[fs/lustre-release.git] / lustre / lod / lod_pool.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.gnu.org/licenses/gpl-2.0.html
 *
 * GPL HEADER END
 */
/*
 * Copyright  2008 Sun Microsystems, Inc. All rights reserved
 * Use is subject to license terms.
 *
 * Copyright (c) 2012, 2014 Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 * Lustre is a trademark of Sun Microsystems, Inc.
 */
/*
 * lustre/lod/lod_pool.c
 *
 * OST pool methods
 *
 * This file provides code related to the Logical Object Device (LOD)
 * handling of OST Pools on the MDT.  Pools are named lists of targets
 * that allow userspace to group targets that share a particlar property
 * together so that users or kernel helpers can make decisions about file
 * allocation based on these properties.  For example, pools could be
 * defined based on fault domains (e.g. separate racks of server nodes) so
 * that RAID-1 mirroring could select targets from independent fault
 * domains, or pools could define target performance characteristics so
 * that applicatins could select IOP-optimized storage or stream-optimized
 * storage for a particular output file.
 *
 * This file handles creation, lookup, and removal of pools themselves, as
 * well as adding and removing targets to pools.  It also handles lprocfs
 * display of configured pool.  The pools are accessed by name in the pool
 * hash, and are refcounted to ensure proper pool structure lifetimes.
 *
 * Author: Jacques-Charles LAFOUCRIERE <jc.lafoucriere@cea.fr>
 * Author: Alex Lyashkov <Alexey.Lyashkov@Sun.COM>
 * Author: Nathaniel Rutman <Nathan.Rutman@Sun.COM>
 */

#define DEBUG_SUBSYSTEM S_LOV

#include <libcfs/libcfs.h>
#include <obd.h>
#include "lod_internal.h"

#define pool_tgt(_p, _i) OST_TGT(lu2lod_dev((_p)->pool_lobd->obd_lu_dev), \
                                 (_p)->pool_obds.op_array[_i])

/**
 * Get a reference on the specified pool.
 *
 * To ensure the pool descriptor is not freed before the caller is finished
 * with it.  Any process that is accessing \a pool directly needs to hold
 * reference on it, including /proc since a userspace thread may be holding
 * the /proc file open and busy in the kernel.
 *
 * \param[in] pool      pool descriptor on which to gain reference
 */
static void pool_getref(struct pool_desc *pool)
{
        CDEBUG(D_INFO, "pool %p\n", pool);
        atomic_inc(&pool->pool_refcount);
}

/**
 * Drop a reference on the specified pool and free its memory if needed.
 *
 * One reference is held by the LOD OBD device while it is configured, from
 * the time the configuration log defines the pool until the time when it is
 * dropped when the LOD OBD is cleaned up or the pool is deleted.  This means
 * that the pool will not be freed while the LOD device is configured, unless
 * it is explicitly destroyed by the sysadmin.  The pool structure is freed
 * after the last reference on the structure is released.
 *
 * \param[in] pool      pool descriptor to drop reference on and possibly free
 */
void lod_pool_putref(struct pool_desc *pool)
{
        CDEBUG(D_INFO, "pool %p\n", pool);
        if (atomic_dec_and_test(&pool->pool_refcount)) {
                LASSERT(cfs_hlist_unhashed(&pool->pool_hash));
                LASSERT(cfs_list_empty(&pool->pool_list));
                LASSERT(pool->pool_proc_entry == NULL);
                lod_ost_pool_free(&(pool->pool_rr.lqr_pool));
                lod_ost_pool_free(&(pool->pool_obds));
                OBD_FREE_PTR(pool);
                EXIT;
        }
}

