LU-12577 llog: protect partial updates from readers

[fs/lustre-release.git] / lustre / obdclass / llog_osd.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 (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.
 * Use is subject to license terms.
 *
 * Copyright (c) 2012, 2017, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 */
/*
 * lustre/obdclass/llog_osd.c
 *
 * Low level llog routines on top of OSD API
 *
 * This file provides set of methods for llog operations on top of
 * dt_device. It contains all supported llog_operations interfaces and
 * supplimental functions.
 *
 * Author: Alexey Zhuravlev <alexey.zhuravlev@intel.com>
 * Author: Mikhail Pershin <mike.pershin@intel.com>
 */

#define DEBUG_SUBSYSTEM S_LOG

#include <linux/delay.h>

#include <dt_object.h>
#include <llog_swab.h>
#include <lustre_fid.h>
#include <obd.h>
#include <obd_class.h>

#include "llog_internal.h"
#include "local_storage.h"

/**
 * Implementation of the llog_operations::lop_declare_create
 *
 * This function is a wrapper over local_storage API function
 * local_object_declare_create().
 *
 * \param[in] env       execution environment
 * \param[in] los       local_storage for bottom storage device
 * \param[in] o         dt_object to create
 * \param[in] th        current transaction handle
 *
 * \retval              0 on successful declaration of the new object
 * \retval              negative error if declaration was failed
 */
static int llog_osd_declare_new_object(const struct lu_env *env,
                                       struct local_oid_storage *los,
                                       struct dt_object *o,
                                       struct thandle *th)
{
        struct llog_thread_info *lgi = llog_info(env);

        lgi->lgi_attr.la_valid = LA_MODE;
        lgi->lgi_attr.la_mode = S_IFREG | S_IRUGO | S_IWUSR;
        lgi->lgi_dof.dof_type = dt_mode_to_dft(S_IFREG);

        return local_object_declare_create(env, los, o, &lgi->lgi_attr,
                                           &lgi->lgi_dof, th);
}

/**
 * Implementation of the llog_operations::lop_create
 *
 * This function is a wrapper over local_storage API function
 * local_object_create().
 *
 * \param[in] env       execution environment
 * \param[in] los       local_storage for bottom storage device
 * \param[in] o         dt_object to create
 * \param[in] th        current transaction handle
 *
 * \retval              0 on successful creation of the new object
 * \retval              negative error if creation was failed
 */
static int llog_osd_create_new_object(const struct lu_env *env,
                                      struct local_oid_storage *los,
                                      struct dt_object *o,
                                      struct thandle *th)
{
        struct llog_thread_info *lgi = llog_info(env);

        lgi->lgi_attr.la_valid = LA_MODE;
        lgi->lgi_attr.la_mode = S_IFREG | S_IRUGO | S_IWUSR;
        lgi->lgi_dof.dof_type = dt_mode_to_dft(S_IFREG);

        return local_object_create(env, los, o, &lgi->lgi_attr,
                                   &lgi->lgi_dof, th);
}

/**
 * Implementation of the llog_operations::lop_exist
 *
 * This function checks that llog exists on storage.
 *
 * \param[in] handle    llog handle of the current llog
 *
 * \retval              true if llog object exists and is not just destroyed
 * \retval              false if llog doesn't exist or just destroyed
 */
static int llog_osd_exist(struct llog_handle *handle)
{
        LASSERT(handle->lgh_obj);
        return dt_object_exists(handle->lgh_obj) && !handle->lgh_destroyed;
}

static void *rec_tail(struct llog_rec_hdr *rec)
{
        return (void *)((char *)rec + rec->lrh_len -
                        sizeof(struct llog_rec_tail));
}

/**
 * Write a padding record to the llog
 *
 * This function writes a padding record to the end of llog. That may
 * be needed if llog contains records of variable size, e.g. config logs
 * or changelogs.
 * The padding record just aligns llog to the llog chunk_size boundary if
 * the current record doesn't fit in the remaining space.
 *
 * It allocates full length to avoid two separate writes for header and tail.
 * Such 2-steps scheme needs extra protection and complex error handling.
 *
 * \param[in]     env   execution environment
 * \param[in]     o     dt_object to create
 * \param[in,out] off   pointer to the padding start offset
 * \param[in]     len   padding length
 * \param[in]     index index of the padding record in a llog
 * \param[in]     th    current transaction handle
 *
 * \retval              0 on successful padding write
 * \retval              negative error if write failed
 */
static int llog_osd_pad(const struct lu_env *env, struct dt_object *o,
                        loff_t *off, int len, int index, struct thandle *th)
{
        struct llog_thread_info *lgi = llog_info(env);
        struct llog_rec_hdr     *rec;
        struct llog_rec_tail    *tail;
        int                      rc;

        ENTRY;

        LASSERT(th);
        LASSERT(off);
        LASSERT(len >= LLOG_MIN_REC_SIZE && (len & 0x7) == 0);

        OBD_ALLOC(rec, len);
        if (rec == NULL)
                RETURN(-ENOMEM);

        rec->lrh_len = len;
        rec->lrh_index = index;
        rec->lrh_type = LLOG_PAD_MAGIC;

        tail = rec_tail(rec);
        tail->lrt_len = len;
        tail->lrt_index = index;

        lgi->lgi_buf.lb_buf = rec;
        lgi->lgi_buf.lb_len = len;
        rc = dt_record_write(env, o, &lgi->lgi_buf, off, th);
        if (rc)
                CERROR("%s: error writing padding record: rc = %d\n",
                       o->do_lu.lo_dev->ld_obd->obd_name, rc);

        OBD_FREE(rec, len);
        RETURN(rc);
}

/**
 * Implementation of the llog_operations::lop_read_header
 *
 * This function reads the current llog header from the bottom storage
 * device.
 *
 * \param[in] env       execution environment
 * \param[in] handle    llog handle of the current llog
 *
 * \retval              0 on successful header read
 * \retval              negative error if read failed
 */
static int llog_osd_read_header(const struct lu_env *env,
                                struct llog_handle *handle)
{
        struct llog_rec_hdr     *llh_hdr;
        struct dt_object        *o;
        struct llog_thread_info *lgi;
        enum llog_flag           flags;
        int                      rc;

        ENTRY;

        o = handle->lgh_obj;
        LASSERT(o);

        lgi = llog_info(env);

        dt_read_lock(env, o, 0);

        rc = dt_attr_get(env, o, &lgi->lgi_attr);
        if (rc)
                GOTO(unlock, rc);

        LASSERT(lgi->lgi_attr.la_valid & LA_SIZE);

        if (lgi->lgi_attr.la_size == 0) {
                CDEBUG(D_HA, "not reading header from 0-byte log\n");
                GOTO(unlock, rc = LLOG_EEMPTY);
        }

        flags = handle->lgh_hdr->llh_flags;

        lgi->lgi_off = 0;
        lgi->lgi_buf.lb_buf = handle->lgh_hdr;
        lgi->lgi_buf.lb_len = handle->lgh_hdr_size;
        rc = dt_read(env, o, &lgi->lgi_buf, &lgi->lgi_off);
        llh_hdr = &handle->lgh_hdr->llh_hdr;
        if (rc < sizeof(*llh_hdr) || rc < llh_hdr->lrh_len) {
                CERROR("%s: error reading "DFID" log header size %d: rc = %d\n",
                       o->do_lu.lo_dev->ld_obd->obd_name,
                       PFID(lu_object_fid(&o->do_lu)), rc < 0 ? 0 : rc,
                       -EFAULT);

                if (rc >= 0)
                        rc = -EFAULT;

                GOTO(unlock, rc);
        }

        if (LLOG_REC_HDR_NEEDS_SWABBING(llh_hdr))
                lustre_swab_llog_hdr(handle->lgh_hdr);

        if (llh_hdr->lrh_type != LLOG_HDR_MAGIC) {
                CERROR("%s: bad log %s "DFID" header magic: %#x "
                       "(expected %#x)\n", o->do_lu.lo_dev->ld_obd->obd_name,
                       handle->lgh_name ? handle->lgh_name : "",
                       PFID(lu_object_fid(&o->do_lu)),
                       llh_hdr->lrh_type, LLOG_HDR_MAGIC);
                GOTO(unlock, rc = -EIO);
        } else if (llh_hdr->lrh_len < LLOG_MIN_CHUNK_SIZE ||
                   llh_hdr->lrh_len > handle->lgh_hdr_size) {
                CERROR("%s: incorrectly sized log %s "DFID" header: "
                       "%#x (expected at least %#x)\n"
                       "you may need to re-run lconf --write_conf.\n",
                       o->do_lu.lo_dev->ld_obd->obd_name,
                       handle->lgh_name ? handle->lgh_name : "",
                       PFID(lu_object_fid(&o->do_lu)),
                       llh_hdr->lrh_len, LLOG_MIN_CHUNK_SIZE);
                GOTO(unlock, rc = -EIO);
        } else if (LLOG_HDR_TAIL(handle->lgh_hdr)->lrt_index >
                   LLOG_HDR_BITMAP_SIZE(handle->lgh_hdr) ||
                   LLOG_HDR_TAIL(handle->lgh_hdr)->lrt_len !=
                        llh_hdr->lrh_len) {
                CERROR("%s: incorrectly sized log %s "DFID" tailer: "
                       "%#x : rc = %d\n",
                       o->do_lu.lo_dev->ld_obd->obd_name,
                       handle->lgh_name ? handle->lgh_name : "",
                       PFID(lu_object_fid(&o->do_lu)),
                       LLOG_HDR_TAIL(handle->lgh_hdr)->lrt_len, -EIO);
                GOTO(unlock, rc = -EIO);
        }

        handle->lgh_hdr->llh_flags |= (flags & LLOG_F_EXT_MASK);
        handle->lgh_last_idx = LLOG_HDR_TAIL(handle->lgh_hdr)->lrt_index;
        rc = 0;

unlock:
        dt_read_unlock(env, o);
        RETURN(rc);
}

/**
 * Implementation of the llog_operations::lop_declare_write
 *
 * This function declares the new record write.
 *
 * \param[in] env       execution environment
 * \param[in] loghandle llog handle of the current llog
 * \param[in] rec       llog record header. This is a real header of the full
 *                      llog record to write. This is the beginning of buffer
 *                      to write, the length of buffer is stored in
 *                      \a rec::lrh_len
 * \param[in] idx       index of the llog record. If \a idx == -1 then this is
 *                      append case, otherwise \a idx is the index of record
 *                      to modify
 * \param[in] th        current transaction handle
 *
 * \retval              0 on successful declaration
 * \retval              negative error if declaration failed
 */
static int llog_osd_declare_write_rec(const struct lu_env *env,
                                      struct llog_handle *loghandle,
                                      struct llog_rec_hdr *rec,
                                      int idx, struct thandle *th)
{
        struct llog_thread_info *lgi = llog_info(env);
        __u32                   chunk_size;
        struct dt_object        *o;
        int                      rc;

