getncchanges.c: Send linked attributes in each chunk
[nivanova/samba-autobuild/.git] / source4 / rpc_server / drsuapi / getncchanges.c
index afed782ed19aef0c07a45eb2045ab18f259d3ea8..cd3f51fc2b0135b69b2c792fd87f3081420be63d 100644 (file)
 #include "lib/dbwrap/dbwrap_rbt.h"
 #include "librpc/gen_ndr/ndr_misc.h"
 
-/* state of a partially completed getncchanges call */
+#undef DBGC_CLASS
+#define DBGC_CLASS            DBGC_DRS_REPL
+
+#define DRS_GUID_SIZE       16
+
+/*
+ * state of a partially-completed replication cycle. This state persists
+ * over multiple calls to dcesrv_drsuapi_DsGetNCChanges()
+ */
 struct drsuapi_getncchanges_state {
-       struct db_context *anc_cache;
+       struct db_context *obj_cache;
        struct GUID *guids;
        uint32_t num_records;
        uint32_t num_processed;
        struct ldb_dn *ncRoot_dn;
        struct GUID ncRoot_guid;
        bool is_schema_nc;
+       bool is_get_anc;
        uint64_t min_usn;
        uint64_t max_usn;
        struct drsuapi_DsReplicaHighWaterMark last_hwm;
@@ -59,15 +68,29 @@ struct drsuapi_getncchanges_state {
        struct drsuapi_DsReplicaCursor2CtrEx *final_udv;
        struct drsuapi_DsReplicaLinkedAttribute *la_list;
        uint32_t la_count;
-       struct la_for_sorting *la_sorted;
        uint32_t la_idx;
+
+       /* these are just used for debugging the replication's progress */
+       uint32_t links_given;
+       uint32_t total_links;
 };
 
 /* We must keep the GUIDs in NDR form for sorting */
 struct la_for_sorting {
-       struct drsuapi_DsReplicaLinkedAttribute *link;
-       uint8_t target_guid[16];
-        uint8_t source_guid[16];
+       const struct drsuapi_DsReplicaLinkedAttribute *link;
+       uint8_t target_guid[DRS_GUID_SIZE];
+       uint8_t source_guid[DRS_GUID_SIZE];
+};
+
+/*
+ * stores the state for a chunk of replication data. This state information
+ * only exists for a single call to dcesrv_drsuapi_DsGetNCChanges()
+ */
+struct getncchanges_repl_chunk {
+       struct drsuapi_DsGetNCChangesCtr6 *ctr6;
+
+       /* the last object written to the response */
+       struct drsuapi_DsReplicaObjectListItemEx *last_object;
 };
 
 static int drsuapi_DsReplicaHighWaterMark_cmp(const struct drsuapi_DsReplicaHighWaterMark *h1,
@@ -437,15 +460,10 @@ static WERROR get_nc_changes_filter_attrs(struct drsuapi_DsReplicaObjectListItem
 static WERROR get_nc_changes_build_object(struct drsuapi_DsReplicaObjectListItemEx *obj,
                                          const struct ldb_message *msg,
                                          struct ldb_context *sam_ctx,
-                                         struct ldb_dn *ncRoot_dn,
-                                         bool   is_schema_nc,
+                                         struct drsuapi_getncchanges_state *getnc_state,
                                          struct dsdb_schema *schema,
                                          DATA_BLOB *session_key,
-                                         uint64_t highest_usn,
-                                         uint32_t replica_flags,
-                                         struct drsuapi_DsPartialAttributeSet *partial_attribute_set,
-                                         struct drsuapi_DsReplicaCursorCtrEx *uptodateness_vector,
-                                         enum drsuapi_DsExtendedOperation extended_op,
+                                         struct drsuapi_DsGetNCChangesRequest10 *req10,
                                          bool force_object_return,
                                          uint32_t *local_pas,
                                          struct ldb_dn *machine_dn,
@@ -466,6 +484,14 @@ static WERROR get_nc_changes_build_object(struct drsuapi_DsReplicaObjectListItem
        struct ldb_result *res = NULL;
        WERROR werr;
        int ret;
+       uint32_t replica_flags = req10->replica_flags;
+       struct drsuapi_DsPartialAttributeSet *partial_attribute_set =
+                       req10->partial_attribute_set;
+       struct drsuapi_DsReplicaCursorCtrEx *uptodateness_vector =
+                       req10->uptodateness_vector;
+       enum drsuapi_DsExtendedOperation extended_op = req10->extended_op;
+       bool is_schema_nc = getnc_state->is_schema_nc;
+       uint64_t highest_usn = getnc_state->min_usn;
 
        /* make dsdb sytanx context for conversions */
        dsdb_syntax_ctx_init(&syntax_ctx, sam_ctx, schema);
@@ -839,7 +865,6 @@ static WERROR get_nc_changes_add_la(TALLOC_CTX *mem_ctx,
  */
 static WERROR get_nc_changes_add_links(struct ldb_context *sam_ctx,
                                       TALLOC_CTX *mem_ctx,
-                                      struct ldb_dn *ncRoot_dn,
                                       bool is_schema_nc,
                                       struct dsdb_schema *schema,
                                       uint64_t highest_usn,
@@ -1932,11 +1957,16 @@ static void dcesrv_drsuapi_update_highwatermark(const struct ldb_message *msg,
        hwm->reserved_usn = 0;
 }
 
