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LU-6684 lfsck: set the lfsck notify as interruptable
[fs/lustre-release.git] / lustre / lfsck / lfsck_lib.c
index c8e26f0..139c95b 100644 (file)
@@ -20,7 +20,7 @@
  * GPL HEADER END
  */
 /*
- * Copyright (c) 2012, 2013, Intel Corporation.
+ * Copyright (c) 2013, 2015, Intel Corporation.
  */
 /*
  * lustre/lfsck/lfsck_lib.c
@@ -30,6 +30,8 @@
 
 #define DEBUG_SUBSYSTEM S_LFSCK
 
+#include <linux/kthread.h>
+#include <linux/sched.h>
 #include <libcfs/list.h>
 #include <lu_object.h>
 #include <dt_object.h>
@@ -42,6 +44,8 @@
 
 #include "lfsck_internal.h"
 
+#define LFSCK_CHECKPOINT_SKIP  1
+
 /* define lfsck thread key */
 LU_KEY_INIT(lfsck, struct lfsck_thread_info);
 
@@ -51,6 +55,7 @@ static void lfsck_key_fini(const struct lu_context *ctx,
        struct lfsck_thread_info *info = data;
 
        lu_buf_free(&info->lti_linkea_buf);
+       lu_buf_free(&info->lti_linkea_buf2);
        lu_buf_free(&info->lti_big_buf);
        OBD_FREE_PTR(info);
 }
@@ -58,7 +63,7 @@ static void lfsck_key_fini(const struct lu_context *ctx,
 LU_CONTEXT_KEY_DEFINE(lfsck, LCT_MD_THREAD | LCT_DT_THREAD);
 LU_KEY_INIT_GENERIC(lfsck);
 
-static CFS_LIST_HEAD(lfsck_instance_list);
+static struct list_head lfsck_instance_list;
 static struct list_head lfsck_ost_orphan_list;
 static struct list_head lfsck_mdt_orphan_list;
 static DEFINE_SPINLOCK(lfsck_instance_lock);
@@ -92,9 +97,18 @@ const char *lfsck_param_names[] = {
        "failout",
        "dryrun",
        "all_targets",
+       "broadcast",
+       "orphan",
+       "create_ostobj",
+       "create_mdtobj",
        NULL
 };
 
+enum lfsck_verify_lpf_types {
+       LVLT_BY_BOOKMARK        = 0,
+       LVLT_BY_NAMEENTRY       = 1,
+};
+
 const char *lfsck_status2names(enum lfsck_status status)
 {
        if (unlikely(status < 0 || status >= LS_MAX))
@@ -136,14 +150,16 @@ static void lfsck_tgt_descs_fini(struct lfsck_tgt_descs *ltds)
        }
 
        cfs_foreach_bit(ltds->ltd_tgts_bitmap, idx) {
-               ltd = LTD_TGT(ltds, idx);
+               ltd = lfsck_ltd2tgt(ltds, idx);
                if (likely(ltd != NULL)) {
                        LASSERT(list_empty(&ltd->ltd_layout_list));
                        LASSERT(list_empty(&ltd->ltd_layout_phase_list));
+                       LASSERT(list_empty(&ltd->ltd_namespace_list));
+                       LASSERT(list_empty(&ltd->ltd_namespace_phase_list));
 
                        ltds->ltd_tgtnr--;
                        cfs_bitmap_clear(ltds->ltd_tgts_bitmap, idx);
-                       LTD_TGT(ltds, idx) = NULL;
+                       lfsck_assign_tgt(ltds, NULL, idx);
                        lfsck_tgt_put(ltd);
                }
        }
@@ -215,7 +231,7 @@ static int __lfsck_add_target(const struct lu_env *env,
                        GOTO(unlock, rc = -ENOMEM);
        }
 
-       LTD_TGT(ltds, index) = ltd;
+       lfsck_assign_tgt(ltds, ltd, index);
        cfs_bitmap_set(ltds->ltd_tgts_bitmap, index);
        ltds->ltd_tgtnr++;
 
@@ -241,11 +257,9 @@ static int lfsck_add_target_from_orphan(const struct lu_env *env,
 again:
        spin_lock(&lfsck_instance_lock);
        list_for_each_entry_safe(ltd, next, head, ltd_orphan_list) {
-               if (ltd->ltd_key == lfsck->li_bottom) {
-                       list_del_init(&ltd->ltd_orphan_list);
-                       list_add_tail(&ltd->ltd_orphan_list,
-                                     &ltds->ltd_orphan);
-               }
+               if (ltd->ltd_key == lfsck->li_bottom)
+                       list_move_tail(&ltd->ltd_orphan_list,
+                                      &ltds->ltd_orphan);
        }
        spin_unlock(&lfsck_instance_lock);
 
@@ -276,11 +290,12 @@ again:
 }
 
 static inline struct lfsck_component *
-__lfsck_component_find(struct lfsck_instance *lfsck, __u16 type, cfs_list_t *list)
+__lfsck_component_find(struct lfsck_instance *lfsck, __u16 type,
+                      struct list_head *list)
 {
        struct lfsck_component *com;
 
-       cfs_list_for_each_entry(com, list, lc_link) {
+       list_for_each_entry(com, list, lc_link) {
                if (com->lc_type == type)
                        return com;
        }
@@ -314,10 +329,10 @@ unlock:
 void lfsck_component_cleanup(const struct lu_env *env,
                             struct lfsck_component *com)
 {
-       if (!cfs_list_empty(&com->lc_link))
-               cfs_list_del_init(&com->lc_link);
-       if (!cfs_list_empty(&com->lc_link_dir))
-               cfs_list_del_init(&com->lc_link_dir);
+       if (!list_empty(&com->lc_link))
+               list_del_init(&com->lc_link);
+       if (!list_empty(&com->lc_link_dir))
+               list_del_init(&com->lc_link_dir);
 
        lfsck_component_put(env, com);
 }
@@ -348,27 +363,298 @@ int lfsck_fid_alloc(const struct lu_env *env, struct lfsck_instance *lfsck,
        RETURN(rc);
 }
 
-static const char dot[] = ".";
-static const char dotdot[] = "..";
+static int __lfsck_ibits_lock(const struct lu_env *env,
+                             struct lfsck_instance *lfsck,
+                             struct dt_object *obj, struct ldlm_res_id *resid,
+                             struct lustre_handle *lh, __u64 bits,
+                             enum ldlm_mode mode)
+{
+       struct lfsck_thread_info        *info   = lfsck_env_info(env);
+       union ldlm_policy_data          *policy = &info->lti_policy;
+       __u64                            flags  = LDLM_FL_ATOMIC_CB;
+       int                              rc;
+
+       LASSERT(lfsck->li_namespace != NULL);
+
+       memset(policy, 0, sizeof(*policy));
+       policy->l_inodebits.bits = bits;
+       if (dt_object_remote(obj)) {
+               struct ldlm_enqueue_info *einfo = &info->lti_einfo;
+
+               memset(einfo, 0, sizeof(*einfo));
+               einfo->ei_type = LDLM_IBITS;
+               einfo->ei_mode = mode;
+               einfo->ei_cb_bl = ldlm_blocking_ast;
+               einfo->ei_cb_cp = ldlm_completion_ast;
+               einfo->ei_res_id = resid;
+
+               rc = dt_object_lock(env, obj, lh, einfo, policy);
+       } else {
+               rc = ldlm_cli_enqueue_local(lfsck->li_namespace, resid,
+                                           LDLM_IBITS, policy, mode,
+                                           &flags, ldlm_blocking_ast,
+                                           ldlm_completion_ast, NULL, NULL,
+                                           0, LVB_T_NONE, NULL, lh);
+       }
+
+       if (rc == ELDLM_OK) {
+               rc = 0;
+       } else {
+               memset(lh, 0, sizeof(*lh));
+               rc = -EIO;
+       }
+
+       return rc;
+}
+
+/**
+ * Request the specified ibits lock for the given object.
+ *
+ * Before the LFSCK modifying on the namespace visible object,
+ * it needs to acquire related ibits ldlm lock.
+ *
+ * \param[in] env      pointer to the thread context
+ * \param[in] lfsck    pointer to the lfsck instance
+ * \param[in] obj      pointer to the dt_object to be locked
+ * \param[out] lh      pointer to the lock handle
+ * \param[in] bits     the bits for the ldlm lock to be acquired
+ * \param[in] mode     the mode for the ldlm lock to be acquired
+ *
+ * \retval             0 for success
+ * \retval             negative error number on failure
+ */
+int lfsck_ibits_lock(const struct lu_env *env, struct lfsck_instance *lfsck,
+                    struct dt_object *obj, struct lustre_handle *lh,
+                    __u64 bits, enum ldlm_mode mode)
+{
+       struct ldlm_res_id *resid = &lfsck_env_info(env)->lti_resid;
+
+       LASSERT(!lustre_handle_is_used(lh));
+
+       fid_build_reg_res_name(lfsck_dto2fid(obj), resid);
+       return __lfsck_ibits_lock(env, lfsck, obj, resid, lh, bits, mode);
+}
+
+/**
+ * Release the the specified ibits lock.
+ *
+ * If the lock has been acquired before, release it
+ * and cleanup the handle. Otherwise, do nothing.
+ *
+ * \param[in] lh       pointer to the lock handle
+ * \param[in] mode     the mode for the ldlm lock to be released
+ */
+void lfsck_ibits_unlock(struct lustre_handle *lh, enum ldlm_mode mode)
+{
+       if (lustre_handle_is_used(lh)) {
+               ldlm_lock_decref(lh, mode);
+               memset(lh, 0, sizeof(*lh));
+       }
+}
+
+/**
+ * Request compound ibits locks for the given <obj, name> pairs.
+ *
+ * Before the LFSCK modifying on the namespace visible object, it needs to
+ * acquire related ibits ldlm lock. Usually, we can use lfsck_ibits_lock for
+ * the lock purpose. But the simple lfsck_ibits_lock for directory-based
+ * modificationis (such as insert name entry to the directory) may be too
+ * coarse-grained and not efficient.
+ *
+ * The lfsck_lock() will request compound ibits locks on the specified
+ * <obj, name> pairs: the PDO (Parallel Directory Operations) ibits (UPDATE)
+ * lock on the directory object, and the regular ibits lock on the name hash.
+ *
+ * \param[in] env      pointer to the thread context
+ * \param[in] lfsck    pointer to the lfsck instance
+ * \param[in] obj      pointer to the dt_object to be locked
+ * \param[in] name     used for building the PDO lock resource
+ * \param[out] llh     pointer to the lfsck_lock_handle
+ * \param[in] bits     the bits for the ldlm lock to be acquired
+ * \param[in] mode     the mode for the ldlm lock to be acquired
+ *
+ * \retval             0 for success
+ * \retval             negative error number on failure
+ */
+int lfsck_lock(const struct lu_env *env, struct lfsck_instance *lfsck,
+              struct dt_object *obj, const char *name,
+              struct lfsck_lock_handle *llh, __u64 bits, enum ldlm_mode mode)
+{
+       struct ldlm_res_id *resid = &lfsck_env_info(env)->lti_resid;
+       int                 rc;
+
+       LASSERT(S_ISDIR(lfsck_object_type(obj)));
+       LASSERT(name != NULL);
+       LASSERT(name[0] != 0);
+       LASSERT(!lustre_handle_is_used(&llh->llh_pdo_lh));
+       LASSERT(!lustre_handle_is_used(&llh->llh_reg_lh));
+
+       switch (mode) {
+       case LCK_EX:
+               llh->llh_pdo_mode = LCK_EX;
+               break;
+       case LCK_PW:
+               llh->llh_pdo_mode = LCK_CW;
+               break;
+       case LCK_PR:
+               llh->llh_pdo_mode = LCK_CR;
+               break;
+       default:
+               CDEBUG(D_LFSCK, "%s: unexpected PDO lock mode %u on the obj "
+                      DFID"\n", lfsck_lfsck2name(lfsck), mode,
+                      PFID(lfsck_dto2fid(obj)));
+               LBUG();
+       }
+
+       fid_build_reg_res_name(lfsck_dto2fid(obj), resid);
+       rc = __lfsck_ibits_lock(env, lfsck, obj, resid, &llh->llh_pdo_lh,
+                               MDS_INODELOCK_UPDATE, llh->llh_pdo_mode);
+       if (rc != 0)
+               return rc;
+
+       llh->llh_reg_mode = mode;
+       resid->name[LUSTRE_RES_ID_HSH_OFF] = full_name_hash(name, strlen(name));
+       LASSERT(resid->name[LUSTRE_RES_ID_HSH_OFF] != 0);
+       rc = __lfsck_ibits_lock(env, lfsck, obj, resid, &llh->llh_reg_lh,
+                               bits, llh->llh_reg_mode);
+       if (rc != 0)
+               lfsck_ibits_unlock(&llh->llh_pdo_lh, llh->llh_pdo_mode);
+
+       return rc;
+}
+
+/**
+ * Release the the compound ibits locks.
+ *
+ * \param[in] llh      pointer to the lfsck_lock_handle to be released
+ */
+void lfsck_unlock(struct lfsck_lock_handle *llh)
+{
+       lfsck_ibits_unlock(&llh->llh_reg_lh, llh->llh_reg_mode);
+       lfsck_ibits_unlock(&llh->llh_pdo_lh, llh->llh_pdo_mode);
+}
+
+int lfsck_find_mdt_idx_by_fid(const struct lu_env *env,
+                             struct lfsck_instance *lfsck,
+                             const struct lu_fid *fid)
+{
+       struct seq_server_site  *ss     = lfsck_dev_site(lfsck);
+       struct lu_seq_range     *range  = &lfsck_env_info(env)->lti_range;
+       int                      rc;
+
+       fld_range_set_mdt(range);
+       rc = fld_server_lookup(env, ss->ss_server_fld, fid_seq(fid), range);
+       if (rc == 0)
+               rc = range->lsr_index;
+
+       return rc;
+}
+
+const char dot[] = ".";
+const char dotdot[] = "..";
+static const char dotlustre[] = ".lustre";
+static const char lostfound[] = "lost+found";
+
+/**
+ * Remove the name entry from the .lustre/lost+found directory.
+ *
+ * No need to care about the object referenced by the name entry,
+ * either the name entry is invalid or redundant, or the referenced
+ * object has been processed or will be handled by others.
+ *
+ * \param[in] env      pointer to the thread context
+ * \param[in] lfsck    pointer to the lfsck instance
+ * \param[in] name     the name for the name entry to be removed
+ *
+ * \retval             0 for success
+ * \retval             negative error number on failure
+ */
+static int lfsck_lpf_remove_name_entry(const struct lu_env *env,
+                                      struct lfsck_instance *lfsck,
+                                      const char *name)
+{
+       struct dt_object        *parent = lfsck->li_lpf_root_obj;
+       struct dt_device        *dev    = lfsck_obj2dev(parent);
+       struct thandle          *th;
+       struct lfsck_lock_handle *llh   = &lfsck_env_info(env)->lti_llh;
+       int                      rc;
+       ENTRY;
+
+       rc = lfsck_lock(env, lfsck, parent, name, llh,
+                       MDS_INODELOCK_UPDATE, LCK_PW);
+       if (rc != 0)
+               RETURN(rc);
+
+       th = dt_trans_create(env, dev);
+       if (IS_ERR(th))
+               GOTO(unlock, rc = PTR_ERR(th));
+
+       rc = dt_declare_delete(env, parent, (const struct dt_key *)name, th);
+       if (rc != 0)
+               GOTO(stop, rc);
+
+       rc = dt_declare_ref_del(env, parent, th);
+       if (rc != 0)
+               GOTO(stop, rc);
+
+       rc = dt_trans_start_local(env, dev, th);
+       if (rc != 0)
+               GOTO(stop, rc);
+
+       rc = dt_delete(env, parent, (const struct dt_key *)name, th);
+       if (rc != 0)
+               GOTO(stop, rc);
+
+       dt_write_lock(env, parent, 0);
+       rc = dt_ref_del(env, parent, th);
+       dt_write_unlock(env, parent);
+
+       GOTO(stop, rc);
+
+stop:
+       dt_trans_stop(env, dev, th);
+
+unlock:
+       lfsck_unlock(llh);
+
+       CDEBUG(D_LFSCK, "%s: remove name entry "DFID"/%s: rc = %d\n",
+              lfsck_lfsck2name(lfsck), PFID(lfsck_dto2fid(parent)), name, rc);
+
+       return rc;
+}
 
 static int lfsck_create_lpf_local(const struct lu_env *env,
                                  struct lfsck_instance *lfsck,
-                                 struct dt_object *parent,
                                  struct dt_object *child,
                                  struct lu_attr *la,
                                  struct dt_object_format *dof,
                                  const char *name)
 {
-       struct dt_device        *dev    = lfsck->li_bottom;
+       struct dt_insert_rec    *rec    = &lfsck_env_info(env)->lti_dt_rec;
+       struct dt_object        *parent = lfsck->li_lpf_root_obj;
+       struct dt_device        *dev    = lfsck_obj2dev(child);
        struct lfsck_bookmark   *bk     = &lfsck->li_bookmark_ram;
        struct dt_object        *bk_obj = lfsck->li_bookmark_obj;
-       const struct lu_fid     *cfid   = lu_object_fid(&child->do_lu);
+       const struct lu_fid     *cfid   = lfsck_dto2fid(child);
        struct thandle          *th     = NULL;
+       struct linkea_data       ldata  = { NULL };
+       struct lu_buf            linkea_buf;
+       const struct lu_name    *cname;
        loff_t                   pos    = 0;
        int                      len    = sizeof(struct lfsck_bookmark);
-       int                      rc     = 0;
+       int                      rc;
        ENTRY;
 
+       rc = linkea_data_new(&ldata,
+                            &lfsck_env_info(env)->lti_linkea_buf2);
+       if (rc != 0)
+               RETURN(rc);
+
+       cname = lfsck_name_get_const(env, name, strlen(name));
+       rc = linkea_add_buf(&ldata, cname, lfsck_dto2fid(parent));
+       if (rc != 0)
+               RETURN(rc);
+
        th = dt_trans_create(env, dev);
        if (IS_ERR(th))
                RETURN(PTR_ERR(th));
@@ -378,23 +664,51 @@ static int lfsck_create_lpf_local(const struct lu_env *env,
        if (rc != 0)
                GOTO(stop, rc);
 