        ENTRY;

        LASSERT(env);
        LASSERT(th);
        LASSERT(loghandle);
        LASSERT(rec);
        LASSERT(rec->lrh_len <= loghandle->lgh_ctxt->loc_chunk_size);

        o = loghandle->lgh_obj;
        LASSERT(o);

        chunk_size = loghandle->lgh_ctxt->loc_chunk_size;
        lgi->lgi_buf.lb_len = chunk_size;
        lgi->lgi_buf.lb_buf = NULL;
        /* each time we update header */
        rc = dt_declare_record_write(env, o, &lgi->lgi_buf, 0,
                                     th);
        if (rc || idx == 0) /* if error or just header */
                RETURN(rc);

        /**
         * the pad record can be inserted so take into account double
         * record size
         */
        lgi->lgi_buf.lb_len = chunk_size * 2;
        lgi->lgi_buf.lb_buf = NULL;
        /* XXX: implement declared window or multi-chunks approach */
        rc = dt_declare_record_write(env, o, &lgi->lgi_buf, -1, th);

        RETURN(rc);
}

/**
 * Implementation of the llog_operations::lop_write
 *
 * This function writes the new record in the llog or modify the existed one.
 *
 * \param[in]  env              execution environment
 * \param[in]  loghandle        llog handle of the current llog
 * \param[in]  rec              llog record header. This is a real header of
 *                              the full llog record to write. This is
 *                              the beginning of buffer to write, the length
 *                              of buffer is stored in \a rec::lrh_len
 * \param[in,out] reccookie     pointer to the cookie to return back if needed.
 *                              It is used for further cancel of this llog
 *                              record.
 * \param[in]  idx              index of the llog record. If \a idx == -1 then
 *                              this is append case, otherwise \a idx is
 *                              the index of record to modify
 * \param[in]  th               current transaction handle
 *
 * \retval                      0 on successful write && \a reccookie == NULL
 *                              1 on successful write && \a reccookie != NULL
 * \retval                      negative error if write failed
 */
static int llog_osd_write_rec(const struct lu_env *env,
                              struct llog_handle *loghandle,
                              struct llog_rec_hdr *rec,
                              struct llog_cookie *reccookie,
                              int idx, struct thandle *th)
{
        struct llog_thread_info *lgi = llog_info(env);
        struct llog_log_hdr *llh;
        int reclen = rec->lrh_len;
        int index, rc;
        struct llog_rec_tail *lrt;
        struct dt_object *o;
        __u32 chunk_size;
        size_t left;
        __u32 orig_last_idx;
        bool pad = false;
        ENTRY;

        llh = loghandle->lgh_hdr;
        o = loghandle->lgh_obj;

        chunk_size = llh->llh_hdr.lrh_len;
        CDEBUG(D_OTHER, "new record %x to "DFID"\n",
               rec->lrh_type, PFID(lu_object_fid(&o->do_lu)));

        if (!llog_osd_exist(loghandle))
                RETURN(-ENOENT);

        /* record length should not bigger than  */
        if (reclen > loghandle->lgh_hdr->llh_hdr.lrh_len)
                RETURN(-E2BIG);

        /* sanity check for fixed-records llog */
        if (idx != LLOG_HEADER_IDX && (llh->llh_flags & LLOG_F_IS_FIXSIZE)) {
                LASSERT(llh->llh_size != 0);
                LASSERT(llh->llh_size == reclen);
        }

        /* return error if osp object is stale */
        if (idx != LLOG_HEADER_IDX && dt_object_stale(o))
                RETURN(-ESTALE);
        rc = dt_attr_get(env, o, &lgi->lgi_attr);
        if (rc)
                RETURN(rc);

        /**
         * The modification case.
         * If idx set then the record with that index must be modified.
         * There are three cases possible:
         * 1) the common case is the llog header update (idx == 0)
         * 2) the llog record modification during llog process.
         *    This is indicated by the \a loghandle::lgh_cur_idx > 0.
         *    In that case the \a loghandle::lgh_cur_offset
         * 3) otherwise this is assumed that llog consist of records of
         *    fixed size, i.e. catalog. The llog header must has llh_size
         *    field equal to record size. The record offset is calculated
         *    just by /a idx value
         *
         * During modification we don't need extra header update because
         * the bitmap and record count are not changed. The record header
         * and tail remains the same too.
         */
        if (idx != LLOG_NEXT_IDX) {
                /* llog can be empty only when first record is being written */
                LASSERT(ergo(idx > 0, lgi->lgi_attr.la_size > 0));

                if (!test_bit_le(idx, LLOG_HDR_BITMAP(llh))) {
                        CERROR("%s: modify unset record %u\n",
                               o->do_lu.lo_dev->ld_obd->obd_name, idx);
                        RETURN(-ENOENT);
                }

                if (idx != rec->lrh_index) {
                        CERROR("%s: modify index mismatch %d %u\n",
                               o->do_lu.lo_dev->ld_obd->obd_name, idx,
                               rec->lrh_index);
                        RETURN(-EFAULT);
                }

                if (idx == LLOG_HEADER_IDX) {
                        /* llog header update */
                        __u32   *bitmap = LLOG_HDR_BITMAP(llh);

                        lgi->lgi_off = 0;

                        /* If it does not indicate the bitmap index
                         * (reccookie == NULL), then it means update
                         * the whole update header. Otherwise only
                         * update header and bits needs to be updated,
                         * and in DNE cases, it will signaficantly
                         * shrink the RPC size.
                         * see distribute_txn_cancel_records()*/
                        if (reccookie == NULL) {
                                lgi->lgi_buf.lb_len = reclen;
                                lgi->lgi_buf.lb_buf = rec;
                                rc = dt_record_write(env, o, &lgi->lgi_buf,
                                                     &lgi->lgi_off, th);
                                RETURN(rc);
                        }

                        /* update the header */
                        lgi->lgi_buf.lb_len = llh->llh_bitmap_offset;
                        lgi->lgi_buf.lb_buf = llh;
                        rc = dt_record_write(env, o, &lgi->lgi_buf,
                                             &lgi->lgi_off, th);
                        if (rc != 0)
                                RETURN(rc);

                        /* update the bitmap */
                        index = reccookie->lgc_index;
                        lgi->lgi_off = llh->llh_bitmap_offset +
                                      (index / (sizeof(*bitmap) * 8)) *
                                                        sizeof(*bitmap);
                        lgi->lgi_buf.lb_len = sizeof(*bitmap);
                        lgi->lgi_buf.lb_buf =
                                        &bitmap[index/(sizeof(*bitmap)*8)];
                        rc = dt_record_write(env, o, &lgi->lgi_buf,
                                             &lgi->lgi_off, th);

                        RETURN(rc);
                } else if (llh->llh_flags & LLOG_F_IS_FIXSIZE) {
                        lgi->lgi_off = llh->llh_hdr.lrh_len +
                                       (idx - 1) * reclen;
                } else if (reccookie != NULL && reccookie->lgc_index > 0) {
                        /**
                         * The lgc_offset can be used only if index is
                         * the same.
                         */
                        if (idx != reccookie->lgc_index) {
                                CERROR("%s: modify index mismatch %d %d\n",
                                       o->do_lu.lo_dev->ld_obd->obd_name, idx,
                                       reccookie->lgc_index);
                                RETURN(-EFAULT);
                        }

                        lgi->lgi_off = reccookie->lgc_offset;
                        CDEBUG(D_OTHER, "modify record "DFID": idx:%u, "
                               "len:%u offset %llu\n",
                               PFID(&loghandle->lgh_id.lgl_oi.oi_fid), idx,
                               rec->lrh_len, (long long)lgi->lgi_off);
                } else {
                        /* This can be result of lgh_cur_idx is not set during
                         * llog processing or llh_size is not set to proper
                         * record size for fixed records llog. Therefore it is
                         * impossible to get record offset. */
                        CERROR("%s: can't get record offset, idx:%d, "
                               "len:%u.\n", o->do_lu.lo_dev->ld_obd->obd_name,
                               idx, rec->lrh_len);
                        RETURN(-EFAULT);
                }

                /* update only data, header and tail remain the same */
                lgi->lgi_off += sizeof(struct llog_rec_hdr);
                lgi->lgi_buf.lb_len = REC_DATA_LEN(rec);
                lgi->lgi_buf.lb_buf = REC_DATA(rec);
                rc = dt_record_write(env, o, &lgi->lgi_buf, &lgi->lgi_off, th);
                if (rc == 0 && reccookie) {
                        reccookie->lgc_lgl = loghandle->lgh_id;
                        reccookie->lgc_index = idx;
                        rc = 1;
                }
                RETURN(rc);
        }

        /**
         * The append case.
         * The most common case of using llog. The new index is assigned to
         * the new record, new bit is set in llog bitmap and llog count is
         * incremented.
         *
         * Make sure that records don't cross a chunk boundary, so we can
         * process them page-at-a-time if needed.  If it will cross a chunk
         * boundary, write in a fake (but referenced) entry to pad the chunk.
         */


        /* simulate ENOSPC when new plain llog is being added to the
         * catalog */
        if (OBD_FAIL_CHECK(OBD_FAIL_MDS_LLOG_CREATE_FAILED2) &&
            llh->llh_flags & LLOG_F_IS_CAT)
                RETURN(-ENOSPC);

