[fs/lustre-release.git] / lustre / osp / osp_trans.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) 2014, 2015, Intel Corporation.
 */
/*
 * lustre/osp/osp_trans.c
 *
 *
 * 1. OSP (Object Storage Proxy) transaction methods
 *
 * Implement OSP layer transaction related interfaces for the dt_device API
 * dt_device_operations.
 *
 *
 * 2. Handle asynchronous idempotent operations
 *
 * The OSP uses OUT (Object Unified Target) RPC to talk with other server
 * (MDT or OST) for kinds of operations, such as create, unlink, insert,
 * delete, lookup, set_(x)attr, get_(x)attr, and etc. To reduce the number
 * of RPCs, we allow multiple operations to be packaged together in single
 * OUT RPC.
 *
 * For the asynchronous idempotent operations, such as get_(x)attr, related
 * RPCs will be inserted into an osp_device based shared asynchronous request
 * queue - osp_device::opd_async_requests. When the queue is full, all the
 * requests in the queue will be packaged into a single OUT RPC and given to
 * the ptlrpcd daemon (for sending), then the queue is purged and other new
 * requests can be inserted into it.
 *
 * When the asynchronous idempotent operation inserts the request into the
 * shared queue, it will register an interpreter. When the packaged OUT RPC
 * is replied (or failed to be sent out), all the registered interpreters
 * will be called one by one to handle each own result.
 *
 *
 * There are three kinds of transactions
 *
 * 1. Local transaction, all of updates of the transaction are in the local MDT.
 * 2. Remote transaction, all of updates of the transaction are in one remote
 * MDT, which only happens in LFSCK now.
 * 3. Distribute transaction, updates for the transaction are in mulitple MDTs.
 *
 * Author: Di Wang <di.wang@intel.com>
 * Author: Fan, Yong <fan.yong@intel.com>
 */

#define DEBUG_SUBSYSTEM S_MDS

#include <lustre_net.h>
#include "osp_internal.h"

/**
 * The argument for the interpreter callback of osp request.
 */
struct osp_update_args {
        struct osp_update_request *oaua_update;
        atomic_t                 *oaua_count;
        wait_queue_head_t        *oaua_waitq;
        bool                      oaua_flow_control;
        const struct lu_env      *oaua_update_env;
};

/**
 * Call back for each update request.
 */
struct osp_update_callback {
        /* list in the osp_update_request::our_cb_items */
        struct list_head                 ouc_list;

        /* The target of the async update request. */
        struct osp_object               *ouc_obj;

        /* The data used by or_interpreter. */
        void                            *ouc_data;

        /* The interpreter function called after the async request handled. */
        osp_update_interpreter_t        ouc_interpreter;
};

static struct object_update_request *object_update_request_alloc(size_t size)
{
        struct object_update_request *ourq;

        OBD_ALLOC_LARGE(ourq, size);
        if (ourq == NULL)
                return ERR_PTR(-ENOMEM);

        ourq->ourq_magic = UPDATE_REQUEST_MAGIC;
        ourq->ourq_count = 0;

        return ourq;
}

/**
 * Allocate new update request
 *
 * Allocate new update request and insert it to the req_update_list.
 *
 * \param [in] our      osp_udate_request where to create a new
 *                      update request
 *
 * \retval      0 if creation succeeds.
 * \retval      negative errno if creation fails.
 */
int osp_object_update_request_create(struct osp_update_request *our,
                                     size_t size)
{
        struct osp_update_request_sub *ours;

        OBD_ALLOC_PTR(ours);
        if (ours == NULL)
                return -ENOMEM;

        if (size < OUT_UPDATE_INIT_BUFFER_SIZE)
                size = OUT_UPDATE_INIT_BUFFER_SIZE;

        ours->ours_req = object_update_request_alloc(size);

        if (IS_ERR(ours->ours_req)) {
                OBD_FREE_PTR(ours);
                return -ENOMEM;
        }

        ours->ours_req_size = size;
        INIT_LIST_HEAD(&ours->ours_list);
        list_add_tail(&ours->ours_list, &our->our_req_list);
        our->our_req_nr++;

        return 0;
}

/**
 * Get current update request
 *
 * Get current object update request from our_req_list in
 * osp_update_request, because we always insert the new update
 * request in the last position, so the last update request
 * in the list will be the current update req.
 *
 * \param[in] our       osp update request where to get the
 *                      current object update.
 *
 * \retval              the current object update.
 **/
struct osp_update_request_sub *
osp_current_object_update_request(struct osp_update_request *our)
{
        if (list_empty(&our->our_req_list))
                return NULL;

        return list_entry(our->our_req_list.prev, struct osp_update_request_sub,
                          ours_list);
}

/**
 * Allocate and initialize osp_update_request
 *
 * osp_update_request is being used to track updates being executed on
 * this dt_device(OSD or OSP). The update buffer will be 4k initially,
 * and increased if needed.
 *
 * \param [in] dt       dt device
 *
 * \retval              osp_update_request being allocated if succeed
 * \retval              ERR_PTR(errno) if failed
 */
struct osp_update_request *osp_update_request_create(struct dt_device *dt)
{
        struct osp_update_request *our;

        OBD_ALLOC_PTR(our);
        if (our == NULL)
                return ERR_PTR(-ENOMEM);

        INIT_LIST_HEAD(&our->our_req_list);
        INIT_LIST_HEAD(&our->our_cb_items);
        INIT_LIST_HEAD(&our->our_list);
        spin_lock_init(&our->our_list_lock);

        osp_object_update_request_create(our, OUT_UPDATE_INIT_BUFFER_SIZE);
        return our;
}

void osp_update_request_destroy(struct osp_update_request *our)
{
        struct osp_update_request_sub *ours;
        struct osp_update_request_sub *tmp;

        if (our == NULL)
                return;

        list_for_each_entry_safe(ours, tmp, &our->our_req_list, ours_list) {
                list_del(&ours->ours_list);
                if (ours->ours_req != NULL)
                        OBD_FREE_LARGE(ours->ours_req, ours->ours_req_size);
                OBD_FREE_PTR(ours);
        }
        OBD_FREE_PTR(our);
}

static void
object_update_request_dump(const struct object_update_request *ourq,
                           unsigned int mask)
{
        unsigned int i;
        size_t total_size = 0;

        for (i = 0; i < ourq->ourq_count; i++) {
                struct object_update    *update;
                size_t                  size = 0;

                update = object_update_request_get(ourq, i, &size);
                LASSERT(update != NULL);
                CDEBUG(mask, "i = %u fid = "DFID" op = %s "
                       "params = %d batchid = "LPU64" size = %zu repsize %u\n",
                       i, PFID(&update->ou_fid),
                       update_op_str(update->ou_type),
                       update->ou_params_count,
                       update->ou_batchid, size,
                       (unsigned)update->ou_result_size);

                total_size += size;
        }

        CDEBUG(mask, "updates = %p magic = %x count = %d size = %zu\n", ourq,
               ourq->ourq_magic, ourq->ourq_count, total_size);
}