+       if (!dt_try_as_dir(env, child))
+               GOTO(stop, rc = -ENOTDIR);
+
        /* 2a. increase child nlink */
        rc = dt_declare_ref_add(env, child, th);
        if (rc != 0)
                GOTO(stop, rc);
 
-       /* 3a. insert name into parent dir */
-       rc = dt_declare_insert(env, parent, (const struct dt_rec *)cfid,
+       /* 3a. insert dot into child dir */
+       rec->rec_type = S_IFDIR;
+       rec->rec_fid = cfid;
+       rc = dt_declare_insert(env, child, (const struct dt_rec *)rec,
+                              (const struct dt_key *)dot, th);
+       if (rc != 0)
+               GOTO(stop, rc);
+
+       /* 4a. insert dotdot into child dir */
+       rec->rec_fid = &LU_LPF_FID;
+       rc = dt_declare_insert(env, child, (const struct dt_rec *)rec,
+                              (const struct dt_key *)dotdot, th);
+       if (rc != 0)
+               GOTO(stop, rc);
+
+       /* 5a. insert linkEA for child */
+       lfsck_buf_init(&linkea_buf, ldata.ld_buf->lb_buf,
+                      ldata.ld_leh->leh_len);
+       rc = dt_declare_xattr_set(env, child, &linkea_buf,
+                                 XATTR_NAME_LINK, 0, th);
+       if (rc != 0)
+               GOTO(stop, rc);
+
+       /* 6a. insert name into parent dir */
+       rec->rec_type = S_IFDIR;
+       rec->rec_fid = cfid;
+       rc = dt_declare_insert(env, parent, (const struct dt_rec *)rec,
                               (const struct dt_key *)name, th);
        if (rc != 0)
                GOTO(stop, rc);
 
-       /* 4a. increase parent nlink */
+       /* 7a. increase parent nlink */
        rc = dt_declare_ref_add(env, parent, th);
        if (rc != 0)
                GOTO(stop, rc);
 
-       /* 5a. update bookmark */
+       /* 8a. update bookmark */
        rc = dt_declare_record_write(env, bk_obj,
                                     lfsck_buf_get(env, bk, len), 0, th);
        if (rc != 0)
@@ -405,40 +719,46 @@ static int lfsck_create_lpf_local(const struct lu_env *env,
                GOTO(stop, rc);
 
        dt_write_lock(env, child, 0);
-       /* 1b.1 create child */
+       /* 1b. create child */
        rc = dt_create(env, child, la, NULL, dof, th);
        if (rc != 0)
                GOTO(unlock, rc);
 
-       if (unlikely(!dt_try_as_dir(env, child)))
-               GOTO(unlock, rc = -ENOTDIR);
+       /* 2b. increase child nlink */
+       rc = dt_ref_add(env, child, th);
+       if (rc != 0)
+               GOTO(unlock, rc);
 
-       /* 1b.2 insert dot into child dir */
-       rc = dt_insert(env, child, (const struct dt_rec *)cfid,
-                      (const struct dt_key *)dot, th, BYPASS_CAPA, 1);
+       /* 3b. insert dot into child dir */
+       rec->rec_fid = cfid;
+       rc = dt_insert(env, child, (const struct dt_rec *)rec,
+                      (const struct dt_key *)dot, th, 1);
        if (rc != 0)
                GOTO(unlock, rc);
 
-       /* 1b.3 insert dotdot into child dir */
-       rc = dt_insert(env, child, (const struct dt_rec *)&LU_LPF_FID,
-                      (const struct dt_key *)dotdot, th, BYPASS_CAPA, 1);
+       /* 4b. insert dotdot into child dir */
+       rec->rec_fid = &LU_LPF_FID;
+       rc = dt_insert(env, child, (const struct dt_rec *)rec,
+                      (const struct dt_key *)dotdot, th, 1);
        if (rc != 0)
                GOTO(unlock, rc);
 
-       /* 2b. increase child nlink */
-       rc = dt_ref_add(env, child, th);
+       /* 5b. insert linkEA for child. */
+       rc = dt_xattr_set(env, child, &linkea_buf,
+                         XATTR_NAME_LINK, 0, th);
        dt_write_unlock(env, child);
        if (rc != 0)
                GOTO(stop, rc);
 
-       /* 3b. insert name into parent dir */
-       rc = dt_insert(env, parent, (const struct dt_rec *)cfid,
-                      (const struct dt_key *)name, th, BYPASS_CAPA, 1);
+       /* 6b. insert name into parent dir */
+       rec->rec_fid = cfid;
+       rc = dt_insert(env, parent, (const struct dt_rec *)rec,
+                      (const struct dt_key *)name, th, 1);
        if (rc != 0)
                GOTO(stop, rc);
 
        dt_write_lock(env, parent, 0);
-       /* 4b. increase parent nlink */
+       /* 7b. increase parent nlink */
        rc = dt_ref_add(env, parent, th);
        dt_write_unlock(env, parent);
        if (rc != 0)
@@ -447,7 +767,7 @@ static int lfsck_create_lpf_local(const struct lu_env *env,
        bk->lb_lpf_fid = *cfid;
        lfsck_bookmark_cpu_to_le(&lfsck->li_bookmark_disk, bk);
 
-       /* 5b. update bookmark */
+       /* 8b. update bookmark */
        rc = dt_record_write(env, bk_obj,
                             lfsck_buf_get(env, bk, len), &pos, th);
 
@@ -464,22 +784,36 @@ stop:
 
 static int lfsck_create_lpf_remote(const struct lu_env *env,
                                   struct lfsck_instance *lfsck,
-                                  struct dt_object *parent,
                                   struct dt_object *child,
                                   struct lu_attr *la,
                                   struct dt_object_format *dof,
                                   const char *name)
 {
+       struct dt_insert_rec    *rec    = &lfsck_env_info(env)->lti_dt_rec;
+       struct dt_object        *parent = lfsck->li_lpf_root_obj;
        struct lfsck_bookmark   *bk     = &lfsck->li_bookmark_ram;
        struct dt_object        *bk_obj = lfsck->li_bookmark_obj;
-       const struct lu_fid     *cfid   = lu_object_fid(&child->do_lu);
+       const struct lu_fid     *cfid   = lfsck_dto2fid(child);
        struct thandle          *th     = NULL;
+       struct linkea_data       ldata  = { NULL };
+       struct lu_buf            linkea_buf;
+       const struct lu_name    *cname;
        struct dt_device        *dev;
        loff_t                   pos    = 0;
        int                      len    = sizeof(struct lfsck_bookmark);
-       int                      rc     = 0;
+       int                      rc;
        ENTRY;
 
+       rc = linkea_data_new(&ldata,
+                            &lfsck_env_info(env)->lti_linkea_buf2);
+       if (rc != 0)
+               RETURN(rc);
+
+       cname = lfsck_name_get_const(env, name, strlen(name));
+       rc = linkea_add_buf(&ldata, cname, lfsck_dto2fid(parent));
+       if (rc != 0)
+               RETURN(rc);
+
        /* Create .lustre/lost+found/MDTxxxx. */
 
        /* XXX: Currently, cross-MDT create operation needs to create the child
@@ -492,133 +826,145 @@ static int lfsck_create_lpf_remote(const struct lu_env *env,
         *      To avoid more inconsistency, we split the create operation into
         *      two transactions:
         *
-        *      1) create the child locally.
+        *      1) create the child and update the lfsck_bookmark::lb_lpf_fid
+        *         locally.
         *      2) insert the name "MDTXXXX" in the parent ".lustre/lost+found"
-        *         remotely and update the lfsck_bookmark::lb_lpf_fid locally.
+        *         remotely.
         *
-        *      If 1) done but 2) failed, then the worst case is that we lose
-        *      one object locally, which is not a big issue. (can be repaird
-        *      by LFSCK phase III) */
+        *      If 1) done, but 2) failed, then go ahead, the LFSCK will try to
+        *      repair such inconsistency when LFSCK run next time. */
 
-       /* Transaction I: */
+       /* Transaction I: locally */
 
-       dev = lfsck->li_bottom;
+       dev = lfsck_obj2dev(child);
        th = dt_trans_create(env, dev);
        if (IS_ERR(th))
                RETURN(PTR_ERR(th));
 
-       /* 1a. create child locally. */
+       /* 1a. create child */
        rc = dt_declare_create(env, child, la, NULL, dof, th);
        if (rc != 0)
                GOTO(stop, rc);
 
-       /* 2a. increase child nlink locally. */
+       if (!dt_try_as_dir(env, child))
+               GOTO(stop, rc = -ENOTDIR);
+
+       /* 2a. increase child nlink */
        rc = dt_declare_ref_add(env, child, th);
        if (rc != 0)
                GOTO(stop, rc);
 
+       /* 3a. insert dot into child dir */
+       rec->rec_type = S_IFDIR;
+       rec->rec_fid = cfid;
+       rc = dt_declare_insert(env, child, (const struct dt_rec *)rec,
+                              (const struct dt_key *)dot, th);
+       if (rc != 0)
+               GOTO(stop, rc);
+
+       /* 4a. insert dotdot into child dir */
+       rec->rec_fid = &LU_LPF_FID;
+       rc = dt_declare_insert(env, child, (const struct dt_rec *)rec,
+                              (const struct dt_key *)dotdot, th);
+       if (rc != 0)
+               GOTO(stop, rc);
+
+       /* 5a. insert linkEA for child */
+       lfsck_buf_init(&linkea_buf, ldata.ld_buf->lb_buf,
+                      ldata.ld_leh->leh_len);
+       rc = dt_declare_xattr_set(env, child, &linkea_buf,
+                                 XATTR_NAME_LINK, 0, th);
+       if (rc != 0)
+               GOTO(stop, rc);
+
+       /* 6a. update bookmark */
+       rc = dt_declare_record_write(env, bk_obj,
+                                    lfsck_buf_get(env, bk, len), 0, th);
+       if (rc != 0)
+               GOTO(stop, rc);
+
        rc = dt_trans_start_local(env, dev, th);
        if (rc != 0)
                GOTO(stop, rc);
 
        dt_write_lock(env, child, 0);
-       /* 1b. create child locally. */
+       /* 1b. create child */
        rc = dt_create(env, child, la, NULL, dof, th);
        if (rc != 0)
                GOTO(unlock, rc);
 
-       if (unlikely(!dt_try_as_dir(env, child)))
-               GOTO(unlock, rc = -ENOTDIR);
+       /* 2b. increase child nlink */
+       rc = dt_ref_add(env, child, th);
+       if (rc != 0)
+               GOTO(unlock, rc);
 
-       /* 2b.1 insert dot into child dir locally. */
-       rc = dt_insert(env, child, (const struct dt_rec *)cfid,
-                      (const struct dt_key *)dot, th, BYPASS_CAPA, 1);
+       /* 3b. insert dot into child dir */
+       rec->rec_type = S_IFDIR;
+       rec->rec_fid = cfid;
+       rc = dt_insert(env, child, (const struct dt_rec *)rec,
+                      (const struct dt_key *)dot, th, 1);
        if (rc != 0)
                GOTO(unlock, rc);
 
-       /* 2b.2 insert dotdot into child dir locally. */
-       rc = dt_insert(env, child, (const struct dt_rec *)&LU_LPF_FID,
-                      (const struct dt_key *)dotdot, th, BYPASS_CAPA, 1);
+       /* 4b. insert dotdot into child dir */
+       rec->rec_fid = &LU_LPF_FID;
+       rc = dt_insert(env, child, (const struct dt_rec *)rec,
+                      (const struct dt_key *)dotdot, th, 1);
        if (rc != 0)
                GOTO(unlock, rc);
 
-       /* 2b.3 increase child nlink locally. */
-       rc = dt_ref_add(env, child, th);
+       /* 5b. insert linkEA for child */
+       rc = dt_xattr_set(env, child, &linkea_buf,
+                         XATTR_NAME_LINK, 0, th);
+       if (rc != 0)
+               GOTO(unlock, rc);
+
+       bk->lb_lpf_fid = *cfid;
+       lfsck_bookmark_cpu_to_le(&lfsck->li_bookmark_disk, bk);
+
+       /* 6b. update bookmark */
+       rc = dt_record_write(env, bk_obj,
+                            lfsck_buf_get(env, bk, len), &pos, th);
+
        dt_write_unlock(env, child);
        dt_trans_stop(env, dev, th);
        if (rc != 0)
                RETURN(rc);
 
-       /* Transaction II: */
+       /* Transaction II: remotely */
 
-       dev = lfsck->li_next;
+       dev = lfsck_obj2dev(parent);
        th = dt_trans_create(env, dev);
        if (IS_ERR(th))
                RETURN(PTR_ERR(th));
 
-       /* 3a. insert name into parent dir remotely. */
-       rc = dt_declare_insert(env, parent, (const struct dt_rec *)cfid,
+       th->th_sync = 1;
+       /* 5a. insert name into parent dir */
+       rec->rec_fid = cfid;
+       rc = dt_declare_insert(env, parent, (const struct dt_rec *)rec,
                               (const struct dt_key *)name, th);
        if (rc != 0)
                GOTO(stop, rc);
 
-       /* 4a. increase parent nlink remotely. */
+       /* 6a. increase parent nlink */
        rc = dt_declare_ref_add(env, parent, th);
        if (rc != 0)
                GOTO(stop, rc);
 
-       /* 5a. decrease child nlink for dotdot locally if former remote
-        *     update failed. */
-       rc = dt_declare_ref_del(env, child, th);
-       if (rc != 0)
-               GOTO(stop, rc);
-
-       /* 6a. decrease child nlink for dot locally if former remote
-        *     update failed. */
-       rc = dt_declare_ref_del(env, child, th);
-       if (rc != 0)
-               GOTO(stop, rc);
-
-       /* 7a. destroy child locally if former remote update failed. */
-       rc = dt_declare_destroy(env, child, th);
-       if (rc != 0)
-               GOTO(stop, rc);
-
-       /* 8a. update bookmark locally. */
-       rc = dt_declare_record_write(env, bk_obj,
-                                    lfsck_buf_get(env, bk, len), 0, th);
+       rc = dt_trans_start_local(env, dev, th);
        if (rc != 0)
                GOTO(stop, rc);
 
-       rc = dt_trans_start(env, dev, th);
+       /* 5b. insert name into parent dir */
+       rc = dt_insert(env, parent, (const struct dt_rec *)rec,
+                      (const struct dt_key *)name, th, 1);
        if (rc != 0)
                GOTO(stop, rc);
 
-       /* 3b. insert name into parent dir remotely. */
-       rc = dt_insert(env, parent, (const struct dt_rec *)cfid,
-                      (const struct dt_key *)name, th, BYPASS_CAPA, 1);
-       if (rc == 0) {
-               dt_write_lock(env, parent, 0);
-               /* 4b. increase parent nlink remotely. */
-               rc = dt_ref_add(env, parent, th);
-               dt_write_unlock(env, parent);
-       }
-       if (rc != 0) {
-               /* 5b. decrease child nlink for dotdot locally. */
-               dt_ref_del(env, child, th);
-               /* 6b. decrease child nlink for dot locally. */
-               dt_ref_del(env, child, th);
-               /* 7b. destroy child locally. */
-               dt_destroy(env, child, th);
-               GOTO(stop, rc);
-       }
-
-       bk->lb_lpf_fid = *cfid;
-       lfsck_bookmark_cpu_to_le(&lfsck->li_bookmark_disk, bk);
-
-       /* 8b. update bookmark locally. */
-       rc = dt_record_write(env, bk_obj,
-                            lfsck_buf_get(env, bk, len), &pos, th);
+       dt_write_lock(env, parent, 0);
+       /* 6b. increase parent nlink */
+       rc = dt_ref_add(env, parent, th);
+       dt_write_unlock(env, parent);
 
        GOTO(stop, rc);
 
@@ -627,52 +973,55 @@ unlock:
 stop:
        dt_trans_stop(env, dev, th);
 
+       if (rc != 0 && dev == lfsck_obj2dev(parent))
+               CDEBUG(D_LFSCK, "%s: partially created the object "DFID
+                      "for orphans, but failed to insert the name %s "
+                      "to the .lustre/lost+found/. Such inconsistency "
+                      "will be repaired when LFSCK run next time: rc = %d\n",
+                      lfsck_lfsck2name(lfsck), PFID(cfid), name, rc);
+
        return rc;
 }
 
-/* Do NOT create .lustre/lost+found/MDTxxxx when register the lfsck instance,
- * because the MDT0 maybe not reaady for sequence allocation yet. We do that
- * only when it is required, such as orphan OST-objects repairing. */
-int lfsck_create_lpf(const struct lu_env *env, struct lfsck_instance *lfsck)
+/**
+ * Create the MDTxxxx directory under /ROOT/.lustre/lost+found/
+ *
+ * The /ROOT/.lustre/lost+found/MDTxxxx/ directory is used for holding
+ * orphans and other uncertain inconsistent objects found during the
+ * LFSCK. Such directory will be created by the LFSCK engine on the
+ * local MDT before the LFSCK scanning.
+ *
+ * \param[in] env      pointer to the thread context
+ * \param[in] lfsck    pointer to the lfsck instance
+ *
+ * \retval             0 for success
+ * \retval             negative error number on failure
+ */
+static int lfsck_create_lpf(const struct lu_env *env,
+                           struct lfsck_instance *lfsck)
 {
        struct lfsck_bookmark    *bk    = &lfsck->li_bookmark_ram;
        struct lfsck_thread_info *info  = lfsck_env_info(env);
        struct lu_fid            *cfid  = &info->lti_fid2;
        struct lu_attr           *la    = &info->lti_la;
        struct dt_object_format  *dof   = &info->lti_dof;
-       struct dt_object         *parent = NULL;
+       struct dt_object         *parent = lfsck->li_lpf_root_obj;
        struct dt_object         *child = NULL;
+       struct lfsck_lock_handle *llh   = &info->lti_llh;
        char                      name[8];
-       int                       node  = lfsck_dev_idx(lfsck->li_bottom);
+       int                       node  = lfsck_dev_idx(lfsck);
        int                       rc    = 0;
        ENTRY;
 
        LASSERT(lfsck->li_master);
+       LASSERT(parent != NULL);
+       LASSERT(lfsck->li_lpf_obj == NULL);
 