/**
 * Drop the refcount in cases where the caller holds a spinlock.
 *
 * This is needed if the caller cannot be blocked while freeing memory.
 * It assumes that there is some other known refcount held on the \a pool
 * and the memory cannot actually be freed, but the refcounting needs to
 * be kept accurate.
 *
 * \param[in] pool      pool descriptor on which to drop reference
 */
static void pool_putref_locked(struct pool_desc *pool)
{
        CDEBUG(D_INFO, "pool %p\n", pool);
        LASSERT(atomic_read(&pool->pool_refcount) > 1);

        atomic_dec(&pool->pool_refcount);
}

/*
 * Group of functions needed for cfs_hash implementation.  This
 * includes pool lookup, refcounting, and cleanup.
 */

/**
 * Hash the pool name for use by the cfs_hash handlers.
 *
 * hash function using a Rotating Hash algorithm
 * Knuth, D. The Art of Computer Programming,
 * Volume 3: Sorting and Searching,
 * Chapter 6.4.
 * Addison Wesley, 1973
 *
 * \param[in] hash_body hash structure where this key is embedded (unused)
 * \param[in] key       key to be hashed (in this case the pool name)
 * \param[in] mask      bitmask to limit the hash value to the desired size
 *
 * \retval              computed hash value from \a key and limited by \a mask
 */
static __u32 pool_hashfn(cfs_hash_t *hash_body, const void *key, unsigned mask)
{
        int i;
        __u32 result;
        char *poolname;

        result = 0;
        poolname = (char *)key;
        for (i = 0; i < LOV_MAXPOOLNAME; i++) {
                if (poolname[i] == '\0')
                        break;
                result = (result << 4) ^ (result >> 28) ^ poolname[i];
        }
        return result % mask;
}

/**
 * Return the actual key (pool name) from the hashed \a hnode.
 *
 * Allows extracting the key name when iterating over all hash entries.
 *
 * \param[in] hnode     hash node found by lookup or iteration
 *
 * \retval              char array referencing the pool name (no refcount)
 */
static void *pool_key(cfs_hlist_node_t *hnode)
{
        struct pool_desc *pool;

        pool = cfs_hlist_entry(hnode, struct pool_desc, pool_hash);
        return pool->pool_name;
}

/**
 * Check if the specified hash key matches the hash node.
 *
 * This is needed in case there is a hash key collision, allowing the hash
 * table lookup/iteration to distinguish between the two entries.
 *
 * \param[in] key       key (pool name) being searched for
 * \param[in] compared  current entry being compared
 *
 * \retval              0 if \a key is the same as the key of \a compared
 * \retval              1 if \a key is different from the key of \a compared
 */
static int pool_hashkey_keycmp(const void *key, cfs_hlist_node_t *compared_hnode)
{
        char *pool_name;
        struct pool_desc *pool;

        pool_name = (char *)key;
        pool = cfs_hlist_entry(compared_hnode, struct pool_desc, pool_hash);
        return !strncmp(pool_name, pool->pool_name, LOV_MAXPOOLNAME);
}

/**
 * Return the actual pool data structure from the hash table entry.
 *
 * Once the hash table entry is found, extract the pool data from it.
 * The return type of this function is void * because it needs to be
 * assigned to the generic hash operations table.
 *
 * \param[in] hnode     hash table entry
 *
 * \retval              struct pool_desc for the specified \a hnode
 */
static void *pool_hashobject(cfs_hlist_node_t *hnode)
{
        return cfs_hlist_entry(hnode, struct pool_desc, pool_hash);
}

static void pool_hashrefcount_get(cfs_hash_t *hs, cfs_hlist_node_t *hnode)
{
        struct pool_desc *pool;

        pool = cfs_hlist_entry(hnode, struct pool_desc, pool_hash);
        pool_getref(pool);
}

static void pool_hashrefcount_put_locked(cfs_hash_t *hs,
                                         cfs_hlist_node_t *hnode)
{
        struct pool_desc *pool;

        pool = cfs_hlist_entry(hnode, struct pool_desc, pool_hash);
        pool_putref_locked(pool);
}

cfs_hash_ops_t pool_hash_operations = {
        .hs_hash        = pool_hashfn,
        .hs_key         = pool_key,
        .hs_keycmp      = pool_hashkey_keycmp,
        .hs_object      = pool_hashobject,
        .hs_get         = pool_hashrefcount_get,
        .hs_put_locked  = pool_hashrefcount_put_locked,
};