/**
 * Prepare inline update request
 *
 * Prepare OUT update ptlrpc inline request, and the request usually includes
 * one update buffer, which does not need bulk transfer.
 *
 * \param[in] env       execution environment
 * \param[in] req       ptlrpc request
 * \param[in] ours      sub osp_update_request to be packed
 *
 * \retval              0 if packing succeeds
 * \retval              negative errno if packing fails
 */
int osp_prep_inline_update_req(const struct lu_env *env,
                               struct ptlrpc_request *req,
                               struct osp_update_request *our,
                               int repsize)
{
        struct osp_update_request_sub *ours;
        struct out_update_header *ouh;
        __u32 update_req_size;
        int rc;

        ours = list_entry(our->our_req_list.next,
                          struct osp_update_request_sub, ours_list);
        update_req_size = object_update_request_size(ours->ours_req);
        req_capsule_set_size(&req->rq_pill, &RMF_OUT_UPDATE_HEADER, RCL_CLIENT,
                             update_req_size + sizeof(*ouh));

        rc = ptlrpc_request_pack(req, LUSTRE_MDS_VERSION, OUT_UPDATE);
        if (rc != 0)
                RETURN(rc);

        ouh = req_capsule_client_get(&req->rq_pill, &RMF_OUT_UPDATE_HEADER);
        ouh->ouh_magic = OUT_UPDATE_HEADER_MAGIC;
        ouh->ouh_count = 1;
        ouh->ouh_inline_length = update_req_size;
        ouh->ouh_reply_size = repsize;

        memcpy(ouh->ouh_inline_data, ours->ours_req, update_req_size);

        req_capsule_set_size(&req->rq_pill, &RMF_OUT_UPDATE_REPLY,
                             RCL_SERVER, repsize);

        ptlrpc_request_set_replen(req);
        req->rq_request_portal = OUT_PORTAL;
        req->rq_reply_portal = OSC_REPLY_PORTAL;

        RETURN(rc);
}

/**
 * Prepare update request.
 *
 * Prepare OUT update ptlrpc request, and the request usually includes
 * all of updates (stored in \param ureq) from one operation.
 *
 * \param[in] env       execution environment
 * \param[in] imp       import on which ptlrpc request will be sent
 * \param[in] ureq      hold all of updates which will be packed into the req
 * \param[in] reqp      request to be created
 *
 * \retval              0 if preparation succeeds.
 * \retval              negative errno if preparation fails.
 */
int osp_prep_update_req(const struct lu_env *env, struct obd_import *imp,
                        struct osp_update_request *our,
                        struct ptlrpc_request **reqp)
{
        struct ptlrpc_request           *req;
        struct ptlrpc_bulk_desc         *desc;
        struct osp_update_request_sub   *ours;
        const struct object_update_request *ourq;
        struct out_update_header        *ouh;
        struct out_update_buffer        *oub;
        __u32                           buf_count = 0;
        int                             repsize = 0;
        struct object_update_reply      *reply;
        int                             rc, i;
        int                             total = 0;
        ENTRY;

        list_for_each_entry(ours, &our->our_req_list, ours_list) {
                object_update_request_dump(ours->ours_req, D_INFO);

                ourq = ours->ours_req;
                for (i = 0; i < ourq->ourq_count; i++) {
                        struct object_update    *update;
                        size_t                  size = 0;


                        /* XXX: it's very inefficient to lookup update
                         *      this way, iterating from the beginning
                         *      each time */
                        update = object_update_request_get(ourq, i, &size);
                        LASSERT(update != NULL);

                        repsize += sizeof(reply->ourp_lens[0]);
                        repsize += sizeof(struct object_update_result);
                        repsize += update->ou_result_size;
                }

                buf_count++;
        }
        repsize += sizeof(*reply);
        repsize = (repsize + OUT_UPDATE_REPLY_SIZE - 1) &
                        ~(OUT_UPDATE_REPLY_SIZE - 1);
        LASSERT(buf_count > 0);

        req = ptlrpc_request_alloc(imp, &RQF_OUT_UPDATE);
        if (req == NULL)
                RETURN(-ENOMEM);

        if (buf_count == 1) {
                ours = list_entry(our->our_req_list.next,
                                  struct osp_update_request_sub, ours_list);

                /* Let's check if it can be packed inline */
                if (object_update_request_size(ours->ours_req) +
                    sizeof(struct out_update_header) <
                                OUT_UPDATE_MAX_INLINE_SIZE) {
                        rc = osp_prep_inline_update_req(env, req, our, repsize);
                        if (rc == 0)
                                *reqp = req;
                        GOTO(out_req, rc);
                }
        }

        req_capsule_set_size(&req->rq_pill, &RMF_OUT_UPDATE_HEADER, RCL_CLIENT,
                             sizeof(struct osp_update_request));

        req_capsule_set_size(&req->rq_pill, &RMF_OUT_UPDATE_BUF, RCL_CLIENT,
                             buf_count * sizeof(*oub));

        rc = ptlrpc_request_pack(req, LUSTRE_MDS_VERSION, OUT_UPDATE);
        if (rc != 0)
                GOTO(out_req, rc);

        ouh = req_capsule_client_get(&req->rq_pill, &RMF_OUT_UPDATE_HEADER);
        ouh->ouh_magic = OUT_UPDATE_HEADER_MAGIC;
        ouh->ouh_count = buf_count;
        ouh->ouh_inline_length = 0;
        ouh->ouh_reply_size = repsize;
        oub = req_capsule_client_get(&req->rq_pill, &RMF_OUT_UPDATE_BUF);
        list_for_each_entry(ours, &our->our_req_list, ours_list) {
                oub->oub_size = ours->ours_req_size;
                oub++;
        }

        req->rq_bulk_write = 1;
        desc = ptlrpc_prep_bulk_imp(req, buf_count,
                MD_MAX_BRW_SIZE >> LNET_MTU_BITS,
                PTLRPC_BULK_GET_SOURCE | PTLRPC_BULK_BUF_KVEC,
                MDS_BULK_PORTAL, &ptlrpc_bulk_kvec_ops);
        if (desc == NULL)
                GOTO(out_req, rc = -ENOMEM);

