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LU-3540 lod: update recovery thread
[fs/lustre-release.git] / lustre / lod / lod_dev.c
index 9bf10d8..7c7a1cb 100644 (file)
@@ -6,13 +6,13 @@
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 only,
  * as published by the Free Software Foundation.
-
+ *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License version 2 for more details.  A copy is
  * included in the COPYING file that accompanied this code.
-
+ *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
@@ -23,8 +23,7 @@
  * Copyright  2009 Sun Microsystems, Inc. All rights reserved
  * Use is subject to license terms.
  *
- * Copyright (c) 2012, Intel Corporation.
- *
+ * Copyright (c) 2012, 2014, Intel Corporation.
  */
 /*
  * This file is part of Lustre, http://www.lustre.org/
  * Author: Alex Zhuravlev <alexey.zhuravlev@intel.com>
  * Author: Mikhail Pershin <mike.pershin@intel.com>
  */
+/**
+ * The Logical Object Device (LOD) layer manages access to striped
+ * objects (both regular files and directories). It implements the DT
+ * device and object APIs and is responsible for creating, storing,
+ * and loading striping information as an extended attribute of the
+ * underlying OSD object. LOD is the server side analog of the LOV and
+ * LMV layers on the client side.
+ *
+ * Metadata LU object stack (layers of the same compound LU object,
+ * all have the same FID):
+ *
+ *        MDT
+ *         |      MD API
+ *        MDD
+ *         |      DT API
+ *        LOD
+ *       /   \    DT API
+ *     OSD   OSP
+ *
+ * During LOD object initialization the localness or remoteness of the
+ * object FID dictates the choice between OSD and OSP.
+ *
+ * An LOD object (file or directory) with N stripes (each has a
+ * different FID):
+ *
+ *          LOD
+ *           |
+ *   +---+---+---+...+
+ *   |   |   |   |   |
+ *   S0  S1  S2  S3  S(N-1)  OS[DP] objects, seen as DT objects by LOD
+ *
+ * When upper layers must access an object's stripes (which are
+ * themselves OST or MDT LU objects) LOD finds these objects by their
+ * FIDs and stores them as an array of DT object pointers on the
+ * object. Declarations and operations on LOD objects are received by
+ * LOD (as DT object operations) and performed on the underlying
+ * OS[DP] object and (as needed) on the stripes. From the perspective
+ * of LOD, a stripe-less file (created by mknod() or open with
+ * O_LOV_DELAY_CREATE) is an object which does not yet have stripes,
+ * while a non-striped directory (created by mkdir()) is an object
+ * which will never have stripes.
+ *
+ * The LOD layer also implements a small subset of the OBD device API
+ * to support MDT stack initialization and finalization (an MDD device
+ * connects and disconnects itself to and from the underlying LOD
+ * device), and pool management. In turn LOD uses the OBD device API
+ * to connect it self to the underlying OSD, and to connect itself to
+ * OSP devices representing the MDTs and OSTs that bear the stripes of
+ * its objects.
+ */
 
-#ifndef EXPORT_SYMTAB
-# define EXPORT_SYMTAB
-#endif
 #define DEBUG_SUBSYSTEM S_MDS
 
+#include <linux/kthread.h>
 #include <obd_class.h>
+#include <md_object.h>
+#include <lustre_fid.h>
 #include <lustre_param.h>
+#include <lustre_update.h>
+#include <lustre_log.h>
 
 #include "lod_internal.h"
 
-/**
- * Lookup MDT/OST index \a tgt by FID \a fid.
+static const char lod_update_log_name[] = "update_log";
+static const char lod_update_log_dir_name[] = "update_log_dir";
+
+/*
+ * Lookup target by FID.
+ *
+ * Lookup MDT/OST target index by FID. Type of the target can be
+ * specific or any.
+ *
+ * \param[in] env              LU environment provided by the caller
+ * \param[in] lod              lod device
+ * \param[in] fid              FID
+ * \param[out] tgt             result target index
+ * \param[in] type             expected type of the target:
+ *                             LU_SEQ_RANGE_{MDT,OST,ANY}
  *
- * \param lod LOD to be lookup at.
- * \param fid FID of object to find MDT/OST.
- * \param tgt MDT/OST index to return.
- * \param flags indidcate the FID is on MDS or OST.
+ * \retval 0                   on success
+ * \retval negative            negated errno on error
  **/
 int lod_fld_lookup(const struct lu_env *env, struct lod_device *lod,
-                  const struct lu_fid *fid, __u32 *tgt, int flags)
+                  const struct lu_fid *fid, __u32 *tgt, int *type)
 {
-       struct lu_seq_range     range;
+       struct lu_seq_range     range = { 0 };
        struct lu_server_fld    *server_fld;
-       int rc = 0;
+       int rc;
        ENTRY;
 
-       LASSERTF(fid_is_sane(fid), "Invalid FID "DFID"\n", PFID(fid));
+       if (!fid_is_sane(fid)) {
+               CERROR("%s: invalid FID "DFID"\n", lod2obd(lod)->obd_name,
+                      PFID(fid));
+               RETURN(-EIO);
+       }
+
        if (fid_is_idif(fid)) {
                *tgt = fid_idif_ost_idx(fid);
-               RETURN(rc);
+               *type = LU_SEQ_RANGE_OST;
+               RETURN(0);
+       }
+
+       if (fid_is_update_log(fid) || fid_is_update_log_dir(fid)) {
+               *tgt = fid_oid(fid);
+               *type = LU_SEQ_RANGE_MDT;
+               RETURN(0);
        }
 
-       if (!lod->lod_initialized || !fid_is_norm(fid)) {
+       if (!lod->lod_initialized || (!fid_seq_in_fldb(fid_seq(fid)))) {
                LASSERT(lu_site2seq(lod2lu_dev(lod)->ld_site) != NULL);
+
                *tgt = lu_site2seq(lod2lu_dev(lod)->ld_site)->ss_node_id;
-               RETURN(rc);
+               *type = LU_SEQ_RANGE_MDT;
+               RETURN(0);
        }
 
        server_fld = lu_site2seq(lod2lu_dev(lod)->ld_site)->ss_server_fld;
-       range.lsr_flags = flags;
+       if (server_fld == NULL)
+               RETURN(-EIO);
+
+       fld_range_set_type(&range, *type);
        rc = fld_server_lookup(env, server_fld, fid_seq(fid), &range);
-       if (rc) {
-               CERROR("%s: Can't find tgt by seq "LPX64", rc %d\n",
-                      lod2obd(lod)->obd_name, fid_seq(fid), rc);
+       if (rc != 0)
                RETURN(rc);
-       }
 
        *tgt = range.lsr_index;
+       *type = range.lsr_flags;
 
-       CDEBUG(D_INFO, "LOD: got tgt %x for sequence: "
-              LPX64"\n", *tgt, fid_seq(fid));
+       CDEBUG(D_INFO, "%s: got tgt %x for sequence: "LPX64"\n",
+              lod2obd(lod)->obd_name, *tgt, fid_seq(fid));
 
-       RETURN(rc);
+       RETURN(0);
 }
 
-extern struct lu_object_operations lod_lu_obj_ops;
-extern struct dt_object_operations lod_obj_ops;
-
 /* Slab for OSD object allocation */
-cfs_mem_cache_t *lod_object_kmem;
+struct kmem_cache *lod_object_kmem;
 
+/* Slab for dt_txn_callback */
+struct kmem_cache *lod_txn_callback_kmem;
 static struct lu_kmem_descr lod_caches[] = {
        {
                .ckd_cache = &lod_object_kmem,
@@ -106,6 +182,11 @@ static struct lu_kmem_descr lod_caches[] = {
                .ckd_size  = sizeof(struct lod_object)
        },
        {
+               .ckd_cache = &lod_txn_callback_kmem,
+               .ckd_name  = "lod_txn_callback",
+               .ckd_size  = sizeof(struct dt_txn_callback)
+       },
+       {
                .ckd_cache = NULL
        }
 };
@@ -113,25 +194,580 @@ static struct lu_kmem_descr lod_caches[] = {
 static struct lu_device *lod_device_fini(const struct lu_env *env,
                                         struct lu_device *d);
 