/*
 * Methods for /proc seq_file iteration of the defined pools.
 */

#define POOL_IT_MAGIC 0xB001CEA0
struct lod_pool_iterator {
        int               lpi_magic;    /* POOL_IT_MAGIC */
        int               lpi_idx;      /* from 0 to pool_tgt_size - 1 */
        struct pool_desc *lpi_pool;
};

/**
 * Return the next configured target within one pool for seq_file iteration.
 *
 * Iterator is used to go through the target entries of a single pool
 * (i.e. the list of OSTs configured for a named pool).
 * lpi_idx is the current target index in the pool's op_array[].
 *
 * The return type is a void * because this function is one of the
 * struct seq_operations methods and must match the function template.
 *
 * \param[in] seq       /proc sequence file iteration tracking structure
 * \param[in] v         unused
 * \param[in] pos       position within iteration; 0 to number of targets - 1
 *
 * \retval      struct pool_iterator of the next pool descriptor
 */
static void *pool_proc_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct lod_pool_iterator *iter = seq->private;
        int prev_idx;

        LASSERTF(iter->lpi_magic == POOL_IT_MAGIC, "%08X\n", iter->lpi_magic);

        /* test if end of file */
        if (*pos >= pool_tgt_count(iter->lpi_pool))
                return NULL;

        /* iterate to find a non empty entry */
        prev_idx = iter->lpi_idx;
        down_read(&pool_tgt_rw_sem(iter->lpi_pool));
        iter->lpi_idx++;
        if (iter->lpi_idx == pool_tgt_count(iter->lpi_pool)) {
                iter->lpi_idx = prev_idx; /* we stay on the last entry */
                up_read(&pool_tgt_rw_sem(iter->lpi_pool));
                return NULL;
        }
        up_read(&pool_tgt_rw_sem(iter->lpi_pool));
        (*pos)++;
        /* return != NULL to continue */
        return iter;
}

/**
 * Start seq_file iteration via /proc for a single pool.
 *
 * The \a pos parameter may be non-zero, indicating that the iteration
 * is starting at some offset in the target list.  Use the seq_file
 * private field to memorize the iterator so we can free it at stop().
 * Need to restore the private pointer to the pool before freeing it.
 *
 * \param[in] seq       new sequence file structure to initialize
 * \param[in] pos       initial target number at which to start iteration
 *
 * \retval              initialized pool iterator private structure
 * \retval              NULL if \a pos exceeds the number of targets in \a pool
 * \retval              negative error number on failure
 */
static void *pool_proc_start(struct seq_file *seq, loff_t *pos)
{
        struct pool_desc *pool = seq->private;
        struct lod_pool_iterator *iter;

        pool_getref(pool);
        if ((pool_tgt_count(pool) == 0) ||
            (*pos >= pool_tgt_count(pool))) {
                /* iter is not created, so stop() has no way to
                 * find pool to dec ref */
                lod_pool_putref(pool);
                return NULL;
        }

        OBD_ALLOC_PTR(iter);
        if (iter == NULL)
                return ERR_PTR(-ENOMEM);
        iter->lpi_magic = POOL_IT_MAGIC;
        iter->lpi_pool = pool;
        iter->lpi_idx = 0;

        seq->private = iter;
        if (*pos > 0) {
                loff_t i;
                void *ptr;

                i = 0;
                do {
                        ptr = pool_proc_next(seq, &iter, &i);
                } while ((i < *pos) && (ptr != NULL));