        /* NB req now owns desc and will free it when it gets freed */
        list_for_each_entry(ours, &our->our_req_list, ours_list) {
                desc->bd_frag_ops->add_iov_frag(desc, ours->ours_req,
                                                ours->ours_req_size);
                total += ours->ours_req_size;
        }
        CDEBUG(D_OTHER, "total %d in %u\n", total, our->our_update_nr);

        req_capsule_set_size(&req->rq_pill, &RMF_OUT_UPDATE_REPLY,
                             RCL_SERVER, repsize);

        ptlrpc_request_set_replen(req);
        req->rq_request_portal = OUT_PORTAL;
        req->rq_reply_portal = OSC_REPLY_PORTAL;
        *reqp = req;

out_req:
        if (rc < 0)
                ptlrpc_req_finished(req);

        RETURN(rc);
}

/**
 * Send update RPC.
 *
 * Send update request to the remote MDT synchronously.
 *
 * \param[in] env       execution environment
 * \param[in] imp       import on which ptlrpc request will be sent
 * \param[in] our       hold all of updates which will be packed into the req
 * \param[in] reqp      request to be created
 *
 * \retval              0 if RPC succeeds.
 * \retval              negative errno if RPC fails.
 */
int osp_remote_sync(const struct lu_env *env, struct osp_device *osp,
                    struct osp_update_request *our,
                    struct ptlrpc_request **reqp)
{
        struct obd_import       *imp = osp->opd_obd->u.cli.cl_import;
        struct ptlrpc_request   *req = NULL;
        int                     rc;
        ENTRY;

        rc = osp_prep_update_req(env, imp, our, &req);
        if (rc != 0)
                RETURN(rc);

        /* This will only be called with read-only update, and these updates
         * might be used to retrieve update log during recovery process, so
         * it will be allowed to send during recovery process */
        req->rq_allow_replay = 1;
        req->rq_allow_intr = 1;

        /* Note: some dt index api might return non-zero result here, like
         * osd_index_ea_lookup, so we should only check rc < 0 here */
        rc = ptlrpc_queue_wait(req);
        our->our_rc = rc;
        if (rc < 0 || reqp == NULL)
                ptlrpc_req_finished(req);
        else
                *reqp = req;

        RETURN(rc);
}

/**
 * Invalidate all objects in the osp thandle
 *
 * invalidate all of objects in the update request, which will be called
 * when the transaction is aborted.
 *
 * \param[in] oth       osp thandle.
 */
static void osp_thandle_invalidate_object(const struct lu_env *env,
                                          struct osp_thandle *oth)
{
        struct osp_update_request *our = oth->ot_our;
        struct osp_update_request_sub *ours;

        if (our == NULL)
                return;

        list_for_each_entry(ours, &our->our_req_list, ours_list) {
                struct object_update_request *our_req = ours->ours_req;
                unsigned int i;
                struct lu_object *obj;

                for (i = 0; i < our_req->ourq_count; i++) {
                        struct object_update *update;

                        update = object_update_request_get(our_req, i, NULL);
                        if (update == NULL)
                                break;

                        if (update->ou_type != OUT_WRITE)
                                continue;

                        if (!fid_is_sane(&update->ou_fid))
                                continue;

                        obj = lu_object_find_slice(env,
                                        &oth->ot_super.th_dev->dd_lu_dev,
                                        &update->ou_fid, NULL);
                        if (IS_ERR(obj))
                                break;

                        osp_invalidate(env, lu2dt_obj(obj));
                        lu_object_put(env, obj);
                }
        }
}

static void osp_trans_stop_cb(const struct lu_env *env,
                              struct osp_thandle *oth, int result)
{
        struct dt_txn_commit_cb *dcb;
        struct dt_txn_commit_cb *tmp;

        /* call per-transaction stop callbacks if any */
        list_for_each_entry_safe(dcb, tmp, &oth->ot_stop_dcb_list,
                                 dcb_linkage) {
                LASSERTF(dcb->dcb_magic == TRANS_COMMIT_CB_MAGIC,
                         "commit callback entry: magic=%x name='%s'\n",
                         dcb->dcb_magic, dcb->dcb_name);
                list_del_init(&dcb->dcb_linkage);
                dcb->dcb_func(NULL, &oth->ot_super, dcb, result);
        }

        if (result < 0)
                osp_thandle_invalidate_object(env, oth);
}

/**
 * Allocate an osp request and initialize it with the given parameters.
 *
 * \param[in] obj               pointer to the operation target
 * \param[in] data              pointer to the data used by the interpreter
 * \param[in] interpreter       pointer to the interpreter function
 *
 * \retval                      pointer to the asychronous request
 * \retval                      NULL if the allocation failed
 */
static struct osp_update_callback *
osp_update_callback_init(struct osp_object *obj, void *data,
                         osp_update_interpreter_t interpreter)
{
        struct osp_update_callback *ouc;

        OBD_ALLOC_PTR(ouc);
        if (ouc == NULL)
                return NULL;

        lu_object_get(osp2lu_obj(obj));
        INIT_LIST_HEAD(&ouc->ouc_list);
        ouc->ouc_obj = obj;
        ouc->ouc_data = data;
        ouc->ouc_interpreter = interpreter;

        return ouc;
}

/**
 * Destroy the osp_update_callback.
 *
 * \param[in] env       pointer to the thread context
 * \param[in] ouc       pointer to osp_update_callback
 */
static void osp_update_callback_fini(const struct lu_env *env,
                                     struct osp_update_callback *ouc)
{
        LASSERT(list_empty(&ouc->ouc_list));

        lu_object_put(env, osp2lu_obj(ouc->ouc_obj));
        OBD_FREE_PTR(ouc);
}

/**
 * Interpret the packaged OUT RPC results.
 *
 * For every packaged sub-request, call its registered interpreter function.
 * Then destroy the sub-request.
 *
 * \param[in] env       pointer to the thread context
 * \param[in] req       pointer to the RPC
 * \param[in] arg       pointer to data used by the interpreter
 * \param[in] rc        the RPC return value
 *
 * \retval              0 for success
 * \retval              negative error number on failure
 */
static int osp_update_interpret(const struct lu_env *env,
                                struct ptlrpc_request *req, void *arg, int rc)
{
        struct object_update_reply      *reply  = NULL;
        struct osp_update_args          *oaua   = arg;
        struct osp_update_request       *our = oaua->oaua_update;
        struct osp_thandle              *oth;
        struct osp_update_callback      *ouc;
        struct osp_update_callback      *next;
        int                              count  = 0;
        int                              index  = 0;
        int                              rc1    = 0;

        ENTRY;

        if (our == NULL)
                RETURN(0);

        /* Sigh env might be NULL in some cases, see
         * this calling path.
         * osp_send_update_thread()
         *  ptlrpc_set_wait() ----> null env.
         *   ptlrpc_check_set()
         *    osp_update_interpret()
         * Let's use env in oaua for this case.
         */
        if (env == NULL)
                env = oaua->oaua_update_env;

        oaua->oaua_update = NULL;
        oth = our->our_th;
        if (oaua->oaua_flow_control) {
                struct osp_device *osp;