-static WERROR dcesrv_drsuapi_anc_cache_add(struct db_context *anc_cache,
+/**
+ * Adds an object's GUID to the cache of objects already sent.
+ * This avoids us sending the same object multiple times when
+ * the GetNCChanges request uses a flag like GET_ANC.
+ */
+static WERROR dcesrv_drsuapi_obj_cache_add(struct db_context *obj_cache,
                                           const struct GUID *guid)
 {
        enum ndr_err_code ndr_err;
-       uint8_t guid_buf[16] = { 0, };
+       uint8_t guid_buf[DRS_GUID_SIZE] = { 0, };
        DATA_BLOB b = {
                .data = guid_buf,
                .length = sizeof(guid_buf),
@@ -1957,7 +1987,7 @@ static WERROR dcesrv_drsuapi_anc_cache_add(struct db_context *anc_cache,
                return WERR_DS_DRA_INTERNAL_ERROR;
        }
 
-       status = dbwrap_store(anc_cache, key, val, TDB_REPLACE);
+       status = dbwrap_store(obj_cache, key, val, TDB_REPLACE);
        if (!NT_STATUS_IS_OK(status)) {
                return WERR_DS_DRA_INTERNAL_ERROR;
        }
@@ -1965,11 +1995,15 @@ static WERROR dcesrv_drsuapi_anc_cache_add(struct db_context *anc_cache,
        return WERR_OK;
 }
 
-static WERROR dcesrv_drsuapi_anc_cache_exists(struct db_context *anc_cache,
+/**
+ * Checks if the object with the GUID specified already exists in the
+ * object cache, i.e. it's already been sent in a GetNCChanges response.
+ */
+static WERROR dcesrv_drsuapi_obj_cache_exists(struct db_context *obj_cache,
                                              const struct GUID *guid)
 {
        enum ndr_err_code ndr_err;
-       uint8_t guid_buf[16] = { 0, };
+       uint8_t guid_buf[DRS_GUID_SIZE] = { 0, };
        DATA_BLOB b = {
                .data = guid_buf,
                .length = sizeof(guid_buf),
@@ -1986,7 +2020,7 @@ static WERROR dcesrv_drsuapi_anc_cache_exists(struct db_context *anc_cache,
                return WERR_DS_DRA_INTERNAL_ERROR;
        }
 
-       exists = dbwrap_exists(anc_cache, key);
+       exists = dbwrap_exists(obj_cache, key);
        if (!exists) {
                return WERR_OBJECT_NOT_FOUND;
        }
@@ -1994,7 +2028,326 @@ static WERROR dcesrv_drsuapi_anc_cache_exists(struct db_context *anc_cache,
        return WERR_OBJECT_NAME_EXISTS;
 }
 