                return ptr;
        }

        return iter;
}

/**
 * Finish seq_file iteration for a single pool.
 *
 * Once iteration has been completed, the pool_iterator struct must be
 * freed, and the seq_file private pointer restored to the pool, as it
 * was initially when pool_proc_start() was called.
 *
 * In some cases the stop() method may be called 2 times, without calling
 * the start() method (see seq_read() from fs/seq_file.c). We have to free
 * the private iterator struct only if seq->private points to the iterator.
 *
 * \param[in] seq       sequence file structure to clean up
 * \param[in] v         (unused)
 */
static void pool_proc_stop(struct seq_file *seq, void *v)
{
        struct lod_pool_iterator *iter = seq->private;

        if (iter != NULL && iter->lpi_magic == POOL_IT_MAGIC) {
                seq->private = iter->lpi_pool;
                lod_pool_putref(iter->lpi_pool);
                OBD_FREE_PTR(iter);
        }
}

/**
 * Print out one target entry from the pool for seq_file iteration.
 *
 * The currently referenced pool target is given by op_array[lpi_idx].
 *
 * \param[in] seq       new sequence file structure to initialize
 * \param[in] v         (unused)
 */
static int pool_proc_show(struct seq_file *seq, void *v)
{
        struct lod_pool_iterator *iter = v;
        struct lod_tgt_desc  *tgt;

        LASSERTF(iter->lpi_magic == POOL_IT_MAGIC, "%08X\n", iter->lpi_magic);
        LASSERT(iter->lpi_pool != NULL);
        LASSERT(iter->lpi_idx <= pool_tgt_count(iter->lpi_pool));

        down_read(&pool_tgt_rw_sem(iter->lpi_pool));
        tgt = pool_tgt(iter->lpi_pool, iter->lpi_idx);
        up_read(&pool_tgt_rw_sem(iter->lpi_pool));
        if (tgt != NULL)
                seq_printf(seq, "%s\n", obd_uuid2str(&(tgt->ltd_uuid)));

        return 0;
}

static const struct seq_operations pool_proc_ops = {
        .start  = pool_proc_start,
        .next   = pool_proc_next,
        .stop   = pool_proc_stop,
        .show   = pool_proc_show,
};

/**
 * Open a new /proc file for seq_file iteration of targets in one pool.
 *
 * Initialize the seq_file private pointer to reference the pool.
 *
 * \param inode inode to store iteration state for /proc
 * \param file  file descriptor to store iteration methods
 *
 * \retval      0 for success
 * \retval      negative error number on failure
 */
static int pool_proc_open(struct inode *inode, struct file *file)
{
        int rc;

        rc = seq_open(file, &pool_proc_ops);
        if (!rc) {
                struct seq_file *seq = file->private_data;
                seq->private = PDE_DATA(inode);
        }
        return rc;
}

static struct file_operations pool_proc_operations = {
        .open           = pool_proc_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release,
};

/**
 * Dump the pool target list into the Lustre debug log.
 *
 * This is a debugging function to allow dumping the list of targets
 * in \a pool to the Lustre kernel debug log at the given \a level.
 *
 * This is not currently called by any existing code, but can be called
 * from within gdb/crash to display the contents of the pool, or from
 * code under development.
 *
 * \param[in] level     Lustre debug level (D_INFO, D_WARN, D_ERROR, etc)
 * \param[in] pool      pool descriptor to be dumped
 */
void lod_dump_pool(int level, struct pool_desc *pool)
{
        int i;

        pool_getref(pool);

        CDEBUG(level, "pool "LOV_POOLNAMEF" has %d members\n",
               pool->pool_name, pool->pool_obds.op_count);
        down_read(&pool_tgt_rw_sem(pool));

        for (i = 0; i < pool_tgt_count(pool) ; i++) {
                if (!pool_tgt(pool, i) || !(pool_tgt(pool, i))->ltd_exp)
                        continue;
                CDEBUG(level, "pool "LOV_POOLNAMEF"[%d] = %s\n",
                       pool->pool_name, i,
                       obd_uuid2str(&((pool_tgt(pool, i))->ltd_uuid)));
        }