        LASSERT(lgi->lgi_attr.la_valid & LA_SIZE);
        orig_last_idx = loghandle->lgh_last_idx;
        lgi->lgi_off = lgi->lgi_attr.la_size;

        if (loghandle->lgh_max_size > 0 &&
            lgi->lgi_off >= loghandle->lgh_max_size) {
                CDEBUG(D_OTHER, "llog is getting too large (%u > %u) at %u "
                       DFID"\n", (unsigned)lgi->lgi_off,
                       loghandle->lgh_max_size, (int)loghandle->lgh_last_idx,
                       PFID(&loghandle->lgh_id.lgl_oi.oi_fid));
                /* this is to signal that this llog is full */
                loghandle->lgh_last_idx = LLOG_HDR_BITMAP_SIZE(llh) - 1;
                RETURN(-ENOSPC);
        }

        left = chunk_size - (lgi->lgi_off & (chunk_size - 1));
        /* NOTE: padding is a record, but no bit is set */
        if (left != 0 && left != reclen &&
            left < (reclen + LLOG_MIN_REC_SIZE)) {
                index = loghandle->lgh_last_idx + 1;
                rc = llog_osd_pad(env, o, &lgi->lgi_off, left, index, th);
                if (rc)
                        RETURN(rc);

                loghandle->lgh_last_idx++; /* for pad rec */
                pad = true;
        }
        /* if it's the last idx in log file, then return -ENOSPC
         * or wrap around if a catalog */
        if (llog_is_full(loghandle) ||
            unlikely(llh->llh_flags & LLOG_F_IS_CAT &&
                     OBD_FAIL_PRECHECK(OBD_FAIL_CAT_RECORDS) &&
                     loghandle->lgh_last_idx >= cfs_fail_val)) {
                if (llh->llh_flags & LLOG_F_IS_CAT)
                        loghandle->lgh_last_idx = 0;
                else
                        RETURN(-ENOSPC);
        }

        down_write(&loghandle->lgh_last_sem);
        /* increment the last_idx along with llh_tail index, they should
         * be equal for a llog lifetime */
        loghandle->lgh_last_idx++;
        index = loghandle->lgh_last_idx;
        LLOG_HDR_TAIL(llh)->lrt_index = index;
        /**
         * NB: the caller should make sure only 1 process access
         * the lgh_last_idx, e.g. append should be exclusive.
         * Otherwise it might hit the assert.
         */
        LASSERT(index < LLOG_HDR_BITMAP_SIZE(llh));
        rec->lrh_index = index;
        lrt = rec_tail(rec);
        lrt->lrt_len = rec->lrh_len;
        lrt->lrt_index = rec->lrh_index;

        /* the lgh_hdr_mutex protects llog header data from concurrent
         * update/cancel, the llh_count and llh_bitmap are protected */
        mutex_lock(&loghandle->lgh_hdr_mutex);
        if (__test_and_set_bit_le(index, LLOG_HDR_BITMAP(llh))) {
                CERROR("%s: index %u already set in llog bitmap "DFID"\n",
                       o->do_lu.lo_dev->ld_obd->obd_name, index,
                       PFID(lu_object_fid(&o->do_lu)));
                mutex_unlock(&loghandle->lgh_hdr_mutex);
                LBUG(); /* should never happen */
        }
        llh->llh_count++;

        if (!(llh->llh_flags & LLOG_F_IS_FIXSIZE)) {
                /* Update the minimum size of the llog record */
                if (llh->llh_size == 0)
                        llh->llh_size = reclen;
                else if (reclen < llh->llh_size)
                        llh->llh_size = reclen;
        }

        /*
         * readers (e.g. llog_osd_read_header()) must not find
         * llog updated partially (bitmap/counter claims record,
         * but a record hasn't been added yet) as this results
         * in EIO.
         */
        dt_write_lock(env, o, 0);

        if (lgi->lgi_attr.la_size == 0) {
                lgi->lgi_off = 0;
                lgi->lgi_buf.lb_len = llh->llh_hdr.lrh_len;
                lgi->lgi_buf.lb_buf = &llh->llh_hdr;
                rc = dt_record_write(env, o, &lgi->lgi_buf, &lgi->lgi_off, th);
                if (rc != 0)
                        GOTO(out_unlock, rc);
        } else {
                __u32   *bitmap = LLOG_HDR_BITMAP(llh);

                /* Note: If this is not initialization (size == 0), then do not
                 * write the whole header (8k bytes), only update header/tail
                 * and bits needs to be updated. Because this update might be
                 * part of cross-MDT operation, which needs to write these
                 * updates into the update log(32KB limit) and also pack inside
                 * the RPC (1MB limit), if we write 8K for each operation, which
                 * will cost a lot space, and keep us adding more updates to one
                 * update log.*/
                lgi->lgi_off = 0;
                lgi->lgi_buf.lb_len = llh->llh_bitmap_offset;
                lgi->lgi_buf.lb_buf = &llh->llh_hdr;
                rc = dt_record_write(env, o, &lgi->lgi_buf, &lgi->lgi_off, th);
                if (rc != 0)
                        GOTO(out_unlock, rc);

                lgi->lgi_off = llh->llh_bitmap_offset +
                              (index / (sizeof(*bitmap) * 8)) * sizeof(*bitmap);
                lgi->lgi_buf.lb_len = sizeof(*bitmap);
                lgi->lgi_buf.lb_buf = &bitmap[index/(sizeof(*bitmap)*8)];
                rc = dt_record_write(env, o, &lgi->lgi_buf, &lgi->lgi_off, th);
                if (rc != 0)
                        GOTO(out_unlock, rc);

                lgi->lgi_off =  (unsigned long)LLOG_HDR_TAIL(llh) -
                                (unsigned long)llh;
                lgi->lgi_buf.lb_len = sizeof(llh->llh_tail);
                lgi->lgi_buf.lb_buf = LLOG_HDR_TAIL(llh);
                rc = dt_record_write(env, o, &lgi->lgi_buf, &lgi->lgi_off, th);
                if (rc != 0)
                        GOTO(out_unlock, rc);
        }
        if (OBD_FAIL_PRECHECK(OBD_FAIL_LLOG_PAUSE_AFTER_PAD) && pad) {
                /* a window for concurrent llog reader, see LU-12577 */
                OBD_FAIL_TIMEOUT(OBD_FAIL_LLOG_PAUSE_AFTER_PAD,
                                 cfs_fail_val ?: 1);
        }

out_unlock:
        /* unlock here for remote object */
        mutex_unlock(&loghandle->lgh_hdr_mutex);
        if (rc) {
                dt_write_unlock(env, o);
                GOTO(out, rc);
        }

        if (OBD_FAIL_PRECHECK(OBD_FAIL_LLOG_PROCESS_TIMEOUT) &&
           cfs_fail_val == (unsigned int)(loghandle->lgh_id.lgl_oi.oi.oi_id &
                                          0xFFFFFFFF)) {
                OBD_RACE(OBD_FAIL_LLOG_PROCESS_TIMEOUT);
                msleep(1 * MSEC_PER_SEC);
        }
        /* computed index can be used to determine offset for fixed-size
         * records. This also allows to handle Catalog wrap around case */
        if (llh->llh_flags & LLOG_F_IS_FIXSIZE) {
                lgi->lgi_off = llh->llh_hdr.lrh_len + (index - 1) * reclen;
        } else {
                rc = dt_attr_get(env, o, &lgi->lgi_attr);
                if (rc) {
                        dt_write_unlock(env, o);
                        GOTO(out, rc);
                }

                LASSERT(lgi->lgi_attr.la_valid & LA_SIZE);
                lgi->lgi_off = max_t(__u64, lgi->lgi_attr.la_size,
                                     lgi->lgi_off);
        }

        lgi->lgi_buf.lb_len = reclen;
        lgi->lgi_buf.lb_buf = rec;
        rc = dt_record_write(env, o, &lgi->lgi_buf, &lgi->lgi_off, th);

        dt_write_unlock(env, o);
        if (rc < 0)
                GOTO(out, rc);

        up_write(&loghandle->lgh_last_sem);

        CDEBUG(D_HA, "added record "DFID".%u, %u off%llu\n",
               PFID(lu_object_fid(&o->do_lu)), index, rec->lrh_len,
               lgi->lgi_off);
        if (reccookie != NULL) {
                reccookie->lgc_lgl = loghandle->lgh_id;
                reccookie->lgc_index = index;
                if ((rec->lrh_type == MDS_UNLINK_REC) ||
                    (rec->lrh_type == MDS_SETATTR64_REC))
                        reccookie->lgc_subsys = LLOG_MDS_OST_ORIG_CTXT;
                else if (rec->lrh_type == OST_SZ_REC)
                        reccookie->lgc_subsys = LLOG_SIZE_ORIG_CTXT;
                else
                        reccookie->lgc_subsys = -1;
                rc = 1;
        }
        RETURN(rc);
out:
        /* cleanup llog for error case */
        mutex_lock(&loghandle->lgh_hdr_mutex);
        clear_bit_le(index, LLOG_HDR_BITMAP(llh));
        llh->llh_count--;
        mutex_unlock(&loghandle->lgh_hdr_mutex);

        /* restore llog last_idx */
        if (dt_object_remote(o)) {
                loghandle->lgh_last_idx = orig_last_idx;
        } else if (--loghandle->lgh_last_idx == 0 &&
            (llh->llh_flags & LLOG_F_IS_CAT) && llh->llh_cat_idx != 0) {
                /* catalog had just wrap-around case */
                loghandle->lgh_last_idx = LLOG_HDR_BITMAP_SIZE(llh) - 1;
        }

        LLOG_HDR_TAIL(llh)->lrt_index = loghandle->lgh_last_idx;
        up_write(&loghandle->lgh_last_sem);

        RETURN(rc);
}

/**
 * We can skip reading at least as many log blocks as the number of
 * minimum sized log records we are skipping.  If it turns out
 * that we are not far enough along the log (because the
 * actual records are larger than minimum size) we just skip
 * some more records.
 *
 * Note: in llog_process_thread, it will use bitmap offset as
 * the index to locate the record, which also includs some pad
 * records, whose record size is very small, and it also does not
 * consider pad record when recording minimum record size (otherwise
 * min_record size might be too small), so in some rare cases,
 * it might skip too much record for @goal, see llog_osd_next_block().
 *
 * When force_mini_rec is true, it means we have to use LLOG_MIN_REC_SIZE
 * as the min record size to skip over, usually because in the previous
 * try, it skip too much record, see loog_osd_next(prev)_block().
 */
static inline void llog_skip_over(struct llog_handle *lgh, __u64 *off,
                                  int curr, int goal, __u32 chunk_size,
                                  bool force_mini_rec)
{
        struct llog_log_hdr *llh = lgh->lgh_hdr;