-       sprintf(name, "MDT%04x", node);
-       if (node == 0) {
-               parent = lfsck_object_find_by_dev(env, lfsck->li_bottom,
-                                                 &LU_LPF_FID);
-       } else {
-               struct lfsck_tgt_desc *ltd;
-
-               ltd = lfsck_tgt_get(&lfsck->li_mdt_descs, 0);
-               if (unlikely(ltd == NULL))
-                       RETURN(-ENXIO);
-
-               parent = lfsck_object_find_by_dev(env, ltd->ltd_tgt,
-                                                 &LU_LPF_FID);
-               lfsck_tgt_put(ltd);
-       }
-       if (IS_ERR(parent))
-               RETURN(PTR_ERR(parent));
-
-       if (unlikely(!dt_try_as_dir(env, parent)))
-               GOTO(out, rc = -ENOTDIR);
-
-       mutex_lock(&lfsck->li_mutex);
-       if (lfsck->li_lpf_obj != NULL)
-               GOTO(unlock, rc = 0);
+       snprintf(name, 8, "MDT%04x", node);
+       rc = lfsck_lock(env, lfsck, parent, name, llh,
+                       MDS_INODELOCK_UPDATE, LCK_PW);
+       if (rc != 0)
+               RETURN(rc);
 
        if (fid_is_zero(&bk->lb_lpf_fid)) {
                /* There is corner case that: in former LFSCK scanning we have
@@ -680,7 +1029,7 @@ int lfsck_create_lpf(const struct lu_env *env, struct lfsck_instance *lfsck)
                 * the lfsck_bookmark::lb_lpf_fid successfully. So need lookup
                 * it from MDT0 firstly. */
                rc = dt_lookup(env, parent, (struct dt_rec *)cfid,
-                              (const struct dt_key *)name, BYPASS_CAPA);
+                              (const struct dt_key *)name);
                if (rc != 0 && rc != -ENOENT)
                        GOTO(unlock, rc);
 
@@ -696,16 +1045,17 @@ int lfsck_create_lpf(const struct lu_env *env, struct lfsck_instance *lfsck)
                *cfid = bk->lb_lpf_fid;
        }
 
-       child = lfsck_object_find_by_dev(env, lfsck->li_bottom, cfid);
+       child = lfsck_object_find_bottom(env, lfsck, cfid);
        if (IS_ERR(child))
                GOTO(unlock, rc = PTR_ERR(child));
 
        if (dt_object_exists(child) != 0) {
                if (unlikely(!dt_try_as_dir(env, child)))
-                       GOTO(unlock, rc = -ENOTDIR);
+                       rc = -ENOTDIR;
+               else
+                       lfsck->li_lpf_obj = child;
 
-               lfsck->li_lpf_obj = child;
-               GOTO(unlock, rc = 0);
+               GOTO(unlock, rc);
        }
 
        memset(la, 0, sizeof(*la));
@@ -717,49 +1067,534 @@ int lfsck_create_lpf(const struct lu_env *env, struct lfsck_instance *lfsck)
        dof->dof_type = dt_mode_to_dft(S_IFDIR);
 
        if (node == 0)
-               rc = lfsck_create_lpf_local(env, lfsck, parent, child, la,
-                                           dof, name);
+               rc = lfsck_create_lpf_local(env, lfsck, child, la, dof, name);
        else
-               rc = lfsck_create_lpf_remote(env, lfsck, parent, child, la,
-                                            dof, name);
+               rc = lfsck_create_lpf_remote(env, lfsck, child, la, dof, name);
        if (rc == 0)
                lfsck->li_lpf_obj = child;
 
        GOTO(unlock, rc);
 
 unlock:
-       mutex_unlock(&lfsck->li_mutex);
+       lfsck_unlock(llh);
        if (rc != 0 && child != NULL && !IS_ERR(child))
-               lu_object_put(env, &child->do_lu);
-out:
-       if (parent != NULL && !IS_ERR(parent))
-               lu_object_put(env, &parent->do_lu);
+               lfsck_object_put(env, child);
 
        return rc;
 }
 
-static int lfsck_fid_init(struct lfsck_instance *lfsck)
+/**
+ * Scan .lustre/lost+found for bad name entries and remove them.
+ *
+ * The valid name entry should be "MDTxxxx", the "xxxx" is the MDT device
+ * index in the system. Any other formatted name is invalid and should be
+ * removed.
+ *
+ * \param[in] env      pointer to the thread context
+ * \param[in] lfsck    pointer to the lfsck instance
+ *
+ * \retval             0 for success
+ * \retval             negative error number on failure
+ */
+static int lfsck_scan_lpf_bad_entries(const struct lu_env *env,
+                                     struct lfsck_instance *lfsck)
 {
-       struct lfsck_bookmark   *bk     = &lfsck->li_bookmark_ram;
-       struct seq_server_site  *ss;
-       char                    *prefix;
-       int                      rc     = 0;
+       struct dt_object        *parent = lfsck->li_lpf_root_obj;
+       struct lu_dirent        *ent    =
+                       (struct lu_dirent *)lfsck_env_info(env)->lti_key;
+       const struct dt_it_ops  *iops   = &parent->do_index_ops->dio_it;
+       struct dt_it            *it;
+       int                      rc;
        ENTRY;
 
-       ss = lu_site2seq(lfsck->li_bottom->dd_lu_dev.ld_site);
-       if (unlikely(ss == NULL))
-               RETURN(-ENXIO);
+       it = iops->init(env, parent, LUDA_64BITHASH);
+       if (IS_ERR(it))
+               RETURN(PTR_ERR(it));
 
-       OBD_ALLOC_PTR(lfsck->li_seq);
-       if (lfsck->li_seq == NULL)
-               RETURN(-ENOMEM);
+       rc = iops->load(env, it, 0);
+       if (rc == 0)
+               rc = iops->next(env, it);
+       else if (rc > 0)
+               rc = 0;
 
-       OBD_ALLOC(prefix, MAX_OBD_NAME + 7);
-       if (prefix == NULL)
-               GOTO(out, rc = -ENOMEM);
+       while (rc == 0) {
+               int off = 3;
 
-       snprintf(prefix, MAX_OBD_NAME + 7, "lfsck-%s", lfsck_lfsck2name(lfsck));
-       rc = seq_client_init(lfsck->li_seq, NULL, LUSTRE_SEQ_METADATA, prefix,
+               rc = iops->rec(env, it, (struct dt_rec *)ent, LUDA_64BITHASH);
+               if (rc != 0)
+                       break;
+
+               ent->lde_namelen = le16_to_cpu(ent->lde_namelen);
+               if (name_is_dot_or_dotdot(ent->lde_name, ent->lde_namelen))
+                       goto next;
+
+               /* name length must be strlen("MDTxxxx") */
+               if (ent->lde_namelen != 7)
+                       goto remove;
+
+               if (memcmp(ent->lde_name, "MDT", off) != 0)
+                       goto remove;
+
+               while (off < 7 && isxdigit(ent->lde_name[off]))
+                       off++;
+
+               if (off != 7) {
+
+remove:
+                       rc = lfsck_lpf_remove_name_entry(env, lfsck,
+                                                        ent->lde_name);
+                       if (rc != 0)
+                               break;
+               }
+
+next:
+               rc = iops->next(env, it);
+       }
+
+       iops->put(env, it);
+       iops->fini(env, it);
+
+       RETURN(rc > 0 ? 0 : rc);
+}
+
+static int lfsck_update_lpf_entry(const struct lu_env *env,
+                                 struct lfsck_instance *lfsck,
+                                 struct dt_object *parent,
+                                 struct dt_object *child,
+                                 const char *name,
+                                 enum lfsck_verify_lpf_types type)
+{
+       int rc;
+
+       if (type == LVLT_BY_BOOKMARK) {
+               rc = lfsck_update_name_entry(env, lfsck, parent, name,
+                                            lfsck_dto2fid(child), S_IFDIR);
+       } else /* if (type == LVLT_BY_NAMEENTRY) */ {
+               lfsck->li_bookmark_ram.lb_lpf_fid = *lfsck_dto2fid(child);
+               rc = lfsck_bookmark_store(env, lfsck);
+
+               CDEBUG(D_LFSCK, "%s: update LPF fid "DFID
+                      " in the bookmark file: rc = %d\n",
+                      lfsck_lfsck2name(lfsck),
+                      PFID(lfsck_dto2fid(child)), rc);
+       }
+
+       return rc;
+}
+
+/**
+ * Check whether the @child back references the @parent.
+ *
+ * Two cases:
+ * 1) The child's FID is stored in the bookmark file. If the child back
+ *    references the parent (LU_LPF_FID object) via its ".." entry, then
+ *    insert the name (MDTxxxx) to the .lustre/lost+found; otherwise, if
+ *    the child back references another parent2, then:
+ * 1.1) If the parent2 recognizes the child, then update the bookmark file;
+ * 1.2) Otherwise, the LFSCK cannot know whether there will be parent3 that
+ *     references the child. So keep them there. As the LFSCK processing,
+ *     the parent3 may be found, then when the LFSCK run next time, the
+ *     inconsistency can be repaired.
+ *
+ * 2) The child's FID is stored in the .lustre/lost+found/ sub-directory name
+ *    entry (MDTxxxx). If the child back references the parent (LU_LPF_FID obj)
+ *    via its ".." entry, then update the bookmark file, otherwise, if the child
+ *    back references another parent2, then:
+ * 2.1) If the parent2 recognizes the child, then remove the sub-directory
+ *     from .lustre/lost+found/;
+ * 2.2) Otherwise, if the parent2 does not recognizes the child, trust the
+ *     sub-directory name entry and update the child;
+ * 2.3) Otherwise, if we do not know whether the parent2 recognizes the child
+ *     or not, then keep them there.
+ *
+ * \param[in] env      pointer to the thread context
+ * \param[in] lfsck    pointer to the lfsck instance
+ * \param[in] child    pointer to the lost+found sub-directory object
+ * \param[in] name     the name for lost+found sub-directory object
+ * \param[out] fid     pointer to the buffer to hold the FID of the object
+ *                     (called it as parent2) that is referenced via the
+ *                     child's dotdot entry; it also can be the FID that
+ *                     is referenced by the name entry under the parent2.
+ * \param[in] type     to indicate where the child's FID is stored in
+ *
+ * \retval             positive number for uncertain inconsistency
+ * \retval             0 for success
+ * \retval             negative error number on failure
+ */
+static int lfsck_verify_lpf_pairs(const struct lu_env *env,
+                                 struct lfsck_instance *lfsck,
+                                 struct dt_object *child, const char *name,
+                                 struct lu_fid *fid,
+                                 enum lfsck_verify_lpf_types type)
+{
+       struct dt_object         *parent  = lfsck->li_lpf_root_obj;
+       struct lfsck_thread_info *info    = lfsck_env_info(env);
+       char                     *name2   = info->lti_key;
+       struct lu_fid            *fid2    = &info->lti_fid3;
+       struct dt_object         *parent2 = NULL;
+       struct lustre_handle      lh      = { 0 };
+       int                       rc;
+       ENTRY;
+
+       fid_zero(fid);
+       rc = dt_lookup(env, child, (struct dt_rec *)fid,
+                      (const struct dt_key *)dotdot);
+       if (rc != 0)
+               GOTO(linkea, rc);
+
+       if (!fid_is_sane(fid))
+               GOTO(linkea, rc = -EINVAL);
+
+       if (lu_fid_eq(fid, &LU_LPF_FID)) {
+               const struct lu_name *cname;
+
+               if (lfsck->li_lpf_obj == NULL) {
+                       lu_object_get(&child->do_lu);
+                       lfsck->li_lpf_obj = child;
+               }
+
+               cname = lfsck_name_get_const(env, name, strlen(name));
+               rc = lfsck_verify_linkea(env, child, cname, &LU_LPF_FID);
+               if (rc == 0)
+                       rc = lfsck_update_lpf_entry(env, lfsck, parent, child,
+                                                   name, type);
+
+               GOTO(out_done, rc);
+       }
+
+       parent2 = lfsck_object_find_bottom(env, lfsck, fid);
+       if (IS_ERR(parent2))
+               GOTO(linkea, parent2);
+
+       if (!dt_object_exists(parent2)) {
+               lfsck_object_put(env, parent2);
+
+               GOTO(linkea, parent2 = ERR_PTR(-ENOENT));
+       }
+
+       if (!dt_try_as_dir(env, parent2)) {
+               lfsck_object_put(env, parent2);
+
+               GOTO(linkea, parent2 = ERR_PTR(-ENOTDIR));
+       }
+
+linkea:
+       /* To prevent rename/unlink race */
+       rc = lfsck_ibits_lock(env, lfsck, child, &lh,
+                             MDS_INODELOCK_UPDATE, LCK_PR);
+       if (rc != 0)
+               GOTO(out_put, rc);
+
+       dt_read_lock(env, child, 0);
+       rc = lfsck_links_get_first(env, child, name2, fid2);
+       if (rc != 0) {
+               dt_read_unlock(env, child);
+               lfsck_ibits_unlock(&lh, LCK_PR);
+
+               GOTO(out_put, rc = 1);
+       }
+
+       /* It is almost impossible that the bookmark file (or the name entry)
+        * and the linkEA hit the same data corruption. Trust the linkEA. */
+       if (lu_fid_eq(fid2, &LU_LPF_FID) && strcmp(name, name2) == 0) {
+               dt_read_unlock(env, child);
+               lfsck_ibits_unlock(&lh, LCK_PR);
+
+               *fid = *fid2;
+               if (lfsck->li_lpf_obj == NULL) {
+                       lu_object_get(&child->do_lu);
+                       lfsck->li_lpf_obj = child;
+               }
+
+               /* Update the child's dotdot entry */
+               rc = lfsck_update_name_entry(env, lfsck, child, dotdot,
+                                            &LU_LPF_FID, S_IFDIR);
+               if (rc == 0)
+                       rc = lfsck_update_lpf_entry(env, lfsck, parent, child,
+                                                   name, type);
+
+               GOTO(out_put, rc);
+       }
+
+       if (parent2 == NULL || IS_ERR(parent2)) {
+               dt_read_unlock(env, child);
+               lfsck_ibits_unlock(&lh, LCK_PR);
+
+               GOTO(out_done, rc = 1);
+       }
+
+       rc = dt_lookup(env, parent2, (struct dt_rec *)fid,
+                      (const struct dt_key *)name2);
+       dt_read_unlock(env, child);
+       lfsck_ibits_unlock(&lh, LCK_PR);
+       if (rc != 0 && rc != -ENOENT)
+               GOTO(out_put, rc);
+
+       if (rc == -ENOENT || !lu_fid_eq(fid, lfsck_dto2fid(child))) {
+               if (type == LVLT_BY_BOOKMARK)
+                       GOTO(out_put, rc = 1);
+
+               /* Trust the name entry, update the child's dotdot entry. */
+               rc = lfsck_update_name_entry(env, lfsck, child, dotdot,
+                                            &LU_LPF_FID, S_IFDIR);
+
+               GOTO(out_put, rc);
+       }
+
+       if (type == LVLT_BY_BOOKMARK) {
+               /* Invalid FID record in the bookmark file, reset it. */
+               fid_zero(&lfsck->li_bookmark_ram.lb_lpf_fid);
+               rc = lfsck_bookmark_store(env, lfsck);
+
+               CDEBUG(D_LFSCK, "%s: reset invalid LPF fid "DFID
+                      " in the bookmark file: rc = %d\n",
+                      lfsck_lfsck2name(lfsck), PFID(lfsck_dto2fid(child)), rc);
+       } else /* if (type == LVLT_BY_NAMEENTRY) */ {
+               /* The name entry is wrong, remove it. */
+               rc = lfsck_lpf_remove_name_entry(env, lfsck, name);
+       }
+
+       GOTO(out_put, rc);
+
+out_put:
+       if (parent2 != NULL && !IS_ERR(parent2))
+               lfsck_object_put(env, parent2);
+
+out_done:
+       return rc;
+}
+
+/**
+ * Verify the /ROOT/.lustre/lost+found/ directory.
+ *
+ * /ROOT/.lustre/lost+found/ is a special directory to hold the objects that
+ * the LFSCK does not exactly know how to handle, such as orphans. So before
+ * the LFSCK scanning the system, the consistency of such directory needs to
+ * be verified firstly to allow the users to use it during the LFSCK.
+ *
+ * \param[in] env      pointer to the thread context
+ * \param[in] lfsck    pointer to the lfsck instance
+ *
+ * \retval             positive number for uncertain inconsistency
+ * \retval             0 for success
+ * \retval             negative error number on failure
+ */
+int lfsck_verify_lpf(const struct lu_env *env, struct lfsck_instance *lfsck)
+{
+       struct lfsck_thread_info *info   = lfsck_env_info(env);
+       struct lu_fid            *pfid   = &info->lti_fid;
+       struct lu_fid            *cfid   = &info->lti_fid2;
+       struct lfsck_bookmark    *bk     = &lfsck->li_bookmark_ram;
+       struct dt_object         *parent;
+       /* child1's FID is in the bookmark file. */
+       struct dt_object         *child1 = NULL;
+       /* child2's FID is in the name entry MDTxxxx. */
+       struct dt_object         *child2 = NULL;
+       const struct lu_name     *cname;
+       char                      name[8];
+       int                       node   = lfsck_dev_idx(lfsck);
+       int                       rc     = 0;
+       ENTRY;
+
+       LASSERT(lfsck->li_master);
+
+       if (lfsck->li_lpf_root_obj != NULL)
+               RETURN(0);
+
+       if (node == 0) {
+               parent = lfsck_object_find_by_dev(env, lfsck->li_bottom,
+                                                 &LU_LPF_FID);
+       } else {
+               struct lfsck_tgt_desc *ltd;
+
+               ltd = lfsck_tgt_get(&lfsck->li_mdt_descs, 0);
+               if (unlikely(ltd == NULL))
+                       RETURN(-ENXIO);
+
+               parent = lfsck_object_find_by_dev(env, ltd->ltd_tgt,
+                                                 &LU_LPF_FID);
+               lfsck_tgt_put(ltd);
+       }
+
+       if (IS_ERR(parent))
+               RETURN(PTR_ERR(parent));
+
+       LASSERT(dt_object_exists(parent));
+
+       if (unlikely(!dt_try_as_dir(env, parent))) {
+               lfsck_object_put(env, parent);
+
+               GOTO(put, rc = -ENOTDIR);
+       }
+
+       lfsck->li_lpf_root_obj = parent;
+       if (node == 0) {
+               rc = lfsck_scan_lpf_bad_entries(env, lfsck);
+               if (rc != 0)
+                       CDEBUG(D_LFSCK, "%s: scan .lustre/lost+found/ "
+                              "for bad sub-directories: rc = %d\n",
+                              lfsck_lfsck2name(lfsck), rc);
+       }
+
+       /* child2 */
+       snprintf(name, 8, "MDT%04x", node);
+       rc = dt_lookup(env, parent, (struct dt_rec *)cfid,
+                      (const struct dt_key *)name);
+       if (rc == -ENOENT) {
+               rc = 0;
+               goto find_child1;
+       }
+
+       if (rc != 0)
+               GOTO(put, rc);
+
+       /* Invalid FID in the name entry, remove the name entry. */
+       if (!fid_is_norm(cfid)) {
+               rc = lfsck_lpf_remove_name_entry(env, lfsck, name);
+               if (rc != 0)
+                       GOTO(put, rc);
+
+               goto find_child1;
+       }
+
+       child2 = lfsck_object_find_bottom(env, lfsck, cfid);
+       if (IS_ERR(child2))
+               GOTO(put, rc = PTR_ERR(child2));
+
+       if (unlikely(!dt_object_exists(child2) ||
+                    dt_object_remote(child2)) ||
+                    !S_ISDIR(lfsck_object_type(child2))) {
+               rc = lfsck_lpf_remove_name_entry(env, lfsck, name);
+               if (rc != 0)
+                       GOTO(put, rc);
+
+               goto find_child1;
+       }
+
+       if (unlikely(!dt_try_as_dir(env, child2))) {
+               lfsck_object_put(env, child2);
+               child2 = NULL;
+               rc = -ENOTDIR;
+       }
+
+find_child1:
+       if (fid_is_zero(&bk->lb_lpf_fid))
+               goto check_child2;
+
+       if (likely(lu_fid_eq(cfid, &bk->lb_lpf_fid))) {
+               if (lfsck->li_lpf_obj == NULL) {
+                       lu_object_get(&child2->do_lu);
+                       lfsck->li_lpf_obj = child2;
+               }
+
+               cname = lfsck_name_get_const(env, name, strlen(name));
+               rc = lfsck_verify_linkea(env, child2, cname, &LU_LPF_FID);
+
+               GOTO(put, rc);
+       }
+
+       if (unlikely(!fid_is_norm(&bk->lb_lpf_fid))) {
+               struct lu_fid tfid = bk->lb_lpf_fid;
+
+               /* Invalid FID record in the bookmark file, reset it. */
+               fid_zero(&bk->lb_lpf_fid);
+               rc = lfsck_bookmark_store(env, lfsck);
+
+               CDEBUG(D_LFSCK, "%s: reset invalid LPF fid "DFID
+                      " in the bookmark file: rc = %d\n",
+                      lfsck_lfsck2name(lfsck), PFID(&tfid), rc);
+
+               if (rc != 0)
+                       GOTO(put, rc);
+
+               goto check_child2;
+       }
+
+       child1 = lfsck_object_find_bottom(env, lfsck, &bk->lb_lpf_fid);
+       if (IS_ERR(child1)) {
+               child1 = NULL;
+               goto check_child2;
+       }
+
+       if (unlikely(!dt_object_exists(child1) ||
+                    dt_object_remote(child1)) ||
+                    !S_ISDIR(lfsck_object_type(child1))) {
+               /* Invalid FID record in the bookmark file, reset it. */
+               fid_zero(&bk->lb_lpf_fid);
+               rc = lfsck_bookmark_store(env, lfsck);
+
+               CDEBUG(D_LFSCK, "%s: reset invalid LPF fid "DFID
+                      " in the bookmark file: rc = %d\n",
+                      lfsck_lfsck2name(lfsck),
+                      PFID(lfsck_dto2fid(child1)), rc);
+
+               if (rc != 0)
+                       GOTO(put, rc);
+
+               lfsck_object_put(env, child1);
+               child1 = NULL;
+               goto check_child2;
+       }
+
+       if (unlikely(!dt_try_as_dir(env, child1))) {
+               lfsck_object_put(env, child1);
+               child1 = NULL;
+               rc = -ENOTDIR;
+               goto check_child2;
+       }
+
+       rc = lfsck_verify_lpf_pairs(env, lfsck, child1, name, pfid,
+                                   LVLT_BY_BOOKMARK);
+       if (lu_fid_eq(pfid, &LU_LPF_FID))
+               GOTO(put, rc);
+
+check_child2:
+       if (child2 != NULL)
+               rc = lfsck_verify_lpf_pairs(env, lfsck, child2, name,
+                                           pfid, LVLT_BY_NAMEENTRY);
+
+       GOTO(put, rc);
+
+put:
+       if (lfsck->li_lpf_obj != NULL) {
+               if (unlikely(!dt_try_as_dir(env, lfsck->li_lpf_obj))) {
+                       lfsck_object_put(env, lfsck->li_lpf_obj);
+                       lfsck->li_lpf_obj = NULL;
+                       rc = -ENOTDIR;
+               }
+       } else if (rc == 0) {
+               rc = lfsck_create_lpf(env, lfsck);
+       }
+
+       if (child2 != NULL && !IS_ERR(child2))
+               lfsck_object_put(env, child2);
+       if (child1 != NULL && !IS_ERR(child1))
+               lfsck_object_put(env, child1);
+
+       return rc;
+}
+
+static int lfsck_fid_init(struct lfsck_instance *lfsck)
+{
+       struct lfsck_bookmark   *bk     = &lfsck->li_bookmark_ram;
+       struct seq_server_site  *ss     = lfsck_dev_site(lfsck);
+       char                    *prefix;
+       int                      rc     = 0;
+       ENTRY;
+
+       if (unlikely(ss == NULL))
+               RETURN(-ENXIO);
+
+       OBD_ALLOC_PTR(lfsck->li_seq);
+       if (lfsck->li_seq == NULL)
+               RETURN(-ENOMEM);
+
+       OBD_ALLOC(prefix, MAX_OBD_NAME + 7);
+       if (prefix == NULL)
+               GOTO(out, rc = -ENOMEM);
+
+       snprintf(prefix, MAX_OBD_NAME + 7, "lfsck-%s", lfsck_lfsck2name(lfsck));
+       rc = seq_client_init(lfsck->li_seq, NULL, LUSTRE_SEQ_METADATA, prefix,
                             ss->ss_server_seq);
        OBD_FREE(prefix, MAX_OBD_NAME + 7);
        if (rc != 0)
@@ -791,54 +1626,71 @@ void lfsck_instance_cleanup(const struct lu_env *env,
 {
        struct ptlrpc_thread    *thread = &lfsck->li_thread;
        struct lfsck_component  *com;
+       struct lfsck_component  *next;
+       struct lfsck_lmv_unit   *llu;
+       struct lfsck_lmv_unit   *llu_next;
+       struct lfsck_lmv        *llmv;
        ENTRY;
 