        up_read(&pool_tgt_rw_sem(pool));
        lod_pool_putref(pool);
}

/**
 * Initialize the pool data structures at startup.
 *
 * Allocate and initialize the pool data structures with the specified
 * array size.  If pool count is not specified (\a count == 0), then
 * POOL_INIT_COUNT will be used.  Allocating a non-zero initial array
 * size avoids the need to reallocate as new pools are added.
 *
 * \param[in] op        pool structure
 * \param[in] count     initial size of the target op_array[] array
 *
 * \retval              0 indicates successful pool initialization
 * \retval              negative error number on failure
 */
#define POOL_INIT_COUNT 2
int lod_ost_pool_init(struct ost_pool *op, unsigned int count)
{
        ENTRY;

        if (count == 0)
                count = POOL_INIT_COUNT;
        op->op_array = NULL;
        op->op_count = 0;
        init_rwsem(&op->op_rw_sem);
        op->op_size = count;
        OBD_ALLOC(op->op_array, op->op_size * sizeof(op->op_array[0]));
        if (op->op_array == NULL) {
                op->op_size = 0;
                RETURN(-ENOMEM);
        }
        EXIT;
        return 0;
}

/**
 * Increase the op_array size to hold more targets in this pool.
 *
 * The size is increased to at least \a min_count, but may be larger
 * for an existing pool since ->op_array[] is growing exponentially.
 * Caller must hold write op_rwlock.
 *
 * \param[in] op        pool structure
 * \param[in] min_count minimum number of entries to handle
 *
 * \retval              0 on success
 * \retval              negative error number on failure.
 */
int lod_ost_pool_extend(struct ost_pool *op, unsigned int min_count)
{
        __u32 *new;
        int new_size;

        LASSERT(min_count != 0);

        if (op->op_count < op->op_size)
                return 0;

        new_size = max(min_count, 2 * op->op_size);
        OBD_ALLOC(new, new_size * sizeof(op->op_array[0]));
        if (new == NULL)
                return -ENOMEM;

        /* copy old array to new one */
        memcpy(new, op->op_array, op->op_size * sizeof(op->op_array[0]));
        OBD_FREE(op->op_array, op->op_size * sizeof(op->op_array[0]));
        op->op_array = new;
        op->op_size = new_size;

        return 0;
}

/**
 * Add a new target to an existing pool.
 *
 * Add a new target device to the pool previously created and returned by
 * lod_pool_new().  Each target can only be in each pool at most one time.
 *
 * \param[in] op        target pool to add new entry
 * \param[in] idx       pool index number to add to the \a op array
 * \param[in] min_count minimum number of entries to expect in the pool
 *
 * \retval              0 if target could be added to the pool
 * \retval              negative error if target \a idx was not added
 */
int lod_ost_pool_add(struct ost_pool *op, __u32 idx, unsigned int min_count)
{
        int rc = 0, i;
        ENTRY;

        down_write(&op->op_rw_sem);

        rc = lod_ost_pool_extend(op, min_count);
        if (rc)
                GOTO(out, rc);

        /* search ost in pool array */
        for (i = 0; i < op->op_count; i++) {
                if (op->op_array[i] == idx)
                        GOTO(out, rc = -EEXIST);
        }
        /* ost not found we add it */
        op->op_array[op->op_count] = idx;
        op->op_count++;
        EXIT;
out:
        up_write(&op->op_rw_sem);
        return rc;
}