                LASSERT(oth != NULL);
                osp = dt2osp_dev(oth->ot_super.th_dev);
                obd_put_request_slot(&osp->opd_obd->u.cli);
        }

        /* Unpack the results from the reply message. */
        if (req->rq_repmsg != NULL && req->rq_replied) {
                reply = req_capsule_server_sized_get(&req->rq_pill,
                                                     &RMF_OUT_UPDATE_REPLY,
                                                     OUT_UPDATE_REPLY_SIZE);
                if (reply == NULL || reply->ourp_magic != UPDATE_REPLY_MAGIC) {
                        if (rc == 0)
                                rc = -EPROTO;
                } else {
                        count = reply->ourp_count;
                }
        }

        list_for_each_entry_safe(ouc, next, &our->our_cb_items, ouc_list) {
                list_del_init(&ouc->ouc_list);

                /* The peer may only have handled some requests (indicated
                 * by the 'count') in the packaged OUT RPC, we can only get
                 * results for the handled part. */
                if (index < count && reply->ourp_lens[index] > 0 && rc >= 0) {
                        struct object_update_result *result;

                        result = object_update_result_get(reply, index, NULL);
                        if (result == NULL)
                                rc1 = rc = -EPROTO;
                        else
                                rc1 = rc = result->our_rc;
                } else if (rc1 >= 0) {
                        /* The peer did not handle these request, let's return
                         * -EINVAL to update interpret for now */
                        if (rc >= 0)
                                rc1 = -EINVAL;
                        else
                                rc1 = rc;
                }

                if (ouc->ouc_interpreter != NULL)
                        ouc->ouc_interpreter(env, reply, req, ouc->ouc_obj,
                                             ouc->ouc_data, index, rc1);

                osp_update_callback_fini(env, ouc);
                index++;
        }

        if (oaua->oaua_count != NULL && atomic_dec_and_test(oaua->oaua_count))
                wake_up_all(oaua->oaua_waitq);

        if (oth != NULL) {
                /* oth and osp_update_requests will be destoryed in
                 * osp_thandle_put */
                osp_trans_stop_cb(env, oth, rc);
                osp_thandle_put(oth);
        } else {
                osp_update_request_destroy(our);
        }

        RETURN(rc);
}

/**
 * Pack all the requests in the shared asynchronous idempotent request queue
 * into a single OUT RPC that will be given to the background ptlrpcd daemon.
 *
 * \param[in] env       pointer to the thread context
 * \param[in] osp       pointer to the OSP device
 * \param[in] our       pointer to the shared queue
 *
 * \retval              0 for success
 * \retval              negative error number on failure
 */
int osp_unplug_async_request(const struct lu_env *env,
                             struct osp_device *osp,
                             struct osp_update_request *our)
{
        struct osp_update_args  *args;
        struct ptlrpc_request   *req = NULL;
        int                      rc;

        rc = osp_prep_update_req(env, osp->opd_obd->u.cli.cl_import,
                                 our, &req);
        if (rc != 0) {
                struct osp_update_callback *ouc;
                struct osp_update_callback *next;

                list_for_each_entry_safe(ouc, next,
                                         &our->our_cb_items, ouc_list) {
                        list_del_init(&ouc->ouc_list);
                        if (ouc->ouc_interpreter != NULL)
                                ouc->ouc_interpreter(env, NULL, NULL,
                                                     ouc->ouc_obj,
                                                     ouc->ouc_data, 0, rc);
                        osp_update_callback_fini(env, ouc);
                }
                osp_update_request_destroy(our);
        } else {
                args = ptlrpc_req_async_args(req);
                args->oaua_update = our;
                args->oaua_count = NULL;
                args->oaua_waitq = NULL;
                /* Note: this is asynchronous call for the request, so the
                 * interrupte cb and current function will be different
                 * thread, so we need use different env */
                args->oaua_update_env = NULL;
                args->oaua_flow_control = false;
                req->rq_interpret_reply = osp_update_interpret;
                ptlrpcd_add_req(req);
        }

        return rc;
}

/**
 * Find or create (if NOT exist or purged) the shared asynchronous idempotent
 * request queue - osp_device::opd_async_requests.
 *
 * If the osp_device::opd_async_requests is not NULL, then return it directly;
 * otherwise create new osp_update_request and attach it to opd_async_requests.
 *
 * \param[in] osp       pointer to the OSP device
 *
 * \retval              pointer to the shared queue
 * \retval              negative error number on failure
 */
static struct osp_update_request *
osp_find_or_create_async_update_request(struct osp_device *osp)
{
        struct osp_update_request *our = osp->opd_async_requests;

        if (our != NULL)
                return our;

        our = osp_update_request_create(&osp->opd_dt_dev);
        if (IS_ERR(our))
                return our;

        osp->opd_async_requests = our;

        return our;
}

/**
 * Insert an osp_update_callback into the osp_update_request.
 *
 * Insert an osp_update_callback to the osp_update_request. Usually each update
 * in the osp_update_request will have one correspondent callback, and these
 * callbacks will be called in rq_interpret_reply.
 *
 * \param[in] env               pointer to the thread context
 * \param[in] obj               pointer to the operation target object
 * \param[in] data              pointer to the data used by the interpreter
 * \param[in] interpreter       pointer to the interpreter function
 *
 * \retval                      0 for success
 * \retval                      negative error number on failure
 */
int osp_insert_update_callback(const struct lu_env *env,
                               struct osp_update_request *our,
                               struct osp_object *obj, void *data,
                               osp_update_interpreter_t interpreter)
{
        struct osp_update_callback  *ouc;

        ouc = osp_update_callback_init(obj, data, interpreter);
        if (ouc == NULL)
                RETURN(-ENOMEM);

        list_add_tail(&ouc->ouc_list, &our->our_cb_items);