        LASSERT(list_empty(&lfsck->li_link));
        LASSERT(thread_is_init(thread) || thread_is_stopped(thread));
 
        if (lfsck->li_obj_oit != NULL) {
-               lu_object_put_nocache(env, &lfsck->li_obj_oit->do_lu);
+               lfsck_object_put(env, lfsck->li_obj_oit);
                lfsck->li_obj_oit = NULL;
        }
 
        LASSERT(lfsck->li_obj_dir == NULL);
+       LASSERT(lfsck->li_lmv == NULL);
 
-       while (!cfs_list_empty(&lfsck->li_list_scan)) {
-               com = cfs_list_entry(lfsck->li_list_scan.next,
-                                    struct lfsck_component,
-                                    lc_link);
+       list_for_each_entry_safe(llu, llu_next, &lfsck->li_list_lmv, llu_link) {
+               llmv = &llu->llu_lmv;
+
+               LASSERTF(atomic_read(&llmv->ll_ref) == 1,
+                        "still in using: %u\n",
+                        atomic_read(&llmv->ll_ref));
+
+               lfsck_lmv_put(env, llmv);
+       }
+
+       list_for_each_entry_safe(com, next, &lfsck->li_list_scan, lc_link) {
                lfsck_component_cleanup(env, com);
        }
 
-       LASSERT(cfs_list_empty(&lfsck->li_list_dir));
+       LASSERT(list_empty(&lfsck->li_list_dir));
 
-       while (!cfs_list_empty(&lfsck->li_list_double_scan)) {
-               com = cfs_list_entry(lfsck->li_list_double_scan.next,
-                                    struct lfsck_component,
-                                    lc_link);
+       list_for_each_entry_safe(com, next, &lfsck->li_list_double_scan,
+                                lc_link) {
                lfsck_component_cleanup(env, com);
        }
 
-       while (!cfs_list_empty(&lfsck->li_list_idle)) {
-               com = cfs_list_entry(lfsck->li_list_idle.next,
-                                    struct lfsck_component,
-                                    lc_link);
+       list_for_each_entry_safe(com, next, &lfsck->li_list_idle, lc_link) {
                lfsck_component_cleanup(env, com);
        }
 
        lfsck_tgt_descs_fini(&lfsck->li_ost_descs);
        lfsck_tgt_descs_fini(&lfsck->li_mdt_descs);
 
+       if (lfsck->li_lfsck_dir != NULL) {
+               lfsck_object_put(env, lfsck->li_lfsck_dir);
+               lfsck->li_lfsck_dir = NULL;
+       }
+
        if (lfsck->li_bookmark_obj != NULL) {
-               lu_object_put_nocache(env, &lfsck->li_bookmark_obj->do_lu);
+               lfsck_object_put(env, lfsck->li_bookmark_obj);
                lfsck->li_bookmark_obj = NULL;
        }
 
        if (lfsck->li_lpf_obj != NULL) {
-               lu_object_put(env, &lfsck->li_lpf_obj->do_lu);
+               lfsck_object_put(env, lfsck->li_lpf_obj);
                lfsck->li_lpf_obj = NULL;
        }
 
+       if (lfsck->li_lpf_root_obj != NULL) {
+               lfsck_object_put(env, lfsck->li_lpf_root_obj);
+               lfsck->li_lpf_root_obj = NULL;
+       }
+
        if (lfsck->li_los != NULL) {
                local_oid_storage_fini(env, lfsck->li_los);
                lfsck->li_los = NULL;
@@ -854,7 +1706,7 @@ __lfsck_instance_find(struct dt_device *key, bool ref, bool unlink)
 {
        struct lfsck_instance *lfsck;
 
-       cfs_list_for_each_entry(lfsck, &lfsck_instance_list, li_link) {
+       list_for_each_entry(lfsck, &lfsck_instance_list, li_link) {
                if (lfsck->li_bottom == key) {
                        if (ref)
                                lfsck_instance_get(lfsck);
@@ -885,89 +1737,85 @@ static inline int lfsck_instance_add(struct lfsck_instance *lfsck)
        struct lfsck_instance *tmp;
 
        spin_lock(&lfsck_instance_lock);
-       cfs_list_for_each_entry(tmp, &lfsck_instance_list, li_link) {
+       list_for_each_entry(tmp, &lfsck_instance_list, li_link) {
                if (lfsck->li_bottom == tmp->li_bottom) {
                        spin_unlock(&lfsck_instance_lock);
                        return -EEXIST;
                }
        }
 
-       cfs_list_add_tail(&lfsck->li_link, &lfsck_instance_list);
+       list_add_tail(&lfsck->li_link, &lfsck_instance_list);
        spin_unlock(&lfsck_instance_lock);
        return 0;
 }
 
-int lfsck_bits_dump(char **buf, int *len, int bits, const char *names[],
+int lfsck_bits_dump(struct seq_file *m, int bits, const char *names[],
                    const char *prefix)
 {
-       int save = *len;
        int flag;
-       int rc;
        int i;
+       bool newline = (bits != 0 ? false : true);
+       int rc;
 
-       rc = snprintf(*buf, *len, "%s:%c", prefix, bits != 0 ? ' ' : '\n');
-       if (rc <= 0)
-               return -ENOSPC;
+       rc = seq_printf(m, "%s:%c", prefix, bits != 0 ? ' ' : '\n');
+       if (rc < 0)
+               return rc;
 
-       *buf += rc;
-       *len -= rc;
        for (i = 0, flag = 1; bits != 0; i++, flag = 1 << i) {
                if (flag & bits) {
                        bits &= ~flag;
                        if (names[i] != NULL) {
-                               rc = snprintf(*buf, *len, "%s%c", names[i],
-                                             bits != 0 ? ',' : '\n');
-                               if (rc <= 0)
-                                       return -ENOSPC;
+                               if (bits == 0)
+                                       newline = true;
 
-                               *buf += rc;
-                               *len -= rc;
+                               rc = seq_printf(m, "%s%c", names[i],
+                                               newline ? '\n' : ',');
+                               if (rc < 0)
+                                       return rc;
                        }
                }
        }
-       return save - *len;
+
+       if (!newline)
+               rc = seq_printf(m, "\n");
+
+       return rc;
 }
 
-int lfsck_time_dump(char **buf, int *len, __u64 time, const char *prefix)
+int lfsck_time_dump(struct seq_file *m, __u64 time, const char *name)
 {
        int rc;
 
-       if (time != 0)
-               rc = snprintf(*buf, *len, "%s: "LPU64" seconds\n", prefix,
-                             cfs_time_current_sec() - time);
-       else
-               rc = snprintf(*buf, *len, "%s: N/A\n", prefix);
-       if (rc <= 0)
-               return -ENOSPC;
+       if (time == 0) {
+               rc = seq_printf(m, "%s_time: N/A\n", name);
+               if (rc == 0)
+                       rc = seq_printf(m, "time_since_%s: N/A\n", name);
+
+               return rc;
+       }
+
+       rc = seq_printf(m, "%s_time: "LPU64"\n", name, time);
+       if (rc == 0)
+               rc = seq_printf(m, "time_since_%s: "LPU64" seconds\n",
+                               name, cfs_time_current_sec() - time);
 
-       *buf += rc;
-       *len -= rc;
        return rc;
 }
 
-int lfsck_pos_dump(char **buf, int *len, struct lfsck_position *pos,
+int lfsck_pos_dump(struct seq_file *m, struct lfsck_position *pos,
                   const char *prefix)
 {
-       int rc;
-
        if (fid_is_zero(&pos->lp_dir_parent)) {
                if (pos->lp_oit_cookie == 0)
-                       rc = snprintf(*buf, *len, "%s: N/A, N/A, N/A\n",
-                                     prefix);
-               else
-                       rc = snprintf(*buf, *len, "%s: "LPU64", N/A, N/A\n",
-                                     prefix, pos->lp_oit_cookie);
-       } else {
-               rc = snprintf(*buf, *len, "%s: "LPU64", "DFID", "LPU64"\n",
-                             prefix, pos->lp_oit_cookie,
-                             PFID(&pos->lp_dir_parent), pos->lp_dir_cookie);
+                       return seq_printf(m, "%s: N/A, N/A, N/A\n", prefix);
+
+               return seq_printf(m, "%s: "LPU64", N/A, N/A\n",
+                                 prefix, pos->lp_oit_cookie);
        }
-       if (rc <= 0)
-               return -ENOSPC;
 
-       *buf += rc;
-       *len -= rc;
-       return rc;
+       return seq_printf(m, "%s: "LPU64", "DFID", "LPX64"\n",
+                         prefix, pos->lp_oit_cookie,
+                         PFID(&pos->lp_dir_parent), pos->lp_dir_cookie);
 }
 
 void lfsck_pos_fill(const struct lu_env *env, struct lfsck_instance *lfsck,
@@ -1004,21 +1852,31 @@ void lfsck_pos_fill(const struct lu_env *env, struct lfsck_instance *lfsck,
        }
 }
 
-static void __lfsck_set_speed(struct lfsck_instance *lfsck, __u32 limit)
+bool __lfsck_set_speed(struct lfsck_instance *lfsck, __u32 limit)
 {
-       lfsck->li_bookmark_ram.lb_speed_limit = limit;
+       bool dirty = false;
+
        if (limit != LFSCK_SPEED_NO_LIMIT) {
-               if (limit > HZ) {
-                       lfsck->li_sleep_rate = limit / HZ;
+               if (limit > msecs_to_jiffies(MSEC_PER_SEC)) {
+                       lfsck->li_sleep_rate = limit /
+                                              msecs_to_jiffies(MSEC_PER_SEC);
                        lfsck->li_sleep_jif = 1;
                } else {
                        lfsck->li_sleep_rate = 1;
-                       lfsck->li_sleep_jif = HZ / limit;
+                       lfsck->li_sleep_jif = msecs_to_jiffies(MSEC_PER_SEC) /
+                                             limit;
                }
        } else {
                lfsck->li_sleep_jif = 0;
                lfsck->li_sleep_rate = 0;
        }
+
+       if (lfsck->li_bookmark_ram.lb_speed_limit != limit) {
+               lfsck->li_bookmark_ram.lb_speed_limit = limit;
+               dirty = true;
+       }
+
+       return dirty;
 }
 
 void lfsck_control_speed(struct lfsck_instance *lfsck)
@@ -1056,106 +1914,10 @@ void lfsck_control_speed_by_self(struct lfsck_component *com)
        }
 }
 