-/* 
+/**
+ * Copies the la_list specified into a sorted array, ready to be sent in a
+ * GetNCChanges response.
+ */
+static WERROR getncchanges_get_sorted_array(const struct drsuapi_DsReplicaLinkedAttribute *la_list,
+                                           const uint32_t link_count,
+                                           struct ldb_context *sam_ctx,
+                                           TALLOC_CTX *mem_ctx,
+                                           const struct dsdb_schema *schema,
+                                           struct la_for_sorting **ret_array)
+{
+       int j;
+       struct la_for_sorting *guid_array;
+       WERROR werr = WERR_OK;
+
+       *ret_array = NULL;
+       guid_array = talloc_array(mem_ctx, struct la_for_sorting, link_count);
+       if (guid_array == NULL) {
+               DEBUG(0, ("Out of memory allocating %u linked attributes for sorting", link_count));
+               return WERR_NOT_ENOUGH_MEMORY;
+       }
+
+       for (j = 0; j < link_count; j++) {
+
+               /* we need to get the target GUIDs to compare */
+               struct dsdb_dn *dn;
+               const struct drsuapi_DsReplicaLinkedAttribute *la = &la_list[j];
+               const struct dsdb_attribute *schema_attrib;
+               const struct ldb_val *target_guid;
+               DATA_BLOB source_guid;
+               TALLOC_CTX *frame = talloc_stackframe();
+               NTSTATUS status;
+
+               schema_attrib = dsdb_attribute_by_attributeID_id(schema, la->attid);
+
+               werr = dsdb_dn_la_from_blob(sam_ctx, schema_attrib, schema, frame, la->value.blob, &dn);
+               if (!W_ERROR_IS_OK(werr)) {
+                       DEBUG(0,(__location__ ": Bad la blob in sort\n"));
+                       TALLOC_FREE(frame);
+                       return werr;
+               }
+
+               /* Extract the target GUID in NDR form */
+               target_guid = ldb_dn_get_extended_component(dn->dn, "GUID");
+               if (target_guid == NULL
+                               || target_guid->length != sizeof(guid_array[0].target_guid)) {
+                       status = NT_STATUS_OBJECT_NAME_NOT_FOUND;
+               } else {
+                       /* Repack the source GUID as NDR for sorting */
+                       status = GUID_to_ndr_blob(&la->identifier->guid,
+                                                 frame,
+                                                 &source_guid);
+               }
+
+               if (!NT_STATUS_IS_OK(status)
+                               || source_guid.length != sizeof(guid_array[0].source_guid)) {
+                       DEBUG(0,(__location__ ": Bad la guid in sort\n"));
+                       TALLOC_FREE(frame);
+                       return ntstatus_to_werror(status);
+               }
+
+               guid_array[j].link = &la_list[j];
+               memcpy(guid_array[j].target_guid, target_guid->data,
+                      sizeof(guid_array[j].target_guid));
+               memcpy(guid_array[j].source_guid, source_guid.data,
+                      sizeof(guid_array[j].source_guid));
+               TALLOC_FREE(frame);
+       }
+
+       LDB_TYPESAFE_QSORT(guid_array, link_count, NULL, linked_attribute_compare);
+
+       *ret_array = guid_array;
+
+       return werr;
+}
+
+
+/**
+ * Adds any ancestor/parent objects of the child_obj specified.
+ * This is needed when the GET_ANC flag is specified in the request.
+ * @param new_objs if parents are added, this gets updated to point to a chain
+ * of parent objects (with the parents first and the child last)
+ */
+static WERROR getncchanges_add_ancestors(struct drsuapi_DsReplicaObjectListItemEx *child_obj,
+                                        struct ldb_dn *child_dn,
+                                        TALLOC_CTX *mem_ctx,
+                                        struct ldb_context *sam_ctx,
+                                        struct drsuapi_getncchanges_state *getnc_state,
+                                        struct dsdb_schema *schema,
+                                        DATA_BLOB *session_key,
+                                        struct drsuapi_DsGetNCChangesRequest10 *req10,
+                                        uint32_t *local_pas,
+                                        struct ldb_dn *machine_dn,
+                                        struct drsuapi_DsReplicaObjectListItemEx **new_objs)
+{
+       int ret;
+       const struct GUID *next_anc_guid = NULL;
+       WERROR werr = WERR_OK;
+       static const char * const msg_attrs[] = {
+                                           "*",
+                                           "nTSecurityDescriptor",
+                                           "parentGUID",
+                                           "replPropertyMetaData",
+                                           DSDB_SECRET_ATTRIBUTES,
+                                           NULL };
+
+       next_anc_guid = child_obj->parent_object_guid;
+
+       while (next_anc_guid != NULL) {
+               struct drsuapi_DsReplicaObjectListItemEx *anc_obj = NULL;
+               struct ldb_message *anc_msg = NULL;
+               struct ldb_result *anc_res = NULL;
+               struct ldb_dn *anc_dn = NULL;
+
+               /*
+                * Don't send an object twice. (If we've sent the object, then
+                * we've also sent all its parents as well)
+                */
+               werr = dcesrv_drsuapi_obj_cache_exists(getnc_state->obj_cache,
+                                                      next_anc_guid);
+               if (W_ERROR_EQUAL(werr, WERR_OBJECT_NAME_EXISTS)) {
+                       return WERR_OK;
+               }
+               if (W_ERROR_IS_OK(werr)) {
+                       return WERR_INTERNAL_ERROR;
+               }
+               if (!W_ERROR_EQUAL(werr, WERR_OBJECT_NOT_FOUND)) {
+                       return werr;
+               }
+
+               anc_obj = talloc_zero(mem_ctx,
+                                     struct drsuapi_DsReplicaObjectListItemEx);
+               if (anc_obj == NULL) {
+                       return WERR_NOT_ENOUGH_MEMORY;
+               }
+
+               anc_dn = ldb_dn_new_fmt(anc_obj, sam_ctx, "<GUID=%s>",
+                                       GUID_string(anc_obj, next_anc_guid));
+               if (anc_dn == NULL) {
+                       return WERR_NOT_ENOUGH_MEMORY;
+               }
+
+               ret = drsuapi_search_with_extended_dn(sam_ctx, anc_obj,
+                                                     &anc_res, anc_dn,
+                                                     LDB_SCOPE_BASE,
+                                                     msg_attrs, NULL);
+               if (ret != LDB_SUCCESS) {
+                       const char *anc_str = NULL;
+                       const char *obj_str = NULL;
+
+                       anc_str = ldb_dn_get_extended_linearized(anc_obj,
+                                                                anc_dn,
+                                                                1);
+                       obj_str = ldb_dn_get_extended_linearized(anc_obj,
+                                                                child_dn,
+                                                                1);
+
+                       DBG_ERR("getncchanges: failed to fetch ANC "
+                               "DN %s for DN %s - %s\n",
+                               anc_str, obj_str, ldb_errstring(sam_ctx));
+                       return WERR_DS_DRA_INCONSISTENT_DIT;
+               }
+
+               anc_msg = anc_res->msgs[0];
+
+               werr = get_nc_changes_build_object(anc_obj, anc_msg,
+                                                  sam_ctx,
+                                                  getnc_state,
+                                                  schema, session_key,
+                                                  req10,
+                                                  false, /* force_object_return */
+                                                  local_pas,
+                                                  machine_dn,
+                                                  next_anc_guid);
+               if (!W_ERROR_IS_OK(werr)) {
+                       return werr;
+               }
+
+               /*
+                * Regardless of whether we actually use it or not,
+                * we add it to the cache so we don't look at it again
+                */
+               werr = dcesrv_drsuapi_obj_cache_add(getnc_state->obj_cache,
+                                                   next_anc_guid);
+               if (!W_ERROR_IS_OK(werr)) {
+                       return werr;
+               }
+
+               /*
+                * Any ancestors which are below the highwatermark
+                * or uptodateness_vector shouldn't be added,
+                * but we still look further up the
+                * tree for ones which have been changed recently.
+                */
+               if (anc_obj->meta_data_ctr != NULL) {
+
+                       /*
+                        * prepend the parent to the list so that the client-side
+                        * adds the parent object before it adds the children
+                        */
+                       anc_obj->next_object = *new_objs;
+                       *new_objs = anc_obj;
+               }
+
+               anc_msg = NULL;
+               TALLOC_FREE(anc_res);
+               TALLOC_FREE(anc_dn);
+
+               /*
+                * We may need to resolve more parents...
+                */
+               next_anc_guid = anc_obj->parent_object_guid;
+       }
+       return werr;
+}
+
+/**
+ * Adds a list of new objects into the getNCChanges response message
+ */
+static void getncchanges_add_objs_to_resp(struct getncchanges_repl_chunk *repl_chunk,
+                                         struct drsuapi_DsReplicaObjectListItemEx *obj_list)
+{
+       struct drsuapi_DsReplicaObjectListItemEx *obj;
+
+       /*
+        * We track the last object added to the response message, so just add
+        * the new object-list onto the end
+        */
+       if (repl_chunk->last_object == NULL) {
+               repl_chunk->ctr6->first_object = obj_list;
+       } else {
+               repl_chunk->last_object->next_object = obj_list;
+       }
+
+       for (obj = obj_list; obj != NULL; obj = obj->next_object) {
+               repl_chunk->ctr6->object_count += 1;
+
+               /*
+                * Remember the last object in the response - we'll use this to
+                * link the next object(s) processed onto the existing list
+                */
+               if (obj->next_object == NULL) {
+                       repl_chunk->last_object = obj;
+               }
+       }
+}
+
+/**
+ * Gets the object to send, packed into an RPC struct ready to send. This also
+ * adds the object to the object cache, and adds any ancestors (if needed).
+ * @param msg - DB search result for the object to add
+ * @param guid - GUID of the object to add
+ * @param ret_obj_list - returns the object ready to be sent (in a list, along
+ * with any ancestors that might be needed). NULL if nothing to send.
+ */
+static WERROR getncchanges_get_obj_to_send(const struct ldb_message *msg,
+                                          TALLOC_CTX *mem_ctx,
+                                          struct ldb_context *sam_ctx,
+                                          struct drsuapi_getncchanges_state *getnc_state,
+                                          struct dsdb_schema *schema,
+                                          DATA_BLOB *session_key,
+                                          struct drsuapi_DsGetNCChangesRequest10 *req10,
+                                          bool force_object_return,
+                                          uint32_t *local_pas,
+                                          struct ldb_dn *machine_dn,
+                                          const struct GUID *guid,
+                                          struct drsuapi_DsReplicaObjectListItemEx **ret_obj_list)
+{
+       struct drsuapi_DsReplicaObjectListItemEx *obj;
+       WERROR werr;
+
+       *ret_obj_list = NULL;
+
+       obj = talloc_zero(mem_ctx, struct drsuapi_DsReplicaObjectListItemEx);
+       W_ERROR_HAVE_NO_MEMORY(obj);
+
+       werr = get_nc_changes_build_object(obj, msg, sam_ctx, getnc_state,
+                                          schema, session_key, req10,
+                                          force_object_return,
+                                          local_pas, machine_dn, guid);
+       if (!W_ERROR_IS_OK(werr)) {
+               return werr;
+       }
+
+       /*
+        * The object may get filtered out by the UTDV's USN and not actually
+        * sent, in which case there's nothing more to do here
+        */
+       if (obj->meta_data_ctr == NULL) {
+               TALLOC_FREE(obj);
+               return WERR_OK;
+       }
+
+       if (getnc_state->obj_cache != NULL) {
+               werr = dcesrv_drsuapi_obj_cache_add(getnc_state->obj_cache,
+                                                   guid);
+               if (!W_ERROR_IS_OK(werr)) {
+                       return werr;
+               }
+       }
+
+       *ret_obj_list = obj;
+
+       /*
+        * If required, also add any ancestors that the client may need to know
+        * about before it can resolve this object. These get prepended to the
+        * ret_obj_list so the client adds them first.
+        */
+       if (getnc_state->is_get_anc) {
+               werr = getncchanges_add_ancestors(obj, msg->dn, mem_ctx,
+                                                 sam_ctx, getnc_state,
+                                                 schema, session_key,
+                                                 req10, local_pas,
+                                                 machine_dn, ret_obj_list);
+       }
+
+       return werr;
+}
+
+/*
   drsuapi_DsGetNCChanges
 