        return 0;
}

/**
 * Insert an asynchronous idempotent request to the shared request queue that
 * is attached to the osp_device.
 *
 * This function generates a new osp_async_request with the given parameters,
 * then tries to insert the request into the osp_device-based shared request
 * queue. If the queue is full, then triggers the packaged OUT RPC to purge
 * the shared queue firstly, and then re-tries.
 *
 * NOTE: must hold the osp::opd_async_requests_mutex to serialize concurrent
 *       osp_insert_async_request call from others.
 *
 * \param[in] env               pointer to the thread context
 * \param[in] op                operation type, see 'enum update_type'
 * \param[in] obj               pointer to the operation target
 * \param[in] count             array size of the subsequent \a lens and \a bufs
 * \param[in] lens              buffer length array for the subsequent \a bufs
 * \param[in] bufs              the buffers to compose the request
 * \param[in] data              pointer to the data used by the interpreter
 * \param[in] repsize           how many bytes the caller allocated for \a data
 * \param[in] interpreter       pointer to the interpreter function
 *
 * \retval                      0 for success
 * \retval                      negative error number on failure
 */
int osp_insert_async_request(const struct lu_env *env, enum update_type op,
                             struct osp_object *obj, int count,
                             __u16 *lens, const void **bufs,
                             void *data, __u32 repsize,
                             osp_update_interpreter_t interpreter)
{
        struct osp_device               *osp;
        struct osp_update_request       *our;
        struct object_update            *object_update;
        size_t                          max_update_size;
        struct object_update_request    *ureq;
        struct osp_update_request_sub   *ours;
        int                             rc = 0;
        ENTRY;

        osp = lu2osp_dev(osp2lu_obj(obj)->lo_dev);
        our = osp_find_or_create_async_update_request(osp);
        if (IS_ERR(our))
                RETURN(PTR_ERR(our));

again:
        ours = osp_current_object_update_request(our);

        ureq = ours->ours_req;
        max_update_size = ours->ours_req_size -
                          object_update_request_size(ureq);

        object_update = update_buffer_get_update(ureq, ureq->ourq_count);
        rc = out_update_pack(env, object_update, &max_update_size, op,
                             lu_object_fid(osp2lu_obj(obj)), count, lens, bufs,
                             repsize);
        /* The queue is full. */
        if (rc == -E2BIG) {
                osp->opd_async_requests = NULL;
                mutex_unlock(&osp->opd_async_requests_mutex);

                rc = osp_unplug_async_request(env, osp, our);
                mutex_lock(&osp->opd_async_requests_mutex);
                if (rc != 0)
                        RETURN(rc);

                our = osp_find_or_create_async_update_request(osp);
                if (IS_ERR(our))
                        RETURN(PTR_ERR(our));

                goto again;
        } else {
                if (rc < 0)
                        RETURN(rc);

                ureq->ourq_count++;
                our->our_update_nr++;
        }

        rc = osp_insert_update_callback(env, our, obj, data, interpreter);

        RETURN(rc);
}

int osp_trans_update_request_create(struct thandle *th)
{
        struct osp_thandle              *oth = thandle_to_osp_thandle(th);
        struct osp_update_request       *our;

        if (oth->ot_our != NULL)
                return 0;

        our = osp_update_request_create(th->th_dev);
        if (IS_ERR(our)) {
                th->th_result = PTR_ERR(our);
                return PTR_ERR(our);
        }

        oth->ot_our = our;
        our->our_th = oth;

        return 0;
}

void osp_thandle_destroy(struct osp_thandle *oth)
{
        LASSERT(oth->ot_magic == OSP_THANDLE_MAGIC);
        LASSERT(list_empty(&oth->ot_commit_dcb_list));
        LASSERT(list_empty(&oth->ot_stop_dcb_list));
        if (oth->ot_our != NULL)
                osp_update_request_destroy(oth->ot_our);
        OBD_FREE_PTR(oth);
}

/**
 * The OSP layer dt_device_operations::dt_trans_create() interface
 * to create a transaction.
 *
 * There are two kinds of transactions that will involve OSP:
 *
 * 1) If the transaction only contains the updates on remote server
 *    (MDT or OST), such as re-generating the lost OST-object for
 *    LFSCK, then it is a remote transaction. For remote transaction,
 *    the upper layer caller (such as the LFSCK engine) will call the
 *    dt_trans_create() (with the OSP dt_device as the parameter),
 *    then the call will be directed to the osp_trans_create() that
 *    creates the transaction handler and returns it to the caller.
 *
 * 2) If the transcation contains both local and remote updates,
 *    such as cross MDTs create under DNE mode, then the upper layer
 *    caller will not trigger osp_trans_create(). Instead, it will
 *    call dt_trans_create() on other dt_device, such as LOD that
 *    will generate the transaction handler. Such handler will be
 *    used by the whole transaction in subsequent sub-operations.
 *
 * \param[in] env       pointer to the thread context
 * \param[in] d         pointer to the OSP dt_device
 *
 * \retval              pointer to the transaction handler
 * \retval              negative error number on failure
 */
struct thandle *osp_trans_create(const struct lu_env *env, struct dt_device *d)
{
        struct osp_thandle              *oth;
        struct thandle                  *th = NULL;
        ENTRY;

        OBD_ALLOC_PTR(oth);
        if (unlikely(oth == NULL))
                RETURN(ERR_PTR(-ENOMEM));

        oth->ot_magic = OSP_THANDLE_MAGIC;
        th = &oth->ot_super;
        th->th_dev = d;
        th->th_tags = LCT_TX_HANDLE;

        atomic_set(&oth->ot_refcount, 1);
        INIT_LIST_HEAD(&oth->ot_commit_dcb_list);
        INIT_LIST_HEAD(&oth->ot_stop_dcb_list);

        RETURN(th);
}

/**
 * Add commit callback to transaction.
 *
 * Add commit callback to the osp thandle, which will be called
 * when the thandle is committed remotely.
 *
 * \param[in] th        the thandle
 * \param[in] dcb       commit callback structure
 *
 * \retval              only return 0 for now.
 */
int osp_trans_cb_add(struct thandle *th, struct dt_txn_commit_cb *dcb)
{
        struct osp_thandle *oth = thandle_to_osp_thandle(th);

        LASSERT(dcb->dcb_magic == TRANS_COMMIT_CB_MAGIC);
        LASSERT(&dcb->dcb_func != NULL);
        if (dcb->dcb_flags & DCB_TRANS_STOP)
                list_add(&dcb->dcb_linkage, &oth->ot_stop_dcb_list);
        else
                list_add(&dcb->dcb_linkage, &oth->ot_commit_dcb_list);
        return 0;
}

static void osp_trans_commit_cb(struct osp_thandle *oth, int result)
{
        struct dt_txn_commit_cb *dcb;
        struct dt_txn_commit_cb *tmp;