-struct lu_object *lod_object_alloc(const struct lu_env *env,
-                                  const struct lu_object_header *hdr,
-                                  struct lu_device *dev)
+/**
+ * Implementation of lu_device_operations::ldo_object_alloc() for LOD
+ *
+ * Allocates and initializes LOD's slice in the given object.
+ *
+ * see include/lu_object.h for the details.
+ */
+static struct lu_object *lod_object_alloc(const struct lu_env *env,
+                                         const struct lu_object_header *hdr,
+                                         struct lu_device *dev)
 {
-       struct lu_object  *lu_obj;
-       struct lod_object *lo;
+       struct lod_object       *lod_obj;
+       struct lu_object        *lu_obj;
+       ENTRY;
 
-       OBD_SLAB_ALLOC_PTR_GFP(lo, lod_object_kmem, CFS_ALLOC_IO);
-       if (lo == NULL)
-               return NULL;
+       OBD_SLAB_ALLOC_PTR_GFP(lod_obj, lod_object_kmem, GFP_NOFS);
+       if (lod_obj == NULL)
+               RETURN(ERR_PTR(-ENOMEM));
 
-       lu_obj = lod2lu_obj(lo);
-       dt_object_init(&lo->ldo_obj, NULL, dev);
-       lo->ldo_obj.do_ops = &lod_obj_ops;
+       lu_obj = lod2lu_obj(lod_obj);
+       dt_object_init(&lod_obj->ldo_obj, NULL, dev);
+       lod_obj->ldo_obj.do_ops = &lod_obj_ops;
        lu_obj->lo_ops = &lod_lu_obj_ops;
 