        /* Goal should not bigger than the record count */
        if (goal > lgh->lgh_last_idx)
                goal = lgh->lgh_last_idx;

        if (goal > curr) {
                if (llh->llh_flags & LLOG_F_IS_FIXSIZE) {
                        *off = chunk_size + (goal - 1) * llh->llh_size;
                } else {
                        __u64 min_rec_size = LLOG_MIN_REC_SIZE;

                        if (llh->llh_size > 0 && !force_mini_rec)
                                min_rec_size = llh->llh_size;

                        *off = *off + (goal - curr - 1) * min_rec_size;
                }
        }
        /* always align with lower chunk boundary*/
        *off &= ~(chunk_size - 1);
}

/**
 * Remove optional fields that the client doesn't expect.
 * This is typically in order to ensure compatibility with older clients.
 * It is assumed that since we exclusively remove fields, the block will be
 * big enough to handle the remapped records. It is also assumed that records
 * of a block have the same format (i.e.: the same features enabled).
 *
 * \param[in,out]    hdr           Header of the block of records to remap.
 * \param[in,out]    last_hdr      Last header, don't read past this point.
 * \param[in]        flags         Flags describing the fields to keep.
 * \param[in]        extra_flags   Flags describing the extra fields to keep.
 */
static void changelog_block_trim_ext(struct llog_rec_hdr *hdr,
                                     struct llog_rec_hdr *last_hdr,
                                     struct llog_handle *loghandle)
{
        enum changelog_rec_flags flags = CLF_SUPPORTED;
        enum changelog_rec_extra_flags extra_flags = CLFE_SUPPORTED;

        if (!(loghandle->lgh_hdr->llh_flags & LLOG_F_EXT_X_XATTR))
                extra_flags &= ~CLFE_XATTR;
        if (!(loghandle->lgh_hdr->llh_flags & LLOG_F_EXT_X_OMODE))
                extra_flags &= ~CLFE_OPEN;
        if (!(loghandle->lgh_hdr->llh_flags & LLOG_F_EXT_X_NID))
                extra_flags &= ~CLFE_NID;
        if (!(loghandle->lgh_hdr->llh_flags & LLOG_F_EXT_X_UIDGID))
                extra_flags &= ~CLFE_UIDGID;
        if (!(loghandle->lgh_hdr->llh_flags & LLOG_F_EXT_EXTRA_FLAGS))
                flags &= ~CLF_EXTRA_FLAGS;
        if (!(loghandle->lgh_hdr->llh_flags & LLOG_F_EXT_JOBID))
                flags &= ~CLF_JOBID;

        if (flags == CLF_SUPPORTED && extra_flags == CLFE_SUPPORTED)
                return;

        if (hdr->lrh_type != CHANGELOG_REC)
                return;

        do {
                struct changelog_rec *rec = (struct changelog_rec *)(hdr + 1);
                enum changelog_rec_extra_flags xflag = CLFE_INVALID;

                if (flags & CLF_EXTRA_FLAGS &&
                    rec->cr_flags & CLF_EXTRA_FLAGS) {
                        xflag = changelog_rec_extra_flags(rec)->cr_extra_flags &
                                extra_flags;
                }

                if (unlikely(hdr->lrh_len == 0)) {
                        /* It is corruption case, we cannot know the next rec,
                         * jump to the last one directly to avoid dead loop. */
                        LCONSOLE(D_WARNING, "Hit invalid llog record: "
                                 "idx %u, type %u, id %u\n",
                                 hdr->lrh_index, hdr->lrh_type, hdr->lrh_id);
                        hdr = llog_rec_hdr_next(last_hdr);
                        if (unlikely(hdr == last_hdr))
                                LCONSOLE(D_WARNING, "The last record crashed: "
                                         "idx %u, type %u, id %u\n",
                                         hdr->lrh_index, hdr->lrh_type,
                                         hdr->lrh_id);
                        break;
                }

                changelog_remap_rec(rec, rec->cr_flags & flags, xflag);
                hdr = llog_rec_hdr_next(hdr);
                /* Yield CPU to avoid soft-lockup if there are too many records
                 * to be handled. */
                cond_resched();
        } while ((char *)hdr <= (char *)last_hdr);
}

/**
 * Implementation of the llog_operations::lop_next_block
 *
 * This function finds the the next llog block to return which contains
 * record with required index. It is main part of llog processing.
 *
 * \param[in]     env           execution environment
 * \param[in]     loghandle     llog handle of the current llog
 * \param[in,out] cur_idx       index preceeding cur_offset
 * \param[in]     next_idx      target index to find
 * \param[in,out] cur_offset    furtherst point read in the file
 * \param[in]     buf           pointer to data buffer to fill
 * \param[in]     len           required len to read, it is
 *                              usually llog chunk_size.
 *
 * \retval                      0 on successful buffer read
 * \retval                      negative value on error
 */
static int llog_osd_next_block(const struct lu_env *env,
                               struct llog_handle *loghandle, int *cur_idx,
                               int next_idx, __u64 *cur_offset, void *buf,
                               int len)
{
        struct llog_thread_info *lgi = llog_info(env);
        struct dt_object        *o;
        struct dt_device        *dt;
        int                      rc;
        __u32                   chunk_size;
        int last_idx = *cur_idx;
        __u64 last_offset = *cur_offset;
        bool force_mini_rec = false;

        ENTRY;

        LASSERT(env);
        LASSERT(lgi);

        chunk_size = loghandle->lgh_hdr->llh_hdr.lrh_len;
        if (len == 0 || len & (chunk_size - 1))
                RETURN(-EINVAL);

        LASSERT(loghandle);
        LASSERT(loghandle->lgh_ctxt);

        if (OBD_FAIL_PRECHECK(OBD_FAIL_MDS_CHANGELOG_DEL) &&
            cfs_fail_val == ((unsigned long)loghandle & 0xFFFFFFFF)) {
                OBD_RACE(OBD_FAIL_MDS_CHANGELOG_DEL);
                msleep(MSEC_PER_SEC >> 2);
        }

        o = loghandle->lgh_obj;
        LASSERT(o);
        dt_read_lock(env, o, 0);
        if (!llog_osd_exist(loghandle))
                GOTO(out, rc = -ESTALE); //object was destroyed

        dt = lu2dt_dev(o->do_lu.lo_dev);
        LASSERT(dt);

        rc = dt_attr_get(env, o, &lgi->lgi_attr);
        if (rc)
                GOTO(out, rc);

        CDEBUG(D_OTHER,
               "looking for log index %u (cur idx %u off %llu), size %llu\n",
               next_idx, *cur_idx,
               *cur_offset, lgi->lgi_attr.la_size);

        while (*cur_offset < lgi->lgi_attr.la_size) {
                struct llog_rec_hdr     *rec, *last_rec;
                struct llog_rec_tail    *tail;

                llog_skip_over(loghandle, cur_offset, *cur_idx,
                               next_idx, chunk_size, force_mini_rec);

                /* read up to next llog chunk_size block */
                lgi->lgi_buf.lb_len = chunk_size -
                                      (*cur_offset & (chunk_size - 1));
                lgi->lgi_buf.lb_buf = buf;

                rc = dt_read(env, o, &lgi->lgi_buf, cur_offset);
                if (rc < 0) {
                        if (rc == -EBADR && !force_mini_rec)
                                goto retry;

                        CERROR("%s: can't read llog block from log "DFID
                               " offset %llu: rc = %d\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               PFID(lu_object_fid(&o->do_lu)), *cur_offset,
                               rc);
                        GOTO(out, rc);
                }

                if (rc < len) {
                        /* signal the end of the valid buffer to
                         * llog_process */
                        memset(buf + rc, 0, len - rc);
                }

                if (rc == 0) { /* end of file, nothing to do */
                        if (!force_mini_rec)
                                goto retry;
                        GOTO(out, rc);
                }

                if (rc < sizeof(*tail)) {
                        if (!force_mini_rec)
                                goto retry;

                        CERROR("%s: invalid llog block at log id "DFID":%x "
                               "offset %llu\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               PFID(&loghandle->lgh_id.lgl_oi.oi_fid),
                               loghandle->lgh_id.lgl_ogen, *cur_offset);
                        GOTO(out, rc = -EINVAL);
                }

                rec = buf;
                if (LLOG_REC_HDR_NEEDS_SWABBING(rec))
                        lustre_swab_llog_rec(rec);
                tail = (struct llog_rec_tail *)((char *)buf + rc -
                                                sizeof(struct llog_rec_tail));

                if (llog_verify_record(loghandle, rec)) {
                        /*
                         * the block seems corrupted. make a pad record so the
                         * caller can skip the block and try with the next one
                         */
                        rec->lrh_len = rc;
                        rec->lrh_index = next_idx;
                        rec->lrh_type = LLOG_PAD_MAGIC;

                        tail = rec_tail(rec);
                        tail->lrt_len = rc;
                        tail->lrt_index = next_idx;

                        GOTO(out, rc = 0);
                }

                /* get the last record in block */
                last_rec = (struct llog_rec_hdr *)((char *)buf + rc -
                                                   tail->lrt_len);

                if (LLOG_REC_HDR_NEEDS_SWABBING(last_rec))
                        lustre_swab_llog_rec(last_rec);

                if (last_rec->lrh_index != tail->lrt_index) {
                        CERROR("%s: invalid llog tail at log id "DFID":%x offset %llu last_rec idx %u tail idx %u lrt len %u read_size %d\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               PFID(&loghandle->lgh_id.lgl_oi.oi_fid),
                               loghandle->lgh_id.lgl_ogen, *cur_offset,
                               last_rec->lrh_index, tail->lrt_index,
                               tail->lrt_len, rc);
                        GOTO(out, rc = -EINVAL);
                }

                *cur_idx = tail->lrt_index;

                /* this shouldn't happen */
                if (tail->lrt_index == 0) {
                        CERROR("%s: invalid llog tail at log id "DFID":%x "
                               "offset %llu bytes %d\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               PFID(&loghandle->lgh_id.lgl_oi.oi_fid),
                               loghandle->lgh_id.lgl_ogen, *cur_offset, rc);
                        GOTO(out, rc = -EINVAL);
                }
                if (tail->lrt_index < next_idx) {
                        last_idx = *cur_idx;
                        last_offset = *cur_offset;
                        continue;
                }

