->lag_oaa_count) {
                                        lag->lag_oss_avoid_array[k] =
                                                                lsq->lsq_id;
                                        lag->lag_oaa_count++;
                                }
                        }
                }
        }
}

/**
 * Create a striping for an obejct.
 *
 * The function creates a new striping for the object. The function tries QoS
 * algorithm first unless free space is distributed evenly among OSTs, but
 * by default RR algorithm is preferred due to internal concurrency (QoS is
 * serialized). The caller must ensure no concurrent calls to the function
 * are made against the same object.
 *
 * \param[in] env       execution environment for this thread
 * \param[in] lo        LOD object
 * \param[in] attr      attributes OST objects will be declared with
 * \param[in] th        transaction handle
 * \param[in] comp_idx  index of ldo_comp_entries
 *
 * \retval 0            on success
 * \retval negative     negated errno on error
 */
int lod_qos_prep_create(const struct lu_env *env, struct lod_object *lo,
                        struct lu_attr *attr, struct thandle *th,
                        int comp_idx)
{
        struct lod_layout_component *lod_comp;
        struct lod_device      *d = lu2lod_dev(lod2lu_obj(lo)->lo_dev);
        int                     stripe_len;
        int                     flag = LOV_USES_ASSIGNED_STRIPE;
        int                     i, rc = 0;
        struct lod_avoid_guide *lag = &lod_env_info(env)->lti_avoid;
        struct dt_object **stripe = NULL;
        __u32 *ost_indices = NULL;
        ENTRY;

        LASSERT(lo);
        LASSERT(lo->ldo_comp_cnt > comp_idx && lo->ldo_comp_entries != NULL);
        lod_comp = &lo->ldo_comp_entries[comp_idx];
        LASSERT(!(lod_comp->llc_flags & LCME_FL_EXTENSION));

        /* A released component is being created */
        if (lod_comp->llc_pattern & LOV_PATTERN_F_RELEASED)
                RETURN(0);

        /* A Data-on-MDT component is being created */
        if (lov_pattern(lod_comp->llc_pattern) == LOV_PATTERN_MDT)
                RETURN(0);

        if (likely(lod_comp->llc_stripe == NULL)) {
                /*
                 * no striping has been created so far
                 */
                LASSERT(lod_comp->llc_stripe_count);
                /*
                 * statfs and check OST targets now, since ld_active_tgt_count
                 * could be changed if some OSTs are [de]activated manually.
                 */
                lod_qos_statfs_update(env, d, &d->lod_ost_descs);
                stripe_len = lod_get_stripe_count(d, lo,
                                                  lod_comp->llc_stripe_count,
                                                  lod_comp->llc_pattern &
                                                  LOV_PATTERN_OVERSTRIPING);

                if (stripe_len == 0)
                        GOTO(out, rc = -ERANGE);
                lod_comp->llc_stripe_count = stripe_len;
                OBD_ALLOC(stripe, sizeof(stripe[0]) * stripe_len);
                if (stripe == NULL)
                        GOTO(out, rc = -ENOMEM);
                OBD_ALLOC(ost_indices, sizeof(*ost_indices) * stripe_len);
                if (!ost_indices)
                        GOTO(out, rc = -ENOMEM);

                lod_getref(&d->lod_ost_descs);
                /* XXX: support for non-0 files w/o objects */
                CDEBUG(D_OTHER, "tgt_count %d stripe_count %d\n",
                       d->lod_ost_count, stripe_len);

                if (lod_comp->llc_ostlist.op_array &&
                    lod_comp->llc_ostlist.op_count) {
                        rc = lod_alloc_ost_list(env, lo, stripe, ost_indices,
                                                th, comp_idx);
                } else if (lod_comp->llc_stripe_offset == LOV_OFFSET_DEFAULT) {
                        /**
                         * collect OSTs and OSSs used in other mirrors whose
                         * components cross the ldo_comp_entries[comp_idx]
                         */
                        rc = lod_prepare_avoidance(env, lo);
                        if (rc)
                                GOTO(put_ldts, rc);