-       return lu_obj;
+       RETURN(lu_obj);
+}
+
+/**
+ * Process the config log for all sub device.
+ *
+ * The function goes through all the targets in the given table
+ * and apply given configuration command on to the targets.
+ * Used to cleanup the targets at unmount.
+ *
+ * \param[in] env              LU environment provided by the caller
+ * \param[in] lod              lod device
+ * \param[in] ltd              target's table to go through
+ * \param[in] lcfg             configuration command to apply
+ *
+ * \retval 0                   on success
+ * \retval negative            negated errno on error
+ **/
+static int lod_sub_process_config(const struct lu_env *env,
+                                struct lod_device *lod,
+                                struct lod_tgt_descs *ltd,
+                                struct lustre_cfg *lcfg)
+{
+       struct lu_device  *next;
+       int rc = 0;
+       unsigned int i;
+
+       lod_getref(ltd);
+       if (ltd->ltd_tgts_size <= 0) {
+               lod_putref(lod, ltd);
+               return 0;
+       }
+       cfs_foreach_bit(ltd->ltd_tgt_bitmap, i) {
+               struct lod_tgt_desc *tgt;
+               int rc1;
+
+               tgt = LTD_TGT(ltd, i);
+               LASSERT(tgt && tgt->ltd_tgt);
+               next = &tgt->ltd_tgt->dd_lu_dev;
+               rc1 = next->ld_ops->ldo_process_config(env, next, lcfg);
+               if (rc1) {
+                       CERROR("%s: error cleaning up LOD index %u: cmd %#x"
+                              ": rc = %d\n", lod2obd(lod)->obd_name, i,
+                              lcfg->lcfg_command, rc1);
+                       rc = rc1;
+               }
+       }
+       lod_putref(lod, ltd);
+       return rc;
+}
+
+struct lod_recovery_data {
+       struct lod_device       *lrd_lod;
+       struct lod_tgt_desc     *lrd_ltd;
+       struct ptlrpc_thread    *lrd_thread;
+       __u32                   lrd_idx;
+};
+
+
+/**
+ * process update recovery record
+ *
+ * Add the update recovery recode to the update recovery list in
+ * lod_recovery_data. Then the recovery thread (target_recovery_thread)
+ * will redo these updates.
+ *
+ * \param[in]env       execution environment
+ * \param[in]llh       log handle of update record
+ * \param[in]rec       update record to be replayed
+ * \param[in]data      update recovery data which holds the necessary
+ *                      arguments for recovery (see struct lod_recovery_data)
+ *
+ * \retval             0 if the record is processed successfully.
+ * \retval             negative errno if the record processing fails.
+ */
+static int lod_process_recovery_updates(const struct lu_env *env,
+                                       struct llog_handle *llh,
+                                       struct llog_rec_hdr *rec,
+                                       void *data)
+{
+       struct lod_recovery_data        *lrd = data;
+       struct llog_cookie      *cookie = &lod_env_info(env)->lti_cookie;
+       struct lu_target                *lut;
+       __u32                           index = 0;
+       ENTRY;
+
+       if (lrd->lrd_ltd == NULL) {
+               int rc;
+
+               rc = lodname2mdt_index(lod2obd(lrd->lrd_lod)->obd_name, &index);
+               if (rc != 0)
+                       return rc;
+       } else {
+               index = lrd->lrd_ltd->ltd_index;
+       }
+
+       if (rec->lrh_len !=
+               llog_update_record_size((struct llog_update_record *)rec)) {
+               CERROR("%s broken update record! index %u "DOSTID":%u : rc = %d\n",
+                      lod2obd(lrd->lrd_lod)->obd_name, index,
+                      POSTID(&llh->lgh_id.lgl_oi), rec->lrh_index, -EIO);
+               return -EIO;
+       }
+
+       cookie->lgc_lgl = llh->lgh_id;
+       cookie->lgc_index = rec->lrh_index;
+       cookie->lgc_subsys = LLOG_UPDATELOG_ORIG_CTXT;
+
+       CDEBUG(D_HA, "%s: process recovery updates "DOSTID":%u\n",
+              lod2obd(lrd->lrd_lod)->obd_name,
+              POSTID(&llh->lgh_id.lgl_oi), rec->lrh_index);
+       lut = lod2lu_dev(lrd->lrd_lod)->ld_site->ls_tgt;
+
+       return insert_update_records_to_replay_list(lut->lut_tdtd,
+                                       (struct llog_update_record *)rec,
+                                       cookie, index);
+}
+
+/**
+ * recovery thread for update log
+ *
+ * Start recovery thread and prepare the sub llog, then it will retrieve
+ * the update records from the correpondent MDT and do recovery.
+ *
+ * \param[in] arg      pointer to the recovery data
+ *
+ * \retval             0 if recovery succeeds
+ * \retval             negative errno if recovery failed.
+ */
+static int lod_sub_recovery_thread(void *arg)
+{
+       struct lod_recovery_data        *lrd = arg;
+       struct lod_device               *lod = lrd->lrd_lod;
+       struct dt_device                *dt;
+       struct ptlrpc_thread            *thread = lrd->lrd_thread;
+       struct llog_ctxt                *ctxt;
+       struct lu_env                   env;
+       int                             rc;
+       ENTRY;
+
+       thread->t_flags = SVC_RUNNING;
+       wake_up(&thread->t_ctl_waitq);
+
+       rc = lu_env_init(&env, LCT_LOCAL | LCT_MD_THREAD);
+       if (rc != 0) {
+               OBD_FREE_PTR(lrd);
+               CERROR("%s: can't initialize env: rc = %d\n",
+                      lod2obd(lod)->obd_name, rc);
+               RETURN(rc);
+       }
+
+       if (lrd->lrd_ltd == NULL)
+               dt = lod->lod_child;
+       else
+               dt = lrd->lrd_ltd->ltd_tgt;
+
+       rc = lod_sub_prep_llog(&env, lod, dt, lrd->lrd_idx);
+       if (rc != 0)
+               GOTO(out, rc);
+
+       /* Process the recovery record */
+       ctxt = llog_get_context(dt->dd_lu_dev.ld_obd, LLOG_UPDATELOG_ORIG_CTXT);
+       LASSERT(ctxt != NULL);
+       LASSERT(ctxt->loc_handle != NULL);
+
+       rc = llog_cat_process(&env, ctxt->loc_handle,
+                             lod_process_recovery_updates, lrd, 0, 0);
+       llog_ctxt_put(ctxt);
+
+       if (rc < 0) {
+               CERROR("%s getting update log failed: rc = %d\n",
+                      dt->dd_lu_dev.ld_obd->obd_name, rc);
+               GOTO(out, rc);
+       }
+
+       CDEBUG(D_HA, "%s retrieve update log: rc = %d\n",
+              dt->dd_lu_dev.ld_obd->obd_name, rc);
+
+       if (lrd->lrd_ltd == NULL)
+               lod->lod_child_got_update_log = 1;
+       else
+               lrd->lrd_ltd->ltd_got_update_log = 1;
+
+       if (lod->lod_child_got_update_log) {
+               struct lod_tgt_descs    *ltd = &lod->lod_mdt_descs;
+               struct lod_tgt_desc     *tgt = NULL;
+               bool                    all_got_log = true;
+               int                     i;
+
+               cfs_foreach_bit(ltd->ltd_tgt_bitmap, i) {
+                       tgt = LTD_TGT(ltd, i);
+                       if (!tgt->ltd_got_update_log) {
+                               all_got_log = false;
+                               break;
+                       }
+               }
+
+               if (all_got_log) {
+                       struct lu_target *lut;
+
+                       lut = lod2lu_dev(lod)->ld_site->ls_tgt;
+                       CDEBUG(D_HA, "%s got update logs from all MDTs.\n",
+                              lut->lut_obd->obd_name);
+                       lut->lut_tdtd->tdtd_replay_ready = 1;
+                       wake_up(&lut->lut_obd->obd_next_transno_waitq);
+               }
+       }
+
+out:
+       OBD_FREE_PTR(lrd);
+       thread->t_flags = SVC_STOPPED;
+       wake_up(&thread->t_ctl_waitq);
+       lu_env_fini(&env);
+       RETURN(rc);
+}
+
+/**
+ * finish sub llog context
+ *
+ * Stop update recovery thread for the sub device, then cleanup the
+ * correspondent llog ctxt.
+ *
+ * \param[in] env      execution environment
+ * \param[in] lod      lod device to do update recovery
+ * \param[in] thread   recovery thread on this sub device
+ */
+void lod_sub_fini_llog(const struct lu_env *env,
+                      struct dt_device *dt, struct ptlrpc_thread *thread)
+{
+       struct obd_device       *obd;
+       struct llog_ctxt        *ctxt;
+       ENTRY;
+
+       obd = dt->dd_lu_dev.ld_obd;
+       CDEBUG(D_INFO, "%s: finish sub llog\n", obd->obd_name);
+       /* Stop recovery thread first */
+       if (thread != NULL && thread->t_flags & SVC_RUNNING) {
+               thread->t_flags = SVC_STOPPING;
+               wake_up(&thread->t_ctl_waitq);
+               wait_event(thread->t_ctl_waitq, thread->t_flags & SVC_STOPPED);
+       }
+
+       ctxt = llog_get_context(obd, LLOG_UPDATELOG_ORIG_CTXT);
+       if (ctxt == NULL)
+               RETURN_EXIT;
+
+       if (ctxt->loc_handle != NULL)
+               llog_cat_close(env, ctxt->loc_handle);
+
+       llog_cleanup(env, ctxt);
+
+       RETURN_EXIT;
+}
+
+/**
+ * Extract MDT target index from a device name.
+ *
+ * a helper function to extract index from the given device name
+ * like "fsname-MDTxxxx-mdtlov"
+ *
+ * \param[in] lodname          device name
+ * \param[out] mdt_index       extracted index
+ *
+ * \retval 0           on success
+ * \retval -EINVAL     if the name is invalid
+ */
+int lodname2mdt_index(char *lodname, __u32 *mdt_index)
+{
+       unsigned long index;
+       char *ptr, *tmp;
+
+       /* 1.8 configs don't have "-MDT0000" at the end */
+       ptr = strstr(lodname, "-MDT");
+       if (ptr == NULL) {
+               *mdt_index = 0;
+               return 0;
+       }
+
+       ptr = strrchr(lodname, '-');
+       if (ptr == NULL) {
+               CERROR("invalid MDT index in '%s'\n", lodname);
+               return -EINVAL;
+       }
+
+       if (strncmp(ptr, "-mdtlov", 7) != 0) {
+               CERROR("invalid MDT index in '%s'\n", lodname);
+               return -EINVAL;
+       }
+
+       if ((unsigned long)ptr - (unsigned long)lodname <= 8) {
+               CERROR("invalid MDT index in '%s'\n", lodname);
+               return -EINVAL;
+       }
+
+       if (strncmp(ptr - 8, "-MDT", 4) != 0) {
+               CERROR("invalid MDT index in '%s'\n", lodname);
+               return -EINVAL;
+       }
+
+       index = simple_strtol(ptr - 4, &tmp, 16);
+       if (*tmp != '-' || index > INT_MAX) {
+               CERROR("invalid MDT index in '%s'\n", lodname);
+               return -EINVAL;
+       }
+       *mdt_index = index;
+       return 0;
+}
+
+/**
+ * Init sub llog context
+ *
+ * Setup update llog ctxt for update recovery threads, then start the
+ * recovery thread (lod_sub_recovery_thread) to read update llog from
+ * the correspondent MDT to do update recovery.
+ *
+ * \param[in] env      execution environment
+ * \param[in] lod      lod device to do update recovery
+ * \param[in] dt       sub dt device for which the recovery thread is
+ *
+ * \retval             0 if initialization succeeds.
+ * \retval             negative errno if initialization fails.
+ */
+int lod_sub_init_llog(const struct lu_env *env, struct lod_device *lod,
+                     struct dt_device *dt)
+{
+       struct obd_device               *obd;
+       struct lod_recovery_data        *lrd = NULL;
+       struct ptlrpc_thread            *thread;
+       struct task_struct              *task;
+       struct l_wait_info              lwi = { 0 };
+       struct lod_tgt_desc             *sub_ltd = NULL;
+       __u32                           index;
+       __u32                           master_index;
+       int                             rc;
+       ENTRY;
+
+       rc = lodname2mdt_index(lod2obd(lod)->obd_name, &master_index);
+       if (rc != 0)
+               RETURN(rc);
+
+       OBD_ALLOC_PTR(lrd);
+       if (lrd == NULL)
+               RETURN(-ENOMEM);
+
+       if (lod->lod_child == dt) {
+               thread = &lod->lod_child_recovery_thread;
+               index = master_index;
+       } else {
+               struct lod_tgt_descs    *ltd = &lod->lod_mdt_descs;
+               struct lod_tgt_desc     *tgt = NULL;
+               unsigned int            i;
+
+               cfs_foreach_bit(ltd->ltd_tgt_bitmap, i) {
+                       tgt = LTD_TGT(ltd, i);
+                       if (tgt->ltd_tgt == dt) {
+                               index = tgt->ltd_index;
+                               sub_ltd = tgt;
+                               break;
+                       }
+               }
+               LASSERT(sub_ltd != NULL);
+               OBD_ALLOC_PTR(sub_ltd->ltd_recovery_thread);
+               if (sub_ltd->ltd_recovery_thread == NULL)
+                       GOTO(free_lrd, rc = -ENOMEM);
+
+               thread = sub_ltd->ltd_recovery_thread;
+       }
+
+       CDEBUG(D_INFO, "%s init sub log %s\n", lod2obd(lod)->obd_name,
+              dt->dd_lu_dev.ld_obd->obd_name);
+       lrd->lrd_lod = lod;
+       lrd->lrd_ltd = sub_ltd;
+       lrd->lrd_thread = thread;
+       lrd->lrd_idx = index;
+       init_waitqueue_head(&thread->t_ctl_waitq);
+
+       obd = dt->dd_lu_dev.ld_obd;
+       obd->obd_lvfs_ctxt.dt = dt;
+       rc = llog_setup(env, obd, &obd->obd_olg, LLOG_UPDATELOG_ORIG_CTXT,
+                       NULL, &llog_common_cat_ops);
+       if (rc < 0) {
+               CERROR("%s: cannot setup updatelog llog: rc = %d\n",
+                      obd->obd_name, rc);
+               GOTO(free_thread, rc);
+       }
+
+       /* Start the recovery thread */
+       task = kthread_run(lod_sub_recovery_thread, lrd, "lod%04x_rec%04x",
+                          master_index, index);
+       if (IS_ERR(task)) {
+               rc = PTR_ERR(task);
+               CERROR("%s: cannot start recovery thread: rc = %d\n",
+                      obd->obd_name, rc);
+               GOTO(out_llog, rc);
+       }
+
+       l_wait_event(thread->t_ctl_waitq, thread->t_flags & SVC_RUNNING ||
+                                         thread->t_flags & SVC_STOPPED, &lwi);
+
+       RETURN(0);
+out_llog:
+       lod_sub_fini_llog(env, dt, thread);
+free_thread:
+       if (lod->lod_child != dt) {
+               OBD_FREE_PTR(sub_ltd->ltd_recovery_thread);
+               sub_ltd->ltd_recovery_thread = NULL;
+       }
+free_lrd:
+       OBD_FREE_PTR(lrd);
+       RETURN(rc);
+}
+
+/**
+ * finish all sub llog
+ *
+ * cleanup all of sub llog ctxt on the LOD.
+ *
+ * \param[in] env      execution environment
+ * \param[in] lod      lod device to do update recovery
+ */
+static void lod_sub_fini_all_llogs(const struct lu_env *env,
+                                  struct lod_device *lod)
+{
+       struct lod_tgt_descs *ltd = &lod->lod_mdt_descs;
+       unsigned int i;
+
+       /* Stop the update log commit cancel threads and finish master
+        * llog ctxt */
+       lod_sub_fini_llog(env, lod->lod_child,
+                         &lod->lod_child_recovery_thread);
+       lod_getref(ltd);
+       cfs_foreach_bit(ltd->ltd_tgt_bitmap, i) {
+               struct lod_tgt_desc     *tgt;
+
+               tgt = LTD_TGT(ltd, i);
+               if (tgt->ltd_recovery_thread != NULL) {
+                       lod_sub_fini_llog(env, tgt->ltd_tgt,
+                                         tgt->ltd_recovery_thread);
+                       OBD_FREE_PTR(tgt->ltd_recovery_thread);
+                       tgt->ltd_recovery_thread = NULL;
+               }
+       }
+
+       lod_putref(lod, ltd);
+}
+
+/**
+ * Prepare distribute txn
+ *
+ * Prepare distribute txn structure for LOD
+ *
+ * \param[in] env      execution environment
+ * \param[in] lod_device  LOD device
+ *
+ * \retval             0 if preparation succeeds.
+ * \retval             negative errno if preparation fails.
+ */
+static int lod_prepare_distribute_txn(const struct lu_env *env,
+                                     struct lod_device *lod)
+{
+       struct target_distribute_txn_data *tdtd;
+       struct lu_target                  *lut;
+       int                               rc;
+       ENTRY;
+
+       /* Init update recovery data */
+       OBD_ALLOC_PTR(tdtd);
+       if (tdtd == NULL)
+               RETURN(-ENOMEM);
+
+       lut = lod2lu_dev(lod)->ld_site->ls_tgt;
+
+       rc = distribute_txn_init(env, lut, tdtd,
+               lu_site2seq(lod2lu_dev(lod)->ld_site)->ss_node_id);
+
+       if (rc < 0) {
+               CERROR("%s: cannot init distribute txn: rc = %d\n",
+                      lod2obd(lod)->obd_name, rc);
+               OBD_FREE_PTR(tdtd);
+               RETURN(rc);
+       }
+
+       tdtd->tdtd_dt = &lod->lod_dt_dev;
+       INIT_LIST_HEAD(&tdtd->tdtd_replay_list);
+       spin_lock_init(&tdtd->tdtd_replay_list_lock);
+       tdtd->tdtd_replay_handler = distribute_txn_replay_handle;
+       tdtd->tdtd_replay_ready = 0;
+
+       lut->lut_tdtd = tdtd;
+
+       RETURN(0);
 }
 