-static int lfsck_parent_fid(const struct lu_env *env, struct dt_object *obj,
-                           struct lu_fid *fid)
-{
-       if (unlikely(!S_ISDIR(lfsck_object_type(obj)) ||
-                    !dt_try_as_dir(env, obj)))
-               return -ENOTDIR;
-
-       return dt_lookup(env, obj, (struct dt_rec *)fid,
-                        (const struct dt_key *)"..", BYPASS_CAPA);
-}
-
-static int lfsck_needs_scan_dir(const struct lu_env *env,
-                               struct lfsck_instance *lfsck,
-                               struct dt_object *obj)
-{
-       struct lu_fid *fid   = &lfsck_env_info(env)->lti_fid;
-       int            depth = 0;
-       int            rc;
-
-       if (!lfsck->li_master || !S_ISDIR(lfsck_object_type(obj)) ||
-           cfs_list_empty(&lfsck->li_list_dir))
-              RETURN(0);
-
-       while (1) {
-               /* XXX: Currently, we do not scan the "/REMOTE_PARENT_DIR",
-                *      which is the agent directory to manage the objects
-                *      which name entries reside on remote MDTs. Related
-                *      consistency verification will be processed in LFSCK
-                *      phase III. */
-               if (lu_fid_eq(lfsck_dto2fid(obj), &lfsck->li_global_root_fid)) {
-                       if (depth > 0)
-                               lfsck_object_put(env, obj);
-                       return 1;
-               }
-
-               /* .lustre doesn't contain "real" user objects, no need lfsck */
-               if (fid_is_dot_lustre(lfsck_dto2fid(obj))) {
-                       if (depth > 0)
-                               lfsck_object_put(env, obj);
-                       return 0;
-               }
-
-               dt_read_lock(env, obj, MOR_TGT_CHILD);
-               if (unlikely(lfsck_is_dead_obj(obj))) {
-                       dt_read_unlock(env, obj);
-                       if (depth > 0)
-                               lfsck_object_put(env, obj);
-                       return 0;
-               }
-
-               rc = dt_xattr_get(env, obj,
-                                 lfsck_buf_get(env, NULL, 0), XATTR_NAME_LINK,
-                                 BYPASS_CAPA);
-               dt_read_unlock(env, obj);
-               if (rc >= 0) {
-                       if (depth > 0)
-                               lfsck_object_put(env, obj);
-                       return 1;
-               }
-
-               if (rc < 0 && rc != -ENODATA) {
-                       if (depth > 0)
-                               lfsck_object_put(env, obj);
-                       return rc;
-               }
-
-               rc = lfsck_parent_fid(env, obj, fid);
-               if (depth > 0)
-                       lfsck_object_put(env, obj);
-               if (rc != 0)
-                       return rc;
-
-               if (unlikely(lu_fid_eq(fid, &lfsck->li_local_root_fid)))
-                       return 0;
-
-               obj = lfsck_object_find(env, lfsck, fid);
-               if (obj == NULL)
-                       return 0;
-               else if (IS_ERR(obj))
-                       return PTR_ERR(obj);
-
-               if (!dt_object_exists(obj)) {
-                       lfsck_object_put(env, obj);
-                       return 0;
-               }
-
-               /* Currently, only client visible directory can be remote. */
-               if (dt_object_remote(obj)) {
-                       lfsck_object_put(env, obj);
-                       return 1;
-               }
-
-               depth++;
-       }
-       return 0;
-}
-
-struct lfsck_thread_args *lfsck_thread_args_init(struct lfsck_instance *lfsck,
-                                                struct lfsck_component *com,
-                                                struct lfsck_start_param *lsp)
+static struct lfsck_thread_args *
+lfsck_thread_args_init(struct lfsck_instance *lfsck,
+                      struct lfsck_component *com,
+                      struct lfsck_start_param *lsp)
 {
        struct lfsck_thread_args *lta;
        int                       rc;
@@ -1188,253 +1950,289 @@ void lfsck_thread_args_fini(struct lfsck_thread_args *lta)
        OBD_FREE_PTR(lta);
 }
 
-/* LFSCK wrap functions */
-
-void lfsck_fail(const struct lu_env *env, struct lfsck_instance *lfsck,
-               bool new_checked)
-{
-       struct lfsck_component *com;
-
-       cfs_list_for_each_entry(com, &lfsck->li_list_scan, lc_link) {
-               com->lc_ops->lfsck_fail(env, com, new_checked);
-       }
-}
-
-int lfsck_checkpoint(const struct lu_env *env, struct lfsck_instance *lfsck)
+struct lfsck_assistant_data *
+lfsck_assistant_data_init(struct lfsck_assistant_operations *lao,
+                         const char *name)
 {
-       struct lfsck_component *com;
-       int                     rc  = 0;
-       int                     rc1 = 0;
-
-       if (likely(cfs_time_beforeq(cfs_time_current(),
-                                   lfsck->li_time_next_checkpoint)))
-               return 0;
+       struct lfsck_assistant_data *lad;
+
+       OBD_ALLOC_PTR(lad);
+       if (lad != NULL) {
+               lad->lad_bitmap = CFS_ALLOCATE_BITMAP(BITS_PER_LONG);
+               if (lad->lad_bitmap == NULL) {
+                       OBD_FREE_PTR(lad);
+                       return NULL;
+               }
 
-       lfsck_pos_fill(env, lfsck, &lfsck->li_pos_current, false);
-       cfs_list_for_each_entry(com, &lfsck->li_list_scan, lc_link) {
-               rc = com->lc_ops->lfsck_checkpoint(env, com, false);
-               if (rc != 0)
-                       rc1 = rc;
+               INIT_LIST_HEAD(&lad->lad_req_list);
+               spin_lock_init(&lad->lad_lock);
+               INIT_LIST_HEAD(&lad->lad_ost_list);
+               INIT_LIST_HEAD(&lad->lad_ost_phase1_list);
+               INIT_LIST_HEAD(&lad->lad_ost_phase2_list);
+               INIT_LIST_HEAD(&lad->lad_mdt_list);
+               INIT_LIST_HEAD(&lad->lad_mdt_phase1_list);
+               INIT_LIST_HEAD(&lad->lad_mdt_phase2_list);
+               init_waitqueue_head(&lad->lad_thread.t_ctl_waitq);
+               lad->lad_ops = lao;
+               lad->lad_name = name;
        }
 
-       lfsck->li_time_last_checkpoint = cfs_time_current();
-       lfsck->li_time_next_checkpoint = lfsck->li_time_last_checkpoint +
-                               cfs_time_seconds(LFSCK_CHECKPOINT_INTERVAL);
-       return rc1 != 0 ? rc1 : rc;
+       return lad;
 }
 
-int lfsck_prep(const struct lu_env *env, struct lfsck_instance *lfsck,
-              struct lfsck_start_param *lsp)
+struct lfsck_assistant_object *
+lfsck_assistant_object_init(const struct lu_env *env, const struct lu_fid *fid,
+                           const struct lu_attr *attr, __u64 cookie,
+                           bool is_dir)
 {
-       struct dt_object       *obj     = NULL;
-       struct lfsck_component *com;
-       struct lfsck_component *next;
-       struct lfsck_position  *pos     = NULL;
-       const struct dt_it_ops *iops    =
-                               &lfsck->li_obj_oit->do_index_ops->dio_it;
-       struct dt_it           *di;
-       int                     rc;
-       ENTRY;
-
-       LASSERT(lfsck->li_obj_dir == NULL);
-       LASSERT(lfsck->li_di_dir == NULL);
-
-       lfsck->li_current_oit_processed = 0;
-       cfs_list_for_each_entry_safe(com, next, &lfsck->li_list_scan, lc_link) {
-               com->lc_new_checked = 0;
-               if (lfsck->li_bookmark_ram.lb_param & LPF_DRYRUN)
-                       com->lc_journal = 0;
-
-               rc = com->lc_ops->lfsck_prep(env, com, lsp);
-               if (rc != 0)
-                       GOTO(out, rc);
-
-               if ((pos == NULL) ||
-                   (!lfsck_pos_is_zero(&com->lc_pos_start) &&
-                    lfsck_pos_is_eq(pos, &com->lc_pos_start) > 0))
-                       pos = &com->lc_pos_start;
-       }
-
-       /* Init otable-based iterator. */
-       if (pos == NULL) {
-               rc = iops->load(env, lfsck->li_di_oit, 0);
-               if (rc > 0) {
-                       lfsck->li_oit_over = 1;
-                       rc = 0;
-               }
-
-               GOTO(out, rc);
-       }
-
-       rc = iops->load(env, lfsck->li_di_oit, pos->lp_oit_cookie);
-       if (rc < 0)
-               GOTO(out, rc);
-       else if (rc > 0)
-               lfsck->li_oit_over = 1;
+       struct lfsck_assistant_object   *lso;
 
-       if (!lfsck->li_master || fid_is_zero(&pos->lp_dir_parent))
-               GOTO(out, rc = 0);
+       OBD_ALLOC_PTR(lso);
+       if (lso == NULL)
+               return ERR_PTR(-ENOMEM);
 
-       /* Find the directory for namespace-based traverse. */
-       obj = lfsck_object_find(env, lfsck, &pos->lp_dir_parent);
-       if (obj == NULL)
-               GOTO(out, rc = 0);
-       else if (IS_ERR(obj))
-               RETURN(PTR_ERR(obj));
+       lso->lso_fid = *fid;
+       if (attr != NULL)
+               lso->lso_attr = *attr;
 
-       /* XXX: Currently, skip remote object, the consistency for
-        *      remote object will be processed in LFSCK phase III. */
-       if (!dt_object_exists(obj) || dt_object_remote(obj) ||
-           unlikely(!S_ISDIR(lfsck_object_type(obj))))
-               GOTO(out, rc = 0);
+       atomic_set(&lso->lso_ref, 1);
+       lso->lso_oit_cookie = cookie;
+       if (is_dir)
+               lso->lso_is_dir = 1;
 
-       if (unlikely(!dt_try_as_dir(env, obj)))
-               GOTO(out, rc = -ENOTDIR);
+       return lso;
+}
 
-       /* Init the namespace-based directory traverse. */
-       iops = &obj->do_index_ops->dio_it;
-       di = iops->init(env, obj, lfsck->li_args_dir, BYPASS_CAPA);
-       if (IS_ERR(di))
-               GOTO(out, rc = PTR_ERR(di));
+struct dt_object *
+lfsck_assistant_object_load(const struct lu_env *env,
+                           struct lfsck_instance *lfsck,
+                           struct lfsck_assistant_object *lso)
+{
+       struct dt_object *obj;
 
-       LASSERT(pos->lp_dir_cookie < MDS_DIR_END_OFF);
+       obj = lfsck_object_find_bottom(env, lfsck, &lso->lso_fid);
+       if (IS_ERR(obj))
+               return obj;
 
-       rc = iops->load(env, di, pos->lp_dir_cookie);
-       if ((rc == 0) || (rc > 0 && pos->lp_dir_cookie > 0))
-               rc = iops->next(env, di);
-       else if (rc > 0)
-               rc = 0;
+       if (unlikely(!dt_object_exists(obj) || lfsck_is_dead_obj(obj))) {
+               lso->lso_dead = 1;
+               lfsck_object_put(env, obj);
 
-       if (rc != 0) {
-               iops->put(env, di);
-               iops->fini(env, di);
-               GOTO(out, rc);
+               return ERR_PTR(-ENOENT);
        }
 
-       lfsck->li_obj_dir = lfsck_object_get(obj);
-       lfsck->li_cookie_dir = iops->store(env, di);
-       spin_lock(&lfsck->li_lock);
-       lfsck->li_di_dir = di;
-       spin_unlock(&lfsck->li_lock);
-
-       GOTO(out, rc = 0);
-
-out:
-       if (obj != NULL)
+       if (lso->lso_is_dir && unlikely(!dt_try_as_dir(env, obj))) {
                lfsck_object_put(env, obj);
 
-       if (rc < 0) {
-               cfs_list_for_each_entry_safe(com, next, &lfsck->li_list_scan,
-                                            lc_link)
-                       com->lc_ops->lfsck_post(env, com, rc, true);
-
-               return rc;
-       }
-
-       rc = 0;
-       lfsck_pos_fill(env, lfsck, &lfsck->li_pos_current, true);
-       cfs_list_for_each_entry(com, &lfsck->li_list_scan, lc_link) {
-               rc = com->lc_ops->lfsck_checkpoint(env, com, true);
-               if (rc != 0)
-                       break;
+               return ERR_PTR(-ENOTDIR);
        }
 
-       lfsck->li_time_last_checkpoint = cfs_time_current();
-       lfsck->li_time_next_checkpoint = lfsck->li_time_last_checkpoint +
-                               cfs_time_seconds(LFSCK_CHECKPOINT_INTERVAL);
-       return rc;
+       return obj;
 }
 
-int lfsck_exec_oit(const struct lu_env *env, struct lfsck_instance *lfsck,
-                  struct dt_object *obj)
+/**
+ * Generic LFSCK asynchronous communication interpretor function.
+ * The LFSCK RPC reply for both the event notification and status
+ * querying will be handled here.
+ *
+ * \param[in] env      pointer to the thread context
+ * \param[in] req      pointer to the LFSCK request
+ * \param[in] args     pointer to the lfsck_async_interpret_args
+ * \param[in] rc       the result for handling the LFSCK request
+ *
+ * \retval             0 for success
+ * \retval             negative error number on failure
+ */
+int lfsck_async_interpret_common(const struct lu_env *env,
+                                struct ptlrpc_request *req,
+                                void *args, int rc)
 {
-       struct lfsck_component *com;
-       const struct dt_it_ops *iops;
-       struct dt_it           *di;
-       int                     rc;
-       ENTRY;
-
-       LASSERT(lfsck->li_obj_dir == NULL);
+       struct lfsck_async_interpret_args *laia = args;
+       struct lfsck_component            *com  = laia->laia_com;
+       struct lfsck_assistant_data       *lad  = com->lc_data;
+       struct lfsck_tgt_descs            *ltds = laia->laia_ltds;
+       struct lfsck_tgt_desc             *ltd  = laia->laia_ltd;
+       struct lfsck_request              *lr   = laia->laia_lr;
 
-       cfs_list_for_each_entry(com, &lfsck->li_list_scan, lc_link) {
-               rc = com->lc_ops->lfsck_exec_oit(env, com, obj);
-               if (rc != 0)
-                       RETURN(rc);
-       }
+       LASSERT(com->lc_lfsck->li_master);
 
-       rc = lfsck_needs_scan_dir(env, lfsck, obj);
-       if (rc <= 0)
-               GOTO(out, rc);
+       switch (lr->lr_event) {
+       case LE_START:
+               if (rc != 0) {
+                       CDEBUG(D_LFSCK, "%s: fail to notify %s %x for %s "
+                              "start: rc = %d\n",
+                              lfsck_lfsck2name(com->lc_lfsck),
+                              (lr->lr_flags & LEF_TO_OST) ? "OST" : "MDT",
+                              ltd->ltd_index, lad->lad_name, rc);
+
+                       if (com->lc_type == LFSCK_TYPE_LAYOUT) {
+                               struct lfsck_layout *lo = com->lc_file_ram;
+
+                               if (lr->lr_flags & LEF_TO_OST)
+                                       lfsck_lad_set_bitmap(env, com,
+                                                            ltd->ltd_index);
+                               else
+                                       lo->ll_flags |= LF_INCOMPLETE;
+                       } else {
+                               struct lfsck_namespace *ns = com->lc_file_ram;
+
+                               /* If some MDT does not join the namespace
+                                * LFSCK, then we cannot know whether there
+                                * is some name entry on such MDT that with
+                                * the referenced MDT-object on this MDT or
+                                * not. So the namespace LFSCK on this MDT
+                                * cannot handle orphan MDT-objects properly.
+                                * So we mark the LFSCK as LF_INCOMPLETE and
+                                * skip orphan MDT-objects handling. */
+                               ns->ln_flags |= LF_INCOMPLETE;
+                       }
+                       break;
+               }
 
-       if (unlikely(!dt_try_as_dir(env, obj)))
-               GOTO(out, rc = -ENOTDIR);
+               spin_lock(&ltds->ltd_lock);
+               if (ltd->ltd_dead) {
+                       spin_unlock(&ltds->ltd_lock);
+                       break;
+               }
 
-       iops = &obj->do_index_ops->dio_it;
-       di = iops->init(env, obj, lfsck->li_args_dir, BYPASS_CAPA);
-       if (IS_ERR(di))
-               GOTO(out, rc = PTR_ERR(di));
+               if (com->lc_type == LFSCK_TYPE_LAYOUT) {
+                       struct list_head *list;
+                       struct list_head *phase_list;
 
-       rc = iops->load(env, di, 0);
-       if (rc == 0)
-               rc = iops->next(env, di);
-       else if (rc > 0)
-               rc = 0;
+                       if (ltd->ltd_layout_done) {
+                               spin_unlock(&ltds->ltd_lock);
+                               break;
+                       }
 
-       if (rc != 0) {
-               iops->put(env, di);
-               iops->fini(env, di);
-               GOTO(out, rc);
-       }
+                       if (lr->lr_flags & LEF_TO_OST) {
+                               list = &lad->lad_ost_list;
+                               phase_list = &lad->lad_ost_phase1_list;
+                       } else {
+                               list = &lad->lad_mdt_list;
+                               phase_list = &lad->lad_mdt_phase1_list;
+                       }
 
-       lfsck->li_obj_dir = lfsck_object_get(obj);
-       lfsck->li_cookie_dir = iops->store(env, di);
-       spin_lock(&lfsck->li_lock);
-       lfsck->li_di_dir = di;
-       spin_unlock(&lfsck->li_lock);
+                       if (list_empty(&ltd->ltd_layout_list))
+                               list_add_tail(&ltd->ltd_layout_list, list);
+                       if (list_empty(&ltd->ltd_layout_phase_list))
+                               list_add_tail(&ltd->ltd_layout_phase_list,
+                                             phase_list);
+               } else {
+                       if (ltd->ltd_namespace_done) {
+                               spin_unlock(&ltds->ltd_lock);
+                               break;
+                       }
 
-       GOTO(out, rc = 0);
+                       if (list_empty(&ltd->ltd_namespace_list))
+                               list_add_tail(&ltd->ltd_namespace_list,
+                                             &lad->lad_mdt_list);
+                       if (list_empty(&ltd->ltd_namespace_phase_list))
+                               list_add_tail(&ltd->ltd_namespace_phase_list,
+                                             &lad->lad_mdt_phase1_list);
+               }
+               spin_unlock(&ltds->ltd_lock);
+               break;
+       case LE_STOP:
+       case LE_PHASE1_DONE:
+       case LE_PHASE2_DONE:
+       case LE_PEER_EXIT:
+               if (rc != 0 && rc != -EALREADY)
+                       CDEBUG(D_LFSCK, "%s: fail to notify %s %x for %s: "
+                             "event = %d, rc = %d\n",
+                             lfsck_lfsck2name(com->lc_lfsck),
+                             (lr->lr_flags & LEF_TO_OST) ? "OST" : "MDT",
+                             ltd->ltd_index, lad->lad_name, lr->lr_event, rc);
+               break;
+       case LE_QUERY: {
+               struct lfsck_reply *reply;
+               struct list_head *list;
+               struct list_head *phase_list;
+
+               if (com->lc_type == LFSCK_TYPE_LAYOUT) {
+                       list = &ltd->ltd_layout_list;
+                       phase_list = &ltd->ltd_layout_phase_list;
+               } else {
+                       list = &ltd->ltd_namespace_list;
+                       phase_list = &ltd->ltd_namespace_phase_list;
+               }
 