/**
 * Remove an existing pool from the system.
 *
 * The specified pool must have previously been allocated by
 * lod_pool_new() and not have any target members in the pool.
 * If the removed target is not the last, compact the array
 * to remove empty spaces.
 *
 * \param[in] op        pointer to the original data structure
 * \param[in] idx       target index to be removed
 *
 * \retval              0 on success
 * \retval              negative error number on failure
 */
int lod_ost_pool_remove(struct ost_pool *op, __u32 idx)
{
        int i;
        ENTRY;

        down_write(&op->op_rw_sem);

        for (i = 0; i < op->op_count; i++) {
                if (op->op_array[i] == idx) {
                        memmove(&op->op_array[i], &op->op_array[i + 1],
                                (op->op_count - i - 1) *
                                sizeof(op->op_array[0]));
                        op->op_count--;
                        up_write(&op->op_rw_sem);
                        EXIT;
                        return 0;
                }
        }

        up_write(&op->op_rw_sem);
        RETURN(-EINVAL);
}

/**
 * Free the pool after it was emptied and removed from /proc.
 *
 * Note that all of the child/target entries referenced by this pool
 * must have been removed by lod_ost_pool_remove() before it can be
 * deleted from memory.
 *
 * \param[in] op        pool to be freed.
 *
 * \retval              0 on success or if pool was already freed
 */
int lod_ost_pool_free(struct ost_pool *op)
{
        ENTRY;

        if (op->op_size == 0)
                RETURN(0);

        down_write(&op->op_rw_sem);

        OBD_FREE(op->op_array, op->op_size * sizeof(op->op_array[0]));
        op->op_array = NULL;
        op->op_count = 0;
        op->op_size = 0;

        up_write(&op->op_rw_sem);
        RETURN(0);
}

/**
 * Allocate a new pool for the specified device.
 *
 * Allocate a new pool_desc structure for the specified \a new_pool
 * device to create a pool with the given \a poolname.  The new pool
 * structure is created with a single reference, and is freed when the
 * reference count drops to zero.
 *
 * \param[in] obd       Lustre OBD device on which to add a pool iterator
 * \param[in] poolname  the name of the pool to be created
 *
 * \retval              0 in case of success
 * \retval              negative error code in case of error
 */
int lod_pool_new(struct obd_device *obd, char *poolname)
{
        struct lod_device *lod = lu2lod_dev(obd->obd_lu_dev);
        struct pool_desc  *new_pool;
        int rc;
        ENTRY;

        if (strlen(poolname) > LOV_MAXPOOLNAME)
                RETURN(-ENAMETOOLONG);

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

        strlcpy(new_pool->pool_name, poolname, sizeof(new_pool->pool_name));
        new_pool->pool_lobd = obd;
        atomic_set(&new_pool->pool_refcount, 1);
        rc = lod_ost_pool_init(&new_pool->pool_obds, 0);
        if (rc)
                GOTO(out_err, rc);

        memset(&new_pool->pool_rr, 0, sizeof(new_pool->pool_rr));
        rc = lod_ost_pool_init(&new_pool->pool_rr.lqr_pool, 0);
        if (rc)
                GOTO(out_free_pool_obds, rc);

        INIT_HLIST_NODE(&new_pool->pool_hash);

#ifdef LPROCFS
        pool_getref(new_pool);
        new_pool->pool_proc_entry = lprocfs_add_simple(lod->lod_pool_proc_entry,
                                                       poolname,
#ifndef HAVE_ONLY_PROCFS_SEQ
                                                       NULL, NULL,
#endif
                                                       new_pool,
                                                       &pool_proc_operations);
        if (IS_ERR(new_pool->pool_proc_entry)) {
                CDEBUG(D_CONFIG, "%s: cannot add proc entry "LOV_POOLNAMEF"\n",
                       obd->obd_name, poolname);
                new_pool->pool_proc_entry = NULL;
                lod_pool_putref(new_pool);
        }
        CDEBUG(D_INFO, "pool %p - proc %p\n", new_pool,
               new_pool->pool_proc_entry);
#endif

        spin_lock(&obd->obd_dev_lock);
        cfs_list_add_tail(&new_pool->pool_list, &lod->lod_pool_list);
        lod->lod_pool_count++;
        spin_unlock(&obd->obd_dev_lock);

        /* add to find only when it fully ready  */
        rc = cfs_hash_add_unique(lod->lod_pools_hash_body, poolname,
                                 &new_pool->pool_hash);
        if (rc)
                GOTO(out_err, rc = -EEXIST);