                /* sanity check that the start of the new buffer is no farther
                 * than the record that we wanted.  This shouldn't happen. */
                if (next_idx && rec->lrh_index > next_idx) {
                        if (!force_mini_rec && next_idx > last_idx)
                                goto retry;

                        CERROR("%s: missed desired record? %u > %u\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               rec->lrh_index, next_idx);
                        GOTO(out, rc = -ENOENT);
                }

                /* Trim unsupported extensions for compat w/ older clients */
                changelog_block_trim_ext(rec, last_rec, loghandle);

                GOTO(out, rc = 0);

retry:
                /* Note: because there are some pad records in the
                 * llog, so llog_skip_over() might skip too much
                 * records, let's try skip again with minimum record */
                force_mini_rec = true;
                *cur_offset = last_offset;
                *cur_idx = last_idx;
        }
        GOTO(out, rc = -EIO);
out:
        dt_read_unlock(env, o);
        return rc;
}

/**
 * Implementation of the llog_operations::lop_prev_block
 *
 * This function finds the llog block to return which contains
 * record with required index but in reverse order - from end of llog
 * to the beginning.
 * It is main part of reverse llog processing.
 *
 * \param[in] env       execution environment
 * \param[in] loghandle llog handle of the current llog
 * \param[in] prev_idx  target index to find
 * \param[in] buf       pointer to data buffer to fill
 * \param[in] len       required len to read, it is llog_chunk_size usually.
 *
 * \retval              0 on successful buffer read
 * \retval              negative value on error
 */
static int llog_osd_prev_block(const struct lu_env *env,
                               struct llog_handle *loghandle,
                               int prev_idx, void *buf, int len)
{
        struct llog_thread_info *lgi = llog_info(env);
        struct dt_object        *o;
        struct dt_device        *dt;
        loff_t                   cur_offset;
        __u32                   chunk_size;
        int                      rc;

        ENTRY;

        chunk_size = loghandle->lgh_hdr->llh_hdr.lrh_len;
        if (len == 0 || len & (chunk_size - 1))
                RETURN(-EINVAL);

        CDEBUG(D_OTHER, "looking for log index %u\n", prev_idx);

        LASSERT(loghandle);
        LASSERT(loghandle->lgh_ctxt);

        o = loghandle->lgh_obj;
        LASSERT(o);
        dt_read_lock(env, o, 0);
        if (!llog_osd_exist(loghandle))
                GOTO(out, rc = -ESTALE);

        dt = lu2dt_dev(o->do_lu.lo_dev);
        LASSERT(dt);

        /* Let's only use mini record size for previous block read
         * for now XXX */
        cur_offset = chunk_size;
        llog_skip_over(loghandle, &cur_offset, 0, prev_idx,
                       chunk_size, true);

        rc = dt_attr_get(env, o, &lgi->lgi_attr);
        if (rc)
                GOTO(out, rc);

        while (cur_offset < lgi->lgi_attr.la_size) {
                struct llog_rec_hdr     *rec, *last_rec;
                struct llog_rec_tail    *tail;

                lgi->lgi_buf.lb_len = len;
                lgi->lgi_buf.lb_buf = buf;
                rc = dt_read(env, o, &lgi->lgi_buf, &cur_offset);
                if (rc < 0) {
                        CERROR("%s: can't read llog block from log "DFID
                               " offset %llu: rc = %d\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               PFID(lu_object_fid(&o->do_lu)), cur_offset, rc);
                        GOTO(out, rc);
                }

                if (rc == 0) /* end of file, nothing to do */
                        GOTO(out, rc);

                if (rc < sizeof(*tail)) {
                        CERROR("%s: invalid llog block at log id "DFID":%x "
                               "offset %llu\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               PFID(&loghandle->lgh_id.lgl_oi.oi_fid),
                               loghandle->lgh_id.lgl_ogen, cur_offset);
                        GOTO(out, rc = -EINVAL);
                }

                rec = buf;
                if (LLOG_REC_HDR_NEEDS_SWABBING(rec))
                        lustre_swab_llog_rec(rec);

                tail = (struct llog_rec_tail *)((char *)buf + rc -
                                                sizeof(struct llog_rec_tail));
                /* get the last record in block */
                last_rec = (struct llog_rec_hdr *)((char *)buf + rc -
                                                   le32_to_cpu(tail->lrt_len));

                if (LLOG_REC_HDR_NEEDS_SWABBING(last_rec))
                        lustre_swab_llog_rec(last_rec);
                LASSERT(last_rec->lrh_index == tail->lrt_index);

                /* this shouldn't happen */
                if (tail->lrt_index == 0) {
                        CERROR("%s: invalid llog tail at log id "DFID":%x "
                               "offset %llu\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               PFID(&loghandle->lgh_id.lgl_oi.oi_fid),
                               loghandle->lgh_id.lgl_ogen, cur_offset);
                        GOTO(out, rc = -EINVAL);
                }
                if (tail->lrt_index < prev_idx)
                        continue;

                /* sanity check that the start of the new buffer is no farther
                 * than the record that we wanted.  This shouldn't happen. */
                if (rec->lrh_index > prev_idx) {
                        CERROR("%s: missed desired record? %u > %u\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               rec->lrh_index, prev_idx);
                        GOTO(out, rc = -ENOENT);
                }

                /* Trim unsupported extensions for compat w/ older clients */
                changelog_block_trim_ext(rec, last_rec, loghandle);

                GOTO(out, rc = 0);
        }
        GOTO(out, rc = -EIO);
out:
        dt_read_unlock(env, o);
        return rc;
}

/**
 * This is helper function to get llog directory object. It is used by named
 * llog operations to find/insert/delete llog entry from llog directory.
 *
 * \param[in] env       execution environment
 * \param[in] ctxt      llog context
 *
 * \retval              dt_object of llog directory
 * \retval              ERR_PTR of negative value on error
 */
static struct dt_object *llog_osd_dir_get(const struct lu_env *env,
                                          struct llog_ctxt *ctxt)
{
        struct dt_device        *dt;
        struct dt_thread_info   *dti = dt_info(env);
        struct dt_object        *dir;
        int                      rc;

        dt = ctxt->loc_exp->exp_obd->obd_lvfs_ctxt.dt;
        if (ctxt->loc_dir == NULL) {
                rc = dt_root_get(env, dt, &dti->dti_fid);
                if (rc)
                        return ERR_PTR(rc);
                dir = dt_locate(env, dt, &dti->dti_fid);

                if (!IS_ERR(dir) && !dt_try_as_dir(env, dir)) {
                        dt_object_put(env, dir);
                        return ERR_PTR(-ENOTDIR);
                }
        } else {
                lu_object_get(&ctxt->loc_dir->do_lu);
                dir = ctxt->loc_dir;
        }

        return dir;
}

/**
 * Implementation of the llog_operations::lop_open
 *
 * This function opens the llog by its logid or by name, it may open also
 * non existent llog and assing then new id to it.
 * The llog_open/llog_close pair works similar to lu_object_find/put,
 * the object may not exist prior open. The result of open is just dt_object
 * in the llog header.
 *
 * \param[in] env               execution environment
 * \param[in] handle            llog handle of the current llog
 * \param[in] logid             logid of llog to open (nameless llog)
 * \param[in] name              name of llog to open (named llog)
 * \param[in] open_param
 *                              LLOG_OPEN_NEW - new llog, may not exist
 *                              LLOG_OPEN_EXIST - old llog, must exist
 *
 * \retval                      0 on successful open, llog_handle::lgh_obj
 *                              contains the dt_object of the llog.
 * \retval                      negative value on error
 */
static int llog_osd_open(const struct lu_env *env, struct llog_handle *handle,
                         struct llog_logid *logid, char *name,
                         enum llog_open_param open_param)
{
        struct llog_thread_info         *lgi = llog_info(env);
        struct llog_ctxt                *ctxt = handle->lgh_ctxt;
        struct dt_object                *o;
        struct dt_device                *dt;
        struct ls_device                *ls;
        struct local_oid_storage        *los = NULL;
        int                              rc = 0;
        bool new_id = false;

        ENTRY;

        LASSERT(env);
        LASSERT(ctxt);
        LASSERT(ctxt->loc_exp);
        LASSERT(ctxt->loc_exp->exp_obd);
        dt = ctxt->loc_exp->exp_obd->obd_lvfs_ctxt.dt;
        LASSERT(dt);
        if (ctxt->loc_flags & LLOG_CTXT_FLAG_NORMAL_FID) {
                struct lu_object_conf conf = { 0 };
                if (logid != NULL) {
                        logid_to_fid(logid, &lgi->lgi_fid);
                } else {
                        /* If logid == NULL, then it means the caller needs
                         * to allocate new FID (llog_cat_declare_add_rec()). */
                        rc = dt_fid_alloc(env, dt, &lgi->lgi_fid, NULL, NULL);
                        if (rc < 0)
                                RETURN(rc);
                        rc = 0;
                        conf.loc_flags = LOC_F_NEW;
                }

                o = dt_locate_at(env, dt, &lgi->lgi_fid,
                                 dt->dd_lu_dev.ld_site->ls_top_dev, &conf);
                if (IS_ERR(o))
                        RETURN(PTR_ERR(o));

                goto after_open;
        }

        ls = ls_device_get(dt);
        if (IS_ERR(ls))
                RETURN(PTR_ERR(ls));

        mutex_lock(&ls->ls_los_mutex);
        los = dt_los_find(ls, name != NULL ? FID_SEQ_LLOG_NAME : FID_SEQ_LLOG);
        mutex_unlock(&ls->ls_los_mutex);
        LASSERT(los);
        ls_device_put(env, ls);

