LU-1346 libcfs: cleanup waitq related primitives

[fs/lustre-release.git] / lustre / obdclass / lu_object.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 LICENSE file that accompanied this code).
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; If not, see
 * http://www.sun.com/software/products/lustre/docs/GPLv2.pdf
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 *
 * GPL HEADER END
 */
/*
 * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
 * Use is subject to license terms.
 *
 * Copyright (c) 2011, 2013, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 * Lustre is a trademark of Sun Microsystems, Inc.
 *
 * lustre/obdclass/lu_object.c
 *
 * Lustre Object.
 * These are the only exported functions, they provide some generic
 * infrastructure for managing object devices
 *
 *   Author: Nikita Danilov <nikita.danilov@sun.com>
 */

#define DEBUG_SUBSYSTEM S_CLASS

#include <libcfs/libcfs.h>

#ifdef __KERNEL__
# include <linux/module.h>
#endif

/* hash_long() */
#include <libcfs/libcfs_hash.h>
#include <obd_class.h>
#include <obd_support.h>
#include <lustre_disk.h>
#include <lustre_fid.h>
#include <lu_object.h>
#include <lu_ref.h>
#include <libcfs/list.h>

static void lu_object_free(const struct lu_env *env, struct lu_object *o);

/**
 * Decrease reference counter on object. If last reference is freed, return
 * object to the cache, unless lu_object_is_dying(o) holds. In the latter
 * case, free object immediately.
 */
void lu_object_put(const struct lu_env *env, struct lu_object *o)
{
        struct lu_site_bkt_data *bkt;
        struct lu_object_header *top;
        struct lu_site          *site;
        struct lu_object        *orig;
        cfs_hash_bd_t            bd;
        const struct lu_fid     *fid;

        top  = o->lo_header;
        site = o->lo_dev->ld_site;
        orig = o;

        /*
         * till we have full fids-on-OST implemented anonymous objects
         * are possible in OSP. such an object isn't listed in the site
         * so we should not remove it from the site.
         */
        fid = lu_object_fid(o);
        if (fid_is_zero(fid)) {
                LASSERT(top->loh_hash.next == NULL
                        && top->loh_hash.pprev == NULL);
                LASSERT(cfs_list_empty(&top->loh_lru));
                if (!cfs_atomic_dec_and_test(&top->loh_ref))
                        return;
                cfs_list_for_each_entry_reverse(o, &top->loh_layers, lo_linkage) {
                        if (o->lo_ops->loo_object_release != NULL)
                                o->lo_ops->loo_object_release(env, o);
                }
                lu_object_free(env, orig);
                return;
        }

        cfs_hash_bd_get(site->ls_obj_hash, &top->loh_fid, &bd);
        bkt = cfs_hash_bd_extra_get(site->ls_obj_hash, &bd);

        if (!cfs_hash_bd_dec_and_lock(site->ls_obj_hash, &bd, &top->loh_ref)) {
                if (lu_object_is_dying(top)) {

                        /*
                         * somebody may be waiting for this, currently only
                         * used for cl_object, see cl_object_put_last().
                         */
                        wake_up_all(&bkt->lsb_marche_funebre);
                }
                return;
        }

        LASSERT(bkt->lsb_busy > 0);
        bkt->lsb_busy--;
        /*
         * When last reference is released, iterate over object
         * layers, and notify them that object is no longer busy.
         */
        cfs_list_for_each_entry_reverse(o, &top->loh_layers, lo_linkage) {
                if (o->lo_ops->loo_object_release != NULL)
                        o->lo_ops->loo_object_release(env, o);
        }

        if (!lu_object_is_dying(top)) {
                LASSERT(cfs_list_empty(&top->loh_lru));
                cfs_list_add_tail(&top->loh_lru, &bkt->lsb_lru);
                cfs_hash_bd_unlock(site->ls_obj_hash, &bd, 1);
                return;
        }

        /*
         * If object is dying (will not be cached), removed it
         * from hash table and LRU.
         *
         * This is done with hash table and LRU lists locked. As the only
         * way to acquire first reference to previously unreferenced
         * object is through hash-table lookup (lu_object_find()),
         * or LRU scanning (lu_site_purge()), that are done under hash-table
         * and LRU lock, no race with concurrent object lookup is possible
         * and we can safely destroy object below.
         */
        if (!test_and_set_bit(LU_OBJECT_UNHASHED, &top->loh_flags))
                cfs_hash_bd_del_locked(site->ls_obj_hash, &bd, &top->loh_hash);
        cfs_hash_bd_unlock(site->ls_obj_hash, &bd, 1);
        /*
         * Object was already removed from hash and lru above, can
         * kill it.
         */
        lu_object_free(env, orig);
}
EXPORT_SYMBOL(lu_object_put);

/**
 * Put object and don't keep in cache. This is temporary solution for
 * multi-site objects when its layering is not constant.
 */
void lu_object_put_nocache(const struct lu_env *env, struct lu_object *o)
{
        set_bit(LU_OBJECT_HEARD_BANSHEE, &o->lo_header->loh_flags);
        return lu_object_put(env, o);
}
EXPORT_SYMBOL(lu_object_put_nocache);

/**
 * Kill the object and take it out of LRU cache.
 * Currently used by client code for layout change.
 */
void lu_object_unhash(const struct lu_env *env, struct lu_object *o)
{
        struct lu_object_header *top;

        top = o->lo_header;
        set_bit(LU_OBJECT_HEARD_BANSHEE, &top->loh_flags);
        if (!test_and_set_bit(LU_OBJECT_UNHASHED, &top->loh_flags)) {
                cfs_hash_t *obj_hash = o->lo_dev->ld_site->ls_obj_hash;
                cfs_hash_bd_t bd;

                cfs_hash_bd_get_and_lock(obj_hash, &top->loh_fid, &bd, 1);
                cfs_list_del_init(&top->loh_lru);
                cfs_hash_bd_del_locked(obj_hash, &bd, &top->loh_hash);
                cfs_hash_bd_unlock(obj_hash, &bd, 1);
        }
}
EXPORT_SYMBOL(lu_object_unhash);

/**
 * Allocate new object.
 *
 * This follows object creation protocol, described in the comment within
 * struct lu_device_operations definition.
 */
static struct lu_object *lu_object_alloc(const struct lu_env *env,
                                         struct lu_device *dev,
                                         const struct lu_fid *f,
                                         const struct lu_object_conf *conf)
{
        struct lu_object *scan;
        struct lu_object *top;
        cfs_list_t *layers;
        unsigned int init_mask = 0;
        unsigned int init_flag;
        int clean;
        int result;
        ENTRY;

        /*
         * Create top-level object slice. This will also create
         * lu_object_header.
         */
        top = dev->ld_ops->ldo_object_alloc(env, NULL, dev);
        if (top == NULL)
                RETURN(ERR_PTR(-ENOMEM));
        if (IS_ERR(top))
                RETURN(top);
        /*
         * This is the only place where object fid is assigned. It's constant
         * after this point.
         */
        top->lo_header->loh_fid = *f;
        layers = &top->lo_header->loh_layers;

        do {
                /*
                 * Call ->loo_object_init() repeatedly, until no more new
                 * object slices are created.
                 */
                clean = 1;
                init_flag = 1;
                cfs_list_for_each_entry(scan, layers, lo_linkage) {
                        if (init_mask & init_flag)
                                goto next;
                        clean = 0;
                        scan->lo_header = top->lo_header;
                        result = scan->lo_ops->loo_object_init(env, scan, conf);
                        if (result != 0) {
                                lu_object_free(env, top);
                                RETURN(ERR_PTR(result));
                        }
                        init_mask |= init_flag;
next:
                        init_flag <<= 1;
                }
        } while (!clean);

        cfs_list_for_each_entry_reverse(scan, layers, lo_linkage) {
                if (scan->lo_ops->loo_object_start != NULL) {
                        result = scan->lo_ops->loo_object_start(env, scan);
                        if (result != 0) {
                                lu_object_free(env, top);
                                RETURN(ERR_PTR(result));
                        }
                }
        }

        lprocfs_counter_incr(dev->ld_site->ls_stats, LU_SS_CREATED);
        RETURN(top);
}

/**
 * Free an object.
 */
static void lu_object_free(const struct lu_env *env, struct lu_object *o)
{
        struct lu_site_bkt_data *bkt;
        struct lu_site          *site;
        struct lu_object        *scan;
        cfs_list_t              *layers;
        cfs_list_t               splice;

        site   = o->lo_dev->ld_site;
        layers = &o->lo_header->loh_layers;
        bkt    = lu_site_bkt_from_fid(site, &o->lo_header->loh_fid);
        /*
         * First call ->loo_object_delete() method to release all resources.
         */
        cfs_list_for_each_entry_reverse(scan, layers, lo_linkage) {
                if (scan->lo_ops->loo_object_delete != NULL)
                        scan->lo_ops->loo_object_delete(env, scan);
        }

        /*
         * Then, splice object layers into stand-alone list, and call
         * ->loo_object_free() on all layers to free memory. Splice is
         * necessary, because lu_object_header is freed together with the
         * top-level slice.
         */
        CFS_INIT_LIST_HEAD(&splice);
        cfs_list_splice_init(layers, &splice);
        while (!cfs_list_empty(&splice)) {
                /*
                 * Free layers in bottom-to-top order, so that object header
                 * lives as long as possible and ->loo_object_free() methods
                 * can look at its contents.
                 */
                o = container_of0(splice.prev, struct lu_object, lo_linkage);
                cfs_list_del_init(&o->lo_linkage);
                LASSERT(o->lo_ops->loo_object_free != NULL);
                o->lo_ops->loo_object_free(env, o);
        }

        if (waitqueue_active(&bkt->lsb_marche_funebre))
                wake_up_all(&bkt->lsb_marche_funebre);
}