        LASSERT(atomic_read(&oth->ot_refcount) > 0);
        /* call per-transaction callbacks if any */
        list_for_each_entry_safe(dcb, tmp, &oth->ot_commit_dcb_list,
                                 dcb_linkage) {
                LASSERTF(dcb->dcb_magic == TRANS_COMMIT_CB_MAGIC,
                         "commit callback entry: magic=%x name='%s'\n",
                         dcb->dcb_magic, dcb->dcb_name);
                list_del_init(&dcb->dcb_linkage);
                dcb->dcb_func(NULL, &oth->ot_super, dcb, result);
        }
}

static void osp_request_commit_cb(struct ptlrpc_request *req)
{
        struct thandle          *th = req->rq_cb_data;
        struct osp_thandle      *oth;
        __u64                   last_committed_transno = 0;
        int                     result = req->rq_status;
        ENTRY;

        if (th == NULL)
                RETURN_EXIT;

        oth = thandle_to_osp_thandle(th);
        if (req->rq_repmsg != NULL &&
            lustre_msg_get_last_committed(req->rq_repmsg))
                last_committed_transno =
                        lustre_msg_get_last_committed(req->rq_repmsg);

        if (last_committed_transno <
                req->rq_import->imp_peer_committed_transno)
                last_committed_transno =
                        req->rq_import->imp_peer_committed_transno;

        CDEBUG(D_HA, "trans no "LPU64" committed transno "LPU64"\n",
               req->rq_transno, last_committed_transno);

        /* If the transaction is not really committed, mark result = 1 */
        if (req->rq_transno != 0 &&
            (req->rq_transno > last_committed_transno) && result == 0)
                result = 1;

        osp_trans_commit_cb(oth, result);
        req->rq_committed = 1;
        osp_thandle_put(oth);
        EXIT;
}

/**
 * callback of osp transaction
 *
 * Call all of callbacks for this osp thandle. This will only be
 * called in error handler path. In the normal processing path,
 * these callback will be called in osp_request_commit_cb() and
 * osp_update_interpret().
 *
 * \param [in] env      execution environment
 * \param [in] oth      osp thandle
 * \param [in] rc       result of the osp thandle
 */
void osp_trans_callback(const struct lu_env *env,
                        struct osp_thandle *oth, int rc)
{
        struct osp_update_callback *ouc;
        struct osp_update_callback *next;

        if (oth->ot_our != NULL) {
                list_for_each_entry_safe(ouc, next,
                                         &oth->ot_our->our_cb_items, ouc_list) {
                        list_del_init(&ouc->ouc_list);
                        if (ouc->ouc_interpreter != NULL)
                                ouc->ouc_interpreter(env, NULL, NULL,
                                                     ouc->ouc_obj,
                                                     ouc->ouc_data, 0, rc);
                        osp_update_callback_fini(env, ouc);
                }
        }
        osp_trans_stop_cb(env, oth, rc);
        osp_trans_commit_cb(oth, rc);
}

/**
 * Send the request for remote updates.
 *
 * Send updates to the remote MDT. Prepare the request by osp_update_req
 * and send them to remote MDT, for sync request, it will wait
 * until the reply return, otherwise hand it to ptlrpcd.
 *
 * Please refer to osp_trans_create() for transaction type.
 *
 * \param[in] env               pointer to the thread context
 * \param[in] osp               pointer to the OSP device
 * \param[in] our               pointer to the osp_update_request
 *
 * \retval                      0 for success
 * \retval                      negative error number on failure
 */
static int osp_send_update_req(const struct lu_env *env,
                               struct osp_device *osp,
                               struct osp_update_request *our)
{
        struct osp_update_args  *args;
        struct ptlrpc_request   *req;
        struct lu_device *top_device;
        struct osp_thandle      *oth = our->our_th;
        int     rc = 0;
        ENTRY;

        LASSERT(oth != NULL);
        rc = osp_prep_update_req(env, osp->opd_obd->u.cli.cl_import,
                                 our, &req);
        if (rc != 0) {
                osp_trans_callback(env, oth, rc);
                RETURN(rc);
        }

        args = ptlrpc_req_async_args(req);
        args->oaua_update = our;
        /* set env to NULL, in case the interrupt cb and current function
         * are in different thread */
        args->oaua_update_env = NULL;
        osp_thandle_get(oth); /* hold for update interpret */
        req->rq_interpret_reply = osp_update_interpret;
        if (!oth->ot_super.th_wait_submit && !oth->ot_super.th_sync) {
                if (!osp->opd_imp_active || !osp->opd_imp_connected) {
                        osp_trans_callback(env, oth, rc);
                        osp_thandle_put(oth);
                        GOTO(out, rc = -ENOTCONN);
                }

                rc = obd_get_request_slot(&osp->opd_obd->u.cli);
                if (rc != 0) {
                        osp_trans_callback(env, oth, rc);
                        osp_thandle_put(oth);
                        GOTO(out, rc = -ENOTCONN);
                }
                args->oaua_flow_control = true;

                if (!osp->opd_connect_mdt) {
                        down_read(&osp->opd_async_updates_rwsem);
                        args->oaua_count = &osp->opd_async_updates_count;
                        args->oaua_waitq = &osp->opd_syn_barrier_waitq;
                        up_read(&osp->opd_async_updates_rwsem);
                        atomic_inc(args->oaua_count);
                }

                ptlrpcd_add_req(req);
                req = NULL;
        } else {
                osp_thandle_get(oth); /* hold for commit callback */
                req->rq_commit_cb = osp_request_commit_cb;
                req->rq_cb_data = &oth->ot_super;
                args->oaua_flow_control = false;

                /* If the transaction is created during MDT recoverying
                 * process, it means this is an recovery update, we need
                 * to let OSP send it anyway without checking recoverying
                 * status, in case the other target is being recoveried
                 * at the same time, and if we wait here for the import
                 * to be recoveryed, it might cause deadlock */
                top_device = osp->opd_dt_dev.dd_lu_dev.ld_site->ls_top_dev;
                if (top_device->ld_obd->obd_recovering)
                        req->rq_allow_replay = 1;

                /* Because this req will be synchronus, i.e. it will be called
                 * in the same thread, so it will be safe to use current
                 * env */
                args->oaua_update_env = env;
                if (osp->opd_connect_mdt)
                        osp_get_rpc_lock(osp);
                rc = ptlrpc_queue_wait(req);
                if (osp->opd_connect_mdt)
                        osp_put_rpc_lock(osp);
                if ((rc == -ENOMEM && req->rq_set == NULL) ||
                    (req->rq_transno == 0 && !req->rq_committed)) {
                        if (args->oaua_update != NULL) {
                                /* If osp_update_interpret is not being called,
                                 * release the osp_thandle */
                                args->oaua_update = NULL;
                                osp_thandle_put(oth);
                        }

                        req->rq_cb_data = NULL;
                        rc = rc == 0 ? req->rq_status : rc;
                        osp_trans_callback(env, oth, rc);
                        osp_thandle_put(oth);
                        GOTO(out, rc);
                }
        }
out:
        if (req != NULL)
                ptlrpc_req_finished(req);