        CDEBUG(D_CONFIG, LOV_POOLNAMEF" is pool #%d\n",
                        poolname, lod->lod_pool_count);

        RETURN(0);

out_err:
        spin_lock(&obd->obd_dev_lock);
        cfs_list_del_init(&new_pool->pool_list);
        lod->lod_pool_count--;
        spin_unlock(&obd->obd_dev_lock);

        lprocfs_remove(&new_pool->pool_proc_entry);

        lod_ost_pool_free(&new_pool->pool_rr.lqr_pool);
out_free_pool_obds:
        lod_ost_pool_free(&new_pool->pool_obds);
        OBD_FREE_PTR(new_pool);
        return rc;
}

/**
 * Remove the named pool from the OBD device.
 *
 * \param[in] obd       OBD device on which pool was previously created
 * \param[in] poolname  name of pool to remove from \a obd
 *
 * \retval              0 on successfully removing the pool
 * \retval              negative error numbers for failures
 */
int lod_pool_del(struct obd_device *obd, char *poolname)
{
        struct lod_device *lod = lu2lod_dev(obd->obd_lu_dev);
        struct pool_desc  *pool;
        ENTRY;

        /* lookup and kill hash reference */
        pool = cfs_hash_del_key(lod->lod_pools_hash_body, poolname);
        if (pool == NULL)
                RETURN(-ENOENT);

        if (pool->pool_proc_entry != NULL) {
                CDEBUG(D_INFO, "proc entry %p\n", pool->pool_proc_entry);
                lprocfs_remove(&pool->pool_proc_entry);
                lod_pool_putref(pool);
        }

        spin_lock(&obd->obd_dev_lock);
        cfs_list_del_init(&pool->pool_list);
        lod->lod_pool_count--;
        spin_unlock(&obd->obd_dev_lock);

        /* release last reference */
        lod_pool_putref(pool);

        RETURN(0);
}

/**
 * Add a single target device to the named pool.
 *
 * Add the target specified by \a ostname to the specified \a poolname.
 *
 * \param[in] obd       OBD device on which to add the pool
 * \param[in] poolname  name of the pool to which to add the target \a ostname
 * \param[in] ostname   name of the target device to be added
 *
 * \retval              0 if \a ostname was (previously) added to the named pool
 * \retval              negative error number on failure
 */
int lod_pool_add(struct obd_device *obd, char *poolname, char *ostname)
{
        struct lod_device       *lod = lu2lod_dev(obd->obd_lu_dev);
        struct obd_uuid          ost_uuid;
        struct pool_desc        *pool;
        unsigned int             idx;
        int                      rc = -EINVAL;
        ENTRY;

        pool = cfs_hash_lookup(lod->lod_pools_hash_body, poolname);
        if (pool == NULL)
                RETURN(-ENOENT);

        obd_str2uuid(&ost_uuid, ostname);

        /* search ost in lod array */
        lod_getref(&lod->lod_ost_descs);
        lod_foreach_ost(lod, idx) {
                if (obd_uuid_equals(&ost_uuid, &OST_TGT(lod, idx)->ltd_uuid)) {
                        rc = 0;
                        break;
                }
        }

        if (rc)
                GOTO(out, rc);

        rc = lod_ost_pool_add(&pool->pool_obds, idx, lod->lod_osts_size);
        if (rc)
                GOTO(out, rc);

        pool->pool_rr.lqr_dirty = 1;

        CDEBUG(D_CONFIG, "Added %s to "LOV_POOLNAMEF" as member %d\n",
                        ostname, poolname,  pool_tgt_count(pool));

        EXIT;
out:
        lod_putref(lod, &lod->lod_ost_descs);
        lod_pool_putref(pool);
        return rc;
}