/**
 * Free \a nr objects from the cold end of the site LRU list.
 */
int lu_site_purge(const struct lu_env *env, struct lu_site *s, int nr)
{
        struct lu_object_header *h;
        struct lu_object_header *temp;
        struct lu_site_bkt_data *bkt;
        cfs_hash_bd_t            bd;
        cfs_hash_bd_t            bd2;
        cfs_list_t               dispose;
        int                      did_sth;
        int                      start;
        int                      count;
        int                      bnr;
        int                      i;

        if (OBD_FAIL_CHECK(OBD_FAIL_OBD_NO_LRU))
                RETURN(0);

        CFS_INIT_LIST_HEAD(&dispose);
        /*
         * Under LRU list lock, scan LRU list and move unreferenced objects to
         * the dispose list, removing them from LRU and hash table.
         */
        start = s->ls_purge_start;
        bnr = (nr == ~0) ? -1 : nr / CFS_HASH_NBKT(s->ls_obj_hash) + 1;
 again:
        did_sth = 0;
        cfs_hash_for_each_bucket(s->ls_obj_hash, &bd, i) {
                if (i < start)
                        continue;
                count = bnr;
                cfs_hash_bd_lock(s->ls_obj_hash, &bd, 1);
                bkt = cfs_hash_bd_extra_get(s->ls_obj_hash, &bd);

                cfs_list_for_each_entry_safe(h, temp, &bkt->lsb_lru, loh_lru) {
                        LASSERT(cfs_atomic_read(&h->loh_ref) == 0);

                        cfs_hash_bd_get(s->ls_obj_hash, &h->loh_fid, &bd2);
                        LASSERT(bd.bd_bucket == bd2.bd_bucket);

                        cfs_hash_bd_del_locked(s->ls_obj_hash,
                                               &bd2, &h->loh_hash);
                        cfs_list_move(&h->loh_lru, &dispose);
                        if (did_sth == 0)
                                did_sth = 1;

                        if (nr != ~0 && --nr == 0)
                                break;

                        if (count > 0 && --count == 0)
                                break;

                }
                cfs_hash_bd_unlock(s->ls_obj_hash, &bd, 1);
                cond_resched();
                /*
                 * Free everything on the dispose list. This is safe against
                 * races due to the reasons described in lu_object_put().
                 */
                while (!cfs_list_empty(&dispose)) {
                        h = container_of0(dispose.next,
                                          struct lu_object_header, loh_lru);
                        cfs_list_del_init(&h->loh_lru);
                        lu_object_free(env, lu_object_top(h));
                        lprocfs_counter_incr(s->ls_stats, LU_SS_LRU_PURGED);
                }

                if (nr == 0)
                        break;
        }

        if (nr != 0 && did_sth && start != 0) {
                start = 0; /* restart from the first bucket */
                goto again;
        }
        /* race on s->ls_purge_start, but nobody cares */
        s->ls_purge_start = i % CFS_HASH_NBKT(s->ls_obj_hash);

        return nr;
}
EXPORT_SYMBOL(lu_site_purge);

/*
 * Object printing.
 *
 * Code below has to jump through certain loops to output object description
 * into libcfs_debug_msg-based log. The problem is that lu_object_print()
 * composes object description from strings that are parts of _lines_ of
 * output (i.e., strings that are not terminated by newline). This doesn't fit
 * very well into libcfs_debug_msg() interface that assumes that each message
 * supplied to it is a self-contained output line.
 *
 * To work around this, strings are collected in a temporary buffer
 * (implemented as a value of lu_cdebug_key key), until terminating newline
 * character is detected.
 *
 */

enum {
        /**
         * Maximal line size.
         *
         * XXX overflow is not handled correctly.
         */
        LU_CDEBUG_LINE = 512
};

struct lu_cdebug_data {
        /**
         * Temporary buffer.
         */
        char lck_area[LU_CDEBUG_LINE];
};

/* context key constructor/destructor: lu_global_key_init, lu_global_key_fini */
LU_KEY_INIT_FINI(lu_global, struct lu_cdebug_data);

/**
 * Key, holding temporary buffer. This key is registered very early by
 * lu_global_init().
 */
struct lu_context_key lu_global_key = {
        .lct_tags = LCT_MD_THREAD | LCT_DT_THREAD |
                    LCT_MG_THREAD | LCT_CL_THREAD | LCT_LOCAL,
        .lct_init = lu_global_key_init,
        .lct_fini = lu_global_key_fini
};

/**
 * Printer function emitting messages through libcfs_debug_msg().
 */
int lu_cdebug_printer(const struct lu_env *env,
                      void *cookie, const char *format, ...)
{
        struct libcfs_debug_msg_data *msgdata = cookie;
        struct lu_cdebug_data        *key;
        int used;
        int complete;
        va_list args;

        va_start(args, format);

        key = lu_context_key_get(&env->le_ctx, &lu_global_key);
        LASSERT(key != NULL);

        used = strlen(key->lck_area);
        complete = format[strlen(format) - 1] == '\n';
        /*
         * Append new chunk to the buffer.
         */
        vsnprintf(key->lck_area + used,
                  ARRAY_SIZE(key->lck_area) - used, format, args);
        if (complete) {
                if (cfs_cdebug_show(msgdata->msg_mask, msgdata->msg_subsys))
                        libcfs_debug_msg(msgdata, "%s", key->lck_area);
                key->lck_area[0] = 0;
        }
        va_end(args);
        return 0;
}
EXPORT_SYMBOL(lu_cdebug_printer);

/**
 * Print object header.
 */
void lu_object_header_print(const struct lu_env *env, void *cookie,
                            lu_printer_t printer,
                            const struct lu_object_header *hdr)
{
        (*printer)(env, cookie, "header@%p[%#lx, %d, "DFID"%s%s%s]",
                   hdr, hdr->loh_flags, cfs_atomic_read(&hdr->loh_ref),
                   PFID(&hdr->loh_fid),
                   cfs_hlist_unhashed(&hdr->loh_hash) ? "" : " hash",
                   cfs_list_empty((cfs_list_t *)&hdr->loh_lru) ? \
                   "" : " lru",
                   hdr->loh_attr & LOHA_EXISTS ? " exist":"");
}
EXPORT_SYMBOL(lu_object_header_print);

/**
 * Print human readable representation of the \a o to the \a printer.
 */
void lu_object_print(const struct lu_env *env, void *cookie,
                     lu_printer_t printer, const struct lu_object *o)
{
        static const char ruler[] = "........................................";
        struct lu_object_header *top;
        int depth = 4;

        top = o->lo_header;
        lu_object_header_print(env, cookie, printer, top);
        (*printer)(env, cookie, "{\n");

        cfs_list_for_each_entry(o, &top->loh_layers, lo_linkage) {
                /*
                 * print `.' \a depth times followed by type name and address
                 */
                (*printer)(env, cookie, "%*.*s%s@%p", depth, depth, ruler,
                           o->lo_dev->ld_type->ldt_name, o);

                if (o->lo_ops->loo_object_print != NULL)
                        (*o->lo_ops->loo_object_print)(env, cookie, printer, o);

                (*printer)(env, cookie, "\n");
        }

        (*printer)(env, cookie, "} header@%p\n", top);
}
EXPORT_SYMBOL(lu_object_print);

/**
 * Check object consistency.
 */
int lu_object_invariant(const struct lu_object *o)
{
        struct lu_object_header *top;

        top = o->lo_header;
        cfs_list_for_each_entry(o, &top->loh_layers, lo_linkage) {
                if (o->lo_ops->loo_object_invariant != NULL &&
                    !o->lo_ops->loo_object_invariant(o))
                        return 0;
        }
        return 1;
}
EXPORT_SYMBOL(lu_object_invariant);

static struct lu_object *htable_lookup(struct lu_site *s,
                                       cfs_hash_bd_t *bd,
                                       const struct lu_fid *f,
                                       wait_queue_t *waiter,
                                       __u64 *version)
{
        struct lu_site_bkt_data *bkt;
        struct lu_object_header *h;
        cfs_hlist_node_t        *hnode;
        __u64  ver = cfs_hash_bd_version_get(bd);

        if (*version == ver)
                return ERR_PTR(-ENOENT);

        *version = ver;
        bkt = cfs_hash_bd_extra_get(s->ls_obj_hash, bd);
        /* cfs_hash_bd_peek_locked is a somehow "internal" function
         * of cfs_hash, it doesn't add refcount on object. */
        hnode = cfs_hash_bd_peek_locked(s->ls_obj_hash, bd, (void *)f);
        if (hnode == NULL) {
                lprocfs_counter_incr(s->ls_stats, LU_SS_CACHE_MISS);
                return ERR_PTR(-ENOENT);
        }

        h = container_of0(hnode, struct lu_object_header, loh_hash);
        if (likely(!lu_object_is_dying(h))) {
                cfs_hash_get(s->ls_obj_hash, hnode);
                lprocfs_counter_incr(s->ls_stats, LU_SS_CACHE_HIT);
                cfs_list_del_init(&h->loh_lru);
                return lu_object_top(h);
        }