   see MS-DRSR 4.1.10.5.2 for basic logic of this function
@@ -2007,7 +2360,7 @@ WERROR dcesrv_drsuapi_DsGetNCChanges(struct dcesrv_call_state *dce_call, TALLOC_
        uint32_t i, k;
        struct dsdb_schema *schema;
        struct drsuapi_DsReplicaOIDMapping_Ctr *ctr;
-       struct drsuapi_DsReplicaObjectListItemEx **currentObject;
+       struct getncchanges_repl_chunk repl_chunk = { 0 };
        NTSTATUS status;
        DATA_BLOB session_key;
        WERROR werr;
@@ -2019,8 +2372,6 @@ WERROR dcesrv_drsuapi_DsGetNCChanges(struct dcesrv_call_state *dce_call, TALLOC_
        uint32_t max_objects;
        uint32_t max_links;
        uint32_t link_count = 0;
-       uint32_t link_total = 0;
-       uint32_t link_given = 0;
        struct ldb_dn *search_dn = NULL;
        bool am_rodc;
        enum security_user_level security_level;
@@ -2039,6 +2390,7 @@ WERROR dcesrv_drsuapi_DsGetNCChanges(struct dcesrv_call_state *dce_call, TALLOC_
        bool full = true;
        uint32_t *local_pas = NULL;
        struct ldb_dn *machine_dn = NULL; /* Only used for REPL SECRET EXOP */
+       bool immediate_link_sync;
 
        DCESRV_PULL_HANDLE_WERR(h, r->in.bind_handle, DRSUAPI_BIND_HANDLE);
        b_state = h->data;
@@ -2049,7 +2401,7 @@ WERROR dcesrv_drsuapi_DsGetNCChanges(struct dcesrv_call_state *dce_call, TALLOC_
        invocation_id = *(samdb_ntds_invocation_id(sam_ctx));
 
        *r->out.level_out = 6;
-       /* TODO: linked attributes*/
+
        r->out.ctr->ctr6.linked_attributes_count = 0;
        r->out.ctr->ctr6.linked_attributes = discard_const_p(struct drsuapi_DsReplicaLinkedAttribute, &no_linked_attr);
 