-out:
-       if (rc < 0)
-               lfsck_fail(env, lfsck, false);
-       return (rc > 0 ? 0 : rc);
-}
+               if (rc != 0) {
+                       spin_lock(&ltds->ltd_lock);
+                       list_del_init(phase_list);
+                       list_del_init(list);
+                       spin_unlock(&ltds->ltd_lock);
+                       break;
+               }
 
-int lfsck_exec_dir(const struct lu_env *env, struct lfsck_instance *lfsck,
-                  struct dt_object *obj, struct lu_dirent *ent)
-{
-       struct lfsck_component *com;
-       int                     rc;
+               reply = req_capsule_server_get(&req->rq_pill,
+                                              &RMF_LFSCK_REPLY);
+               if (reply == NULL) {
+                       rc = -EPROTO;
+                       CDEBUG(D_LFSCK, "%s: invalid query reply for %s: "
+                              "rc = %d\n", lfsck_lfsck2name(com->lc_lfsck),
+                              lad->lad_name, rc);
+                       spin_lock(&ltds->ltd_lock);
+                       list_del_init(phase_list);
+                       list_del_init(list);
+                       spin_unlock(&ltds->ltd_lock);
+                       break;
+               }
 
-       cfs_list_for_each_entry(com, &lfsck->li_list_scan, lc_link) {
-               rc = com->lc_ops->lfsck_exec_dir(env, com, obj, ent);
-               if (rc != 0)
-                       return rc;
-       }
-       return 0;
-}
+               switch (reply->lr_status) {
+               case LS_SCANNING_PHASE1:
+                       break;
+               case LS_SCANNING_PHASE2:
+                       spin_lock(&ltds->ltd_lock);
+                       list_del_init(phase_list);
+                       if (ltd->ltd_dead) {
+                               spin_unlock(&ltds->ltd_lock);
+                               break;
+                       }
 
-int lfsck_post(const struct lu_env *env, struct lfsck_instance *lfsck,
-              int result)
-{
-       struct lfsck_component *com;
-       struct lfsck_component *next;
-       int                     rc  = 0;
-       int                     rc1 = 0;
+                       if (com->lc_type == LFSCK_TYPE_LAYOUT) {
+                               if (ltd->ltd_layout_done) {
+                                       spin_unlock(&ltds->ltd_lock);
+                                       break;
+                               }
 
-       lfsck_pos_fill(env, lfsck, &lfsck->li_pos_current, false);
-       cfs_list_for_each_entry_safe(com, next, &lfsck->li_list_scan, lc_link) {
-               rc = com->lc_ops->lfsck_post(env, com, result, false);
-               if (rc != 0)
-                       rc1 = rc;
+                               if (lr->lr_flags & LEF_TO_OST)
+                                       list_add_tail(phase_list,
+                                               &lad->lad_ost_phase2_list);
+                               else
+                                       list_add_tail(phase_list,
+                                               &lad->lad_mdt_phase2_list);
+                       } else {
+                               if (ltd->ltd_namespace_done) {
+                                       spin_unlock(&ltds->ltd_lock);
+                                       break;
+                               }
+
+                               list_add_tail(phase_list,
+                                             &lad->lad_mdt_phase2_list);
+                       }
+                       spin_unlock(&ltds->ltd_lock);
+                       break;
+               default:
+                       spin_lock(&ltds->ltd_lock);
+                       list_del_init(phase_list);
+                       list_del_init(list);
+                       spin_unlock(&ltds->ltd_lock);
+                       break;
+               }
+               break;
+       }
+       default:
+               CDEBUG(D_LFSCK, "%s: unexpected event: rc = %d\n",
+                      lfsck_lfsck2name(com->lc_lfsck), lr->lr_event);
+               break;
        }
 
-       lfsck->li_time_last_checkpoint = cfs_time_current();
-       lfsck->li_time_next_checkpoint = lfsck->li_time_last_checkpoint +
-                               cfs_time_seconds(LFSCK_CHECKPOINT_INTERVAL);
+       if (!laia->laia_shared) {
+               lfsck_tgt_put(ltd);
+               lfsck_component_put(env, com);
+       }
 
-       /* Ignore some component post failure to make other can go ahead. */
-       return result;
+       return 0;
 }
 
 static void lfsck_interpret(const struct lu_env *env,
@@ -1449,66 +2247,28 @@ static void lfsck_interpret(const struct lu_env *env,
 
        spin_lock(&lfsck->li_lock);
        list_for_each_entry(com, &lfsck->li_list_scan, lc_link) {
-               if (com->lc_ops->lfsck_interpret != NULL) {
-                       laia->laia_com = com;
-                       com->lc_ops->lfsck_interpret(env, req, laia, result);
-               }
+               laia->laia_com = com;
+               lfsck_async_interpret_common(env, req, laia, result);
        }
 
        list_for_each_entry(com, &lfsck->li_list_double_scan, lc_link) {
-               if (com->lc_ops->lfsck_interpret != NULL) {
-                       laia->laia_com = com;
-                       com->lc_ops->lfsck_interpret(env, req, laia, result);
-               }
+               laia->laia_com = com;
+               lfsck_async_interpret_common(env, req, laia, result);
        }
        spin_unlock(&lfsck->li_lock);
 }
 
-int lfsck_double_scan(const struct lu_env *env, struct lfsck_instance *lfsck)
-{
-       struct lfsck_component *com;
-       struct lfsck_component *next;
-       struct l_wait_info      lwi = { 0 };
-       int                     rc  = 0;
-       int                     rc1 = 0;
-
-       list_for_each_entry(com, &lfsck->li_list_double_scan, lc_link) {
-               if (lfsck->li_bookmark_ram.lb_param & LPF_DRYRUN)
-                       com->lc_journal = 0;
-
-               rc = com->lc_ops->lfsck_double_scan(env, com);
-               if (rc != 0)
-                       rc1 = rc;
-       }
-
-       l_wait_event(lfsck->li_thread.t_ctl_waitq,
-                    atomic_read(&lfsck->li_double_scan_count) == 0,
-                    &lwi);
-
-       if (lfsck->li_status != LS_PAUSED &&
-           lfsck->li_status != LS_CO_PAUSED) {
-               list_for_each_entry_safe(com, next, &lfsck->li_list_double_scan,
-                                        lc_link) {
-                       spin_lock(&lfsck->li_lock);
-                       list_del_init(&com->lc_link);
-                       list_add_tail(&com->lc_link, &lfsck->li_list_idle);
-                       spin_unlock(&lfsck->li_lock);
-               }
-       }
-
-       return rc1 != 0 ? rc1 : rc;
-}
-
 static int lfsck_stop_notify(const struct lu_env *env,
                             struct lfsck_instance *lfsck,
                             struct lfsck_tgt_descs *ltds,
                             struct lfsck_tgt_desc *ltd, __u16 type)
 {
-       struct ptlrpc_request_set *set;
-       struct lfsck_component    *com;
-       int                        rc  = 0;
+       struct lfsck_component *com;
+       int                     rc = 0;
        ENTRY;
 
+       LASSERT(lfsck->li_master);
+
        spin_lock(&lfsck->li_lock);
        com = __lfsck_component_find(lfsck, type, &lfsck->li_list_scan);
        if (com == NULL)
@@ -1516,58 +2276,79 @@ static int lfsck_stop_notify(const struct lu_env *env,
                                             &lfsck->li_list_double_scan);
        if (com != NULL)
                lfsck_component_get(com);
-       spin_lock(&lfsck->li_lock);
+       spin_unlock(&lfsck->li_lock);
 
        if (com != NULL) {
-               if (com->lc_ops->lfsck_stop_notify != NULL) {
-                       set = ptlrpc_prep_set();
-                       if (set == NULL) {
-                               lfsck_component_put(env, com);
+               struct lfsck_thread_info          *info  = lfsck_env_info(env);
+               struct lfsck_async_interpret_args *laia  = &info->lti_laia;
+               struct lfsck_request              *lr    = &info->lti_lr;
+               struct lfsck_assistant_data       *lad   = com->lc_data;
+               struct list_head                  *list;
+               struct list_head                  *phase_list;
+               struct ptlrpc_request_set         *set;
+
+               set = ptlrpc_prep_set();
+               if (set == NULL) {
+                       lfsck_component_put(env, com);
 
-                               RETURN(-ENOMEM);
-                       }
+                       RETURN(-ENOMEM);
+               }
 
-                       rc = com->lc_ops->lfsck_stop_notify(env, com, ltds,
-                                                           ltd, set);
-                       if (rc == 0)
-                               rc = ptlrpc_set_wait(set);
+               if (type == LFSCK_TYPE_LAYOUT) {
+                       list = &ltd->ltd_layout_list;
+                       phase_list = &ltd->ltd_layout_phase_list;
+               } else {
+                       list = &ltd->ltd_namespace_list;
+                       phase_list = &ltd->ltd_namespace_phase_list;
+               }
 
+               spin_lock(&ltds->ltd_lock);
+               if (list_empty(list)) {
+                       LASSERT(list_empty(phase_list));
+                       spin_unlock(&ltds->ltd_lock);
                        ptlrpc_set_destroy(set);
-               }
 
-               lfsck_component_put(env, com);
-       }
+                       RETURN(0);
+               }
 
-       RETURN(rc);
-}
+               list_del_init(phase_list);
+               list_del_init(list);
+               spin_unlock(&ltds->ltd_lock);
 
-void lfsck_quit(const struct lu_env *env, struct lfsck_instance *lfsck)
-{
-       struct lfsck_component *com;
-       struct lfsck_component *next;
+               memset(lr, 0, sizeof(*lr));
+               lr->lr_index = lfsck_dev_idx(lfsck);
+               lr->lr_event = LE_PEER_EXIT;
+               lr->lr_active = type;
+               lr->lr_status = LS_CO_PAUSED;
+               if (ltds == &lfsck->li_ost_descs)
+                       lr->lr_flags = LEF_TO_OST;
+
+               laia->laia_com = com;
+               laia->laia_ltds = ltds;
+               atomic_inc(&ltd->ltd_ref);
+               laia->laia_ltd = ltd;
+               laia->laia_lr = lr;
+               laia->laia_shared = 0;
 
-       list_for_each_entry_safe(com, next, &lfsck->li_list_scan,
-                                lc_link) {
-               if (com->lc_ops->lfsck_quit != NULL)
-                       com->lc_ops->lfsck_quit(env, com);
+               rc = lfsck_async_request(env, ltd->ltd_exp, lr, set,
+                                        lfsck_async_interpret_common,
+                                        laia, LFSCK_NOTIFY);
+               if (rc != 0) {
+                       CDEBUG(D_LFSCK, "%s: fail to notify %s %x for "
+                              "co-stop for %s: rc = %d\n",
+                              lfsck_lfsck2name(lfsck),
+                              (lr->lr_flags & LEF_TO_OST) ? "OST" : "MDT",
+                              ltd->ltd_index, lad->lad_name, rc);
+                       lfsck_tgt_put(ltd);
+               } else {
+                       rc = ptlrpc_set_wait(set);
+               }
 
-               spin_lock(&lfsck->li_lock);
-               list_del_init(&com->lc_link);
-               list_del_init(&com->lc_link_dir);
-               list_add_tail(&com->lc_link, &lfsck->li_list_idle);
-               spin_unlock(&lfsck->li_lock);
+               ptlrpc_set_destroy(set);
+               lfsck_component_put(env, com);
        }
 
-       list_for_each_entry_safe(com, next, &lfsck->li_list_double_scan,
-                                lc_link) {
-               if (com->lc_ops->lfsck_quit != NULL)
-                       com->lc_ops->lfsck_quit(env, com);
-
-               spin_lock(&lfsck->li_lock);
-               list_del_init(&com->lc_link);
-               list_add_tail(&com->lc_link, &lfsck->li_list_idle);
-               spin_unlock(&lfsck->li_lock);
-       }
+       RETURN(rc);
 }
 
 static int lfsck_async_interpret(const struct lu_env *env,
@@ -1599,9 +2380,6 @@ int lfsck_async_request(const struct lu_env *env, struct obd_export *exp,
        struct req_format                 *format;
        int                                rc;
 
-       if (!(exp_connect_flags(exp) & OBD_CONNECT_LFSCK))
-               return -EOPNOTSUPP;
-
        switch (request) {
        case LFSCK_NOTIFY:
                format = &RQF_LFSCK_NOTIFY;
@@ -1610,8 +2388,8 @@ int lfsck_async_request(const struct lu_env *env, struct obd_export *exp,
                format = &RQF_LFSCK_QUERY;
                break;
        default:
-               CERROR("%s: unknown async request: opc = %d\n",
-                      exp->exp_obd->obd_name, request);
+               CDEBUG(D_LFSCK, "%s: unknown async request %d: rc = %d\n",
+                      exp->exp_obd->obd_name, request, -EINVAL);
                return -EINVAL;
        }
 
@@ -1635,14 +2413,160 @@ int lfsck_async_request(const struct lu_env *env, struct obd_export *exp,
        if (laia->laia_com != NULL)
                lfsck_component_get(laia->laia_com);
        req->rq_interpret_reply = interpreter;
+       req->rq_allow_intr = 1;
        ptlrpc_set_add_req(set, req);
 
        return 0;
 }
 
+int lfsck_start_assistant(const struct lu_env *env, struct lfsck_component *com,
+                         struct lfsck_start_param *lsp)
+{
+       struct lfsck_instance           *lfsck   = com->lc_lfsck;
+       struct lfsck_assistant_data     *lad     = com->lc_data;
+       struct ptlrpc_thread            *mthread = &lfsck->li_thread;
+       struct ptlrpc_thread            *athread = &lad->lad_thread;
+       struct lfsck_thread_args        *lta;
+       struct task_struct              *task;
+       int                              rc;
+       ENTRY;
+
+       lad->lad_assistant_status = 0;
+       lad->lad_post_result = 0;
+       lad->lad_to_post = 0;
+       lad->lad_to_double_scan = 0;
+       lad->lad_in_double_scan = 0;
+       lad->lad_exit = 0;
+       lad->lad_advance_lock = false;
+       thread_set_flags(athread, 0);
+
+       lta = lfsck_thread_args_init(lfsck, com, lsp);
+       if (IS_ERR(lta))
+               RETURN(PTR_ERR(lta));
+
+       task = kthread_run(lfsck_assistant_engine, lta, lad->lad_name);
+       if (IS_ERR(task)) {
+               rc = PTR_ERR(task);
+               CERROR("%s: cannot start LFSCK assistant thread for %s: "
+                      "rc = %d\n", lfsck_lfsck2name(lfsck), lad->lad_name, rc);
+               lfsck_thread_args_fini(lta);
+       } else {
+               struct l_wait_info lwi = { 0 };
+
+               l_wait_event(mthread->t_ctl_waitq,
+                            thread_is_running(athread) ||
+                            thread_is_stopped(athread),
+                            &lwi);
+               if (unlikely(!thread_is_running(athread)))
+                       rc = lad->lad_assistant_status;
+               else
+                       rc = 0;
+       }
+
+       RETURN(rc);
+}
+
+int lfsck_checkpoint_generic(const struct lu_env *env,
+                            struct lfsck_component *com)
+{
+       struct lfsck_assistant_data     *lad     = com->lc_data;
+       struct ptlrpc_thread            *mthread = &com->lc_lfsck->li_thread;
+       struct ptlrpc_thread            *athread = &lad->lad_thread;
+       struct l_wait_info               lwi     = { 0 };
+
+       l_wait_event(mthread->t_ctl_waitq,
+                    list_empty(&lad->lad_req_list) ||
+                    !thread_is_running(mthread) ||
+                    thread_is_stopped(athread),
+                    &lwi);
+
+       if (!thread_is_running(mthread) || thread_is_stopped(athread))
+               return LFSCK_CHECKPOINT_SKIP;
+
+       return 0;
+}
+
+void lfsck_post_generic(const struct lu_env *env,
+                       struct lfsck_component *com, int *result)
+{
+       struct lfsck_assistant_data     *lad     = com->lc_data;
+       struct ptlrpc_thread            *athread = &lad->lad_thread;
+       struct ptlrpc_thread            *mthread = &com->lc_lfsck->li_thread;
+       struct l_wait_info               lwi     = { 0 };
+
+       lad->lad_post_result = *result;
+       if (*result <= 0)
+               lad->lad_exit = 1;
+       lad->lad_to_post = 1;
+
+       CDEBUG(D_LFSCK, "%s: waiting for assistant to do %s post, rc = %d\n",
+              lfsck_lfsck2name(com->lc_lfsck), lad->lad_name, *result);
+
+       wake_up_all(&athread->t_ctl_waitq);
+       l_wait_event(mthread->t_ctl_waitq,
+                    (*result > 0 && list_empty(&lad->lad_req_list)) ||
+                    thread_is_stopped(athread),
+                    &lwi);
+
+       if (lad->lad_assistant_status < 0)
+               *result = lad->lad_assistant_status;
+
+       CDEBUG(D_LFSCK, "%s: the assistant has done %s post, rc = %d\n",
+              lfsck_lfsck2name(com->lc_lfsck), lad->lad_name, *result);
+}
+
+int lfsck_double_scan_generic(const struct lu_env *env,
+                             struct lfsck_component *com, int status)
+{
+       struct lfsck_assistant_data     *lad     = com->lc_data;
+       struct ptlrpc_thread            *mthread = &com->lc_lfsck->li_thread;
+       struct ptlrpc_thread            *athread = &lad->lad_thread;
+       struct l_wait_info               lwi     = { 0 };
+
+       if (status != LS_SCANNING_PHASE2)
+               lad->lad_exit = 1;
+       else
+               lad->lad_to_double_scan = 1;
+
+       CDEBUG(D_LFSCK, "%s: waiting for assistant to do %s double_scan, "
+              "status %d\n",
+              lfsck_lfsck2name(com->lc_lfsck), lad->lad_name, status);
+
+       wake_up_all(&athread->t_ctl_waitq);
+       l_wait_event(mthread->t_ctl_waitq,
+                    lad->lad_in_double_scan ||
+                    thread_is_stopped(athread),
+                    &lwi);
+
+       CDEBUG(D_LFSCK, "%s: the assistant has done %s double_scan, "
+              "status %d\n", lfsck_lfsck2name(com->lc_lfsck), lad->lad_name,
+              lad->lad_assistant_status);
+
+       if (lad->lad_assistant_status < 0)
+               return lad->lad_assistant_status;
+
+       return 0;
+}
+
+void lfsck_quit_generic(const struct lu_env *env,
+                       struct lfsck_component *com)
+{
+       struct lfsck_assistant_data     *lad     = com->lc_data;
+       struct ptlrpc_thread            *mthread = &com->lc_lfsck->li_thread;
+       struct ptlrpc_thread            *athread = &lad->lad_thread;
+       struct l_wait_info               lwi     = { 0 };
+
+       lad->lad_exit = 1;
+       wake_up_all(&athread->t_ctl_waitq);
+       l_wait_event(mthread->t_ctl_waitq,
+                    thread_is_init(athread) ||
+                    thread_is_stopped(athread),
+                    &lwi);
+}
+
 /* external interfaces */
 