+/**
+ * Finish distribute txn
+ *
+ * Release the resource holding by distribute txn, i.e. stop distribute
+ * txn thread.
+ *
+ * \param[in] env      execution environment
+ * \param[in] lod      lod device
+ */
+static void lod_fini_distribute_txn(const struct lu_env *env,
+                                   struct lod_device *lod)
+{
+       struct lu_target                  *lut;
+
+       lut = lod2lu_dev(lod)->ld_site->ls_tgt;
+       if (lut->lut_tdtd == NULL)
+               return;
+
+       distribute_txn_fini(env, lut->lut_tdtd);
+
+       OBD_FREE_PTR(lut->lut_tdtd);
+       lut->lut_tdtd = NULL;
+}
+
+/**
+ * Implementation of lu_device_operations::ldo_process_config() for LOD
+ *
+ * The method is called by the configuration subsystem during setup,
+ * cleanup and when the configuration changes. The method processes
+ * few specific commands like adding/removing the targets, changing
+ * the runtime parameters.
+
+ * \param[in] env              LU environment provided by the caller
+ * \param[in] dev              lod device
+ * \param[in] lcfg             configuration command to apply
+ *
+ * \retval 0                   on success
+ * \retval negative            negated errno on error
+ *
+ * The examples are below.
+ *
+ * Add osc config log:
+ * marker  20 (flags=0x01, v2.2.49.56) lustre-OST0001  'add osc'
+ * add_uuid  nid=192.168.122.162@tcp(0x20000c0a87aa2)  0:  1:nidxxx
+ * attach    0:lustre-OST0001-osc-MDT0001  1:osc  2:lustre-MDT0001-mdtlov_UUID
+ * setup     0:lustre-OST0001-osc-MDT0001  1:lustre-OST0001_UUID  2:nid
+ * lov_modify_tgts add 0:lustre-MDT0001-mdtlov  1:lustre-OST0001_UUID  2:1  3:1
+ * marker  20 (flags=0x02, v2.2.49.56) lustre-OST0001  'add osc'
+ *
+ * Add mdc config log:
+ * marker  10 (flags=0x01, v2.2.49.56) lustre-MDT0000  'add osp'
+ * add_uuid  nid=192.168.122.162@tcp(0x20000c0a87aa2)  0:  1:nid
+ * attach 0:lustre-MDT0000-osp-MDT0001  1:osp  2:lustre-MDT0001-mdtlov_UUID
+ * setup     0:lustre-MDT0000-osp-MDT0001  1:lustre-MDT0000_UUID  2:nid
+ * modify_mdc_tgts add 0:lustre-MDT0001  1:lustre-MDT0000_UUID  2:0  3:1
+ * marker  10 (flags=0x02, v2.2.49.56) lustre-MDT0000_UUID  'add osp'
+ */
 static int lod_process_config(const struct lu_env *env,
                              struct lu_device *dev,
                              struct lustre_cfg *lcfg)
@@ -139,17 +775,21 @@ static int lod_process_config(const struct lu_env *env,
        struct lod_device *lod = lu2lod_dev(dev);
        struct lu_device  *next = &lod->lod_child->dd_lu_dev;
        char              *arg1;
-       int                rc, i;
+       int                rc = 0;
        ENTRY;
 
        switch(lcfg->lcfg_command) {
-
        case LCFG_LOV_DEL_OBD:
        case LCFG_LOV_ADD_INA:
-       case LCFG_LOV_ADD_OBD: {
+       case LCFG_LOV_ADD_OBD:
+       case LCFG_ADD_MDC: {
                __u32 index;
+               __u32 mdt_index;
                int gen;
-               /* lov_modify_tgts add  0:lov_mdsA  1:osp  2:0  3:1 */
+               /* lov_modify_tgts add  0:lov_mdsA  1:osp  2:0  3:1
+                * modify_mdc_tgts add  0:lustre-MDT0001
+                *                    1:lustre-MDT0001-mdc0002
+                *                    2:2  3:1*/
                arg1 = lustre_cfg_string(lcfg, 1);
 
                if (sscanf(lustre_cfg_buf(lcfg, 2), "%d", &index) != 1)
@@ -157,48 +797,64 @@ static int lod_process_config(const struct lu_env *env,
                if (sscanf(lustre_cfg_buf(lcfg, 3), "%d", &gen) != 1)
                        GOTO(out, rc = -EINVAL);
 