        RETURN(rc);
}

/**
 * Get local thandle for osp_thandle
 *
 * Get the local OSD thandle from the OSP thandle. Currently, there
 * are a few OSP API (osp_object_create() and osp_sync_add()) needs
 * to update the object on local OSD device.
 *
 * If the osp_thandle comes from normal stack (MDD->LOD->OSP), then
 * we will get local thandle by thandle_get_sub_by_dt.
 *
 * If the osp_thandle is remote thandle (th_top == NULL, only used
 * by LFSCK), then it will create a local thandle, and stop it in
 * osp_trans_stop(). And this only happens on OSP for OST.
 *
 * These are temporary solution, once OSP accessing OSD object is
 * being fixed properly, this function should be removed. XXX
 *
 * \param[in] env               pointer to the thread context
 * \param[in] th                pointer to the transaction handler
 * \param[in] dt                pointer to the OSP device
 *
 * \retval                      pointer to the local thandle
 * \retval                      ERR_PTR(errno) if it fails.
 **/
struct thandle *osp_get_storage_thandle(const struct lu_env *env,
                                        struct thandle *th,
                                        struct osp_device *osp)
{
        struct osp_thandle      *oth;
        struct thandle          *local_th;

        if (th->th_top != NULL)
                return thandle_get_sub_by_dt(env, th->th_top,
                                             osp->opd_storage);

        LASSERT(!osp->opd_connect_mdt);
        oth = thandle_to_osp_thandle(th);
        if (oth->ot_storage_th != NULL)
                return oth->ot_storage_th;

        local_th = dt_trans_create(env, osp->opd_storage);
        if (IS_ERR(local_th))
                return local_th;

        oth->ot_storage_th = local_th;

        return local_th;
}

/**
 * Set version for the transaction
 *
 * Set the version for the transaction and add the request to
 * the sending list, then after transaction stop, the request
 * will be picked in the order of version, by sending thread.
 *
 * \param [in] oth      osp thandle to be set version.
 *
 * \retval              0 if set version succeeds
 *                      negative errno if set version fails.
 */
int osp_check_and_set_rpc_version(struct osp_thandle *oth,
                                  struct osp_object *obj)
{
        struct osp_device *osp = dt2osp_dev(oth->ot_super.th_dev);
        struct osp_updates *ou = osp->opd_update;

        if (ou == NULL)
                return -EIO;

        if (oth->ot_our->our_version != 0)
                return 0;

        spin_lock(&ou->ou_lock);
        spin_lock(&oth->ot_our->our_list_lock);
        if (obj->opo_stale) {
                spin_unlock(&oth->ot_our->our_list_lock);
                spin_unlock(&ou->ou_lock);
                return -ESTALE;
        }

        /* Assign the version and add it to the sending list */
        osp_thandle_get(oth);
        oth->ot_our->our_version = ou->ou_version++;
        list_add_tail(&oth->ot_our->our_list,
                      &osp->opd_update->ou_list);
        oth->ot_our->our_req_ready = 0;
        spin_unlock(&oth->ot_our->our_list_lock);
        spin_unlock(&ou->ou_lock);

        LASSERT(oth->ot_super.th_wait_submit == 1);
        CDEBUG(D_INFO, "%s: version "LPU64" oth:version %p:"LPU64"\n",
               osp->opd_obd->obd_name, ou->ou_version, oth,
               oth->ot_our->our_version);

        return 0;
}

/**
 * Get next OSP update request in the sending list
 * Get next OSP update request in the sending list by version number, next
 * request will be
 * 1. transaction which does not have a version number.
 * 2. transaction whose version == opd_rpc_version.
 *
 * \param [in] ou       osp update structure.
 * \param [out] ourp    the pointer holding the next update request.
 *
 * \retval              true if getting the next transaction.
 * \retval              false if not getting the next transaction.
 */
static bool
osp_get_next_request(struct osp_updates *ou, struct osp_update_request **ourp)
{
        struct osp_update_request *our;
        struct osp_update_request *tmp;
        bool                    got_req = false;

        spin_lock(&ou->ou_lock);
        list_for_each_entry_safe(our, tmp, &ou->ou_list, our_list) {
                LASSERT(our->our_th != NULL);
                CDEBUG(D_HA, "ou %p version "LPU64" rpc_version "LPU64"\n",
                       ou, our->our_version, ou->ou_rpc_version);
                spin_lock(&our->our_list_lock);
                /* Find next osp_update_request in the list */
                if (our->our_version == ou->ou_rpc_version &&
                    our->our_req_ready) {
                        list_del_init(&our->our_list);
                        spin_unlock(&our->our_list_lock);
                        *ourp = our;
                        got_req = true;
                        break;
                }
                spin_unlock(&our->our_list_lock);
        }
        spin_unlock(&ou->ou_lock);

        return got_req;
}

/**
 * Invalidate update request
 *
 * Invalidate update request in the OSP sending list, so all of
 * requests in the sending list will return error, which happens
 * when it finds one update (with writing llog) requests fails or
 * the OSP is evicted by remote target. see osp_send_update_thread().
 *
 * \param[in] osp       OSP device whose update requests will be
 *                      invalidated.
 **/
void osp_invalidate_request(struct osp_device *osp)
{
        struct lu_env env;
        struct osp_updates *ou = osp->opd_update;
        struct osp_update_request *our;
        struct osp_update_request *tmp;
        LIST_HEAD(list);
        int                     rc;
        ENTRY;

        if (ou == NULL)
                return;

        rc = lu_env_init(&env, osp->opd_dt_dev.dd_lu_dev.ld_type->ldt_ctx_tags);
        if (rc < 0) {
                CERROR("%s: init env error: rc = %d\n", osp->opd_obd->obd_name,
                       rc);
                return;
        }

        INIT_LIST_HEAD(&list);

        spin_lock(&ou->ou_lock);
        /* invalidate all of request in the sending list */
        list_for_each_entry_safe(our, tmp, &ou->ou_list, our_list) {
                spin_lock(&our->our_list_lock);
                if (our->our_req_ready)
                        list_move(&our->our_list, &list);
                else
                        list_del_init(&our->our_list);

                if (our->our_th->ot_super.th_result == 0)
                        our->our_th->ot_super.th_result = -EIO;

                if (our->our_version >= ou->ou_rpc_version)
                        ou->ou_rpc_version = our->our_version + 1;
                spin_unlock(&our->our_list_lock);

                CDEBUG(D_HA, "%s invalidate our %p\n", osp->opd_obd->obd_name,
                       our);
        }

        spin_unlock(&ou->ou_lock);

        /* invalidate all of request in the sending list */
        list_for_each_entry_safe(our, tmp, &list, our_list) {
                spin_lock(&our->our_list_lock);
                list_del_init(&our->our_list);
                spin_unlock(&our->our_list_lock);
                osp_trans_callback(&env, our->our_th,
                                   our->our_th->ot_super.th_result);
                osp_thandle_put(our->our_th);
        }
        lu_env_fini(&env);
}