@@ -2494,10 +2846,11 @@ allowed:
                if (req10->extended_op != DRSUAPI_EXOP_NONE) {
                        /* Do nothing */
                } else if (req10->replica_flags & DRSUAPI_DRS_GET_ANC) {
-                       getnc_state->anc_cache = db_open_rbt(getnc_state);
-                       if (getnc_state->anc_cache == NULL) {
+                       getnc_state->obj_cache = db_open_rbt(getnc_state);
+                       if (getnc_state->obj_cache == NULL) {
                                return WERR_NOT_ENOUGH_MEMORY;
                        }
+                       getnc_state->is_get_anc = true;
                }
        }
 
@@ -2533,7 +2886,8 @@ allowed:
        r->out.ctr->ctr6.old_highwatermark = req10->highwatermark;
        r->out.ctr->ctr6.new_highwatermark = req10->highwatermark;
 
-       currentObject = &r->out.ctr->ctr6.first_object;
+       repl_chunk.ctr6 = &r->out.ctr->ctr6;
+       repl_chunk.last_object = NULL;
 
        max_objects = lpcfg_parm_int(dce_call->conn->dce_ctx->lp_ctx, NULL, "drs", "max object sync", 1000);
        /*
@@ -2554,6 +2908,9 @@ allowed:
         */
        max_links = lpcfg_parm_int(dce_call->conn->dce_ctx->lp_ctx, NULL, "drs", "max link sync", 1500);
 
+       immediate_link_sync = lpcfg_parm_bool(dce_call->conn->dce_ctx->lp_ctx, NULL,
+                                             "drs", "immediate link sync", false);
+
        /*
         * Maximum time that we can spend in a getncchanges
         * in order to avoid timeout of the other part.
@@ -2590,7 +2947,6 @@ allowed:
                     && !max_wait_reached;
            i++) {
                struct drsuapi_DsReplicaObjectListItemEx *new_objs = NULL;
-               struct drsuapi_DsReplicaObjectListItemEx *obj;
                struct ldb_message *msg;
                static const char * const msg_attrs[] = {
                                            "*",
@@ -2601,15 +2957,14 @@ allowed:
                                            NULL };
                struct ldb_result *msg_res;
                struct ldb_dn *msg_dn;
-               const struct GUID *next_anc_guid = NULL;
+               bool obj_already_sent = false;
+               TALLOC_CTX *tmp_ctx = talloc_new(mem_ctx);
+               uint32_t old_la_index;
 
-               obj = talloc_zero(mem_ctx, struct drsuapi_DsReplicaObjectListItemEx);
-               W_ERROR_HAVE_NO_MEMORY(obj);
-
-               msg_dn = ldb_dn_new_fmt(obj, sam_ctx, "<GUID=%s>", GUID_string(obj, &getnc_state->guids[i]));
+               msg_dn = ldb_dn_new_fmt(tmp_ctx, sam_ctx, "<GUID=%s>",
+                                       GUID_string(tmp_ctx, &getnc_state->guids[i]));
                W_ERROR_HAVE_NO_MEMORY(msg_dn);
 
-
                /*
                 * by re-searching here we avoid having a lot of full
                 * records in memory between calls to getncchanges.
@@ -2618,15 +2973,16 @@ allowed:
                 * (tombstone expunge) between the first and second
                 * check.
                 */
-               ret = drsuapi_search_with_extended_dn(sam_ctx, obj, &msg_res,
+               ret = drsuapi_search_with_extended_dn(sam_ctx, tmp_ctx, &msg_res,
                                                      msg_dn,
                                                      LDB_SCOPE_BASE, msg_attrs, NULL);
                if (ret != LDB_SUCCESS) {
                        if (ret != LDB_ERR_NO_SUCH_OBJECT) {
                                DEBUG(1,("getncchanges: failed to fetch DN %s - %s\n",
-                                        ldb_dn_get_extended_linearized(obj, msg_dn, 1), ldb_errstring(sam_ctx)));
+                                        ldb_dn_get_extended_linearized(tmp_ctx, msg_dn, 1),
+                                        ldb_errstring(sam_ctx)));
                        }
-                       talloc_free(obj);
+                       TALLOC_FREE(tmp_ctx);
                        continue;
                }
 
@@ -2634,51 +2990,53 @@ allowed:
                        DEBUG(1,("getncchanges: got LDB_SUCCESS but failed"
                                 "to get any results in fetch of DN "
                                 "%s (race with tombstone expunge?)\n",
-                                ldb_dn_get_extended_linearized(obj,
+                                ldb_dn_get_extended_linearized(tmp_ctx,
                                                                msg_dn, 1)));
-                       talloc_free(obj);
+                       TALLOC_FREE(tmp_ctx);
                        continue;
                }
 
                msg = msg_res->msgs[0];
 
                /*
-                * If it has already been added as an ancestor of
-                * an object, we don't need to do anything more,
-                * as we've already added the links.
+                * Check if we've already sent the object as an ancestor of
+                * another object. If so, we don't need to send it again
                 */
-               if (getnc_state->anc_cache != NULL) {
-                       werr = dcesrv_drsuapi_anc_cache_exists(getnc_state->anc_cache,
+               if (getnc_state->obj_cache != NULL) {
+                       werr = dcesrv_drsuapi_obj_cache_exists(getnc_state->obj_cache,
                                                               &getnc_state->guids[i]);
                        if (W_ERROR_EQUAL(werr, WERR_OBJECT_NAME_EXISTS)) {
-                               dcesrv_drsuapi_update_highwatermark(msg,
-                                               getnc_state->max_usn,
-                                               &r->out.ctr->ctr6.new_highwatermark);
-                               /* no attributes to send */
-                               talloc_free(obj);
-                               continue;
+                               obj_already_sent = true;
                        }
                }
 