-               if (lcfg->lcfg_command == LCFG_LOV_ADD_OBD)
-                       rc = lod_add_device(env, lod, arg1, index, gen, 1);
-               else if (lcfg->lcfg_command == LCFG_LOV_ADD_INA)
-                       rc = lod_add_device(env, lod, arg1, index, gen, 0);
-               else
-                       rc = lod_del_device(env, lod, arg1, index, gen);
+               if (lcfg->lcfg_command == LCFG_LOV_ADD_OBD) {
+                       __u32 mdt_index;
+
+                       rc = lodname2mdt_index(lustre_cfg_string(lcfg, 0),
+                                              &mdt_index);
+                       if (rc != 0)
+                               GOTO(out, rc);
+
+                       rc = lod_add_device(env, lod, arg1, index, gen,
+                                           mdt_index, LUSTRE_OSC_NAME, 1);
+               } else if (lcfg->lcfg_command == LCFG_ADD_MDC) {
+                       mdt_index = index;
+                       rc = lod_add_device(env, lod, arg1, index, gen,
+                                           mdt_index, LUSTRE_MDC_NAME, 1);
+               } else if (lcfg->lcfg_command == LCFG_LOV_ADD_INA) {
+                       /*FIXME: Add mdt_index for LCFG_LOV_ADD_INA*/
+                       mdt_index = 0;
+                       rc = lod_add_device(env, lod, arg1, index, gen,
+                                           mdt_index, LUSTRE_OSC_NAME, 0);
+               } else {
+                       rc = lod_del_device(env, lod,
+                                           &lod->lod_ost_descs,
+                                           arg1, index, gen, true);
+               }
 
                break;
        }
 
        case LCFG_PARAM: {
-               struct lprocfs_static_vars  v = { 0 };
-               struct obd_device         *obd = lod2obd(lod);
+               struct obd_device *obd = lod2obd(lod);
 
-               lprocfs_lod_init_vars(&v);
-
-               rc = class_process_proc_param(PARAM_LOV, v.obd_vars, lcfg, obd);
+               rc = class_process_proc_param(PARAM_LOV, obd->obd_vars,
+                                             lcfg, obd);
                if (rc > 0)
                        rc = 0;
                GOTO(out, rc);
-        }
-
-       case LCFG_CLEANUP:
-               lu_dev_del_linkage(dev->ld_site, dev);
-               lod_getref(lod);
-               lod_foreach_ost(lod, i) {
-                       struct lod_ost_desc *ost;
-                       ost = OST_TGT(lod, i);
-                       LASSERT(ost && ost->ltd_ost);
-                       next = &ost->ltd_ost->dd_lu_dev;
-                       rc = next->ld_ops->ldo_process_config(env, next, lcfg);
-                       if (rc)
-                               CERROR("%s: can't process %u: %d\n",
-                                      lod2obd(lod)->obd_name,
-                                      lcfg->lcfg_command, rc);
-               }
-               lod_putref(lod);
+       }
+       case LCFG_PRE_CLEANUP: {
+               lod_sub_process_config(env, lod, &lod->lod_mdt_descs, lcfg);
+               lod_sub_process_config(env, lod, &lod->lod_ost_descs, lcfg);
+               next = &lod->lod_child->dd_lu_dev;
+               rc = next->ld_ops->ldo_process_config(env, next, lcfg);
+               if (rc != 0)
+                       CDEBUG(D_HA, "%s: can't process %u: %d\n",
+                              lod2obd(lod)->obd_name, lcfg->lcfg_command, rc);
 
+               lod_fini_distribute_txn(env, lod);
+               lod_sub_fini_all_llogs(env, lod);
+               break;
+       }
+       case LCFG_CLEANUP: {
                /*
                 * do cleanup on underlying storage only when
                 * all OSPs are cleaned up, as they use that OSD as well
                 */
+               lu_dev_del_linkage(dev->ld_site, dev);
+               lod_sub_process_config(env, lod, &lod->lod_mdt_descs, lcfg);
+               lod_sub_process_config(env, lod, &lod->lod_ost_descs, lcfg);
                next = &lod->lod_child->dd_lu_dev;
                rc = next->ld_ops->ldo_process_config(env, next, lcfg);
                if (rc)
@@ -209,7 +865,7 @@ static int lod_process_config(const struct lu_env *env,
                if (rc)
                        CERROR("error in disconnect from storage: %d\n", rc);
                break;
-
+       }
        default:
               CERROR("%s: unknown command %u\n", lod2obd(lod)->obd_name,
                      lcfg->lcfg_command);
@@ -221,13 +877,21 @@ out:
        RETURN(rc);
 }
 
+/**
+ * Implementation of lu_device_operations::ldo_recovery_complete() for LOD
+ *
+ * The method is called once the recovery is complete. This implementation
+ * distributes the notification to all the known targets.
+ *
+ * see include/lu_object.h for the details
+ */
 static int lod_recovery_complete(const struct lu_env *env,
                                 struct lu_device *dev)
 {
        struct lod_device   *lod = lu2lod_dev(dev);
        struct lu_device    *next = &lod->lod_child->dd_lu_dev;
-       struct lod_ost_desc *ost;
-       int                  i, rc;
+       unsigned int         i;
+       int                  rc;
        ENTRY;
 
        LASSERT(lod->lod_recovery_completed == 0);
@@ -235,27 +899,78 @@ static int lod_recovery_complete(const struct lu_env *env,
 
        rc = next->ld_ops->ldo_recovery_complete(env, next);
 
-       lod_getref(lod);
-       lod_foreach_ost(lod, i) {
-               ost = OST_TGT(lod, i);
-               LASSERT(ost && ost->ltd_ost);
-               next = &ost->ltd_ost->dd_lu_dev;
-               rc = next->ld_ops->ldo_recovery_complete(env, next);
-               if (rc)
-                       CERROR("%s: can't complete recovery on #%d: %d\n",
-                              lod2obd(lod)->obd_name, i, rc);
+       lod_getref(&lod->lod_ost_descs);
+       if (lod->lod_osts_size > 0) {
+               cfs_foreach_bit(lod->lod_ost_bitmap, i) {
+                       struct lod_tgt_desc *tgt;
+                       tgt = OST_TGT(lod, i);
+                       LASSERT(tgt && tgt->ltd_tgt);
+                       next = &tgt->ltd_ost->dd_lu_dev;
+                       rc = next->ld_ops->ldo_recovery_complete(env, next);
+                       if (rc)
+                               CERROR("%s: can't complete recovery on #%d:"
+                                       "%d\n", lod2obd(lod)->obd_name, i, rc);
+               }
+       }
+       lod_putref(lod, &lod->lod_ost_descs);
+       RETURN(rc);
+}
+
+/**
+ * Init update logs on all sub device
+ *
+ * LOD initialize update logs on all of sub devices. Because the initialization
+ * process might need FLD lookup, see llog_osd_open()->dt_locate()->...->
+ * lod_object_init(), this API has to be called after LOD is initialized.
+ * \param[in] env      execution environment
+ * \param[in] lod      lod device
+ *
+ * \retval             0 if update log is initialized successfully.
+ * \retval             negative errno if initialization fails.
+ */
+static int lod_sub_init_llogs(const struct lu_env *env, struct lod_device *lod)
+{
+       struct lod_tgt_descs    *ltd = &lod->lod_mdt_descs;
+       int                     rc;
+       unsigned int            i;
+       ENTRY;
+
+       /* llog must be setup after LOD is initialized, because llog
+        * initialization include FLD lookup */
+       LASSERT(lod->lod_initialized);
+
+       /* Init the llog in its own stack */
+       rc = lod_sub_init_llog(env, lod, lod->lod_child);
+       if (rc < 0)
+               RETURN(rc);
+
+       cfs_foreach_bit(ltd->ltd_tgt_bitmap, i) {
+               struct lod_tgt_desc     *tgt;
+
+               tgt = LTD_TGT(ltd, i);
+               rc = lod_sub_init_llog(env, lod, tgt->ltd_tgt);
+               if (rc != 0)
+                       break;
        }
-       lod_putref(lod);
 