        /*
         * Lookup found an object being destroyed this object cannot be
         * returned (to assure that references to dying objects are eventually
         * drained), and moreover, lookup has to wait until object is freed.
         */

        init_waitqueue_entry_current(waiter);
        add_wait_queue(&bkt->lsb_marche_funebre, waiter);
        set_current_state(TASK_UNINTERRUPTIBLE);
        lprocfs_counter_incr(s->ls_stats, LU_SS_CACHE_DEATH_RACE);
        return ERR_PTR(-EAGAIN);
}

static struct lu_object *htable_lookup_nowait(struct lu_site *s,
                                              cfs_hash_bd_t *bd,
                                              const struct lu_fid *f)
{
        cfs_hlist_node_t        *hnode;
        struct lu_object_header *h;

        /* cfs_hash_bd_peek_locked is a somehow "internal" function
         * of cfs_hash, it doesn't add refcount on object. */
        hnode = cfs_hash_bd_peek_locked(s->ls_obj_hash, bd, (void *)f);
        if (hnode == NULL) {
                lprocfs_counter_incr(s->ls_stats, LU_SS_CACHE_MISS);
                return ERR_PTR(-ENOENT);
        }

        h = container_of0(hnode, struct lu_object_header, loh_hash);
        if (unlikely(lu_object_is_dying(h)))
                return ERR_PTR(-ENOENT);

        cfs_hash_get(s->ls_obj_hash, hnode);
        lprocfs_counter_incr(s->ls_stats, LU_SS_CACHE_HIT);
        cfs_list_del_init(&h->loh_lru);
        return lu_object_top(h);
}

/**
 * Search cache for an object with the fid \a f. If such object is found,
 * return it. Otherwise, create new object, insert it into cache and return
 * it. In any case, additional reference is acquired on the returned object.
 */
struct lu_object *lu_object_find(const struct lu_env *env,
                                 struct lu_device *dev, const struct lu_fid *f,
                                 const struct lu_object_conf *conf)
{
        return lu_object_find_at(env, dev->ld_site->ls_top_dev, f, conf);
}
EXPORT_SYMBOL(lu_object_find);

static struct lu_object *lu_object_new(const struct lu_env *env,
                                       struct lu_device *dev,
                                       const struct lu_fid *f,
                                       const struct lu_object_conf *conf)
{
        struct lu_object        *o;
        cfs_hash_t              *hs;
        cfs_hash_bd_t            bd;
        struct lu_site_bkt_data *bkt;

        o = lu_object_alloc(env, dev, f, conf);
        if (unlikely(IS_ERR(o)))
                return o;

        hs = dev->ld_site->ls_obj_hash;
        cfs_hash_bd_get_and_lock(hs, (void *)f, &bd, 1);
        bkt = cfs_hash_bd_extra_get(hs, &bd);
        cfs_hash_bd_add_locked(hs, &bd, &o->lo_header->loh_hash);
        bkt->lsb_busy++;
        cfs_hash_bd_unlock(hs, &bd, 1);
        return o;
}

/**
 * Core logic of lu_object_find*() functions.
 */
static struct lu_object *lu_object_find_try(const struct lu_env *env,
                                            struct lu_device *dev,
                                            const struct lu_fid *f,
                                            const struct lu_object_conf *conf,
                                            wait_queue_t *waiter)
{
        struct lu_object      *o;
        struct lu_object      *shadow;
        struct lu_site        *s;
        cfs_hash_t            *hs;
        cfs_hash_bd_t          bd;
        __u64                  version = 0;

        /*
         * This uses standard index maintenance protocol:
         *
         *     - search index under lock, and return object if found;
         *     - otherwise, unlock index, allocate new object;
         *     - lock index and search again;
         *     - if nothing is found (usual case), insert newly created
         *       object into index;
         *     - otherwise (race: other thread inserted object), free
         *       object just allocated.
         *     - unlock index;
         *     - return object.
         *
         * For "LOC_F_NEW" case, we are sure the object is new established.
         * It is unnecessary to perform lookup-alloc-lookup-insert, instead,
         * just alloc and insert directly.
         *
         * If dying object is found during index search, add @waiter to the
         * site wait-queue and return ERR_PTR(-EAGAIN).
         */
        if (conf != NULL && conf->loc_flags & LOC_F_NEW)
                return lu_object_new(env, dev, f, conf);

        s  = dev->ld_site;
        hs = s->ls_obj_hash;
        cfs_hash_bd_get_and_lock(hs, (void *)f, &bd, 1);
        o = htable_lookup(s, &bd, f, waiter, &version);
        cfs_hash_bd_unlock(hs, &bd, 1);
        if (!IS_ERR(o) || PTR_ERR(o) != -ENOENT)
                return o;

        /*
         * Allocate new object. This may result in rather complicated
         * operations, including fld queries, inode loading, etc.
         */
        o = lu_object_alloc(env, dev, f, conf);
        if (unlikely(IS_ERR(o)))
                return o;

        LASSERT(lu_fid_eq(lu_object_fid(o), f));

        cfs_hash_bd_lock(hs, &bd, 1);

        shadow = htable_lookup(s, &bd, f, waiter, &version);
        if (likely(IS_ERR(shadow) && PTR_ERR(shadow) == -ENOENT)) {
                struct lu_site_bkt_data *bkt;

                bkt = cfs_hash_bd_extra_get(hs, &bd);
                cfs_hash_bd_add_locked(hs, &bd, &o->lo_header->loh_hash);
                bkt->lsb_busy++;
                cfs_hash_bd_unlock(hs, &bd, 1);
                return o;
        }

        lprocfs_counter_incr(s->ls_stats, LU_SS_CACHE_RACE);
        cfs_hash_bd_unlock(hs, &bd, 1);
        lu_object_free(env, o);
        return shadow;
}

/**
 * Much like lu_object_find(), but top level device of object is specifically
 * \a dev rather than top level device of the site. This interface allows
 * objects of different "stacking" to be created within the same site.
 */
struct lu_object *lu_object_find_at(const struct lu_env *env,
                                    struct lu_device *dev,
                                    const struct lu_fid *f,
                                    const struct lu_object_conf *conf)
{
        struct lu_site_bkt_data *bkt;
        struct lu_object        *obj;
        wait_queue_t           wait;

        while (1) {
                obj = lu_object_find_try(env, dev, f, conf, &wait);
                if (obj != ERR_PTR(-EAGAIN))
                        return obj;
                /*
                 * lu_object_find_try() already added waiter into the
                 * wait queue.
                 */
                waitq_wait(&wait, TASK_UNINTERRUPTIBLE);
                bkt = lu_site_bkt_from_fid(dev->ld_site, (void *)f);
                remove_wait_queue(&bkt->lsb_marche_funebre, &wait);
        }
}
EXPORT_SYMBOL(lu_object_find_at);

/**
 * Try to find the object in cache without waiting for the dead object
 * to be released nor allocating object if no cached one was found.
 *
 * The found object will be set as LU_OBJECT_HEARD_BANSHEE for purging.
 */
void lu_object_purge(const struct lu_env *env, struct lu_device *dev,
                     const struct lu_fid *f)
{
        struct lu_site          *s  = dev->ld_site;
        cfs_hash_t              *hs = s->ls_obj_hash;
        cfs_hash_bd_t            bd;
        struct lu_object        *o;

        cfs_hash_bd_get_and_lock(hs, f, &bd, 1);
        o = htable_lookup_nowait(s, &bd, f);
        cfs_hash_bd_unlock(hs, &bd, 1);
        if (!IS_ERR(o)) {
                set_bit(LU_OBJECT_HEARD_BANSHEE, &o->lo_header->loh_flags);
                lu_object_put(env, o);
        }
}
EXPORT_SYMBOL(lu_object_purge);

/**
 * Find object with given fid, and return its slice belonging to given device.
 */
struct lu_object *lu_object_find_slice(const struct lu_env *env,
                                       struct lu_device *dev,
                                       const struct lu_fid *f,
                                       const struct lu_object_conf *conf)
{
        struct lu_object *top;
        struct lu_object *obj;

        top = lu_object_find(env, dev, f, conf);
        if (!IS_ERR(top)) {
                obj = lu_object_locate(top->lo_header, dev->ld_type);
                if (obj == NULL)
                        lu_object_put(env, top);
        } else
                obj = top;
        return obj;
}
EXPORT_SYMBOL(lu_object_find_slice);

/**
 * Global list of all device types.
 */
static CFS_LIST_HEAD(lu_device_types);

int lu_device_type_init(struct lu_device_type *ldt)
{
        int result = 0;

        CFS_INIT_LIST_HEAD(&ldt->ldt_linkage);
        if (ldt->ldt_ops->ldto_init)
                result = ldt->ldt_ops->ldto_init(ldt);
        if (result == 0)
                cfs_list_add(&ldt->ldt_linkage, &lu_device_types);
        return result;
}
EXPORT_SYMBOL(lu_device_type_init);

void lu_device_type_fini(struct lu_device_type *ldt)
{
        cfs_list_del_init(&ldt->ldt_linkage);
        if (ldt->ldt_ops->ldto_fini)
                ldt->ldt_ops->ldto_fini(ldt);
}
EXPORT_SYMBOL(lu_device_type_fini);

void lu_types_stop(void)
{
        struct lu_device_type *ldt;

        cfs_list_for_each_entry(ldt, &lu_device_types, ldt_linkage) {
                if (ldt->ldt_device_nr == 0 && ldt->ldt_ops->ldto_stop)
                        ldt->ldt_ops->ldto_stop(ldt);
        }
}
EXPORT_SYMBOL(lu_types_stop);