        LASSERT(handle);

        if (logid != NULL) {
                logid_to_fid(logid, &lgi->lgi_fid);
        } else if (name) {
                struct dt_object *llog_dir;

                llog_dir = llog_osd_dir_get(env, ctxt);
                if (IS_ERR(llog_dir))
                        GOTO(out, rc = PTR_ERR(llog_dir));
                dt_read_lock(env, llog_dir, 0);
                rc = dt_lookup_dir(env, llog_dir, name, &lgi->lgi_fid);
                dt_read_unlock(env, llog_dir);
                dt_object_put(env, llog_dir);
                if (rc == -ENOENT && open_param == LLOG_OPEN_NEW) {
                        /* generate fid for new llog */
                        rc = local_object_fid_generate(env, los,
                                                       &lgi->lgi_fid);
                        new_id = true;
                }
                if (rc < 0)
                        GOTO(out, rc);
                OBD_ALLOC(handle->lgh_name, strlen(name) + 1);
                if (handle->lgh_name)
                        strcpy(handle->lgh_name, name);
                else
                        GOTO(out, rc = -ENOMEM);
        } else {
                LASSERTF(open_param & LLOG_OPEN_NEW, "%#x\n", open_param);
                /* generate fid for new llog */
generate:
                rc = local_object_fid_generate(env, los, &lgi->lgi_fid);
                if (rc < 0)
                        GOTO(out, rc);
                new_id = true;
        }
        if (OBD_FAIL_PRECHECK(OBD_FAIL_MDS_LLOG_UMOUNT_RACE) &&
            cfs_fail_val == 1) {
                cfs_fail_val = 2;
                OBD_RACE(OBD_FAIL_MDS_LLOG_UMOUNT_RACE);
                msleep(MSEC_PER_SEC);
        }
        o = ls_locate(env, ls, &lgi->lgi_fid, NULL);
        if (IS_ERR(o))
                GOTO(out_name, rc = PTR_ERR(o));

        if (dt_object_exists(o) && new_id) {
                /* llog exists with just generated ID, e.g. some old llog file
                 * still is in use or is orphan, drop a warn and skip it. */
                CDEBUG(D_INFO, "%s: llog exists with the same FID: "DFID
                       ", skipping\n",
                       o->do_lu.lo_dev->ld_obd->obd_name,
                       PFID(lu_object_fid(&o->do_lu)));
                dt_object_put(env, o);
                /* just skip this llog ID, we shouldn't delete it because we
                 * don't know exactly what is its purpose and state. */
                goto generate;
        }

after_open:
        /* No new llog is expected but doesn't exist */
        if (open_param != LLOG_OPEN_NEW && !dt_object_exists(o)) {
                CDEBUG(D_INFO, "%s: llog FID: "DFID" obj %p doesn`t exist\n",
                       o->do_lu.lo_dev->ld_obd->obd_name,
                       PFID(lu_object_fid(&o->do_lu)), o);
                GOTO(out_put, rc = -ENOENT);
        }
        fid_to_logid(&lgi->lgi_fid, &handle->lgh_id);
        handle->lgh_obj = o;
        handle->private_data = los;
        LASSERT(handle->lgh_ctxt);

        RETURN(rc);

out_put:
        dt_object_put(env, o);
out_name:
        if (handle->lgh_name != NULL)
                OBD_FREE(handle->lgh_name, strlen(name) + 1);
out:
        if (los != NULL)
                dt_los_put(los);
        RETURN(rc);
}

/**
 * Get dir for regular fid log object
 *
 * Get directory for regular fid log object, and these regular fid log
 * object will be inserted under this directory, to satisfy the FS
 * consistency check, e2fsck etc.
 *
 * \param [in] env      execution environment
 * \param [in] dto      llog object
 *
 * \retval              pointer to the directory if it is found.
 * \retval              ERR_PTR(negative errno) if it fails.
 */
struct dt_object *llog_osd_get_regular_fid_dir(const struct lu_env *env,
                                               struct dt_object *dto)
{
        struct llog_thread_info *lgi = llog_info(env);
        struct seq_server_site *ss = dto->do_lu.lo_dev->ld_site->ld_seq_site;
        struct lu_seq_range     *range = &lgi->lgi_range;
        struct lu_fid           *dir_fid = &lgi->lgi_fid;
        struct dt_object        *dir;
        int                     rc;
        ENTRY;

        fld_range_set_any(range);
        LASSERT(ss != NULL);
        rc = ss->ss_server_fld->lsf_seq_lookup(env, ss->ss_server_fld,
                                   fid_seq(lu_object_fid(&dto->do_lu)), range);
        if (rc < 0)
                RETURN(ERR_PTR(rc));

        lu_update_log_dir_fid(dir_fid, range->lsr_index);
        dir = dt_locate(env, lu2dt_dev(dto->do_lu.lo_dev), dir_fid);
        if (IS_ERR(dir))
                RETURN(dir);

        if (!dt_try_as_dir(env, dir)) {
                dt_object_put(env, dir);
                RETURN(ERR_PTR(-ENOTDIR));
        }

        RETURN(dir);
}

/**
 * Add llog object with regular FID to name entry
 *
 * Add llog object with regular FID to name space, and each llog
 * object on each MDT will be /update_log_dir/[seq:oid:ver],
 * so to satisfy the namespace consistency check, e2fsck etc.
 *
 * \param [in] env      execution environment
 * \param [in] dto      llog object
 * \param [in] th       thandle
 * \param [in] declare  if it is declare or execution
 *
 * \retval              0 if insertion succeeds.
 * \retval              negative errno if insertion fails.
 */
static int
llog_osd_regular_fid_add_name_entry(const struct lu_env *env,
                                    struct dt_object *dto,
                                    struct thandle *th, bool declare)
{
        struct llog_thread_info *lgi = llog_info(env);
        const struct lu_fid     *fid = lu_object_fid(&dto->do_lu);
        struct dt_insert_rec    *rec = &lgi->lgi_dt_rec;
        struct dt_object        *dir;
        char                    *name = lgi->lgi_name;
        int                     rc;
        ENTRY;

        if (!fid_is_norm(fid))
                RETURN(0);

        dir = llog_osd_get_regular_fid_dir(env, dto);
        if (IS_ERR(dir))
                RETURN(PTR_ERR(dir));

        rec->rec_fid = fid;
        rec->rec_type = S_IFREG;
        snprintf(name, sizeof(lgi->lgi_name), DFID, PFID(fid));
        dt_write_lock(env, dir, 0);
        if (declare) {
                rc = dt_declare_insert(env, dir, (struct dt_rec *)rec,
                               (struct dt_key *)name, th);
        } else {
                rc = dt_insert(env, dir, (struct dt_rec *)rec,
                               (struct dt_key *)name, th);
        }
        dt_write_unlock(env, dir);

        dt_object_put(env, dir);
        RETURN(rc);
}


/**
 * Implementation of the llog_operations::lop_declare_create
 *
 * This function declares the llog create. It declares also name insert
 * into llog directory in case of named llog.
 *
 * \param[in] env       execution environment
 * \param[in] res       llog handle of the current llog
 * \param[in] th        current transaction handle
 *
 * \retval              0 on successful create declaration
 * \retval              negative value on error
 */
static int llog_osd_declare_create(const struct lu_env *env,
                                   struct llog_handle *res, struct thandle *th)
{
        struct llog_thread_info         *lgi = llog_info(env);
        struct dt_insert_rec            *rec = &lgi->lgi_dt_rec;
        struct local_oid_storage        *los;
        struct dt_object                *o;
        int                              rc;

        ENTRY;

        LASSERT(res->lgh_obj);
        LASSERT(th);

        /* object can be created by another thread */
        o = res->lgh_obj;
        if (dt_object_exists(o))
                RETURN(0);

        if (res->lgh_ctxt->loc_flags & LLOG_CTXT_FLAG_NORMAL_FID) {
                struct llog_thread_info *lgi = llog_info(env);

                lgi->lgi_attr.la_valid = LA_MODE | LA_SIZE;
                lgi->lgi_attr.la_size = 0;
                lgi->lgi_attr.la_mode = S_IFREG | S_IRUGO | S_IWUSR;
                lgi->lgi_dof.dof_type = dt_mode_to_dft(S_IFREG);

                rc = dt_declare_create(env, o, &lgi->lgi_attr, NULL,
                                       &lgi->lgi_dof, th);
                if (rc < 0)
                        RETURN(rc);


                rc = llog_osd_regular_fid_add_name_entry(env, o, th, true);

                RETURN(rc);
        }
        los = res->private_data;
        LASSERT(los);

        rc = llog_osd_declare_new_object(env, los, o, th);
        if (rc)
                RETURN(rc);

        /* do not declare header initialization here as it's declared
         * in llog_osd_declare_write_rec() which is always called */

        if (res->lgh_name) {
                struct dt_object *llog_dir;

                llog_dir = llog_osd_dir_get(env, res->lgh_ctxt);
                if (IS_ERR(llog_dir))
                        RETURN(PTR_ERR(llog_dir));
                logid_to_fid(&res->lgh_id, &lgi->lgi_fid);
                rec->rec_fid = &lgi->lgi_fid;
                rec->rec_type = S_IFREG;
                rc = dt_declare_insert(env, llog_dir,
                                       (struct dt_rec *)rec,
                                       (struct dt_key *)res->lgh_name, th);
                dt_object_put(env, llog_dir);
                if (rc)
                        CERROR("%s: can't declare named llog %s: rc = %d\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               res->lgh_name, rc);
        }
        RETURN(rc);
}

/**
 * Implementation of the llog_operations::lop_create
 *
 * This function creates the llog according with llog_handle::lgh_obj
 * and llog_handle::lgh_name.
 *
 * \param[in] env       execution environment
 * \param[in] res       llog handle of the current llog
 * \param[in] th        current transaction handle
 *
 * \retval              0 on successful create
 * \retval              negative value on error
 */
static int llog_osd_create(const struct lu_env *env, struct llog_handle *res,
                           struct thandle *th)
{
        struct llog_thread_info *lgi = llog_info(env);
        struct dt_insert_rec    *rec = &lgi->lgi_dt_rec;
        struct local_oid_storage *los;
        struct dt_object        *o;
        int                      rc = 0;

        ENTRY;

        LASSERT(env);
        o = res->lgh_obj;
        LASSERT(o);

        /* llog can be already created */
        if (dt_object_exists(o))
                RETURN(-EEXIST);

        if (res->lgh_ctxt->loc_flags & LLOG_CTXT_FLAG_NORMAL_FID) {
                struct llog_thread_info *lgi = llog_info(env);

                lgi->lgi_attr.la_valid = LA_MODE | LA_SIZE | LA_TYPE;
                lgi->lgi_attr.la_size = 0;
                lgi->lgi_attr.la_mode = S_IFREG | S_IRUGO | S_IWUSR;
                lgi->lgi_dof.dof_type = dt_mode_to_dft(S_IFREG);

                dt_write_lock(env, o, 0);
                rc = dt_create(env, o, &lgi->lgi_attr, NULL,
                               &lgi->lgi_dof, th);
                dt_write_unlock(env, o);
                if (rc < 0)
                        RETURN(rc);

                rc = llog_osd_regular_fid_add_name_entry(env, o, th, false);