        RETURN(rc);
 }
 
+/**
+ * Implementation of lu_device_operations::ldo_prepare() for LOD
+ *
+ * see include/lu_object.h for the details.
+ */
 static int lod_prepare(const struct lu_env *env, struct lu_device *pdev,
                       struct lu_device *cdev)
 {
-       struct lod_device   *lod = lu2lod_dev(cdev);
-       struct lu_device    *next = &lod->lod_child->dd_lu_dev;
-       int                  rc;
+       struct lod_device       *lod = lu2lod_dev(cdev);
+       struct lu_device        *next = &lod->lod_child->dd_lu_dev;
+       struct lu_fid           *fid = &lod_env_info(env)->lti_fid;
+       int                     rc;
+       struct dt_object        *root;
+       struct dt_object        *dto;
+       __u32                   index;
        ENTRY;
 
        rc = next->ld_ops->ldo_prepare(env, pdev, next);
@@ -267,6 +982,49 @@ static int lod_prepare(const struct lu_env *env, struct lu_device *pdev,
 
        lod->lod_initialized = 1;
 
+       rc = dt_root_get(env, lod->lod_child, fid);
+       if (rc < 0)
+               RETURN(rc);
+
+       root = dt_locate(env, lod->lod_child, fid);
+       if (IS_ERR(root))
+               RETURN(PTR_ERR(root));
+
+       /* Create update log object */
+       index = lu_site2seq(lod2lu_dev(lod)->ld_site)->ss_node_id;
+       lu_update_log_fid(fid, index);
+
+       dto = local_file_find_or_create_with_fid(env, lod->lod_child,
+                                                fid, root,
+                                                lod_update_log_name,
+                                                S_IFREG | S_IRUGO | S_IWUSR);
+       if (IS_ERR(dto))
+               GOTO(out_put, rc = PTR_ERR(dto));
+
+       lu_object_put(env, &dto->do_lu);
+
+       /* Create update log dir */
+       lu_update_log_dir_fid(fid, index);
+       dto = local_file_find_or_create_with_fid(env, lod->lod_child,
+                                                fid, root,
+                                                lod_update_log_dir_name,
+                                                S_IFDIR | S_IRUGO | S_IWUSR);
+       if (IS_ERR(dto))
+               GOTO(out_put, rc = PTR_ERR(dto));
+
+       lu_object_put(env, &dto->do_lu);
+
+       rc = lod_prepare_distribute_txn(env, lod);
+       if (rc != 0)
+               GOTO(out_put, rc);
+
+       rc = lod_sub_init_llogs(env, lod);
+       if (rc != 0)
+               GOTO(out_put, rc);
+
+out_put:
+       lu_object_put(env, &root->do_lu);
+
        RETURN(rc);
 }
 
@@ -277,36 +1035,92 @@ const struct lu_device_operations lod_lu_ops = {
        .ldo_prepare            = lod_prepare,
 };
 
+/**
+ * Implementation of dt_device_operations::dt_root_get() for LOD
+ *
+ * see include/dt_object.h for the details.
+ */
 static int lod_root_get(const struct lu_env *env,
                        struct dt_device *dev, struct lu_fid *f)
 {
        return dt_root_get(env, dt2lod_dev(dev)->lod_child, f);
 }
 
+/**
+ * Implementation of dt_device_operations::dt_statfs() for LOD
+ *
+ * see include/dt_object.h for the details.
+ */
 static int lod_statfs(const struct lu_env *env,
                      struct dt_device *dev, struct obd_statfs *sfs)
 {
        return dt_statfs(env, dt2lod_dev(dev)->lod_child, sfs);
 }
 
+/**
+ * Implementation of dt_device_operations::dt_trans_create() for LOD
+ *
+ * Creates a transaction using local (to this node) OSD.
+ *
+ * see include/dt_object.h for the details.
+ */
 static struct thandle *lod_trans_create(const struct lu_env *env,
-                                       struct dt_device *dev)
+                                       struct dt_device *dt)
 {
-       return dt_trans_create(env, dt2lod_dev(dev)->lod_child);
+       struct thandle *th;
+
+       th = top_trans_create(env, dt2lod_dev(dt)->lod_child);
+       if (IS_ERR(th))
+               return th;
+
+       th->th_dev = dt;
+
+       return th;
 }
 
-static int lod_trans_start(const struct lu_env *env, struct dt_device *dev,
+/**
+ * Implementation of dt_device_operations::dt_trans_start() for LOD
+ *
+ * Starts the set of local transactions using the targets involved
+ * in declare phase. Initial support for the distributed transactions.
+ *
+ * see include/dt_object.h for the details.
+ */
+static int lod_trans_start(const struct lu_env *env, struct dt_device *dt,
                           struct thandle *th)
 {
-       return dt_trans_start(env, dt2lod_dev(dev)->lod_child, th);
+       return top_trans_start(env, dt2lod_dev(dt)->lod_child, th);
 }
 
-static int lod_trans_stop(const struct lu_env *env, struct thandle *th)
+static int lod_trans_cb_add(struct thandle *th,
+                           struct dt_txn_commit_cb *dcb)
 {
-       /* XXX: we don't know next device, will be fixed with DNE */
-       return dt_trans_stop(env, th->th_dev, th);
+       struct top_thandle      *top_th = container_of(th, struct top_thandle,
+                                                      tt_super);
+       return dt_trans_cb_add(top_th->tt_master_sub_thandle, dcb);
 }
 
+/**
+ * Implementation of dt_device_operations::dt_trans_stop() for LOD
+ *
+ * Stops the set of local transactions using the targets involved
+ * in declare phase. Initial support for the distributed transactions.
+ *
+ * see include/dt_object.h for the details.
+ */
+static int lod_trans_stop(const struct lu_env *env, struct dt_device *dt,
+                         struct thandle *th)
+{
+       return top_trans_stop(env, dt2lod_dev(dt)->lod_child, th);
+}
+
+/**
+ * Implementation of dt_device_operations::dt_conf_get() for LOD
+ *
+ * Currently returns the configuration provided by the local OSD.
+ *
+ * see include/dt_object.h for the details.
+ */
 static void lod_conf_get(const struct lu_env *env,
                         const struct dt_device *dev,
                         struct dt_device_param *param)
@@ -314,14 +1128,23 @@ static void lod_conf_get(const struct lu_env *env,
        dt_conf_get(env, dt2lod_dev((struct dt_device *)dev)->lod_child, param);
 }
 
+/**
+ * Implementation of dt_device_operations::dt_sync() for LOD
+ *
+ * Syncs all known OST targets. Very very expensive and used
+ * rarely by LFSCK now. Should not be used in general.
+ *
+ * see include/dt_object.h for the details.
+ */
 static int lod_sync(const struct lu_env *env, struct dt_device *dev)
 {
        struct lod_device   *lod = dt2lod_dev(dev);
        struct lod_ost_desc *ost;
-       int                  rc = 0, i;
+       unsigned int         i;
+       int                  rc = 0;
        ENTRY;
 
-       lod_getref(lod);
+       lod_getref(&lod->lod_ost_descs);
        lod_foreach_ost(lod, i) {
                ost = OST_TGT(lod, i);
                LASSERT(ost && ost->ltd_ost);
@@ -332,31 +1155,37 @@ static int lod_sync(const struct lu_env *env, struct dt_device *dev)
                        break;
                }
        }
-       lod_putref(lod);
+       lod_putref(lod, &lod->lod_ost_descs);
        if (rc == 0)
                rc = dt_sync(env, lod->lod_child);
 
        RETURN(rc);
 }
 
+/**
+ * Implementation of dt_device_operations::dt_ro() for LOD
+ *
+ * Turns local OSD read-only, used for the testing only.
+ *
+ * see include/dt_object.h for the details.
+ */
 static int lod_ro(const struct lu_env *env, struct dt_device *dev)
 {
        return dt_ro(env, dt2lod_dev(dev)->lod_child);
 }
 
+/**
+ * Implementation of dt_device_operations::dt_commit_async() for LOD
+ *
+ * Asks local OSD to commit sooner.
+ *
+ * see include/dt_object.h for the details.
+ */
 static int lod_commit_async(const struct lu_env *env, struct dt_device *dev)
 {
        return dt_commit_async(env, dt2lod_dev(dev)->lod_child);
 }
 