/**
 * Sending update thread
 *
 * Create thread to send update request to other MDTs, this thread will pull
 * out update request from the list in OSP by version number, i.e. it will
 * make sure the update request with lower version number will be sent first.
 *
 * \param[in] arg       hold the OSP device.
 *
 * \retval              0 if the thread is created successfully.
 * \retal               negative error if the thread is not created
 *                      successfully.
 */
int osp_send_update_thread(void *arg)
{
        struct lu_env           env;
        struct osp_device       *osp = arg;
        struct l_wait_info       lwi = { 0 };
        struct osp_updates      *ou = osp->opd_update;
        struct ptlrpc_thread    *thread = &osp->opd_update_thread;
        struct osp_update_request *our = NULL;
        int                     rc;
        ENTRY;

        LASSERT(ou != NULL);
        rc = lu_env_init(&env, osp->opd_dt_dev.dd_lu_dev.ld_type->ldt_ctx_tags);
        if (rc < 0) {
                CERROR("%s: init env error: rc = %d\n", osp->opd_obd->obd_name,
                       rc);
                RETURN(rc);
        }

        thread->t_flags = SVC_RUNNING;
        wake_up(&thread->t_ctl_waitq);
        while (1) {
                our = NULL;
                l_wait_event(ou->ou_waitq,
                             !osp_send_update_thread_running(osp) ||
                             osp_get_next_request(ou, &our), &lwi);

                if (!osp_send_update_thread_running(osp)) {
                        if (our != NULL) {
                                osp_trans_callback(&env, our->our_th, -EINTR);
                                osp_thandle_put(our->our_th);
                        }
                        break;
                }

                LASSERT(our->our_th != NULL);
                if (our->our_th->ot_super.th_result != 0) {
                        osp_trans_callback(&env, our->our_th,
                                our->our_th->ot_super.th_result);
                        rc = our->our_th->ot_super.th_result;
                } else if (OBD_FAIL_CHECK(OBD_FAIL_INVALIDATE_UPDATE)) {
                        rc = -EIO;
                        osp_trans_callback(&env, our->our_th, rc);
                } else {
                        rc = osp_send_update_req(&env, osp, our);
                }

                /* Update the rpc version */
                spin_lock(&ou->ou_lock);
                if (our->our_version == ou->ou_rpc_version)
                        ou->ou_rpc_version++;
                spin_unlock(&ou->ou_lock);

                /* If one update request fails, let's fail all of the requests
                 * in the sending list, because the request in the sending
                 * list are dependent on either other, continue sending these
                 * request might cause llog or filesystem corruption */
                if (rc < 0)
                        osp_invalidate_request(osp);

                /* Balanced for thandle_get in osp_check_and_set_rpc_version */
                osp_thandle_put(our->our_th);
        }

        thread->t_flags = SVC_STOPPED;
        lu_env_fini(&env);
        wake_up(&thread->t_ctl_waitq);

        RETURN(0);
}

/**
 * The OSP layer dt_device_operations::dt_trans_start() interface
 * to start the transaction.
 *
 * If the transaction is a remote transaction, then related remote
 * updates will be triggered in the osp_trans_stop().
 * Please refer to osp_trans_create() for transaction type.
 *
 * \param[in] env               pointer to the thread context
 * \param[in] dt                pointer to the OSP dt_device
 * \param[in] th                pointer to the transaction handler
 *
 * \retval                      0 for success
 * \retval                      negative error number on failure
 */
int osp_trans_start(const struct lu_env *env, struct dt_device *dt,
                    struct thandle *th)
{
        struct osp_thandle      *oth = thandle_to_osp_thandle(th);

        if (oth->ot_super.th_sync)
                oth->ot_our->our_flags |= UPDATE_FL_SYNC;
        /* For remote thandle, if there are local thandle, start it here*/
        if (is_only_remote_trans(th) && oth->ot_storage_th != NULL)
                return dt_trans_start(env, oth->ot_storage_th->th_dev,
                                      oth->ot_storage_th);
        return 0;
}

/**
 * The OSP layer dt_device_operations::dt_trans_stop() interface
 * to stop the transaction.
 *
 * If the transaction is a remote transaction, related remote
 * updates will be triggered at the end of this function.
 *
 * For synchronous mode update or any failed update, the request
 * will be destroyed explicitly when the osp_trans_stop().
 *
 * Please refer to osp_trans_create() for transaction type.
 *
 * \param[in] env               pointer to the thread context
 * \param[in] dt                pointer to the OSP dt_device
 * \param[in] th                pointer to the transaction handler
 *
 * \retval                      0 for success
 * \retval                      negative error number on failure
 */
int osp_trans_stop(const struct lu_env *env, struct dt_device *dt,
                   struct thandle *th)
{
        struct osp_thandle       *oth = thandle_to_osp_thandle(th);
        struct osp_update_request *our = oth->ot_our;
        struct osp_device        *osp = dt2osp_dev(dt);
        int                      rc = 0;
        ENTRY;

        /* For remote transaction, if there is local storage thandle,
         * stop it first */
        if (oth->ot_storage_th != NULL && th->th_top == NULL) {
                dt_trans_stop(env, oth->ot_storage_th->th_dev,
                              oth->ot_storage_th);
                oth->ot_storage_th = NULL;
        }

        if (our == NULL || list_empty(&our->our_req_list)) {
                osp_trans_callback(env, oth, th->th_result);
                GOTO(out, rc = th->th_result);
        }

        if (!osp->opd_connect_mdt) {
                osp_trans_callback(env, oth, th->th_result);
                rc = osp_send_update_req(env, osp, oth->ot_our);
                GOTO(out, rc);
        }

        if (osp->opd_update == NULL ||
            !osp_send_update_thread_running(osp)) {
                osp_trans_callback(env, oth, -EIO);
                GOTO(out, rc = -EIO);
        }

        CDEBUG(D_HA, "%s: add oth %p with version "LPU64"\n",
               osp->opd_obd->obd_name, oth, our->our_version);

        LASSERT(our->our_req_ready == 0);
        spin_lock(&our->our_list_lock);
        if (likely(!list_empty(&our->our_list))) {
                /* notify sending thread */
                our->our_req_ready = 1;
                wake_up(&osp->opd_update->ou_waitq);
                spin_unlock(&our->our_list_lock);
        } else if (th->th_result == 0) {
                /* if the request does not needs to be serialized,
                 * read-only request etc, let's send it right away */
                spin_unlock(&our->our_list_lock);
                rc = osp_send_update_req(env, osp, our);
        } else {
                spin_unlock(&our->our_list_lock);
                osp_trans_callback(env, oth, th->th_result);
        }
out:
        osp_thandle_put(oth);

        RETURN(rc);
}