                RETURN(rc);
        }

        los = res->private_data;
        LASSERT(los);

        dt_write_lock(env, o, 0);
        if (!dt_object_exists(o))
                rc = llog_osd_create_new_object(env, los, o, th);
        else
                rc = -EEXIST;

        dt_write_unlock(env, o);
        if (rc)
                RETURN(rc);

        if (res->lgh_name) {
                struct dt_object *llog_dir;

                llog_dir = llog_osd_dir_get(env, res->lgh_ctxt);
                if (IS_ERR(llog_dir))
                        RETURN(PTR_ERR(llog_dir));

                logid_to_fid(&res->lgh_id, &lgi->lgi_fid);
                rec->rec_fid = &lgi->lgi_fid;
                rec->rec_type = S_IFREG;
                dt_read_lock(env, llog_dir, 0);
                rc = dt_insert(env, llog_dir, (struct dt_rec *)rec,
                               (struct dt_key *)res->lgh_name, th);
                dt_read_unlock(env, llog_dir);
                dt_object_put(env, llog_dir);
                if (rc)
                        CERROR("%s: can't create named llog %s: rc = %d\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               res->lgh_name, rc);
        }
        RETURN(rc);
}

/**
 * Implementation of the llog_operations::lop_close
 *
 * This function closes the llog. It just put llog object and referenced
 * local storage.
 *
 * \param[in] env       execution environment
 * \param[in] handle    llog handle of the current llog
 *
 * \retval              0 on successful llog close
 * \retval              negative value on error
 */
static int llog_osd_close(const struct lu_env *env, struct llog_handle *handle)
{
        struct local_oid_storage        *los;
        int                              rc = 0;

        ENTRY;

        LASSERT(handle->lgh_obj);

        if (handle->lgh_ctxt->loc_flags & LLOG_CTXT_FLAG_NORMAL_FID) {
                /* Remove the object from the cache, otherwise it may
                 * hold LOD being released during cleanup process */
                dt_object_put_nocache(env, handle->lgh_obj);
                LASSERT(handle->private_data == NULL);
                RETURN(rc);
        } else {
                dt_object_put(env, handle->lgh_obj);
        }
        los = handle->private_data;
        LASSERT(los);
        dt_los_put(los);

        if (handle->lgh_name)
                OBD_FREE(handle->lgh_name, strlen(handle->lgh_name) + 1);

        RETURN(rc);
}

/**
 * delete llog object name entry
 *
 * Delete llog object (with regular FID) from name space (under
 * update_log_dir).
 *
 * \param [in] env      execution environment
 * \param [in] dto      llog object
 * \param [in] th       thandle
 * \param [in] declare  if it is declare or execution
 *
 * \retval              0 if deletion succeeds.
 * \retval              negative errno if deletion fails.
 */
static int
llog_osd_regular_fid_del_name_entry(const struct lu_env *env,
                                    struct dt_object *dto,
                                    struct thandle *th, bool declare)
{
        struct llog_thread_info *lgi = llog_info(env);
        const struct lu_fid     *fid = lu_object_fid(&dto->do_lu);
        struct dt_object        *dir;
        char                    *name = lgi->lgi_name;
        int                     rc;
        ENTRY;

        if (!fid_is_norm(fid))
                RETURN(0);

        dir = llog_osd_get_regular_fid_dir(env, dto);
        if (IS_ERR(dir))
                RETURN(PTR_ERR(dir));

        snprintf(name, sizeof(lgi->lgi_name), DFID, PFID(fid));
        dt_write_lock(env, dir, 0);
        if (declare) {
                rc = dt_declare_delete(env, dir, (struct dt_key *)name,
                                       th);
        } else {
                rc = dt_delete(env, dir, (struct dt_key *)name, th);
        }
        dt_write_unlock(env, dir);

        dt_object_put(env, dir);
        RETURN(rc);
}

/**
 * Implementation of the llog_operations::lop_declare_destroy
 *
 * This function declare destroys the llog and deletes also entry in the
 * llog directory in case of named llog. Llog should be opened prior that.
 *
 * \param[in] env               execution environment
 * \param[in] loghandle llog handle of the current llog
 *
 * \retval              0 on successful destroy
 * \retval              negative value on error
 */
static int llog_osd_declare_destroy(const struct lu_env *env,
                                    struct llog_handle *loghandle,
                                    struct thandle *th)
{
        struct llog_ctxt        *ctxt;
        struct dt_object        *o, *llog_dir = NULL;
        int                      rc;

        ENTRY;

        ctxt = loghandle->lgh_ctxt;
        LASSERT(ctxt);

        o = loghandle->lgh_obj;
        LASSERT(o);

        if (loghandle->lgh_name) {
                llog_dir = llog_osd_dir_get(env, ctxt);
                if (IS_ERR(llog_dir))
                        RETURN(PTR_ERR(llog_dir));

                rc = dt_declare_delete(env, llog_dir,
                                       (struct dt_key *)loghandle->lgh_name,
                                       th);
                if (rc < 0)
                        GOTO(out_put, rc);
        }

        rc = dt_declare_ref_del(env, o, th);
        if (rc < 0)
                GOTO(out_put, rc);

        rc = dt_declare_destroy(env, o, th);
        if (rc < 0)
                GOTO(out_put, rc);

        if (loghandle->lgh_ctxt->loc_flags & LLOG_CTXT_FLAG_NORMAL_FID) {
                rc = llog_osd_regular_fid_del_name_entry(env, o, th, true);
                if (rc < 0)
                        GOTO(out_put, rc);
        }

out_put:
        if (!(IS_ERR_OR_NULL(llog_dir)))
                dt_object_put(env, llog_dir);

        RETURN(rc);
}


/**
 * Implementation of the llog_operations::lop_destroy
 *
 * This function destroys the llog and deletes also entry in the
 * llog directory in case of named llog. Llog should be opened prior that.
 * Destroy method is not part of external transaction and does everything
 * inside.
 *
 * \param[in] env               execution environment
 * \param[in] loghandle llog handle of the current llog
 *
 * \retval              0 on successful destroy
 * \retval              negative value on error
 */
static int llog_osd_destroy(const struct lu_env *env,
                            struct llog_handle *loghandle, struct thandle *th)
{
        struct llog_ctxt        *ctxt;
        struct dt_object        *o, *llog_dir = NULL;
        int                      rc;

        ENTRY;

        ctxt = loghandle->lgh_ctxt;
        LASSERT(ctxt != NULL);

        o = loghandle->lgh_obj;
        LASSERT(o != NULL);

        dt_write_lock(env, o, 0);
        if (!llog_osd_exist(loghandle))
                GOTO(out_unlock, rc = 0);

        if (loghandle->lgh_name) {
                llog_dir = llog_osd_dir_get(env, ctxt);
                if (IS_ERR(llog_dir))
                        GOTO(out_unlock, rc = PTR_ERR(llog_dir));

                dt_read_lock(env, llog_dir, 0);
                rc = dt_delete(env, llog_dir,
                               (struct dt_key *)loghandle->lgh_name,
                               th);
                dt_read_unlock(env, llog_dir);
                if (rc) {
                        CERROR("%s: can't remove llog %s: rc = %d\n",
                               o->do_lu.lo_dev->ld_obd->obd_name,
                               loghandle->lgh_name, rc);
                        GOTO(out_unlock, rc);
                }
        }

        dt_ref_del(env, o, th);
        rc = dt_destroy(env, o, th);
        if (rc < 0)
                GOTO(out_unlock, rc);

        loghandle->lgh_destroyed = true;
        if (loghandle->lgh_ctxt->loc_flags & LLOG_CTXT_FLAG_NORMAL_FID) {
                rc = llog_osd_regular_fid_del_name_entry(env, o, th, false);
                if (rc < 0)
                        GOTO(out_unlock, rc);
        }

out_unlock:
        dt_write_unlock(env, o);
        if (!(IS_ERR_OR_NULL(llog_dir)))
                dt_object_put(env, llog_dir);
        RETURN(rc);
}

/**
 * Implementation of the llog_operations::lop_setup
 *
 * This function setup the llog on local storage.
 *
 * \param[in] env       execution environment
 * \param[in] obd       obd device the llog belongs to
 * \param[in] olg       the llog group, it is always zero group now.
 * \param[in] ctxt_idx  the llog index, it defines the purpose of this llog.
 *                      Every new llog type have to use own index.
 * \param[in] disk_obd  the storage obd, where llog is stored.
 *
 * \retval              0 on successful llog setup
 * \retval              negative value on error
 */
static int llog_osd_setup(const struct lu_env *env, struct obd_device *obd,
                          struct obd_llog_group *olg, int ctxt_idx,
                          struct obd_device *disk_obd)
{
        struct llog_thread_info         *lgi = llog_info(env);
        struct llog_ctxt                *ctxt;
        int                              rc = 0;
        ENTRY;

        LASSERT(obd);
        LASSERT(olg->olg_ctxts[ctxt_idx]);

        ctxt = llog_ctxt_get(olg->olg_ctxts[ctxt_idx]);
        LASSERT(ctxt);

        if (disk_obd == NULL)
                GOTO(out, rc = 0);

        /* initialize data allowing to generate new fids,
         * literally we need a sequece */
        lgi->lgi_fid.f_seq = FID_SEQ_LLOG;
        lgi->lgi_fid.f_oid = 1;
        lgi->lgi_fid.f_ver = 0;
        rc = local_oid_storage_init(env, disk_obd->obd_lvfs_ctxt.dt,
                                    &lgi->lgi_fid,
                                    &ctxt->loc_los_nameless);
        if (rc != 0)
                GOTO(out, rc);

        lgi->lgi_fid.f_seq = FID_SEQ_LLOG_NAME;
        lgi->lgi_fid.f_oid = 1;
        lgi->lgi_fid.f_ver = 0;
        rc = local_oid_storage_init(env, disk_obd->obd_lvfs_ctxt.dt,
                                    &lgi->lgi_fid,
                                    &ctxt->loc_los_named);
        if (rc != 0) {
                local_oid_storage_fini(env, ctxt->loc_los_nameless);
                ctxt->loc_los_nameless = NULL;
        }