-               max_wait_reached = (time(NULL) - start > max_wait);
+               if (!obj_already_sent) {
+                       max_wait_reached = (time(NULL) - start > max_wait);
 
-               werr = get_nc_changes_build_object(obj, msg,
-                                                  sam_ctx, getnc_state->ncRoot_dn,
-                                                  getnc_state->is_schema_nc,
-                                                  schema, &session_key, getnc_state->min_usn,
-                                                  req10->replica_flags,
-                                                  req10->partial_attribute_set,
-                                                  req10->uptodateness_vector,
-                                                  req10->extended_op,
-                                                  max_wait_reached,
-                                                  local_pas, machine_dn,
-                                                  &getnc_state->guids[i]);
-               if (!W_ERROR_IS_OK(werr)) {
-                       return werr;
+                       /*
+                        * Construct an object, ready to send (this will include
+                        * the object's ancestors as well, if needed)
+                        */
+                       werr = getncchanges_get_obj_to_send(msg, mem_ctx, sam_ctx,
+                                                           getnc_state, schema,
+                                                           &session_key, req10,
+                                                           max_wait_reached,
+                                                           local_pas, machine_dn,
+                                                           &getnc_state->guids[i],
+                                                           &new_objs);
+                       if (!W_ERROR_IS_OK(werr)) {
+                               return werr;
+                       }
                }
 
+               old_la_index = getnc_state->la_count;
+
+               /*
+                * We've reached the USN where this object naturally occurs.
+                * Regardless of whether we've already sent the object (as an
+                * ancestor), we add its links and update the HWM at this point
+                */
                werr = get_nc_changes_add_links(sam_ctx, getnc_state,
-                                               getnc_state->ncRoot_dn,
                                                getnc_state->is_schema_nc,
                                                schema, getnc_state->min_usn,
                                                req10->replica_flags,
@@ -2694,169 +3052,33 @@ allowed:
                                        getnc_state->max_usn,
                                        &r->out.ctr->ctr6.new_highwatermark);
 
-               if (obj->meta_data_ctr == NULL) {
-                       DEBUG(8,(__location__ ": getncchanges skipping send of object %s\n",
-                                ldb_dn_get_linearized(msg->dn)));
-                       /* no attributes to send */
-                       talloc_free(obj);
-                       continue;
-               }
-
-               new_objs = obj;
-
-               if (getnc_state->anc_cache != NULL) {
-                       werr = dcesrv_drsuapi_anc_cache_add(getnc_state->anc_cache,
-                                                           &getnc_state->guids[i]);
-                       if (!W_ERROR_IS_OK(werr)) {
-                               return werr;
-                       }
-
-                       next_anc_guid = obj->parent_object_guid;
-               }
-
-               while (next_anc_guid != NULL) {
-                       struct drsuapi_DsReplicaObjectListItemEx *anc_obj = NULL;
-                       struct ldb_message *anc_msg = NULL;
-                       struct ldb_result *anc_res = NULL;
-                       struct ldb_dn *anc_dn = NULL;
-
-                       werr = dcesrv_drsuapi_anc_cache_exists(getnc_state->anc_cache,
-                                                              next_anc_guid);
-                       if (W_ERROR_EQUAL(werr, WERR_OBJECT_NAME_EXISTS)) {
-                               /*
-                                * We don't need to send it twice.
-                                */
-                               break;
-                       }
-                       if (W_ERROR_IS_OK(werr)) {
-                               return WERR_INTERNAL_ERROR;
-                       }
-                       if (!W_ERROR_EQUAL(werr, WERR_OBJECT_NOT_FOUND)) {
-                               return werr;
-                       }
-                       werr = WERR_OK;
-
-                       anc_obj = talloc_zero(mem_ctx,
-                                       struct drsuapi_DsReplicaObjectListItemEx);
-                       if (anc_obj == NULL) {
-                               return WERR_NOT_ENOUGH_MEMORY;
-                       }
-
-                       anc_dn = ldb_dn_new_fmt(anc_obj, sam_ctx, "<GUID=%s>",
-                                       GUID_string(anc_obj, next_anc_guid));
-                       if (anc_dn == NULL) {
-                               return WERR_NOT_ENOUGH_MEMORY;
-                       }
-
-                       ret = drsuapi_search_with_extended_dn(sam_ctx, anc_obj,
-                                                             &anc_res, anc_dn,
-                                                             LDB_SCOPE_BASE,
-                                                             msg_attrs, NULL);
-                       if (ret != LDB_SUCCESS) {
-                               const char *anc_str = NULL;
-                               const char *obj_str = NULL;
-
-                               anc_str = ldb_dn_get_extended_linearized(anc_obj,
-                                                                        anc_dn,
-                                                                        1);
-                               obj_str = ldb_dn_get_extended_linearized(anc_obj,
-                                                                        msg->dn,
-                                                                        1),
-
-                               DBG_ERR("getncchanges: failed to fetch ANC "
-                                       "DN %s for DN %s - %s\n",
-                                       anc_str, obj_str,
-                                       ldb_errstring(sam_ctx));
-                               return WERR_DS_DRA_INCONSISTENT_DIT;
-                       }
-
-                       anc_msg = anc_res->msgs[0];
-
-                       werr = get_nc_changes_build_object(anc_obj, anc_msg,
-                                                          sam_ctx,
-                                                          getnc_state->ncRoot_dn,
-                                                          getnc_state->is_schema_nc,
-                                                          schema, &session_key,
-                                                          getnc_state->min_usn,
-                                                          req10->replica_flags,
-                                                          req10->partial_attribute_set,
-                                                          req10->uptodateness_vector,
-                                                          req10->extended_op,
-                                                          false, /* force_object_return */
-                                                          local_pas,
-                                                          machine_dn,
-                                                          next_anc_guid);
-                       if (!W_ERROR_IS_OK(werr)) {
-                               return werr;
-                       }
-
-                       werr = get_nc_changes_add_links(sam_ctx, getnc_state,
-                                                       getnc_state->ncRoot_dn,
-                                                       getnc_state->is_schema_nc,
-                                                       schema, getnc_state->min_usn,
-                                                       req10->replica_flags,
-                                                       anc_msg,
-                                                       &getnc_state->la_list,
-                                                       &getnc_state->la_count,
-                                                       req10->uptodateness_vector);
-                       if (!W_ERROR_IS_OK(werr)) {
-                               return werr;
-                       }
-
-                       /*
-                        * Regardless of if we actually use it or not,
-                        * we add it to the cache so we don't look at it again
-                        */
-                       werr = dcesrv_drsuapi_anc_cache_add(getnc_state->anc_cache,
-                                                           next_anc_guid);
-                       if (!W_ERROR_IS_OK(werr)) {
-                               return werr;
-                       }
-
-                       /*
-                        * Any ancestors which are below the highwatermark
-                        * or uptodateness_vector shouldn't be added,
-                        * but we still look further up the
-                        * tree for ones which have been changed recently.
-                        */
-                       if (anc_obj->meta_data_ctr != NULL) {
-                               /*
-                                * prepend it to the list
-                                */
-                               anc_obj->next_object = new_objs;
-                               new_objs = anc_obj;
-                       }
-
-                       anc_msg = NULL;
-                       TALLOC_FREE(anc_res);
-                       TALLOC_FREE(anc_dn);
+               if (new_objs != NULL) {
 