/**
 * Global list of all sites on this node
 */
static CFS_LIST_HEAD(lu_sites);
static DEFINE_MUTEX(lu_sites_guard);

/**
 * Global environment used by site shrinker.
 */
static struct lu_env lu_shrink_env;

struct lu_site_print_arg {
        struct lu_env   *lsp_env;
        void            *lsp_cookie;
        lu_printer_t     lsp_printer;
};

static int
lu_site_obj_print(cfs_hash_t *hs, cfs_hash_bd_t *bd,
                  cfs_hlist_node_t *hnode, void *data)
{
        struct lu_site_print_arg *arg = (struct lu_site_print_arg *)data;
        struct lu_object_header  *h;

        h = cfs_hlist_entry(hnode, struct lu_object_header, loh_hash);
        if (!cfs_list_empty(&h->loh_layers)) {
                const struct lu_object *o;

                o = lu_object_top(h);
                lu_object_print(arg->lsp_env, arg->lsp_cookie,
                                arg->lsp_printer, o);
        } else {
                lu_object_header_print(arg->lsp_env, arg->lsp_cookie,
                                       arg->lsp_printer, h);
        }
        return 0;
}

/**
 * Print all objects in \a s.
 */
void lu_site_print(const struct lu_env *env, struct lu_site *s, void *cookie,
                   lu_printer_t printer)
{
        struct lu_site_print_arg arg = {
                .lsp_env     = (struct lu_env *)env,
                .lsp_cookie  = cookie,
                .lsp_printer = printer,
        };

        cfs_hash_for_each(s->ls_obj_hash, lu_site_obj_print, &arg);
}
EXPORT_SYMBOL(lu_site_print);

enum {
        LU_CACHE_PERCENT_MAX     = 50,
        LU_CACHE_PERCENT_DEFAULT = 20
};

static unsigned int lu_cache_percent = LU_CACHE_PERCENT_DEFAULT;
CFS_MODULE_PARM(lu_cache_percent, "i", int, 0644,
                "Percentage of memory to be used as lu_object cache");

/**
 * Return desired hash table order.
 */
static int lu_htable_order(void)
{
        unsigned long cache_size;
        int bits;

        /*
         * Calculate hash table size, assuming that we want reasonable
         * performance when 20% of total memory is occupied by cache of
         * lu_objects.
         *
         * Size of lu_object is (arbitrary) taken as 1K (together with inode).
         */
        cache_size = num_physpages;

#if BITS_PER_LONG == 32
        /* limit hashtable size for lowmem systems to low RAM */
        if (cache_size > 1 << (30 - PAGE_CACHE_SHIFT))
                cache_size = 1 << (30 - PAGE_CACHE_SHIFT) * 3 / 4;
#endif

        /* clear off unreasonable cache setting. */
        if (lu_cache_percent == 0 || lu_cache_percent > LU_CACHE_PERCENT_MAX) {
                CWARN("obdclass: invalid lu_cache_percent: %u, it must be in"
                      " the range of (0, %u]. Will use default value: %u.\n",
                      lu_cache_percent, LU_CACHE_PERCENT_MAX,
                      LU_CACHE_PERCENT_DEFAULT);

                lu_cache_percent = LU_CACHE_PERCENT_DEFAULT;
        }
        cache_size = cache_size / 100 * lu_cache_percent *
                (PAGE_CACHE_SIZE / 1024);

        for (bits = 1; (1 << bits) < cache_size; ++bits) {
                ;
        }
        return bits;
}

static unsigned lu_obj_hop_hash(cfs_hash_t *hs,
                                const void *key, unsigned mask)
{
        struct lu_fid  *fid = (struct lu_fid *)key;
        __u32           hash;

        hash = fid_flatten32(fid);
        hash += (hash >> 4) + (hash << 12); /* mixing oid and seq */
        hash = cfs_hash_long(hash, hs->hs_bkt_bits);

        /* give me another random factor */
        hash -= cfs_hash_long((unsigned long)hs, fid_oid(fid) % 11 + 3);

        hash <<= hs->hs_cur_bits - hs->hs_bkt_bits;
        hash |= (fid_seq(fid) + fid_oid(fid)) & (CFS_HASH_NBKT(hs) - 1);

        return hash & mask;
}

static void *lu_obj_hop_object(cfs_hlist_node_t *hnode)
{
        return cfs_hlist_entry(hnode, struct lu_object_header, loh_hash);
}

static void *lu_obj_hop_key(cfs_hlist_node_t *hnode)
{
        struct lu_object_header *h;

        h = cfs_hlist_entry(hnode, struct lu_object_header, loh_hash);
        return &h->loh_fid;
}

static int lu_obj_hop_keycmp(const void *key, cfs_hlist_node_t *hnode)
{
        struct lu_object_header *h;

        h = cfs_hlist_entry(hnode, struct lu_object_header, loh_hash);
        return lu_fid_eq(&h->loh_fid, (struct lu_fid *)key);
}

static void lu_obj_hop_get(cfs_hash_t *hs, cfs_hlist_node_t *hnode)
{
        struct lu_object_header *h;

        h = cfs_hlist_entry(hnode, struct lu_object_header, loh_hash);
        if (cfs_atomic_add_return(1, &h->loh_ref) == 1) {
                struct lu_site_bkt_data *bkt;
                cfs_hash_bd_t            bd;

                cfs_hash_bd_get(hs, &h->loh_fid, &bd);
                bkt = cfs_hash_bd_extra_get(hs, &bd);
                bkt->lsb_busy++;
        }
}

static void lu_obj_hop_put_locked(cfs_hash_t *hs, cfs_hlist_node_t *hnode)
{
        LBUG(); /* we should never called it */
}

cfs_hash_ops_t lu_site_hash_ops = {
        .hs_hash        = lu_obj_hop_hash,
        .hs_key         = lu_obj_hop_key,
        .hs_keycmp      = lu_obj_hop_keycmp,
        .hs_object      = lu_obj_hop_object,
        .hs_get         = lu_obj_hop_get,
        .hs_put_locked  = lu_obj_hop_put_locked,
};

void lu_dev_add_linkage(struct lu_site *s, struct lu_device *d)
{
        spin_lock(&s->ls_ld_lock);
        if (cfs_list_empty(&d->ld_linkage))
                cfs_list_add(&d->ld_linkage, &s->ls_ld_linkage);
        spin_unlock(&s->ls_ld_lock);
}
EXPORT_SYMBOL(lu_dev_add_linkage);

void lu_dev_del_linkage(struct lu_site *s, struct lu_device *d)
{
        spin_lock(&s->ls_ld_lock);
        cfs_list_del_init(&d->ld_linkage);
        spin_unlock(&s->ls_ld_lock);
}
EXPORT_SYMBOL(lu_dev_del_linkage);

/**
 * Initialize site \a s, with \a d as the top level device.
 */
#define LU_SITE_BITS_MIN    12
#define LU_SITE_BITS_MAX    24
/**
 * total 256 buckets, we don't want too many buckets because:
 * - consume too much memory
 * - avoid unbalanced LRU list
 */
#define LU_SITE_BKT_BITS    8

int lu_site_init(struct lu_site *s, struct lu_device *top)
{
        struct lu_site_bkt_data *bkt;
        cfs_hash_bd_t bd;
        char name[16];
        int bits;
        int i;
        ENTRY;

        memset(s, 0, sizeof *s);
        bits = lu_htable_order();
        snprintf(name, 16, "lu_site_%s", top->ld_type->ldt_name);
        for (bits = min(max(LU_SITE_BITS_MIN, bits), LU_SITE_BITS_MAX);
             bits >= LU_SITE_BITS_MIN; bits--) {
                s->ls_obj_hash = cfs_hash_create(name, bits, bits,
                                                 bits - LU_SITE_BKT_BITS,
                                                 sizeof(*bkt), 0, 0,
                                                 &lu_site_hash_ops,
                                                 CFS_HASH_SPIN_BKTLOCK |
                                                 CFS_HASH_NO_ITEMREF |
                                                 CFS_HASH_DEPTH |
                                                 CFS_HASH_ASSERT_EMPTY);
                if (s->ls_obj_hash != NULL)
                        break;
        }

        if (s->ls_obj_hash == NULL) {
                CERROR("failed to create lu_site hash with bits: %d\n", bits);
                return -ENOMEM;
        }

        cfs_hash_for_each_bucket(s->ls_obj_hash, &bd, i) {
                bkt = cfs_hash_bd_extra_get(s->ls_obj_hash, &bd);
                CFS_INIT_LIST_HEAD(&bkt->lsb_lru);
                init_waitqueue_head(&bkt->lsb_marche_funebre);
        }

        s->ls_stats = lprocfs_alloc_stats(LU_SS_LAST_STAT, 0);
        if (s->ls_stats == NULL) {
                cfs_hash_putref(s->ls_obj_hash);
                s->ls_obj_hash = NULL;
                return -ENOMEM;
        }

        lprocfs_counter_init(s->ls_stats, LU_SS_CREATED,
                             0, "created", "created");
        lprocfs_counter_init(s->ls_stats, LU_SS_CACHE_HIT,
                             0, "cache_hit", "cache_hit");
        lprocfs_counter_init(s->ls_stats, LU_SS_CACHE_MISS,
                             0, "cache_miss", "cache_miss");
        lprocfs_counter_init(s->ls_stats, LU_SS_CACHE_RACE,
                             0, "cache_race", "cache_race");
        lprocfs_counter_init(s->ls_stats, LU_SS_CACHE_DEATH_RACE,
                             0, "cache_death_race", "cache_death_race");
        lprocfs_counter_init(s->ls_stats, LU_SS_LRU_PURGED,
                             0, "lru_purged", "lru_purged");