/**
 * Remove the named target from the specified pool.
 *
 * Remove one target named \a ostname from \a poolname.  The \a ostname
 * is searched for in the lod_device lod_ost_bitmap array, to ensure the
 * specified name actually exists in the pool.
 *
 * \param[in] obd       OBD device from which to remove \a poolname
 * \param[in] poolname  name of the pool to be changed
 * \param[in] ostname   name of the target to remove from \a poolname
 *
 * \retval              0 on successfully removing \a ostname from the pool
 * \retval              negative number on error (e.g. \a ostname not in pool)
 */
int lod_pool_remove(struct obd_device *obd, char *poolname, char *ostname)
{
        struct lod_device       *lod = lu2lod_dev(obd->obd_lu_dev);
        struct obd_uuid          ost_uuid;
        struct pool_desc        *pool;
        unsigned int             idx;
        int                      rc = -EINVAL;
        ENTRY;

        pool = cfs_hash_lookup(lod->lod_pools_hash_body, poolname);
        if (pool == NULL)
                RETURN(-ENOENT);

        obd_str2uuid(&ost_uuid, ostname);

        lod_getref(&lod->lod_ost_descs);
        cfs_foreach_bit(lod->lod_ost_bitmap, idx) {
                if (obd_uuid_equals(&ost_uuid, &OST_TGT(lod, idx)->ltd_uuid)) {
                        rc = 0;
                        break;
                }
        }

        /* test if ost found in lod array */
        if (rc)
                GOTO(out, rc);

        lod_ost_pool_remove(&pool->pool_obds, idx);

        pool->pool_rr.lqr_dirty = 1;

        CDEBUG(D_CONFIG, "%s removed from "LOV_POOLNAMEF"\n", ostname,
               poolname);

        EXIT;
out:
        lod_putref(lod, &lod->lod_ost_descs);
        lod_pool_putref(pool);
        return rc;
}

/**
 * Check if the specified target exists in the pool.
 *
 * The caller may not have a reference on \a pool if it got the pool without
 * calling lod_find_pool() (e.g. directly from the lod pool list)
 *
 * \param[in] idx       Target index to check
 * \param[in] pool      Pool in which to check if target is added.
 *
 * \retval              0 successfully found index in \a pool
 * \retval              negative error if device not found in \a pool
 */
int lod_check_index_in_pool(__u32 idx, struct pool_desc *pool)
{
        int i, rc;
        ENTRY;

        pool_getref(pool);

        down_read(&pool_tgt_rw_sem(pool));

        for (i = 0; i < pool_tgt_count(pool); i++) {
                if (pool_tgt_array(pool)[i] == idx)
                        GOTO(out, rc = 0);
        }
        rc = -ENOENT;
        EXIT;
out:
        up_read(&pool_tgt_rw_sem(pool));

        lod_pool_putref(pool);
        return rc;
}

/**
 * Find the pool descriptor for the specified pool and return it with a
 * reference to the caller if found.
 *
 * \param[in] lod       LOD on which the pools are configured
 * \param[in] poolname  NUL-terminated name of the pool
 *
 * \retval      pointer to pool descriptor on success
 * \retval      NULL if \a poolname could not be found or poolname is empty
 */
struct pool_desc *lod_find_pool(struct lod_device *lod, char *poolname)
{
        struct pool_desc *pool;

        pool = NULL;
        if (poolname[0] != '\0') {
                pool = cfs_hash_lookup(lod->lod_pools_hash_body, poolname);
                if (pool == NULL)
                        CDEBUG(D_CONFIG, "%s: request for an unknown pool ("
                               LOV_POOLNAMEF")\n",
                               lod->lod_child_exp->exp_obd->obd_name, poolname);
                if (pool != NULL && pool_tgt_count(pool) == 0) {
                        CDEBUG(D_CONFIG, "%s: request for an empty pool ("
                               LOV_POOLNAMEF")\n",
                               lod->lod_child_exp->exp_obd->obd_name, poolname);
                        /* pool is ignored, so we remove ref on it */
                        lod_pool_putref(pool);
                        pool = NULL;
                }
        }
        return pool;
}