                        /*
-                        * We may need to resolve more...
+                        * Add the object (and, if GET_ANC, any parents it may
+                        * have) into the current chunk of replication data
                         */
-                       next_anc_guid = anc_obj->parent_object_guid;
-               }
+                       getncchanges_add_objs_to_resp(&repl_chunk, new_objs);
 
-               *currentObject = new_objs;
-               while (new_objs != NULL) {
-                       r->out.ctr->ctr6.object_count += 1;
-                       if (new_objs->next_object == NULL) {
-                               currentObject = &new_objs->next_object;
-                       }
-                       new_objs = new_objs->next_object;
+                       talloc_free(getnc_state->last_dn);
+                       getnc_state->last_dn = talloc_move(getnc_state, &msg->dn);
                }
 
-               DEBUG(8,(__location__ ": replicating object %s\n", ldb_dn_get_linearized(msg->dn)));
+               DEBUG(8,(__location__ ": %s object %s\n",
+                        new_objs ? "replicating" : "skipping send of",
+                        ldb_dn_get_linearized(msg->dn)));
 
-               talloc_free(getnc_state->last_dn);
-               getnc_state->last_dn = talloc_move(getnc_state, &msg->dn);
+               getnc_state->total_links += (getnc_state->la_count - old_la_index);
 
-               talloc_free(msg_res);
-               talloc_free(msg_dn);
+               TALLOC_FREE(tmp_ctx);
        }
 
        getnc_state->num_processed = i;
 
+       if (i < getnc_state->num_records) {
+               r->out.ctr->ctr6.more_data = true;
+       }
+
        /* the client can us to call UpdateRefs on its behalf to
           re-establish monitoring of the NC */
        if ((req10->replica_flags & (DRSUAPI_DRS_ADD_REF | DRSUAPI_DRS_REF_GCSPN)) &&
@@ -2902,71 +3124,33 @@ allowed:
                max_links -= r->out.ctr->ctr6.object_count;
        }
 
-       link_total = getnc_state->la_count;
-
-       if (i < getnc_state->num_records) {
-               r->out.ctr->ctr6.more_data = true;
-       } else {
-               /* sort the whole array the first time */
-               if (getnc_state->la_sorted == NULL) {
-                       int j;
-                       struct la_for_sorting *guid_array = talloc_array(getnc_state, struct la_for_sorting, getnc_state->la_count);
-                       if (guid_array == NULL) {
-                               DEBUG(0, ("Out of memory allocating %u linked attributes for sorting", getnc_state->la_count));
-                               return WERR_NOT_ENOUGH_MEMORY;
-                       }
-                       for (j = 0; j < getnc_state->la_count; j++) {
-                               /* we need to get the target GUIDs to compare */
-                               struct dsdb_dn *dn;
-                               const struct drsuapi_DsReplicaLinkedAttribute *la = &getnc_state->la_list[j];
-                               const struct dsdb_attribute *schema_attrib;
-                               const struct ldb_val *target_guid;
-                               DATA_BLOB source_guid;
-                               TALLOC_CTX *frame = talloc_stackframe();
-
-                               schema_attrib = dsdb_attribute_by_attributeID_id(schema, la->attid);
-
-                               werr = dsdb_dn_la_from_blob(sam_ctx, schema_attrib, schema, frame, la->value.blob, &dn);
-                               if (!W_ERROR_IS_OK(werr)) {
-                                       DEBUG(0,(__location__ ": Bad la blob in sort\n"));
-                                       TALLOC_FREE(frame);
-                                       return werr;
-                               }
-
-                               /* Extract the target GUID in NDR form */
-                               target_guid = ldb_dn_get_extended_component(dn->dn, "GUID");
-                               if (target_guid == NULL
-                                   || target_guid->length != sizeof(guid_array[0].target_guid)) {
-                                       status = NT_STATUS_OBJECT_NAME_NOT_FOUND;
-                               } else {
-                                       /* Repack the source GUID as NDR for sorting */
-                                       status = GUID_to_ndr_blob(&la->identifier->guid,
-                                                                 frame,
-                                                                 &source_guid);
-                               }
-
-                               if (!NT_STATUS_IS_OK(status)
-                                   || source_guid.length != sizeof(guid_array[0].source_guid)) {
-                                       DEBUG(0,(__location__ ": Bad la guid in sort\n"));
-                                       TALLOC_FREE(frame);
-                                       return ntstatus_to_werror(status);
-                               }
+       /*
+        * Work out how many links we can send in this chunk. The default is to
+        * send all the links last, but there is a config option to send them
+        * immediately, in the same chunk as their source object
+        */
+       if (!r->out.ctr->ctr6.more_data || immediate_link_sync) {
+               link_count = getnc_state->la_count - getnc_state->la_idx;
+               link_count = MIN(max_links, link_count);
+       }
 