        CFS_INIT_LIST_HEAD(&s->ls_linkage);
        s->ls_top_dev = top;
        top->ld_site = s;
        lu_device_get(top);
        lu_ref_add(&top->ld_reference, "site-top", s);

        CFS_INIT_LIST_HEAD(&s->ls_ld_linkage);
        spin_lock_init(&s->ls_ld_lock);

        lu_dev_add_linkage(s, top);

        RETURN(0);
}
EXPORT_SYMBOL(lu_site_init);

/**
 * Finalize \a s and release its resources.
 */
void lu_site_fini(struct lu_site *s)
{
        mutex_lock(&lu_sites_guard);
        cfs_list_del_init(&s->ls_linkage);
        mutex_unlock(&lu_sites_guard);

        if (s->ls_obj_hash != NULL) {
                cfs_hash_putref(s->ls_obj_hash);
                s->ls_obj_hash = NULL;
        }

        if (s->ls_top_dev != NULL) {
                s->ls_top_dev->ld_site = NULL;
                lu_ref_del(&s->ls_top_dev->ld_reference, "site-top", s);
                lu_device_put(s->ls_top_dev);
                s->ls_top_dev = NULL;
        }

        if (s->ls_stats != NULL)
                lprocfs_free_stats(&s->ls_stats);
}
EXPORT_SYMBOL(lu_site_fini);

/**
 * Called when initialization of stack for this site is completed.
 */
int lu_site_init_finish(struct lu_site *s)
{
        int result;
        mutex_lock(&lu_sites_guard);
        result = lu_context_refill(&lu_shrink_env.le_ctx);
        if (result == 0)
                cfs_list_add(&s->ls_linkage, &lu_sites);
        mutex_unlock(&lu_sites_guard);
        return result;
}
EXPORT_SYMBOL(lu_site_init_finish);

/**
 * Acquire additional reference on device \a d
 */
void lu_device_get(struct lu_device *d)
{
        cfs_atomic_inc(&d->ld_ref);
}
EXPORT_SYMBOL(lu_device_get);

/**
 * Release reference on device \a d.
 */
void lu_device_put(struct lu_device *d)
{
        LASSERT(cfs_atomic_read(&d->ld_ref) > 0);
        cfs_atomic_dec(&d->ld_ref);
}
EXPORT_SYMBOL(lu_device_put);

/**
 * Initialize device \a d of type \a t.
 */
int lu_device_init(struct lu_device *d, struct lu_device_type *t)
{
        if (t->ldt_device_nr++ == 0 && t->ldt_ops->ldto_start != NULL)
                t->ldt_ops->ldto_start(t);
        memset(d, 0, sizeof *d);
        cfs_atomic_set(&d->ld_ref, 0);
        d->ld_type = t;
        lu_ref_init(&d->ld_reference);
        CFS_INIT_LIST_HEAD(&d->ld_linkage);
        return 0;
}
EXPORT_SYMBOL(lu_device_init);

/**
 * Finalize device \a d.
 */
void lu_device_fini(struct lu_device *d)
{
        struct lu_device_type *t;

        t = d->ld_type;
        if (d->ld_obd != NULL) {
                d->ld_obd->obd_lu_dev = NULL;
                d->ld_obd = NULL;
        }

        lu_ref_fini(&d->ld_reference);
        LASSERTF(cfs_atomic_read(&d->ld_ref) == 0,
                 "Refcount is %u\n", cfs_atomic_read(&d->ld_ref));
        LASSERT(t->ldt_device_nr > 0);
        if (--t->ldt_device_nr == 0 && t->ldt_ops->ldto_stop != NULL)
                t->ldt_ops->ldto_stop(t);
}
EXPORT_SYMBOL(lu_device_fini);

/**
 * Initialize object \a o that is part of compound object \a h and was created
 * by device \a d.
 */
int lu_object_init(struct lu_object *o, struct lu_object_header *h,
                   struct lu_device *d)
{
        memset(o, 0, sizeof(*o));
        o->lo_header = h;
        o->lo_dev = d;
        lu_device_get(d);
        lu_ref_add_at(&d->ld_reference, &o->lo_dev_ref, "lu_object", o);
        CFS_INIT_LIST_HEAD(&o->lo_linkage);

        return 0;
}
EXPORT_SYMBOL(lu_object_init);

/**
 * Finalize object and release its resources.
 */
void lu_object_fini(struct lu_object *o)
{
        struct lu_device *dev = o->lo_dev;

        LASSERT(cfs_list_empty(&o->lo_linkage));

        if (dev != NULL) {
                lu_ref_del_at(&dev->ld_reference, &o->lo_dev_ref,
                              "lu_object", o);
                lu_device_put(dev);
                o->lo_dev = NULL;
        }
}
EXPORT_SYMBOL(lu_object_fini);

/**
 * Add object \a o as first layer of compound object \a h
 *
 * This is typically called by the ->ldo_object_alloc() method of top-level
 * device.
 */
void lu_object_add_top(struct lu_object_header *h, struct lu_object *o)
{
        cfs_list_move(&o->lo_linkage, &h->loh_layers);
}
EXPORT_SYMBOL(lu_object_add_top);

/**
 * Add object \a o as a layer of compound object, going after \a before.
 *
 * This is typically called by the ->ldo_object_alloc() method of \a
 * before->lo_dev.
 */
void lu_object_add(struct lu_object *before, struct lu_object *o)
{
        cfs_list_move(&o->lo_linkage, &before->lo_linkage);
}
EXPORT_SYMBOL(lu_object_add);

/**
 * Initialize compound object.
 */
int lu_object_header_init(struct lu_object_header *h)
{
        memset(h, 0, sizeof *h);
        cfs_atomic_set(&h->loh_ref, 1);
        CFS_INIT_HLIST_NODE(&h->loh_hash);
        CFS_INIT_LIST_HEAD(&h->loh_lru);
        CFS_INIT_LIST_HEAD(&h->loh_layers);
        lu_ref_init(&h->loh_reference);
        return 0;
}
EXPORT_SYMBOL(lu_object_header_init);

/**
 * Finalize compound object.
 */
void lu_object_header_fini(struct lu_object_header *h)
{
        LASSERT(cfs_list_empty(&h->loh_layers));
        LASSERT(cfs_list_empty(&h->loh_lru));
        LASSERT(cfs_hlist_unhashed(&h->loh_hash));
        lu_ref_fini(&h->loh_reference);
}
EXPORT_SYMBOL(lu_object_header_fini);

/**
 * Given a compound object, find its slice, corresponding to the device type
 * \a dtype.
 */
struct lu_object *lu_object_locate(struct lu_object_header *h,
                                   const struct lu_device_type *dtype)
{
        struct lu_object *o;

        cfs_list_for_each_entry(o, &h->loh_layers, lo_linkage) {
                if (o->lo_dev->ld_type == dtype)
                        return o;
        }
        return NULL;
}
EXPORT_SYMBOL(lu_object_locate);



/**
 * Finalize and free devices in the device stack.
 *
 * Finalize device stack by purging object cache, and calling
 * lu_device_type_operations::ldto_device_fini() and
 * lu_device_type_operations::ldto_device_free() on all devices in the stack.
 */
void lu_stack_fini(const struct lu_env *env, struct lu_device *top)
{
        struct lu_site   *site = top->ld_site;
        struct lu_device *scan;
        struct lu_device *next;

        lu_site_purge(env, site, ~0);
        for (scan = top; scan != NULL; scan = next) {
                next = scan->ld_type->ldt_ops->ldto_device_fini(env, scan);
                lu_ref_del(&scan->ld_reference, "lu-stack", &lu_site_init);
                lu_device_put(scan);
        }

        /* purge again. */
        lu_site_purge(env, site, ~0);

        for (scan = top; scan != NULL; scan = next) {
                const struct lu_device_type *ldt = scan->ld_type;
                struct obd_type             *type;

                next = ldt->ldt_ops->ldto_device_free(env, scan);
                type = ldt->ldt_obd_type;
                if (type != NULL) {
                        type->typ_refcnt--;
                        class_put_type(type);
                }
        }
}
EXPORT_SYMBOL(lu_stack_fini);

enum {
        /**
         * Maximal number of tld slots.
         */
        LU_CONTEXT_KEY_NR = 40
};

static struct lu_context_key *lu_keys[LU_CONTEXT_KEY_NR] = { NULL, };

static DEFINE_SPINLOCK(lu_keys_guard);

/**
 * Global counter incremented whenever key is registered, unregistered,
 * revived or quiesced. This is used to void unnecessary calls to
 * lu_context_refill(). No locking is provided, as initialization and shutdown
 * are supposed to be externally serialized.
 */
static unsigned key_set_version = 0;

/**
 * Register new key.
 */
int lu_context_key_register(struct lu_context_key *key)
{
        int result;
        int i;