-int lfsck_get_speed(struct dt_device *key, void *buf, int len)
+int lfsck_get_speed(struct seq_file *m, struct dt_device *key)
 {
        struct lu_env           env;
        struct lfsck_instance  *lfsck;
@@ -1655,8 +2579,7 @@ int lfsck_get_speed(struct dt_device *key, void *buf, int len)
 
        lfsck = lfsck_instance_find(key, true, false);
        if (likely(lfsck != NULL)) {
-               rc = snprintf(buf, len, "%u\n",
-                             lfsck->li_bookmark_ram.lb_speed_limit);
+               seq_printf(m, "%u\n", lfsck->li_bookmark_ram.lb_speed_limit);
                lfsck_instance_put(&env, lfsck);
        } else {
                rc = -ENXIO;
@@ -1682,8 +2605,8 @@ int lfsck_set_speed(struct dt_device *key, int val)
        lfsck = lfsck_instance_find(key, true, false);
        if (likely(lfsck != NULL)) {
                mutex_lock(&lfsck->li_mutex);
-               __lfsck_set_speed(lfsck, val);
-               rc = lfsck_bookmark_store(&env, lfsck);
+               if (__lfsck_set_speed(lfsck, val))
+                       rc = lfsck_bookmark_store(&env, lfsck);
                mutex_unlock(&lfsck->li_mutex);
                lfsck_instance_put(&env, lfsck);
        } else {
@@ -1696,7 +2619,7 @@ int lfsck_set_speed(struct dt_device *key, int val)
 }
 EXPORT_SYMBOL(lfsck_set_speed);
 
-int lfsck_get_windows(struct dt_device *key, void *buf, int len)
+int lfsck_get_windows(struct seq_file *m, struct dt_device *key)
 {
        struct lu_env           env;
        struct lfsck_instance  *lfsck;
@@ -1709,8 +2632,7 @@ int lfsck_get_windows(struct dt_device *key, void *buf, int len)
 
        lfsck = lfsck_instance_find(key, true, false);
        if (likely(lfsck != NULL)) {
-               rc = snprintf(buf, len, "%u\n",
-                             lfsck->li_bookmark_ram.lb_async_windows);
+               seq_printf(m, "%u\n", lfsck->li_bookmark_ram.lb_async_windows);
                lfsck_instance_put(&env, lfsck);
        } else {
                rc = -ENXIO;
@@ -1735,13 +2657,11 @@ int lfsck_set_windows(struct dt_device *key, int val)
 
        lfsck = lfsck_instance_find(key, true, false);
        if (likely(lfsck != NULL)) {
-               if (val > LFSCK_ASYNC_WIN_MAX) {
-                       CERROR("%s: Too large async windows size, which "
-                              "may cause memory issues. The valid range "
-                              "is [0 - %u]. If you do not want to restrict "
-                              "the windows size for async requests pipeline, "
-                              "just set it as 0.\n",
-                              lfsck_lfsck2name(lfsck), LFSCK_ASYNC_WIN_MAX);
+               if (val < 1 || val > LFSCK_ASYNC_WIN_MAX) {
+                       CWARN("%s: invalid async windows size that may "
+                             "cause memory issues. The valid range is "
+                             "[1 - %u].\n",
+                             lfsck_lfsck2name(lfsck), LFSCK_ASYNC_WIN_MAX);
                        rc = -EINVAL;
                } else if (lfsck->li_bookmark_ram.lb_async_windows != val) {
                        mutex_lock(&lfsck->li_mutex);
@@ -1760,7 +2680,7 @@ int lfsck_set_windows(struct dt_device *key, int val)
 }
 EXPORT_SYMBOL(lfsck_set_windows);
 
-int lfsck_dump(struct dt_device *key, void *buf, int len, enum lfsck_type type)
+int lfsck_dump(struct seq_file *m, struct dt_device *key, enum lfsck_type type)
 {
        struct lu_env           env;
        struct lfsck_instance  *lfsck;
@@ -1776,7 +2696,7 @@ int lfsck_dump(struct dt_device *key, void *buf, int len, enum lfsck_type type)
        if (likely(lfsck != NULL)) {
                com = lfsck_component_find(lfsck, type);
                if (likely(com != NULL)) {
-                       rc = com->lc_ops->lfsck_dump(&env, com, buf, len);
+                       rc = com->lc_ops->lfsck_dump(&env, com, m);
                        lfsck_component_put(&env, com);
                } else {
                        rc = -ENOTSUPP;
@@ -1812,16 +2732,12 @@ static int lfsck_stop_all(const struct lu_env *env,
        LASSERT(stop->ls_flags & LPF_BROADCAST);
 
        set = ptlrpc_prep_set();
-       if (unlikely(set == NULL)) {
-               CERROR("%s: cannot allocate memory for stop LFSCK on "
-                      "all targets\n", lfsck_lfsck2name(lfsck));
-
+       if (unlikely(set == NULL))
                RETURN(-ENOMEM);
-       }
 
        memset(lr, 0, sizeof(*lr));
        lr->lr_event = LE_STOP;
-       lr->lr_index = lfsck_dev_idx(lfsck->li_bottom);
+       lr->lr_index = lfsck_dev_idx(lfsck);
        lr->lr_status = stop->ls_status;
        lr->lr_version = bk->lb_version;
        lr->lr_active = LFSCK_TYPES_ALL;
@@ -1845,8 +2761,8 @@ static int lfsck_stop_all(const struct lu_env *env,
                if (rc != 0) {
                        lfsck_interpret(env, lfsck, NULL, laia, rc);
                        lfsck_tgt_put(ltd);
-                       CWARN("%s: cannot notify MDT %x for LFSCK stop: "
-                             "rc = %d\n", lfsck_lfsck2name(lfsck), idx, rc);
+                       CERROR("%s: cannot notify MDT %x for LFSCK stop: "
+                              "rc = %d\n", lfsck_lfsck2name(lfsck), idx, rc);
                        rc1 = rc;
                }
        }
@@ -1862,8 +2778,8 @@ static int lfsck_stop_all(const struct lu_env *env,
                rc = 0;
 
        if (rc != 0)
-               CWARN("%s: fail to stop LFSCK on some MDTs: rc = %d\n",
-                     lfsck_lfsck2name(lfsck), rc);
+               CERROR("%s: fail to stop LFSCK on some MDTs: rc = %d\n",
+                      lfsck_lfsck2name(lfsck), rc);
 
        RETURN(rc != 0 ? rc : rc1);
 }
@@ -1886,32 +2802,20 @@ static int lfsck_start_all(const struct lu_env *env,
        LASSERT(start->ls_flags & LPF_BROADCAST);
 
        set = ptlrpc_prep_set();
-       if (unlikely(set == NULL)) {
-               if (bk->lb_param & LPF_FAILOUT) {
-                       CERROR("%s: cannot allocate memory for start LFSCK on "
-                              "all targets, failout.\n",
-                              lfsck_lfsck2name(lfsck));
-
-                       RETURN(-ENOMEM);
-               } else {
-                       CWARN("%s: cannot allocate memory for start LFSCK on "
-                             "all targets, partly scan.\n",
-                             lfsck_lfsck2name(lfsck));
-
-                       RETURN(0);
-               }
-       }
+       if (unlikely(set == NULL))
+               RETURN(-ENOMEM);
 
        memset(lr, 0, sizeof(*lr));
        lr->lr_event = LE_START;
-       lr->lr_index = lfsck_dev_idx(lfsck->li_bottom);
+       lr->lr_index = lfsck_dev_idx(lfsck);
        lr->lr_speed = bk->lb_speed_limit;
        lr->lr_version = bk->lb_version;
        lr->lr_active = start->ls_active;
        lr->lr_param = start->ls_flags;
        lr->lr_async_windows = bk->lb_async_windows;
        lr->lr_valid = LSV_SPEED_LIMIT | LSV_ERROR_HANDLE | LSV_DRYRUN |
-                      LSV_ASYNC_WINDOWS;
+                      LSV_ASYNC_WINDOWS | LSV_CREATE_OSTOBJ |
+                      LSV_CREATE_MDTOBJ;
 
        laia->laia_com = NULL;
        laia->laia_ltds = ltds;
@@ -1926,23 +2830,18 @@ static int lfsck_start_all(const struct lu_env *env,
 
                laia->laia_ltd = ltd;
                ltd->ltd_layout_done = 0;
+               ltd->ltd_namespace_done = 0;
+               ltd->ltd_synced_failures = 0;
                rc = lfsck_async_request(env, ltd->ltd_exp, lr, set,
                                         lfsck_async_interpret, laia,
                                         LFSCK_NOTIFY);
                if (rc != 0) {
                        lfsck_interpret(env, lfsck, NULL, laia, rc);
                        lfsck_tgt_put(ltd);
-                       if (bk->lb_param & LPF_FAILOUT) {
-                               CERROR("%s: cannot notify MDT %x for LFSCK "
-                                      "start, failout: rc = %d\n",
-                                      lfsck_lfsck2name(lfsck), idx, rc);
-                               break;
-                       } else {
-                               CWARN("%s: cannot notify MDT %x for LFSCK "
-                                     "start, partly scan: rc = %d\n",
-                                     lfsck_lfsck2name(lfsck), idx, rc);
-                               rc = 0;
-                       }
+                       CERROR("%s: cannot notify MDT %x for LFSCK "
+                              "start, failout: rc = %d\n",
+                              lfsck_lfsck2name(lfsck), idx, rc);
+                       break;
                }
        }
        up_read(&ltds->ltd_rw_sem);
@@ -1960,22 +2859,15 @@ static int lfsck_start_all(const struct lu_env *env,
                rc = laia->laia_result;
 
        if (rc != 0) {
-               if (bk->lb_param & LPF_FAILOUT) {
-                       struct lfsck_stop *stop = &info->lti_stop;
+               struct lfsck_stop *stop = &info->lti_stop;
 
-                       CERROR("%s: cannot start LFSCK on some MDTs, "
-                              "stop all: rc = %d\n",
-                              lfsck_lfsck2name(lfsck), rc);
-                       if (rc != -EALREADY) {
-                               stop->ls_status = LS_FAILED;
-                               stop->ls_flags = LPF_ALL_TGT | LPF_BROADCAST;
-                               lfsck_stop_all(env, lfsck, stop);
-                       }
-               } else {
-                       CWARN("%s: cannot start LFSCK on some MDTs, "
-                             "partly scan: rc = %d\n",
-                             lfsck_lfsck2name(lfsck), rc);
-                       rc = 0;
+               CERROR("%s: cannot start LFSCK on some MDTs, "
+                      "stop all: rc = %d\n",
+                      lfsck_lfsck2name(lfsck), rc);
+               if (rc != -EALREADY) {
+                       stop->ls_status = LS_FAILED;
+                       stop->ls_flags = LPF_ALL_TGT | LPF_BROADCAST;
+                       lfsck_stop_all(env, lfsck, stop);
                }
        }
 
@@ -1992,8 +2884,8 @@ int lfsck_start(const struct lu_env *env, struct dt_device *key,
        struct lfsck_component          *com;
        struct l_wait_info               lwi    = { 0 };
        struct lfsck_thread_args        *lta;
-       bool                             dirty  = false;
-       long                             rc     = 0;
+       struct task_struct              *task;
+       int                              rc     = 0;
        __u16                            valid  = 0;
        __u16                            flags  = 0;
        __u16                            type   = 1;
@@ -2009,7 +2901,7 @@ int lfsck_start(const struct lu_env *env, struct dt_device *key,
 
        /* start == NULL means auto trigger paused LFSCK. */
        if ((start == NULL) &&
-           (cfs_list_empty(&lfsck->li_list_scan) ||
+           (list_empty(&lfsck->li_list_scan) ||
             OBD_FAIL_CHECK(OBD_FAIL_LFSCK_NO_AUTO)))
                GOTO(put, rc = 0);
 
@@ -2019,6 +2911,11 @@ int lfsck_start(const struct lu_env *env, struct dt_device *key,
        spin_lock(&lfsck->li_lock);
        if (!thread_is_init(thread) && !thread_is_stopped(thread)) {
                rc = -EALREADY;
+               if (unlikely(start == NULL)) {
+                       spin_unlock(&lfsck->li_lock);
+                       GOTO(out, rc);
+               }
+
                while (start->ls_active != 0) {
                        if (!(type & start->ls_active)) {
                                type <<= 1;
@@ -2066,78 +2963,6 @@ int lfsck_start(const struct lu_env *env, struct dt_device *key,
        }
 
        start->ls_version = bk->lb_version;
-       if (start->ls_valid & LSV_SPEED_LIMIT) {
-               __lfsck_set_speed(lfsck, start->ls_speed_limit);
-               dirty = true;
-       }
-
-       if (start->ls_valid & LSV_ASYNC_WINDOWS &&
-           bk->lb_async_windows != start->ls_async_windows) {
-               bk->lb_async_windows = start->ls_async_windows;
-               dirty = true;
-       }
-
-       if (start->ls_valid & LSV_ERROR_HANDLE) {
-               valid |= DOIV_ERROR_HANDLE;
-               if (start->ls_flags & LPF_FAILOUT)
-                       flags |= DOIF_FAILOUT;
-
-               if ((start->ls_flags & LPF_FAILOUT) &&
-                   !(bk->lb_param & LPF_FAILOUT)) {
-                       bk->lb_param |= LPF_FAILOUT;
-                       dirty = true;
-               } else if (!(start->ls_flags & LPF_FAILOUT) &&
-                          (bk->lb_param & LPF_FAILOUT)) {
-                       bk->lb_param &= ~LPF_FAILOUT;
-                       dirty = true;
-               }
-       }
-
-       if (start->ls_valid & LSV_DRYRUN) {
-               valid |= DOIV_DRYRUN;
-               if (start->ls_flags & LPF_DRYRUN)
-                       flags |= DOIF_DRYRUN;
-
-               if ((start->ls_flags & LPF_DRYRUN) &&
-                   !(bk->lb_param & LPF_DRYRUN)) {
-                       bk->lb_param |= LPF_DRYRUN;
-                       dirty = true;
-               } else if (!(start->ls_flags & LPF_DRYRUN) &&
-                          (bk->lb_param & LPF_DRYRUN)) {
-                       bk->lb_param &= ~LPF_DRYRUN;
-                       lfsck->li_drop_dryrun = 1;
-                       dirty = true;
-               }
-       }
-
-       if (bk->lb_param & LPF_ALL_TGT &&
-           !(start->ls_flags & LPF_ALL_TGT)) {
-               bk->lb_param &= ~LPF_ALL_TGT;
-               dirty = true;
-       } else if (!(bk->lb_param & LPF_ALL_TGT) &&
-                  start->ls_flags & LPF_ALL_TGT) {
-               bk->lb_param |= LPF_ALL_TGT;
-               dirty = true;
-       }
-
-       if (bk->lb_param & LPF_ORPHAN &&
-           !(start->ls_flags & LPF_ORPHAN)) {
-               bk->lb_param &= ~LPF_ORPHAN;
-               dirty = true;
-       } else if (!(bk->lb_param & LPF_ORPHAN) &&
-                  start->ls_flags & LPF_ORPHAN) {
-               bk->lb_param |= LPF_ORPHAN;
-               dirty = true;
-       }
-
-       if (dirty) {
-               rc = lfsck_bookmark_store(env, lfsck);
-               if (rc != 0)
-                       GOTO(out, rc);
-       }
-
-       if (start->ls_flags & LPF_RESET)
-               flags |= DOIF_RESET;
 
        if (start->ls_active != 0) {
                struct lfsck_component *next;
@@ -2150,8 +2975,8 @@ int lfsck_start(const struct lu_env *env, struct dt_device *key,
                        GOTO(out, rc = -ENOTSUPP);
                }
 
-               cfs_list_for_each_entry_safe(com, next,
-                                            &lfsck->li_list_scan, lc_link) {
+               list_for_each_entry_safe(com, next,
+                                        &lfsck->li_list_scan, lc_link) {
                        if (!(com->lc_type & start->ls_active)) {
                                rc = com->lc_ops->lfsck_post(env, com, 0,
                                                             false);
@@ -2164,21 +2989,40 @@ int lfsck_start(const struct lu_env *env, struct dt_device *key,
                        if (type & start->ls_active) {
                                com = __lfsck_component_find(lfsck, type,
                                                        &lfsck->li_list_idle);
-                               if (com != NULL) {
+                               if (com != NULL)
                                        /* The component status will be updated
                                         * when its prep() is called later by
                                         * the LFSCK main engine. */
-                                       cfs_list_del_init(&com->lc_link);
-                                       cfs_list_add_tail(&com->lc_link,
-                                                         &lfsck->li_list_scan);
-                               }
+                                       list_move_tail(&com->lc_link,
+                                                      &lfsck->li_list_scan);
                                start->ls_active &= ~type;
                        }
                        type <<= 1;
                }
        }
 