                        QOS_DEBUG("collecting conflict osts for comp[%d]\n",
                                  comp_idx);
                        lod_collect_avoidance(lo, lag, comp_idx);

                        rc = lod_ost_alloc_qos(env, lo, stripe, ost_indices,
                                               flag, th, comp_idx);
                        if (rc == -EAGAIN)
                                rc = lod_ost_alloc_rr(env, lo, stripe,
                                                      ost_indices, flag, th,
                                                      comp_idx);
                } else {
                        rc = lod_ost_alloc_specific(env, lo, stripe,
                                                    ost_indices, flag, th,
                                                    comp_idx);
                }
put_ldts:
                lod_putref(d, &d->lod_ost_descs);
                if (rc < 0) {
                        for (i = 0; i < stripe_len; i++)
                                if (stripe[i] != NULL)
                                        dt_object_put(env, stripe[i]);
                        lod_comp->llc_stripe_count = 0;
                } else {
                        lod_comp->llc_stripe = stripe;
                        lod_comp->llc_ost_indices = ost_indices;
                        lod_comp->llc_stripes_allocated = stripe_len;
                }
        } else {
                /*
                 * lod_qos_parse_config() found supplied buf as a predefined
                 * striping (not a hint), so it allocated all the object
                 * now we need to create them
                 */
                for (i = 0; i < lod_comp->llc_stripe_count; i++) {
                        struct dt_object  *o;

                        o = lod_comp->llc_stripe[i];
                        LASSERT(o);

                        rc = lod_sub_declare_create(env, o, attr, NULL,
                                                    NULL, th);
                        if (rc < 0) {
                                CERROR("can't declare create: %d\n", rc);
                                break;
                        }
                }
                /**
                 * Clear LCME_FL_INIT for the component so that
                 * lod_striping_create() can create the striping objects
                 * in replay.
                 */
                lod_comp_unset_init(lod_comp);
        }

out:
        if (rc < 0) {
                if (stripe)
                        OBD_FREE(stripe, sizeof(stripe[0]) * stripe_len);
                if (ost_indices)
                        OBD_FREE(ost_indices,
                                 sizeof(*ost_indices) * stripe_len);
        }
        RETURN(rc);
}

int lod_prepare_create(const struct lu_env *env, struct lod_object *lo,
                       struct lu_attr *attr, const struct lu_buf *buf,
                       struct thandle *th)

{
        struct lod_device *d = lu2lod_dev(lod2lu_obj(lo)->lo_dev);
        uint64_t size = 0;
        int i;
        int rc;
        ENTRY;

        LASSERT(lo);

        /* no OST available */
        /* XXX: should we be waiting a bit to prevent failures during
         * cluster initialization? */
        if (!d->lod_ost_count)
                RETURN(-EIO);

        /*
         * by this time, the object's ldo_stripe_count and ldo_stripe_size
         * contain default value for striping: taken from the parent
         * or from filesystem defaults
         *
         * in case the caller is passing lovea with new striping config,
         * we may need to parse lovea and apply new configuration
         */
        rc = lod_qos_parse_config(env, lo, buf);
        if (rc)
                RETURN(rc);

        if (attr->la_valid & LA_SIZE)
                size = attr->la_size;

        /**
         * prepare OST object creation for the component covering file's
         * size, the 1st component (including plain layout file) is always
         * instantiated.
         */
        for (i = 0; i < lo->ldo_comp_cnt; i++) {
                struct lod_layout_component *lod_comp;
                struct lu_extent *extent;

                lod_comp = &lo->ldo_comp_entries[i];
                extent = &lod_comp->llc_extent;
                QOS_DEBUG("comp[%d] %lld "DEXT"\n", i, size, PEXT(extent));
                if (!lo->ldo_is_composite || size >= extent->e_start) {
                        rc = lod_qos_prep_create(env, lo, attr, th, i);
                        if (rc)
                                break;
                }
        }

        RETURN(rc);
}