        LASSERT(key->lct_init != NULL);
        LASSERT(key->lct_fini != NULL);
        LASSERT(key->lct_tags != 0);
        LASSERT(key->lct_owner != NULL);

        result = -ENFILE;
        spin_lock(&lu_keys_guard);
        for (i = 0; i < ARRAY_SIZE(lu_keys); ++i) {
                if (lu_keys[i] == NULL) {
                        key->lct_index = i;
                        cfs_atomic_set(&key->lct_used, 1);
                        lu_keys[i] = key;
                        lu_ref_init(&key->lct_reference);
                        result = 0;
                        ++key_set_version;
                        break;
                }
        }
        spin_unlock(&lu_keys_guard);
        return result;
}
EXPORT_SYMBOL(lu_context_key_register);

static void key_fini(struct lu_context *ctx, int index)
{
        if (ctx->lc_value != NULL && ctx->lc_value[index] != NULL) {
                struct lu_context_key *key;

                key = lu_keys[index];
                LASSERT(key != NULL);
                LASSERT(key->lct_fini != NULL);
                LASSERT(cfs_atomic_read(&key->lct_used) > 1);

                key->lct_fini(ctx, key, ctx->lc_value[index]);
                lu_ref_del(&key->lct_reference, "ctx", ctx);
                cfs_atomic_dec(&key->lct_used);

                LASSERT(key->lct_owner != NULL);
                if ((ctx->lc_tags & LCT_NOREF) == 0) {
                        LINVRNT(module_refcount(key->lct_owner) > 0);
                        module_put(key->lct_owner);
                }
                ctx->lc_value[index] = NULL;
        }
}

/**
 * Deregister key.
 */
void lu_context_key_degister(struct lu_context_key *key)
{
        LASSERT(cfs_atomic_read(&key->lct_used) >= 1);
        LINVRNT(0 <= key->lct_index && key->lct_index < ARRAY_SIZE(lu_keys));

        lu_context_key_quiesce(key);

        ++key_set_version;
        spin_lock(&lu_keys_guard);
        key_fini(&lu_shrink_env.le_ctx, key->lct_index);
        if (lu_keys[key->lct_index]) {
                lu_keys[key->lct_index] = NULL;
                lu_ref_fini(&key->lct_reference);
        }
        spin_unlock(&lu_keys_guard);

        LASSERTF(cfs_atomic_read(&key->lct_used) == 1,
                 "key has instances: %d\n",
                 cfs_atomic_read(&key->lct_used));
}
EXPORT_SYMBOL(lu_context_key_degister);

/**
 * Register a number of keys. This has to be called after all keys have been
 * initialized by a call to LU_CONTEXT_KEY_INIT().
 */
int lu_context_key_register_many(struct lu_context_key *k, ...)
{
        struct lu_context_key *key = k;
        va_list args;
        int result;

        va_start(args, k);
        do {
                result = lu_context_key_register(key);
                if (result)
                        break;
                key = va_arg(args, struct lu_context_key *);
        } while (key != NULL);
        va_end(args);

        if (result != 0) {
                va_start(args, k);
                while (k != key) {
                        lu_context_key_degister(k);
                        k = va_arg(args, struct lu_context_key *);
                }
                va_end(args);
        }

        return result;
}
EXPORT_SYMBOL(lu_context_key_register_many);

/**
 * De-register a number of keys. This is a dual to
 * lu_context_key_register_many().
 */
void lu_context_key_degister_many(struct lu_context_key *k, ...)
{
        va_list args;

        va_start(args, k);
        do {
                lu_context_key_degister(k);
                k = va_arg(args, struct lu_context_key*);
        } while (k != NULL);
        va_end(args);
}
EXPORT_SYMBOL(lu_context_key_degister_many);

/**
 * Revive a number of keys.
 */
void lu_context_key_revive_many(struct lu_context_key *k, ...)
{
        va_list args;

        va_start(args, k);
        do {
                lu_context_key_revive(k);
                k = va_arg(args, struct lu_context_key*);
        } while (k != NULL);
        va_end(args);
}
EXPORT_SYMBOL(lu_context_key_revive_many);

/**
 * Quiescent a number of keys.
 */
void lu_context_key_quiesce_many(struct lu_context_key *k, ...)
{
        va_list args;

        va_start(args, k);
        do {
                lu_context_key_quiesce(k);
                k = va_arg(args, struct lu_context_key*);
        } while (k != NULL);
        va_end(args);
}
EXPORT_SYMBOL(lu_context_key_quiesce_many);

/**
 * Return value associated with key \a key in context \a ctx.
 */
void *lu_context_key_get(const struct lu_context *ctx,
                         const struct lu_context_key *key)
{
        LINVRNT(ctx->lc_state == LCS_ENTERED);
        LINVRNT(0 <= key->lct_index && key->lct_index < ARRAY_SIZE(lu_keys));
        LASSERT(lu_keys[key->lct_index] == key);
        return ctx->lc_value[key->lct_index];
}
EXPORT_SYMBOL(lu_context_key_get);

/**
 * List of remembered contexts. XXX document me.
 */
static CFS_LIST_HEAD(lu_context_remembered);

/**
 * Destroy \a key in all remembered contexts. This is used to destroy key
 * values in "shared" contexts (like service threads), when a module owning
 * the key is about to be unloaded.
 */
void lu_context_key_quiesce(struct lu_context_key *key)
{
        struct lu_context *ctx;

        if (!(key->lct_tags & LCT_QUIESCENT)) {
                /*
                 * XXX layering violation.
                 */
                key->lct_tags |= LCT_QUIESCENT;
                /*
                 * XXX memory barrier has to go here.
                 */
                spin_lock(&lu_keys_guard);
                cfs_list_for_each_entry(ctx, &lu_context_remembered,
                                        lc_remember)
                        key_fini(ctx, key->lct_index);
                spin_unlock(&lu_keys_guard);
                ++key_set_version;
        }
}
EXPORT_SYMBOL(lu_context_key_quiesce);

void lu_context_key_revive(struct lu_context_key *key)
{
        key->lct_tags &= ~LCT_QUIESCENT;
        ++key_set_version;
}
EXPORT_SYMBOL(lu_context_key_revive);

static void keys_fini(struct lu_context *ctx)
{
        int     i;

        if (ctx->lc_value == NULL)
                return;

        for (i = 0; i < ARRAY_SIZE(lu_keys); ++i)
                key_fini(ctx, i);

        OBD_FREE(ctx->lc_value, ARRAY_SIZE(lu_keys) * sizeof ctx->lc_value[0]);
        ctx->lc_value = NULL;
}

static int keys_fill(struct lu_context *ctx)
{
        int i;

        LINVRNT(ctx->lc_value != NULL);
        for (i = 0; i < ARRAY_SIZE(lu_keys); ++i) {
                struct lu_context_key *key;

                key = lu_keys[i];
                if (ctx->lc_value[i] == NULL && key != NULL &&
                    (key->lct_tags & ctx->lc_tags) &&
                    /*
                     * Don't create values for a LCT_QUIESCENT key, as this
                     * will pin module owning a key.
                     */
                    !(key->lct_tags & LCT_QUIESCENT)) {
                        void *value;

                        LINVRNT(key->lct_init != NULL);
                        LINVRNT(key->lct_index == i);

                        value = key->lct_init(ctx, key);
                        if (unlikely(IS_ERR(value)))
                                return PTR_ERR(value);

                        LASSERT(key->lct_owner != NULL);
                        if (!(ctx->lc_tags & LCT_NOREF))
                                try_module_get(key->lct_owner);
                        lu_ref_add_atomic(&key->lct_reference, "ctx", ctx);
                        cfs_atomic_inc(&key->lct_used);
                        /*
                         * This is the only place in the code, where an
                         * element of ctx->lc_value[] array is set to non-NULL
                         * value.
                         */
                        ctx->lc_value[i] = value;
                        if (key->lct_exit != NULL)
                                ctx->lc_tags |= LCT_HAS_EXIT;
                }
                ctx->lc_version = key_set_version;
        }
        return 0;
}

static int keys_init(struct lu_context *ctx)
{
        OBD_ALLOC(ctx->lc_value, ARRAY_SIZE(lu_keys) * sizeof ctx->lc_value[0]);
        if (likely(ctx->lc_value != NULL))
                return keys_fill(ctx);

        return -ENOMEM;
}

/**
 * Initialize context data-structure. Create values for all keys.
 */
int lu_context_init(struct lu_context *ctx, __u32 tags)
{
        int     rc;

        memset(ctx, 0, sizeof *ctx);
        ctx->lc_state = LCS_INITIALIZED;
        ctx->lc_tags = tags;
        if (tags & LCT_REMEMBER) {
                spin_lock(&lu_keys_guard);
                cfs_list_add(&ctx->lc_remember, &lu_context_remembered);
                spin_unlock(&lu_keys_guard);
        } else {
                CFS_INIT_LIST_HEAD(&ctx->lc_remember);
        }

        rc = keys_init(ctx);
        if (rc != 0)
                lu_context_fini(ctx);

        return rc;
}
EXPORT_SYMBOL(lu_context_init);

/**
 * Finalize context data-structure. Destroy key values.
 */
void lu_context_fini(struct lu_context *ctx)
{
        LINVRNT(ctx->lc_state == LCS_INITIALIZED || ctx->lc_state == LCS_LEFT);
        ctx->lc_state = LCS_FINALIZED;

        if ((ctx->lc_tags & LCT_REMEMBER) == 0) {
                LASSERT(cfs_list_empty(&ctx->lc_remember));
                keys_fini(ctx);

        } else { /* could race with key degister */
                spin_lock(&lu_keys_guard);
                keys_fini(ctx);
                cfs_list_del_init(&ctx->lc_remember);
                spin_unlock(&lu_keys_guard);
        }
}
EXPORT_SYMBOL(lu_context_fini);