-static int lod_init_capa_ctxt(const struct lu_env *env, struct dt_device *dev,
-                             int mode, unsigned long timeout,
-                             __u32 alg, struct lustre_capa_key *keys)
-{
-       struct dt_device *next = dt2lod_dev(dev)->lod_child;
-       return dt_init_capa_ctxt(env, next, mode, timeout, alg, keys);
-}
-
 static const struct dt_device_operations lod_dt_ops = {
        .dt_root_get         = lod_root_get,
        .dt_statfs           = lod_statfs,
@@ -367,9 +1196,23 @@ static const struct dt_device_operations lod_dt_ops = {
        .dt_sync             = lod_sync,
        .dt_ro               = lod_ro,
        .dt_commit_async     = lod_commit_async,
-       .dt_init_capa_ctxt   = lod_init_capa_ctxt,
+       .dt_trans_cb_add     = lod_trans_cb_add,
 };
 
+/**
+ * Connect to a local OSD.
+ *
+ * Used to connect to the local OSD at mount. OSD name is taken from the
+ * configuration command passed. This connection is used to identify LU
+ * site and pin the OSD from early removal.
+ *
+ * \param[in] env              LU environment provided by the caller
+ * \param[in] lod              lod device
+ * \param[in] cfg              configuration command to apply
+ *
+ * \retval 0                   on success
+ * \retval negative            negated errno on error
+ **/
 static int lod_connect_to_osd(const struct lu_env *env, struct lod_device *lod,
                              struct lustre_cfg *cfg)
 {
@@ -454,6 +1297,51 @@ out:
        RETURN(rc);
 }
 
+/**
+ * Allocate and initialize target table.
+ *
+ * A helper function to initialize the target table and allocate
+ * a bitmap of the available targets.
+ *
+ * \param[in] ltd              target's table to initialize
+ *
+ * \retval 0                   on success
+ * \retval negative            negated errno on error
+ **/
+static int lod_tgt_desc_init(struct lod_tgt_descs *ltd)
+{
+       mutex_init(&ltd->ltd_mutex);
+       init_rwsem(&ltd->ltd_rw_sem);
+
+       /* the OST array and bitmap are allocated/grown dynamically as OSTs are
+        * added to the LOD, see lod_add_device() */
+       ltd->ltd_tgt_bitmap = CFS_ALLOCATE_BITMAP(32);
+       if (ltd->ltd_tgt_bitmap == NULL)
+               RETURN(-ENOMEM);
+
+       ltd->ltd_tgts_size  = 32;
+       ltd->ltd_tgtnr      = 0;
+
+       ltd->ltd_death_row = 0;
+       ltd->ltd_refcount  = 0;
+       return 0;
+}
+
+/**
+ * Initialize LOD device at setup.
+ *
+ * Initializes the given LOD device using the original configuration command.
+ * The function initiates a connection to the local OSD and initializes few
+ * internal structures like pools, target tables, etc.
+ *
+ * \param[in] env              LU environment provided by the caller
+ * \param[in] lod              lod device
+ * \param[in] ldt              not used
+ * \param[in] cfg              configuration command
+ *
+ * \retval 0                   on success
+ * \retval negative            negated errno on error
+ **/
 static int lod_init0(const struct lu_env *env, struct lod_device *lod,
                     struct lu_device_type *ldt, struct lustre_cfg *cfg)
 {
@@ -490,9 +1378,10 @@ static int lod_init0(const struct lu_env *env, struct lod_device *lod,
        if (rc)
                GOTO(out_pools, rc);
 
-       mutex_init(&lod->lod_mutex);
-       init_rwsem(&lod->lod_rw_sem);
        spin_lock_init(&lod->lod_desc_lock);
+       spin_lock_init(&lod->lod_connects_lock);
+       lod_tgt_desc_init(&lod->lod_mdt_descs);
+       lod_tgt_desc_init(&lod->lod_ost_descs);
 
        RETURN(0);
 
@@ -503,6 +1392,13 @@ out_disconnect:
        RETURN(rc);
 }
 
+/**
+ * Implementation of lu_device_type_operations::ldto_device_free() for LOD
+ *
+ * Releases the memory allocated for LOD device.
+ *
+ * see include/lu_object.h for the details.
+ */
 static struct lu_device *lod_device_free(const struct lu_env *env,
                                         struct lu_device *lu)
 {
@@ -510,12 +1406,19 @@ static struct lu_device *lod_device_free(const struct lu_env *env,
        struct lu_device  *next = &lod->lod_child->dd_lu_dev;
        ENTRY;
 
-       LASSERT(cfs_atomic_read(&lu->ld_ref) == 0);
+       LASSERTF(atomic_read(&lu->ld_ref) == 0, "lu is %p\n", lu);
        dt_device_fini(&lod->lod_dt_dev);
        OBD_FREE_PTR(lod);
        RETURN(next);
 }
 
+/**
+ * Implementation of lu_device_type_operations::ldto_device_alloc() for LOD
+ *
+ * Allocates LOD device and calls the helpers to initialize it.
+ *
+ * see include/lu_object.h for the details.
+ */
 static struct lu_device *lod_device_alloc(const struct lu_env *env,
                                          struct lu_device_type *type,
                                          struct lustre_cfg *lcfg)
@@ -541,22 +1444,53 @@ static struct lu_device *lod_device_alloc(const struct lu_env *env,
        return lu_dev;
 }
 
+/**
+ * Implementation of lu_device_type_operations::ldto_device_fini() for LOD
+ *
+ * Releases the internal resources used by LOD device.
+ *
+ * see include/lu_object.h for the details.
+ */
 static struct lu_device *lod_device_fini(const struct lu_env *env,
                                         struct lu_device *d)
 {
        struct lod_device *lod = lu2lod_dev(d);
+       int                rc;
        ENTRY;
 
        lod_pools_fini(lod);
 
        lod_procfs_fini(lod);
 
+       rc = lod_fini_tgt(env, lod, &lod->lod_ost_descs, true);
+       if (rc)
+               CERROR("%s:can not fini ost descs %d\n",
+                       lod2obd(lod)->obd_name, rc);
+
+       rc = lod_fini_tgt(env, lod, &lod->lod_mdt_descs, false);
+       if (rc)
+               CERROR("%s:can not fini mdt descs %d\n",
+                       lod2obd(lod)->obd_name, rc);
+
        RETURN(NULL);
 }
 
-/*
- * we use exports to track all LOD users
- */
+/**
+ * Implementation of obd_ops::o_connect() for LOD
+ *
+ * Used to track all the users of this specific LOD device,
+ * so the device stays up until the last user disconnected.
+ *
+ * \param[in] env              LU environment provided by the caller
+ * \param[out] exp             export the caller will be using to access LOD
+ * \param[in] obd              OBD device representing LOD device
+ * \param[in] cluuid           unique identifier of the caller
+ * \param[in] data             not used
+ * \param[in] localdata                not used
+ *
+ * \retval 0                   on success
+ * \retval negative            negated errno on error
+ **/
 static int lod_obd_connect(const struct lu_env *env, struct obd_export **exp,
                           struct obd_device *obd, struct obd_uuid *cluuid,
                           struct obd_connect_data *data, void *localdata)
@@ -574,19 +1508,28 @@ static int lod_obd_connect(const struct lu_env *env, struct obd_export **exp,
 
        *exp = class_conn2export(&conn);
 
-       mutex_lock(&lod->lod_mutex);
+       spin_lock(&lod->lod_connects_lock);
        lod->lod_connects++;
        /* at the moment we expect the only user */
        LASSERT(lod->lod_connects == 1);
-       mutex_unlock(&lod->lod_mutex);
+       spin_unlock(&lod->lod_connects_lock);
 
        RETURN(0);
 }
 
-/*
- * once last export (we don't count self-export) disappeared
- * lod can be released
- */
+/**
+ *
+ * Implementation of obd_ops::o_disconnect() for LOD
+ *
+ * When the caller doesn't need to use this LOD instance, it calls
+ * obd_disconnect() and LOD releases corresponding export/reference count.
+ * Once all the users gone, LOD device is released.
+ *
+ * \param[in] exp              export provided to the caller in obd_connect()
+ *
+ * \retval 0                   on success
+ * \retval negative            negated errno on error
+ **/
 static int lod_obd_disconnect(struct obd_export *exp)
 {
        struct obd_device *obd = exp->exp_obd;
@@ -595,16 +1538,16 @@ static int lod_obd_disconnect(struct obd_export *exp)
        ENTRY;
 