        GOTO(out, rc);

out:
        llog_ctxt_put(ctxt);
        return rc;
}

/**
 * Implementation of the llog_operations::lop_cleanup
 *
 * This function cleanups the llog on local storage.
 *
 * \param[in] env       execution environment
 * \param[in] ctxt      the llog context
 *
 * \retval              0
 */
static int llog_osd_cleanup(const struct lu_env *env, struct llog_ctxt *ctxt)
{
        if (ctxt->loc_los_nameless != NULL) {
                local_oid_storage_fini(env, ctxt->loc_los_nameless);
                ctxt->loc_los_nameless = NULL;
        }

        if (ctxt->loc_los_named != NULL) {
                local_oid_storage_fini(env, ctxt->loc_los_named);
                ctxt->loc_los_named = NULL;
        }

        return 0;
}

const struct llog_operations llog_osd_ops = {
        .lop_next_block         = llog_osd_next_block,
        .lop_prev_block         = llog_osd_prev_block,
        .lop_read_header        = llog_osd_read_header,
        .lop_declare_destroy    = llog_osd_declare_destroy,
        .lop_destroy            = llog_osd_destroy,
        .lop_setup              = llog_osd_setup,
        .lop_cleanup            = llog_osd_cleanup,
        .lop_open               = llog_osd_open,
        .lop_exist              = llog_osd_exist,
        .lop_declare_create     = llog_osd_declare_create,
        .lop_create             = llog_osd_create,
        .lop_declare_write_rec  = llog_osd_declare_write_rec,
        .lop_write_rec          = llog_osd_write_rec,
        .lop_close              = llog_osd_close,
};
EXPORT_SYMBOL(llog_osd_ops);

const struct llog_operations llog_common_cat_ops = {
        .lop_next_block         = llog_osd_next_block,
        .lop_prev_block         = llog_osd_prev_block,
        .lop_read_header        = llog_osd_read_header,
        .lop_declare_destroy    = llog_osd_declare_destroy,
        .lop_destroy            = llog_osd_destroy,
        .lop_setup              = llog_osd_setup,
        .lop_cleanup            = llog_osd_cleanup,
        .lop_open               = llog_osd_open,
        .lop_exist              = llog_osd_exist,
        .lop_declare_create     = llog_osd_declare_create,
        .lop_create             = llog_osd_create,
        .lop_declare_write_rec  = llog_osd_declare_write_rec,
        .lop_write_rec          = llog_osd_write_rec,
        .lop_close              = llog_osd_close,
        .lop_add                = llog_cat_add_rec,
        .lop_declare_add        = llog_cat_declare_add_rec,
};
EXPORT_SYMBOL(llog_common_cat_ops);

/**
 * Read the special file which contains the list of llog catalogs IDs
 *
 * This function reads the CATALOGS file which contains the array of llog
 * catalogs IDs. The main purpose of this file is to store OSP llogs indexed
 * by OST/MDT number.
 *
 * \param[in]  env              execution environment
 * \param[in]  d                corresponding storage device
 * \param[in]  idx              position to start from, usually OST/MDT index
 * \param[in]  count            how many catalog IDs to read
 * \param[out] idarray          the buffer for the data. If it is NULL then
 *                              function returns just number of catalog IDs
 *                              in the file.
 * \param[in]  fid              LLOG_CATALOGS_OID for CATALOG object
 *
 * \retval                      0 on successful read of catalog IDs
 * \retval                      negative value on error
 * \retval                      positive value which is number of records in
 *                              the file if \a idarray is NULL
 */
int llog_osd_get_cat_list(const struct lu_env *env, struct dt_device *d,
                          int idx, int count, struct llog_catid *idarray,
                          const struct lu_fid *fid)
{
        struct llog_thread_info *lgi = llog_info(env);
        struct dt_object        *o = NULL;
        struct thandle          *th;
        int                      rc, size;

        ENTRY;

        LASSERT(d);

        size = sizeof(*idarray) * count;
        lgi->lgi_off = idx *  sizeof(*idarray);

        lgi->lgi_fid = *fid;
        o = dt_locate(env, d, &lgi->lgi_fid);
        if (IS_ERR(o))
                RETURN(PTR_ERR(o));

        if (!dt_object_exists(o)) {
                th = dt_trans_create(env, d);
                if (IS_ERR(th))
                        GOTO(out, rc = PTR_ERR(th));

                lgi->lgi_attr.la_valid = LA_MODE | LA_TYPE;
                lgi->lgi_attr.la_mode = S_IFREG | S_IRUGO | S_IWUSR;
                lgi->lgi_dof.dof_type = dt_mode_to_dft(S_IFREG);

                th->th_wait_submit = 1;
                /* Make the llog object creation synchronization, so
                 * it will be reliable to the reference, especially
                 * for remote reference */
                th->th_sync = 1;

                rc = dt_declare_create(env, o, &lgi->lgi_attr, NULL,
                                       &lgi->lgi_dof, th);
                if (rc)
                        GOTO(out_trans, rc);

                rc = dt_trans_start_local(env, d, th);
                if (rc)
                        GOTO(out_trans, rc);

                dt_write_lock(env, o, 0);
                if (!dt_object_exists(o))
                        rc = dt_create(env, o, &lgi->lgi_attr, NULL,
                                       &lgi->lgi_dof, th);
                dt_write_unlock(env, o);
out_trans:
                dt_trans_stop(env, d, th);
                if (rc)
                        GOTO(out, rc);
        }

        rc = dt_attr_get(env, o, &lgi->lgi_attr);
        if (rc)
                GOTO(out, rc);

        if (!S_ISREG(lgi->lgi_attr.la_mode)) {
                CERROR("%s: CATALOGS is not a regular file!: mode = %o\n",
                       o->do_lu.lo_dev->ld_obd->obd_name,
                       lgi->lgi_attr.la_mode);
                GOTO(out, rc = -ENOENT);
        }

        CDEBUG(D_CONFIG, "cat list: disk size=%d, read=%d\n",
               (int)lgi->lgi_attr.la_size, size);

        /* return just number of llogs */
        if (idarray == NULL) {
                rc = lgi->lgi_attr.la_size / sizeof(*idarray);
                GOTO(out, rc);
        }

        /* read for new ost index or for empty file */
        memset(idarray, 0, size);
        if (lgi->lgi_attr.la_size <= lgi->lgi_off)
                GOTO(out, rc = 0);
        if (lgi->lgi_attr.la_size < lgi->lgi_off + size)
                size = lgi->lgi_attr.la_size - lgi->lgi_off;

        lgi->lgi_buf.lb_buf = idarray;
        lgi->lgi_buf.lb_len = size;
        rc = dt_record_read(env, o, &lgi->lgi_buf, &lgi->lgi_off);
        /* -EFAULT means the llog is a sparse file. This is not an error
         * after arbitrary OST index is supported. */
        if (rc < 0 && rc != -EFAULT) {
                CERROR("%s: error reading CATALOGS: rc = %d\n",
                       o->do_lu.lo_dev->ld_obd->obd_name,  rc);
                GOTO(out, rc);
        }

        EXIT;
out:
        dt_object_put(env, o);
        RETURN(rc);
}
EXPORT_SYMBOL(llog_osd_get_cat_list);

/**
 * Write the special file which contains the list of llog catalogs IDs
 *
 * This function writes the CATALOG file which contains the array of llog
 * catalogs IDs. It is used mostly to store OSP llogs indexed by OST/MDT
 * number.
 *
 * \param[in]  env      execution environment
 * \param[in]  d        corresponding storage device
 * \param[in]  idx      position to start from, usually OST/MDT index
 * \param[in]  count    how many catalog IDs to write
 * \param[out] idarray  the buffer with the data to write.
 * \param[in]  fid      LLOG_CATALOGS_OID for CATALOG object
 *
 * \retval              0 on successful write of catalog IDs
 * \retval              negative value on error
 */
int llog_osd_put_cat_list(const struct lu_env *env, struct dt_device *d,
                          int idx, int count, struct llog_catid *idarray,
                          const struct lu_fid *fid)
{
        struct llog_thread_info *lgi = llog_info(env);
        struct dt_object        *o = NULL;
        struct thandle          *th;
        int                      rc, size;

        if (count == 0)
                RETURN(0);

        LASSERT(d);

        size = sizeof(*idarray) * count;
        lgi->lgi_off = idx * sizeof(*idarray);
        lgi->lgi_fid = *fid;

        o = dt_locate(env, d, &lgi->lgi_fid);
        if (IS_ERR(o))
                RETURN(PTR_ERR(o));

        if (!dt_object_exists(o))
                GOTO(out, rc = -ENOENT);

        rc = dt_attr_get(env, o, &lgi->lgi_attr);
        if (rc)
                GOTO(out, rc);

        if (!S_ISREG(lgi->lgi_attr.la_mode)) {
                CERROR("%s: CATALOGS is not a regular file!: mode = %o\n",
                       o->do_lu.lo_dev->ld_obd->obd_name,
                       lgi->lgi_attr.la_mode);
                GOTO(out, rc = -ENOENT);
        }

        th = dt_trans_create(env, d);
        if (IS_ERR(th))
                GOTO(out, rc = PTR_ERR(th));

        lgi->lgi_buf.lb_len = size;
        lgi->lgi_buf.lb_buf = idarray;
        rc = dt_declare_record_write(env, o, &lgi->lgi_buf, lgi->lgi_off, th);
        if (rc)
                GOTO(out_trans, rc);

        /* For update log, this happens during initialization,
         * see lod_sub_prep_llog(), and we need make sure catlog
         * file ID is written to catlist file(committed) before
         * cross-MDT operation write update records to catlog FILE,
         * otherwise, during failover these update records might
         * missing */
        if (fid_is_update_log(fid))
                th->th_sync = 1;

        rc = dt_trans_start_local(env, d, th);
        if (rc)
                GOTO(out_trans, rc);

        th->th_wait_submit = 1;

        rc = dt_record_write(env, o, &lgi->lgi_buf, &lgi->lgi_off, th);
        if (rc)
                CDEBUG(D_INODE, "can't write CATALOGS at index %d: rc = %d\n",
                       idx, rc);
out_trans:
        dt_trans_stop(env, d, th);
out:
        dt_object_put(env, o);
        RETURN(rc);
}
EXPORT_SYMBOL(llog_osd_put_cat_list);