/**
 * Called before entering context.
 */
void lu_context_enter(struct lu_context *ctx)
{
        LINVRNT(ctx->lc_state == LCS_INITIALIZED || ctx->lc_state == LCS_LEFT);
        ctx->lc_state = LCS_ENTERED;
}
EXPORT_SYMBOL(lu_context_enter);

/**
 * Called after exiting from \a ctx
 */
void lu_context_exit(struct lu_context *ctx)
{
        int i;

        LINVRNT(ctx->lc_state == LCS_ENTERED);
        ctx->lc_state = LCS_LEFT;
        if (ctx->lc_tags & LCT_HAS_EXIT && ctx->lc_value != NULL) {
                for (i = 0; i < ARRAY_SIZE(lu_keys); ++i) {
                        if (ctx->lc_value[i] != NULL) {
                                struct lu_context_key *key;

                                key = lu_keys[i];
                                LASSERT(key != NULL);
                                if (key->lct_exit != NULL)
                                        key->lct_exit(ctx,
                                                      key, ctx->lc_value[i]);
                        }
                }
        }
}
EXPORT_SYMBOL(lu_context_exit);

/**
 * Allocate for context all missing keys that were registered after context
 * creation. key_set_version is only changed in rare cases when modules
 * are loaded and removed.
 */
int lu_context_refill(struct lu_context *ctx)
{
        return likely(ctx->lc_version == key_set_version) ? 0 : keys_fill(ctx);
}
EXPORT_SYMBOL(lu_context_refill);

/**
 * lu_ctx_tags/lu_ses_tags will be updated if there are new types of
 * obd being added. Currently, this is only used on client side, specifically
 * for echo device client, for other stack (like ptlrpc threads), context are
 * predefined when the lu_device type are registered, during the module probe
 * phase.
 */
__u32 lu_context_tags_default = 0;
__u32 lu_session_tags_default = 0;

void lu_context_tags_update(__u32 tags)
{
        spin_lock(&lu_keys_guard);
        lu_context_tags_default |= tags;
        key_set_version++;
        spin_unlock(&lu_keys_guard);
}
EXPORT_SYMBOL(lu_context_tags_update);

void lu_context_tags_clear(__u32 tags)
{
        spin_lock(&lu_keys_guard);
        lu_context_tags_default &= ~tags;
        key_set_version++;
        spin_unlock(&lu_keys_guard);
}
EXPORT_SYMBOL(lu_context_tags_clear);

void lu_session_tags_update(__u32 tags)
{
        spin_lock(&lu_keys_guard);
        lu_session_tags_default |= tags;
        key_set_version++;
        spin_unlock(&lu_keys_guard);
}
EXPORT_SYMBOL(lu_session_tags_update);

void lu_session_tags_clear(__u32 tags)
{
        spin_lock(&lu_keys_guard);
        lu_session_tags_default &= ~tags;
        key_set_version++;
        spin_unlock(&lu_keys_guard);
}
EXPORT_SYMBOL(lu_session_tags_clear);

int lu_env_init(struct lu_env *env, __u32 tags)
{
        int result;

        env->le_ses = NULL;
        result = lu_context_init(&env->le_ctx, tags);
        if (likely(result == 0))
                lu_context_enter(&env->le_ctx);
        return result;
}
EXPORT_SYMBOL(lu_env_init);

void lu_env_fini(struct lu_env *env)
{
        lu_context_exit(&env->le_ctx);
        lu_context_fini(&env->le_ctx);
        env->le_ses = NULL;
}
EXPORT_SYMBOL(lu_env_fini);

int lu_env_refill(struct lu_env *env)
{
        int result;

        result = lu_context_refill(&env->le_ctx);
        if (result == 0 && env->le_ses != NULL)
                result = lu_context_refill(env->le_ses);
        return result;
}
EXPORT_SYMBOL(lu_env_refill);

/**
 * Currently, this API will only be used by echo client.
 * Because echo client and normal lustre client will share
 * same cl_env cache. So echo client needs to refresh
 * the env context after it get one from the cache, especially
 * when normal client and echo client co-exist in the same client.
 */
int lu_env_refill_by_tags(struct lu_env *env, __u32 ctags,
                          __u32 stags)
{
        int    result;

        if ((env->le_ctx.lc_tags & ctags) != ctags) {
                env->le_ctx.lc_version = 0;
                env->le_ctx.lc_tags |= ctags;
        }

        if (env->le_ses && (env->le_ses->lc_tags & stags) != stags) {
                env->le_ses->lc_version = 0;
                env->le_ses->lc_tags |= stags;
        }

        result = lu_env_refill(env);

        return result;
}
EXPORT_SYMBOL(lu_env_refill_by_tags);

static struct shrinker *lu_site_shrinker;

typedef struct lu_site_stats{
        unsigned        lss_populated;
        unsigned        lss_max_search;
        unsigned        lss_total;
        unsigned        lss_busy;
} lu_site_stats_t;

static void lu_site_stats_get(cfs_hash_t *hs,
                              lu_site_stats_t *stats, int populated)
{
        cfs_hash_bd_t bd;
        int           i;

        cfs_hash_for_each_bucket(hs, &bd, i) {
                struct lu_site_bkt_data *bkt = cfs_hash_bd_extra_get(hs, &bd);
                cfs_hlist_head_t        *hhead;

                cfs_hash_bd_lock(hs, &bd, 1);
                stats->lss_busy  += bkt->lsb_busy;
                stats->lss_total += cfs_hash_bd_count_get(&bd);
                stats->lss_max_search = max((int)stats->lss_max_search,
                                            cfs_hash_bd_depmax_get(&bd));
                if (!populated) {
                        cfs_hash_bd_unlock(hs, &bd, 1);
                        continue;
                }

                cfs_hash_bd_for_each_hlist(hs, &bd, hhead) {
                        if (!cfs_hlist_empty(hhead))
                                stats->lss_populated++;
                }
                cfs_hash_bd_unlock(hs, &bd, 1);
        }
}

#ifdef __KERNEL__

/*
 * There exists a potential lock inversion deadlock scenario when using
 * Lustre on top of ZFS. This occurs between one of ZFS's
 * buf_hash_table.ht_lock's, and Lustre's lu_sites_guard lock. Essentially,
 * thread A will take the lu_sites_guard lock and sleep on the ht_lock,
 * while thread B will take the ht_lock and sleep on the lu_sites_guard
 * lock. Obviously neither thread will wake and drop their respective hold
 * on their lock.
 *
 * To prevent this from happening we must ensure the lu_sites_guard lock is
 * not taken while down this code path. ZFS reliably does not set the
 * __GFP_FS bit in its code paths, so this can be used to determine if it
 * is safe to take the lu_sites_guard lock.
 *
 * Ideally we should accurately return the remaining number of cached
 * objects without taking the  lu_sites_guard lock, but this is not
 * possible in the current implementation.
 */
static int lu_cache_shrink(SHRINKER_ARGS(sc, nr_to_scan, gfp_mask))
{
        lu_site_stats_t stats;
        struct lu_site *s;
        struct lu_site *tmp;
        int cached = 0;
        int remain = shrink_param(sc, nr_to_scan);
        CFS_LIST_HEAD(splice);

        if (!(shrink_param(sc, gfp_mask) & __GFP_FS)) {
                if (remain != 0)
                        return -1;
                else
                        /* We must not take the lu_sites_guard lock when
                         * __GFP_FS is *not* set because of the deadlock
                         * possibility detailed above. Additionally,
                         * since we cannot determine the number of
                         * objects in the cache without taking this
                         * lock, we're in a particularly tough spot. As
                         * a result, we'll just lie and say our cache is
                         * empty. This _should_ be ok, as we can't
                         * reclaim objects when __GFP_FS is *not* set
                         * anyways.
                         */
                        return 0;
        }

        CDEBUG(D_INODE, "Shrink %d objects\n", remain);

        mutex_lock(&lu_sites_guard);
        cfs_list_for_each_entry_safe(s, tmp, &lu_sites, ls_linkage) {
                if (shrink_param(sc, nr_to_scan) != 0) {
                        remain = lu_site_purge(&lu_shrink_env, s, remain);
                        /*
                         * Move just shrunk site to the tail of site list to
                         * assure shrinking fairness.
                         */
                        cfs_list_move_tail(&s->ls_linkage, &splice);
                }

                memset(&stats, 0, sizeof(stats));
                lu_site_stats_get(s->ls_obj_hash, &stats, 0);
                cached += stats.lss_total - stats.lss_busy;
                if (shrink_param(sc, nr_to_scan) && remain <= 0)
                        break;
        }
        cfs_list_splice(&splice, lu_sites.prev);
        mutex_unlock(&lu_sites_guard);

        cached = (cached / 100) * sysctl_vfs_cache_pressure;
        if (shrink_param(sc, nr_to_scan) == 0)
                CDEBUG(D_INODE, "%d objects cached\n", cached);
        return cached;
}

/*
 * Debugging stuff.
 */

/**
 * Environment to be used in debugger, contains all tags.
 */
struct lu_env lu_debugging_env;