-                               guid_array[j].link = &getnc_state->la_list[j];
-                               memcpy(guid_array[j].target_guid, target_guid->data,
-                                      sizeof(guid_array[j].target_guid));
-                               memcpy(guid_array[j].source_guid, source_guid.data,
-                                      sizeof(guid_array[j].source_guid));
-                               TALLOC_FREE(frame);
-                       }
+       /* If we've got linked attributes to send, add them now */
+       if (link_count > 0) {
+               struct la_for_sorting *la_sorted;
 
-                       LDB_TYPESAFE_QSORT(guid_array, getnc_state->la_count, NULL, linked_attribute_compare);
-                       getnc_state->la_sorted = guid_array;
+               /*
+                * Grab a chunk of linked attributes off the list and put them
+                * in sorted array, ready to send
+                */
+               werr = getncchanges_get_sorted_array(&getnc_state->la_list[getnc_state->la_idx],
+                                                    link_count,
+                                                    sam_ctx, getnc_state,
+                                                    schema,
+                                                    &la_sorted);
+               if (!W_ERROR_IS_OK(werr)) {
+                       return werr;
                }
 
-               link_count = getnc_state->la_count - getnc_state->la_idx;
-               link_count = MIN(max_links, link_count);
-
                r->out.ctr->ctr6.linked_attributes_count = link_count;
                r->out.ctr->ctr6.linked_attributes = talloc_array(r->out.ctr, struct drsuapi_DsReplicaLinkedAttribute, link_count);
                if (r->out.ctr->ctr6.linked_attributes == NULL) {
@@ -2975,16 +3159,29 @@ allowed:
                }
 
                for (k = 0; k < link_count; k++) {
-                       r->out.ctr->ctr6.linked_attributes[k]
-                               = *getnc_state->la_sorted[getnc_state->la_idx + k].link;
+                       r->out.ctr->ctr6.linked_attributes[k] = *la_sorted[k].link;
                }
 
                getnc_state->la_idx += link_count;
-               link_given = getnc_state->la_idx;
+               getnc_state->links_given += link_count;
 
                if (getnc_state->la_idx < getnc_state->la_count) {
                        r->out.ctr->ctr6.more_data = true;
+               } else {
+
+                       /*
+                        * We've now sent all the links seen so far, so we can
+                        * reset la_list back to an empty list again. Note that
+                        * the steal means the linked attribute memory gets
+                        * freed after this RPC message is sent on the wire.
+                        */
+                       talloc_steal(mem_ctx, getnc_state->la_list);
+                       getnc_state->la_list = NULL;
+                       getnc_state->la_idx = 0;
+                       getnc_state->la_count = 0;
                }
+
+               TALLOC_FREE(la_sorted);
        }
 
        if (req10->replica_flags & DRSUAPI_DRS_GET_NC_SIZE) {
@@ -3000,17 +3197,23 @@ allowed:
                 * of links we found so far during the cycle.
                 */
                r->out.ctr->ctr6.nc_object_count = getnc_state->num_records;
-               r->out.ctr->ctr6.nc_linked_attributes_count = getnc_state->la_count;
+               r->out.ctr->ctr6.nc_linked_attributes_count = getnc_state->total_links;
        }
 
        if (!r->out.ctr->ctr6.more_data) {
-               talloc_steal(mem_ctx, getnc_state->la_list);
 
+               /* this is the last response in the replication cycle */
                r->out.ctr->ctr6.new_highwatermark = getnc_state->final_hwm;
                r->out.ctr->ctr6.uptodateness_vector = talloc_move(mem_ctx,
                                                        &getnc_state->final_udv);
 
-               talloc_free(getnc_state);
+               /*
+                * Free the state info stored for the replication cycle. Note
+                * that the RPC message we're sending contains links stored in
+                * getnc_state. mem_ctx is local to this RPC call, so the memory
+                * will get freed after the RPC message is sent on the wire.
+                */
+               talloc_steal(mem_ctx, getnc_state);
                b_state->getncchanges_state = NULL;
        } else {
                ret = drsuapi_DsReplicaHighWaterMark_cmp(&r->out.ctr->ctr6.old_highwatermark,
@@ -3046,7 +3249,7 @@ allowed:
               r->out.ctr->ctr6.object_count,
               i, r->out.ctr->ctr6.more_data?getnc_state->num_records:i,
               r->out.ctr->ctr6.linked_attributes_count,
-              link_given, link_total,
+              getnc_state->links_given, getnc_state->total_links,
               dom_sid_string(mem_ctx, user_sid)));
 
 #if 0