        /* Only disconnect the underlying layers on the final disconnect. */
-       mutex_lock(&lod->lod_mutex);
+       spin_lock(&lod->lod_connects_lock);
        lod->lod_connects--;
        if (lod->lod_connects != 0) {
                /* why should there be more than 1 connect? */
-               mutex_unlock(&lod->lod_mutex);
+               spin_unlock(&lod->lod_connects_lock);
                CERROR("%s: disconnect #%d\n", exp->exp_obd->obd_name,
                       lod->lod_connects);
                goto out;
        }
-       mutex_unlock(&lod->lod_mutex);
+       spin_unlock(&lod->lod_connects_lock);
 
        /* the last user of lod has gone, let's release the device */
        release = 1;
@@ -632,6 +1575,7 @@ static void lod_key_fini(const struct lu_context *ctx,
                info->lti_ea_store = NULL;
                info->lti_ea_store_size = 0;
        }
+       lu_buf_free(&info->lti_linkea_buf);
        OBD_FREE_PTR(info);
 }
 
@@ -660,25 +1604,79 @@ static struct lu_device_type lod_device_type = {
        .ldt_ctx_tags = LCT_MD_THREAD,
 };
 
-static int lod_obd_health_check(const struct lu_env *env,
-               struct obd_device *obd)
+/**
+ * Implementation of obd_ops::o_get_info() for LOD
+ *
+ * Currently, there is only one supported key: KEY_OSP_CONNECTED , to provide
+ * the caller binary status whether LOD has seen connection to any OST target.
+ * It will also check if the MDT update log context being initialized (if
+ * needed).
+ *
+ * \param[in] env              LU environment provided by the caller
+ * \param[in] exp              export of the caller
+ * \param[in] keylen           len of the key
+ * \param[in] key              the key
+ * \param[in] vallen           not used
+ * \param[in] val              not used
+ *
+ * \retval                     0 if a connection was seen
+ * \retval                     -EAGAIN if LOD isn't running yet or no
+ *                             connection has been seen yet
+ * \retval                     -EINVAL if not supported key is requested
+ **/
+static int lod_obd_get_info(const struct lu_env *env, struct obd_export *exp,
+                           __u32 keylen, void *key, __u32 *vallen, void *val)
 {
-       struct lod_device   *d = lu2lod_dev(obd->obd_lu_dev);
-       struct lod_ost_desc *ost;
-       int                  i, rc = 1;
-       ENTRY;
+       int rc = -EINVAL;
+
+       if (KEY_IS(KEY_OSP_CONNECTED)) {
+               struct obd_device       *obd = exp->exp_obd;
+               struct lod_device       *d;
+               struct lod_tgt_desc     *tgt;
+               unsigned int            i;
+               int                     rc = 1;
+
+               if (!obd->obd_set_up || obd->obd_stopping)
+                       RETURN(-EAGAIN);
+
+               d = lu2lod_dev(obd->obd_lu_dev);
+               lod_getref(&d->lod_ost_descs);
+               lod_foreach_ost(d, i) {
+                       tgt = OST_TGT(d, i);
+                       LASSERT(tgt && tgt->ltd_tgt);
+                       rc = obd_get_info(env, tgt->ltd_exp, keylen, key,
+                                         vallen, val);
+                       /* one healthy device is enough */
+                       if (rc == 0)
+                               break;
+               }
+               lod_putref(d, &d->lod_ost_descs);
+
+               lod_getref(&d->lod_mdt_descs);
+               lod_foreach_mdt(d, i) {
+                       struct llog_ctxt *ctxt;
+
+                       tgt = MDT_TGT(d, i);
+                       LASSERT(tgt != NULL);
+                       LASSERT(tgt->ltd_tgt != NULL);
+                       ctxt = llog_get_context(tgt->ltd_tgt->dd_lu_dev.ld_obd,
+                                               LLOG_UPDATELOG_ORIG_CTXT);
+                       if (ctxt == NULL) {
+                               rc = -EAGAIN;
+                               break;
+                       }
+                       if (ctxt->loc_handle == NULL) {
+                               rc = -EAGAIN;
+                               llog_ctxt_put(ctxt);
+                               break;
+                       }
+                       llog_ctxt_put(ctxt);
+               }
+               lod_putref(d, &d->lod_mdt_descs);
 
-       LASSERT(d);
-       lod_getref(d);
-       lod_foreach_ost(d, i) {
-               ost = OST_TGT(d, i);
-               LASSERT(ost && ost->ltd_ost);
-               rc = obd_health_check(env, ost->ltd_exp->exp_obd);
-               /* one healthy device is enough */
-               if (rc == 0)
-                       break;
+               RETURN(rc);
        }
-       lod_putref(d);
+
        RETURN(rc);
 }
 
@@ -686,7 +1684,7 @@ static struct obd_ops lod_obd_device_ops = {
        .o_owner        = THIS_MODULE,
        .o_connect      = lod_obd_connect,
        .o_disconnect   = lod_obd_disconnect,
-       .o_health_check = lod_obd_health_check,
+       .o_get_info     = lod_obd_get_info,
        .o_pool_new     = lod_pool_new,
        .o_pool_rem     = lod_pool_remove,
        .o_pool_add     = lod_pool_add,
@@ -695,17 +1693,14 @@ static struct obd_ops lod_obd_device_ops = {
 
 static int __init lod_mod_init(void)
 {
-       struct lprocfs_static_vars  lvars = { 0 };
-       cfs_proc_dir_entry_t       *lov_proc_dir;
-       int                         rc;
+       struct obd_type *type;
+       int rc;
 
        rc = lu_kmem_init(lod_caches);
        if (rc)
                return rc;
 
-       lprocfs_lod_init_vars(&lvars);
-
-       rc = class_register_type(&lod_obd_device_ops, NULL, lvars.module_vars,
+       rc = class_register_type(&lod_obd_device_ops, NULL, true, NULL,
                                 LUSTRE_LOD_NAME, &lod_device_type);
        if (rc) {
                lu_kmem_fini(lod_caches);
@@ -713,28 +1708,28 @@ static int __init lod_mod_init(void)
        }
 
        /* create "lov" entry in procfs for compatibility purposes */
-       lov_proc_dir = lprocfs_srch(proc_lustre_root, "lov");
-       if (lov_proc_dir == NULL) {
-               lov_proc_dir = lprocfs_register("lov", proc_lustre_root,
-                                               NULL, NULL);
-               if (IS_ERR(lov_proc_dir))
-                       CERROR("lod: can't create compat entry \"lov\": %d\n",
-                              (int)PTR_ERR(lov_proc_dir));
-       }
+       type = class_search_type(LUSTRE_LOV_NAME);
+       if (type != NULL && type->typ_procroot != NULL)
+               return rc;
 
+       type = class_search_type(LUSTRE_LOD_NAME);
+       type->typ_procsym = lprocfs_register("lov", proc_lustre_root,
+                                            NULL, NULL);
+       if (IS_ERR(type->typ_procsym)) {
+               CERROR("lod: can't create compat entry \"lov\": %d\n",
+                      (int)PTR_ERR(type->typ_procsym));
+               type->typ_procsym = NULL;
+       }
        return rc;
 }
 
 static void __exit lod_mod_exit(void)
 {
-
-       lprocfs_try_remove_proc_entry("lov", proc_lustre_root);
-
        class_unregister_type(LUSTRE_LOD_NAME);
        lu_kmem_fini(lod_caches);
 }
 
-MODULE_AUTHOR("Whamcloud, Inc. <http://www.whamcloud.com/>");
+MODULE_AUTHOR("Intel Corporation. <https://wiki.hpdd.intel.com/>");
 MODULE_DESCRIPTION("Lustre Logical Object Device ("LUSTRE_LOD_NAME")");
 MODULE_LICENSE("GPL");