/**
 * Debugging printer function using printk().
 */
int lu_printk_printer(const struct lu_env *env,
                      void *unused, const char *format, ...)
{
        va_list args;

        va_start(args, format);
        vprintk(format, args);
        va_end(args);
        return 0;
}

int lu_debugging_setup(void)
{
        return lu_env_init(&lu_debugging_env, ~0);
}

void lu_context_keys_dump(void)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(lu_keys); ++i) {
                struct lu_context_key *key;

                key = lu_keys[i];
                if (key != NULL) {
                        CERROR("[%d]: %p %x (%p,%p,%p) %d %d \"%s\"@%p\n",
                               i, key, key->lct_tags,
                               key->lct_init, key->lct_fini, key->lct_exit,
                               key->lct_index, cfs_atomic_read(&key->lct_used),
                               key->lct_owner ? key->lct_owner->name : "",
                               key->lct_owner);
                        lu_ref_print(&key->lct_reference);
                }
        }
}
EXPORT_SYMBOL(lu_context_keys_dump);
#else  /* !__KERNEL__ */
static int lu_cache_shrink(int nr, unsigned int gfp_mask)
{
        return 0;
}
#endif /* __KERNEL__ */

/**
 * Initialization of global lu_* data.
 */
int lu_global_init(void)
{
        int result;

        CDEBUG(D_INFO, "Lustre LU module (%p).\n", &lu_keys);

        result = lu_ref_global_init();
        if (result != 0)
                return result;

        LU_CONTEXT_KEY_INIT(&lu_global_key);
        result = lu_context_key_register(&lu_global_key);
        if (result != 0)
                return result;

        /*
         * At this level, we don't know what tags are needed, so allocate them
         * conservatively. This should not be too bad, because this
         * environment is global.
         */
        mutex_lock(&lu_sites_guard);
        result = lu_env_init(&lu_shrink_env, LCT_SHRINKER);
        mutex_unlock(&lu_sites_guard);
        if (result != 0)
                return result;

        /*
         * seeks estimation: 3 seeks to read a record from oi, one to read
         * inode, one for ea. Unfortunately setting this high value results in
         * lu_object/inode cache consuming all the memory.
         */
        lu_site_shrinker = set_shrinker(DEFAULT_SEEKS, lu_cache_shrink);
        if (lu_site_shrinker == NULL)
                return -ENOMEM;

        return result;
}

/**
 * Dual to lu_global_init().
 */
void lu_global_fini(void)
{
        if (lu_site_shrinker != NULL) {
                remove_shrinker(lu_site_shrinker);
                lu_site_shrinker = NULL;
        }

        lu_context_key_degister(&lu_global_key);

        /*
         * Tear shrinker environment down _after_ de-registering
         * lu_global_key, because the latter has a value in the former.
         */
        mutex_lock(&lu_sites_guard);
        lu_env_fini(&lu_shrink_env);
        mutex_unlock(&lu_sites_guard);

        lu_ref_global_fini();
}

static __u32 ls_stats_read(struct lprocfs_stats *stats, int idx)
{
#ifdef LPROCFS
        struct lprocfs_counter ret;

        lprocfs_stats_collect(stats, idx, &ret);
        return (__u32)ret.lc_count;
#else
        return 0;
#endif
}

/**
 * Output site statistical counters into a buffer. Suitable for
 * lprocfs_rd_*()-style functions.
 */
int lu_site_stats_print(const struct lu_site *s, char *page, int count)
{
        lu_site_stats_t stats;

        memset(&stats, 0, sizeof(stats));
        lu_site_stats_get(s->ls_obj_hash, &stats, 1);

        return snprintf(page, count, "%d/%d %d/%d %d %d %d %d %d %d %d\n",
                        stats.lss_busy,
                        stats.lss_total,
                        stats.lss_populated,
                        CFS_HASH_NHLIST(s->ls_obj_hash),
                        stats.lss_max_search,
                        ls_stats_read(s->ls_stats, LU_SS_CREATED),
                        ls_stats_read(s->ls_stats, LU_SS_CACHE_HIT),
                        ls_stats_read(s->ls_stats, LU_SS_CACHE_MISS),
                        ls_stats_read(s->ls_stats, LU_SS_CACHE_RACE),
                        ls_stats_read(s->ls_stats, LU_SS_CACHE_DEATH_RACE),
                        ls_stats_read(s->ls_stats, LU_SS_LRU_PURGED));
}
EXPORT_SYMBOL(lu_site_stats_print);

/**
 * Helper function to initialize a number of kmem slab caches at once.
 */
int lu_kmem_init(struct lu_kmem_descr *caches)
{
        int result;
        struct lu_kmem_descr *iter = caches;

        for (result = 0; iter->ckd_cache != NULL; ++iter) {
                *iter->ckd_cache = kmem_cache_create(iter->ckd_name,
                                                     iter->ckd_size,
                                                     0, 0, NULL);
                if (*iter->ckd_cache == NULL) {
                        result = -ENOMEM;
                        /* free all previously allocated caches */
                        lu_kmem_fini(caches);
                        break;
                }
        }
        return result;
}
EXPORT_SYMBOL(lu_kmem_init);

/**
 * Helper function to finalize a number of kmem slab cached at once. Dual to
 * lu_kmem_init().
 */
void lu_kmem_fini(struct lu_kmem_descr *caches)
{
        for (; caches->ckd_cache != NULL; ++caches) {
                if (*caches->ckd_cache != NULL) {
                        kmem_cache_destroy(*caches->ckd_cache);
                        *caches->ckd_cache = NULL;
                }
        }
}
EXPORT_SYMBOL(lu_kmem_fini);

/**
 * Temporary solution to be able to assign fid in ->do_create()
 * till we have fully-functional OST fids
 */
void lu_object_assign_fid(const struct lu_env *env, struct lu_object *o,
                          const struct lu_fid *fid)
{
        struct lu_site          *s = o->lo_dev->ld_site;
        struct lu_fid           *old = &o->lo_header->loh_fid;
        struct lu_site_bkt_data *bkt;
        struct lu_object        *shadow;
        wait_queue_t             waiter;
        cfs_hash_t              *hs;
        cfs_hash_bd_t            bd;
        __u64                    version = 0;

        LASSERT(fid_is_zero(old));

        hs = s->ls_obj_hash;
        cfs_hash_bd_get_and_lock(hs, (void *)fid, &bd, 1);
        shadow = htable_lookup(s, &bd, fid, &waiter, &version);
        /* supposed to be unique */
        LASSERT(IS_ERR(shadow) && PTR_ERR(shadow) == -ENOENT);
        *old = *fid;
        bkt = cfs_hash_bd_extra_get(hs, &bd);
        cfs_hash_bd_add_locked(hs, &bd, &o->lo_header->loh_hash);
        bkt->lsb_busy++;
        cfs_hash_bd_unlock(hs, &bd, 1);
}
EXPORT_SYMBOL(lu_object_assign_fid);

/**
 * allocates object with 0 (non-assiged) fid
 * XXX: temporary solution to be able to assign fid in ->do_create()
 *      till we have fully-functional OST fids
 */
struct lu_object *lu_object_anon(const struct lu_env *env,
                                 struct lu_device *dev,
                                 const struct lu_object_conf *conf)
{
        struct lu_fid     fid;
        struct lu_object *o;

        fid_zero(&fid);
        o = lu_object_alloc(env, dev, &fid, conf);

        return o;
}
EXPORT_SYMBOL(lu_object_anon);

struct lu_buf LU_BUF_NULL = {
        .lb_buf = NULL,
        .lb_len = 0
};
EXPORT_SYMBOL(LU_BUF_NULL);

void lu_buf_free(struct lu_buf *buf)
{
        LASSERT(buf);
        if (buf->lb_buf) {
                LASSERT(buf->lb_len > 0);
                OBD_FREE_LARGE(buf->lb_buf, buf->lb_len);
                buf->lb_buf = NULL;
                buf->lb_len = 0;
        }
}
EXPORT_SYMBOL(lu_buf_free);

void lu_buf_alloc(struct lu_buf *buf, int size)
{
        LASSERT(buf);
        LASSERT(buf->lb_buf == NULL);
        LASSERT(buf->lb_len == 0);
        OBD_ALLOC_LARGE(buf->lb_buf, size);
        if (likely(buf->lb_buf))
                buf->lb_len = size;
}
EXPORT_SYMBOL(lu_buf_alloc);

void lu_buf_realloc(struct lu_buf *buf, int size)
{
        lu_buf_free(buf);
        lu_buf_alloc(buf, size);
}
EXPORT_SYMBOL(lu_buf_realloc);

struct lu_buf *lu_buf_check_and_alloc(struct lu_buf *buf, int len)
{
        if (buf->lb_buf == NULL && buf->lb_len == 0)
                lu_buf_alloc(buf, len);

        if ((len > buf->lb_len) && (buf->lb_buf != NULL))
                lu_buf_realloc(buf, len);

        return buf;
}
EXPORT_SYMBOL(lu_buf_check_and_alloc);

/**
 * Increase the size of the \a buf.
 * preserves old data in buffer
 * old buffer remains unchanged on error
 * \retval 0 or -ENOMEM
 */
int lu_buf_check_and_grow(struct lu_buf *buf, int len)
{
        char *ptr;

        if (len <= buf->lb_len)
                return 0;

        OBD_ALLOC_LARGE(ptr, len);
        if (ptr == NULL)
                return -ENOMEM;

        /* Free the old buf */
        if (buf->lb_buf != NULL) {
                memcpy(ptr, buf->lb_buf, buf->lb_len);
                OBD_FREE_LARGE(buf->lb_buf, buf->lb_len);
        }

        buf->lb_buf = ptr;
        buf->lb_len = len;
        return 0;
}
EXPORT_SYMBOL(lu_buf_check_and_grow);