-       cfs_list_for_each_entry(com, &lfsck->li_list_scan, lc_link) {
+       if (list_empty(&lfsck->li_list_scan)) {
+               /* The speed limit will be used to control both the LFSCK and
+                * low layer scrub (if applied), need to be handled firstly. */
+               if (start->ls_valid & LSV_SPEED_LIMIT) {
+                       if (__lfsck_set_speed(lfsck, start->ls_speed_limit)) {
+                               rc = lfsck_bookmark_store(env, lfsck);
+                               if (rc != 0)
+                                       GOTO(out, rc);
+                       }
+               }
+
+               goto trigger;
+       }
+
+       if (start->ls_flags & LPF_RESET)
+               flags |= DOIF_RESET;
+
+       rc = lfsck_set_param(env, lfsck, start, !!(flags & DOIF_RESET));
+       if (rc != 0)
+               GOTO(out, rc);
+
+       list_for_each_entry(com, &lfsck->li_list_scan, lc_link) {
                start->ls_active |= com->lc_type;
                if (flags & DOIF_RESET) {
                        rc = com->lc_ops->lfsck_reset(env, com, false);
@@ -2188,19 +3032,23 @@ int lfsck_start(const struct lu_env *env, struct dt_device *key,
        }
 
 trigger:
-       lfsck->li_args_dir = LUDA_64BITHASH | LUDA_VERIFY;
-       if (bk->lb_param & LPF_DRYRUN) {
+       lfsck->li_args_dir = LUDA_64BITHASH | LUDA_VERIFY | LUDA_TYPE;
+       if (bk->lb_param & LPF_DRYRUN)
                lfsck->li_args_dir |= LUDA_VERIFY_DRYRUN;
-               valid |= DOIV_DRYRUN;
-               flags |= DOIF_DRYRUN;
-       }
 
-       if (bk->lb_param & LPF_FAILOUT) {
+       if (start != NULL && start->ls_valid & LSV_ERROR_HANDLE) {
                valid |= DOIV_ERROR_HANDLE;
-               flags |= DOIF_FAILOUT;
+               if (start->ls_flags & LPF_FAILOUT)
+                       flags |= DOIF_FAILOUT;
+       }
+
+       if (start != NULL && start->ls_valid & LSV_DRYRUN) {
+               valid |= DOIV_DRYRUN;
+               if (start->ls_flags & LPF_DRYRUN)
+                       flags |= DOIF_DRYRUN;
        }
 
-       if (!cfs_list_empty(&lfsck->li_list_scan))
+       if (!list_empty(&lfsck->li_list_scan))
                flags |= DOIF_OUTUSED;
 
        lfsck->li_args_oit = (flags << DT_OTABLE_IT_FLAGS_SHIFT) | valid;
@@ -2209,9 +3057,11 @@ trigger:
        if (IS_ERR(lta))
                GOTO(out, rc = PTR_ERR(lta));
 
-       rc = PTR_ERR(kthread_run(lfsck_master_engine, lta, "lfsck"));
-       if (IS_ERR_VALUE(rc)) {
-               CERROR("%s: cannot start LFSCK thread: rc = %ld\n",
+       __lfsck_set_speed(lfsck, bk->lb_speed_limit);
+       task = kthread_run(lfsck_master_engine, lta, "lfsck");
+       if (IS_ERR(task)) {
+               rc = PTR_ERR(task);
+               CERROR("%s: cannot start LFSCK thread: rc = %d\n",
                       lfsck_lfsck2name(lfsck), rc);
                lfsck_thread_args_fini(lta);
 
@@ -2294,9 +3144,10 @@ int lfsck_stop(const struct lu_env *env, struct dt_device *key,
 
        mutex_lock(&lfsck->li_mutex);
        spin_lock(&lfsck->li_lock);
+       /* no error if LFSCK is already stopped, or was never started */
        if (thread_is_init(thread) || thread_is_stopped(thread)) {
                spin_unlock(&lfsck->li_lock);
-               GOTO(out, rc = -EALREADY);
+               GOTO(out, rc = 0);
        }
 
        if (stop != NULL) {
@@ -2308,6 +3159,28 @@ int lfsck_stop(const struct lu_env *env, struct dt_device *key,
        }
 
        thread_set_flags(thread, SVC_STOPPING);
+
+       if (lfsck->li_master) {
+               struct lfsck_component *com;
+               struct lfsck_assistant_data *lad;
+
+               list_for_each_entry(com, &lfsck->li_list_scan, lc_link) {
+                       lad = com->lc_data;
+                       spin_lock(&lad->lad_lock);
+                       if (lad->lad_task != NULL)
+                               force_sig(SIGINT, lad->lad_task);
+                       spin_unlock(&lad->lad_lock);
+               }
+
+               list_for_each_entry(com, &lfsck->li_list_double_scan, lc_link) {
+                       lad = com->lc_data;
+                       spin_lock(&lad->lad_lock);
+                       if (lad->lad_task != NULL)
+                               force_sig(SIGINT, lad->lad_task);
+                       spin_unlock(&lad->lad_lock);
+               }
+       }
+
        spin_unlock(&lfsck->li_lock);
 
        wake_up_all(&thread->t_ctl_waitq);
@@ -2326,7 +3199,7 @@ out:
 EXPORT_SYMBOL(lfsck_stop);
 
 int lfsck_in_notify(const struct lu_env *env, struct dt_device *key,
-                   struct lfsck_request *lr)
+                   struct lfsck_request *lr, struct thandle *th)
 {
        int rc = -EOPNOTSUPP;
        ENTRY;
@@ -2364,6 +3237,10 @@ int lfsck_in_notify(const struct lu_env *env, struct dt_device *key,
        case LE_FID_ACCESSED:
        case LE_PEER_EXIT:
        case LE_CONDITIONAL_DESTROY:
+       case LE_SKIP_NLINK_DECLARE:
+       case LE_SKIP_NLINK:
+       case LE_SET_LMV_MASTER:
+       case LE_SET_LMV_SLAVE:
        case LE_PAIRS_VERIFY: {
                struct lfsck_instance  *lfsck;
                struct lfsck_component *com;
@@ -2374,7 +3251,7 @@ int lfsck_in_notify(const struct lu_env *env, struct dt_device *key,
 
                com = lfsck_component_find(lfsck, lr->lr_active);
                if (likely(com != NULL)) {
-                       rc = com->lc_ops->lfsck_in_notify(env, com, lr);
+                       rc = com->lc_ops->lfsck_in_notify(env, com, lr, th);
                        lfsck_component_put(env, com);
                }
 
@@ -2413,7 +3290,6 @@ int lfsck_query(const struct lu_env *env, struct dt_device *key,
 
        RETURN(rc);
 }
-EXPORT_SYMBOL(lfsck_query);
 
 int lfsck_register_namespace(const struct lu_env *env, struct dt_device *key,
                             struct ldlm_namespace *ns)
@@ -2438,7 +3314,7 @@ int lfsck_register(const struct lu_env *env, struct dt_device *key,
 {
        struct lfsck_instance   *lfsck;
        struct dt_object        *root  = NULL;
-       struct dt_object        *obj;
+       struct dt_object        *obj   = NULL;
        struct lu_fid           *fid   = &lfsck_env_info(env)->lti_fid;
        int                      rc;
        ENTRY;
@@ -2453,11 +3329,12 @@ int lfsck_register(const struct lu_env *env, struct dt_device *key,
 
        mutex_init(&lfsck->li_mutex);
        spin_lock_init(&lfsck->li_lock);
-       CFS_INIT_LIST_HEAD(&lfsck->li_link);
-       CFS_INIT_LIST_HEAD(&lfsck->li_list_scan);
-       CFS_INIT_LIST_HEAD(&lfsck->li_list_dir);
-       CFS_INIT_LIST_HEAD(&lfsck->li_list_double_scan);
-       CFS_INIT_LIST_HEAD(&lfsck->li_list_idle);
+       INIT_LIST_HEAD(&lfsck->li_link);
+       INIT_LIST_HEAD(&lfsck->li_list_scan);
+       INIT_LIST_HEAD(&lfsck->li_list_dir);
+       INIT_LIST_HEAD(&lfsck->li_list_double_scan);
+       INIT_LIST_HEAD(&lfsck->li_list_idle);
+       INIT_LIST_HEAD(&lfsck->li_list_lmv);
        atomic_set(&lfsck->li_ref, 1);
        atomic_set(&lfsck->li_double_scan_count, 0);
        init_waitqueue_head(&lfsck->li_thread.t_ctl_waitq);
@@ -2478,7 +3355,7 @@ int lfsck_register(const struct lu_env *env, struct dt_device *key,
        fid->f_seq = FID_SEQ_LOCAL_NAME;
        fid->f_oid = 1;
        fid->f_ver = 0;
-       rc = local_oid_storage_init(env, lfsck->li_bottom, fid, &lfsck->li_los);
+       rc = local_oid_storage_init(env, key, fid, &lfsck->li_los);
        if (rc != 0)
                GOTO(out, rc);
 
@@ -2486,7 +3363,7 @@ int lfsck_register(const struct lu_env *env, struct dt_device *key,
        if (rc != 0)
                GOTO(out, rc);
 
-       root = dt_locate(env, lfsck->li_bottom, fid);
+       root = dt_locate(env, key, fid);
        if (IS_ERR(root))
                GOTO(out, rc = PTR_ERR(root));
 
@@ -2496,31 +3373,84 @@ int lfsck_register(const struct lu_env *env, struct dt_device *key,
        lfsck->li_local_root_fid = *fid;
        if (master) {
                lfsck->li_master = 1;
-               if (lfsck_dev_idx(lfsck->li_bottom) == 0) {
+               if (lfsck_dev_idx(lfsck) == 0) {
+                       struct lu_fid *pfid = &lfsck_env_info(env)->lti_fid2;
+                       const struct lu_name *cname;
+
                        rc = dt_lookup(env, root,
                                (struct dt_rec *)(&lfsck->li_global_root_fid),
-                               (const struct dt_key *)"ROOT", BYPASS_CAPA);
+                               (const struct dt_key *)"ROOT");
                        if (rc != 0)
                                GOTO(out, rc);
+
+                       obj = dt_locate(env, key, &lfsck->li_global_root_fid);
+                       if (IS_ERR(obj))
+                               GOTO(out, rc = PTR_ERR(obj));
+
+                       if (unlikely(!dt_try_as_dir(env, obj)))
+                               GOTO(out, rc = -ENOTDIR);
+
+                       rc = dt_lookup(env, obj, (struct dt_rec *)fid,
+                               (const struct dt_key *)dotlustre);
+                       if (rc != 0)
+                               GOTO(out, rc);
+
+                       lfsck_object_put(env, obj);
+                       obj = dt_locate(env, key, fid);
+                       if (IS_ERR(obj))
+                               GOTO(out, rc = PTR_ERR(obj));
+
+                       cname = lfsck_name_get_const(env, dotlustre,
+                                                    strlen(dotlustre));
+                       rc = lfsck_verify_linkea(env, obj, cname,
+                                                &lfsck->li_global_root_fid);
+                       if (rc != 0)
+                               GOTO(out, rc);
+
+                       if (unlikely(!dt_try_as_dir(env, obj)))
+                               GOTO(out, rc = -ENOTDIR);
+
+                       *pfid = *fid;
+                       rc = dt_lookup(env, obj, (struct dt_rec *)fid,
+                                      (const struct dt_key *)lostfound);
+                       if (rc != 0)
+                               GOTO(out, rc);
+
+                       lfsck_object_put(env, obj);
+                       obj = dt_locate(env, key, fid);
+                       if (IS_ERR(obj))
+                               GOTO(out, rc = PTR_ERR(obj));
+
+                       cname = lfsck_name_get_const(env, lostfound,
+                                                    strlen(lostfound));
+                       rc = lfsck_verify_linkea(env, obj, cname, pfid);
+                       if (rc != 0)
+                               GOTO(out, rc);
+
+                       lfsck_object_put(env, obj);
+                       obj = NULL;
                }
        }
 
        fid->f_seq = FID_SEQ_LOCAL_FILE;
        fid->f_oid = OTABLE_IT_OID;
        fid->f_ver = 0;
-       obj = dt_locate(env, lfsck->li_bottom, fid);
+       obj = dt_locate(env, key, fid);
        if (IS_ERR(obj))
                GOTO(out, rc = PTR_ERR(obj));
 
-       lfsck->li_obj_oit = obj;
        rc = obj->do_ops->do_index_try(env, obj, &dt_otable_features);
-       if (rc != 0) {
-               if (rc == -ENOTSUPP)
-                       GOTO(add, rc = 0);
-
+       if (rc != 0)
                GOTO(out, rc);
-       }
 
+       lfsck->li_obj_oit = obj;
+       obj = local_file_find_or_create(env, lfsck->li_los, root, LFSCK_DIR,
+                                       S_IFDIR | S_IRUGO | S_IWUSR);
+       if (IS_ERR(obj))
+               GOTO(out, rc = PTR_ERR(obj));
+
+       lu_object_get(&obj->do_lu);
+       lfsck->li_lfsck_dir = obj;
        rc = lfsck_bookmark_setup(env, lfsck);
        if (rc != 0)
                GOTO(out, rc);
@@ -2541,13 +3471,14 @@ int lfsck_register(const struct lu_env *env, struct dt_device *key,
 
        /* XXX: more LFSCK components initialization to be added here. */
 
-add:
        rc = lfsck_instance_add(lfsck);
        if (rc == 0)
                rc = lfsck_add_target_from_orphan(env, lfsck);
 out:
+       if (obj != NULL && !IS_ERR(obj))
+               lfsck_object_put(env, obj);
        if (root != NULL && !IS_ERR(root))
-               lu_object_put(env, &root->do_lu);
+               lfsck_object_put(env, root);
        if (rc != 0)
                lfsck_instance_cleanup(env, lfsck);
        return rc;
@@ -2583,6 +3514,8 @@ int lfsck_add_target(const struct lu_env *env, struct dt_device *key,
        INIT_LIST_HEAD(&ltd->ltd_orphan_list);
        INIT_LIST_HEAD(&ltd->ltd_layout_list);
        INIT_LIST_HEAD(&ltd->ltd_layout_phase_list);
+       INIT_LIST_HEAD(&ltd->ltd_namespace_list);
+       INIT_LIST_HEAD(&ltd->ltd_namespace_phase_list);
        atomic_set(&ltd->ltd_ref, 1);
        ltd->ltd_index = index;
 
@@ -2616,7 +3549,7 @@ void lfsck_del_target(const struct lu_env *env, struct dt_device *key,
 {
        struct lfsck_instance   *lfsck;
        struct lfsck_tgt_descs  *ltds;
-       struct lfsck_tgt_desc   *ltd    = NULL;
+       struct lfsck_tgt_desc   *ltd;
        struct list_head        *head;
 
        if (for_ost)
@@ -2635,6 +3568,7 @@ void lfsck_del_target(const struct lu_env *env, struct dt_device *key,
                }
        }
 
+       ltd = NULL;
        lfsck = __lfsck_instance_find(key, true, false);
        spin_unlock(&lfsck_instance_lock);
        if (unlikely(lfsck == NULL))
@@ -2651,7 +3585,7 @@ void lfsck_del_target(const struct lu_env *env, struct dt_device *key,
        if (unlikely(index >= ltds->ltd_tgts_bitmap->size))
                goto unlock;
 
-       ltd = LTD_TGT(ltds, index);
+       ltd = lfsck_ltd2tgt(ltds, index);
        if (unlikely(ltd == NULL))
                goto unlock;
 
@@ -2659,14 +3593,14 @@ void lfsck_del_target(const struct lu_env *env, struct dt_device *key,
 
        ltds->ltd_tgtnr--;
        cfs_bitmap_clear(ltds->ltd_tgts_bitmap, index);
-       LTD_TGT(ltds, index) = NULL;
+       lfsck_assign_tgt(ltds, NULL, index);
 
 unlock:
        if (ltd == NULL) {
                if (for_ost)
                        head = &lfsck->li_ost_descs.ltd_orphan;
                else
-                       head = &lfsck->li_ost_descs.ltd_orphan;
+                       head = &lfsck->li_mdt_descs.ltd_orphan;
 
                list_for_each_entry(ltd, head, ltd_orphan_list) {
                        if (ltd->ltd_tgt == tgt) {
@@ -2681,7 +3615,8 @@ unlock:
                spin_lock(&ltds->ltd_lock);
                ltd->ltd_dead = 1;
                spin_unlock(&ltds->ltd_lock);
-               lfsck_stop_notify(env, lfsck, ltds, ltd, LT_LAYOUT);
+               lfsck_stop_notify(env, lfsck, ltds, ltd, LFSCK_TYPE_NAMESPACE);
+               lfsck_stop_notify(env, lfsck, ltds, ltd, LFSCK_TYPE_LAYOUT);
                lfsck_tgt_put(ltd);
        }
 
@@ -2693,6 +3628,7 @@ static int __init lfsck_init(void)
 {
        int rc;
 
+       INIT_LIST_HEAD(&lfsck_instance_list);
        INIT_LIST_HEAD(&lfsck_ost_orphan_list);
        INIT_LIST_HEAD(&lfsck_mdt_orphan_list);
        lfsck_key_init_generic(&lfsck_thread_key, NULL);
@@ -2710,7 +3646,7 @@ static void __exit lfsck_exit(void)
        struct lfsck_tgt_desc *ltd;
        struct lfsck_tgt_desc *next;
 
-       LASSERT(cfs_list_empty(&lfsck_instance_list));
+       LASSERT(list_empty(&lfsck_instance_list));
 
        list_for_each_entry_safe(ltd, next, &lfsck_ost_orphan_list,
                                 ltd_orphan_list) {
@@ -2727,8 +3663,10 @@ static void __exit lfsck_exit(void)
        lu_context_key_degister(&lfsck_thread_key);
 }
 
-MODULE_AUTHOR("Intel Corporation <http://www.intel.com/>");
-MODULE_DESCRIPTION("LFSCK");
+MODULE_AUTHOR("OpenSFS, Inc. <http://www.lustre.org/>");
+MODULE_DESCRIPTION("Lustre File System Checker");
+MODULE_VERSION(LUSTRE_VERSION_STRING);
 MODULE_LICENSE("GPL");
 
-cfs_module(lfsck, LUSTRE_VERSION_STRING, lfsck_init, lfsck_exit);
+module_init(lfsck_init);
+module_exit(lfsck_exit);