jsonrpc-server: Split out monitor backend functions to monitor.c/h

Added new files monitor.[ch] for monitor backend functions.
There is no functional changes.

Signed-off-by: Andy Zhou <azhou@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>

5 files changed, 661 insertions, 576 deletions

diff --git a/ovsdb/automake.mk b/ovsdb/automake.mk
index a66974a57..cc3e656dc 100644
--- a/ovsdb/automake.mk
+++ b/ovsdb/automake.mk
@@ -20,6 +20,8 @@ ovsdb_libovsdb_la_SOURCES = \
 	ovsdb/mutation.h \
 	ovsdb/ovsdb.c \
 	ovsdb/ovsdb.h \
+	ovsdb/monitor.c \
+	ovsdb/monitor.h \
 	ovsdb/query.c \
 	ovsdb/query.h \
 	ovsdb/row.c \
diff --git a/ovsdb/jsonrpc-server.c b/ovsdb/jsonrpc-server.c
index 6bbda5296..55148971a 100644
--- a/ovsdb/jsonrpc-server.c
+++ b/ovsdb/jsonrpc-server.c
@@ -37,13 +37,13 @@
 #include "timeval.h"
 #include "transaction.h"
 #include "trigger.h"
+#include "monitor.h"
 #include "openvswitch/vlog.h"
 
 VLOG_DEFINE_THIS_MODULE(ovsdb_jsonrpc_server);
 
 struct ovsdb_jsonrpc_remote;
 struct ovsdb_jsonrpc_session;
-struct ovsdb_jsonrpc_monitor;
 
 /* Message rate-limiting. */
 static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
@@ -82,7 +82,6 @@ static void ovsdb_jsonrpc_trigger_complete_done(
 static struct jsonrpc_msg *ovsdb_jsonrpc_monitor_create(
     struct ovsdb_jsonrpc_session *, struct ovsdb *, struct json *params,
     const struct json *request_id);
-static void ovsdb_jsonrpc_monitor_destroy(struct ovsdb_jsonrpc_monitor *);
 static struct jsonrpc_msg *ovsdb_jsonrpc_monitor_cancel(
     struct ovsdb_jsonrpc_session *,
     struct json_array *params,
@@ -1028,86 +1027,16 @@ ovsdb_jsonrpc_trigger_complete_done(struct ovsdb_jsonrpc_session *s)
     }
 }
 
-/* database table monitors. */
-
-enum ovsdb_monitor_selection {
-    OJMS_INITIAL = 1 << 0,      /* All rows when monitor is created. */
-    OJMS_INSERT = 1 << 1,       /* New rows. */
-    OJMS_DELETE = 1 << 2,       /* Deleted rows. */
-    OJMS_MODIFY = 1 << 3        /* Modified rows. */
-};
-
-/* A particular column being monitored. */
-struct ovsdb_monitor_column {
-    const struct ovsdb_column *column;
-    enum ovsdb_monitor_selection select;
-};
-
-/* A row that has changed in a monitored table. */
-struct ovsdb_monitor_row {
-    struct hmap_node hmap_node; /* In ovsdb_jsonrpc_monitor_table.changes. */
-    struct uuid uuid;           /* UUID of row that changed. */
-    struct ovsdb_datum *old;    /* Old data, NULL for an inserted row. */
-    struct ovsdb_datum *new;    /* New data, NULL for a deleted row. */
-};
-
-/* A particular table being monitored. */
-struct ovsdb_monitor_table {
-    const struct ovsdb_table *table;
-
-    /* This is the union (bitwise-OR) of the 'select' values in all of the
-     * members of 'columns' below. */
-    enum ovsdb_monitor_selection select;
-
-    /* Columns being monitored. */
-    struct ovsdb_monitor_column *columns;
-    size_t n_columns;
-
-    /* Contains 'struct ovsdb_monitor_row's for rows that have been
-     * updated but not yet flushed to the jsonrpc connection. */
-    struct hmap changes;
-};
-
-struct ovsdb_jsonrpc_monitor;
-/*  Backend monitor.
- *
- *  ovsdb_monitor keep track of the ovsdb changes.
- */
-/* A collection of tables being monitored. */
-struct ovsdb_monitor {
-    struct ovsdb_replica replica;
-    struct shash tables;     /* Holds "struct ovsdb_monitor_table"s. */
-    struct ovsdb_jsonrpc_monitor *jsonrpc_monitor;
-};
-
 /* Jsonrpc front end monitor. */
 struct ovsdb_jsonrpc_monitor {
     struct ovsdb_jsonrpc_session *session;
     struct ovsdb *db;
     struct hmap_node node;      /* In ovsdb_jsonrpc_session's "monitors". */
-
     struct json *monitor_id;
     struct ovsdb_monitor *dbmon;
 };
 
-static const struct ovsdb_replica_class ovsdb_jsonrpc_replica_class;
-
-struct ovsdb_jsonrpc_monitor *ovsdb_jsonrpc_monitor_find(
-    struct ovsdb_jsonrpc_session *, const struct json *monitor_id);
-static void ovsdb_monitor_destroy(struct ovsdb_monitor *);
-static struct json *ovsdb_monitor_get_initial(
-    const struct ovsdb_monitor *);
-
-static bool
-parse_bool(struct ovsdb_parser *parser, const char *name, bool default_value)
-{
-    const struct json *json;
-
-    json = ovsdb_parser_member(parser, name, OP_BOOLEAN | OP_OPTIONAL);
-    return json ? json_boolean(json) : default_value;
-}
-
-struct ovsdb_jsonrpc_monitor *
+static struct ovsdb_jsonrpc_monitor *
 ovsdb_jsonrpc_monitor_find(struct ovsdb_jsonrpc_session *s,
                            const struct json *monitor_id)
 {
@@ -1122,45 +1051,13 @@ ovsdb_jsonrpc_monitor_find(struct ovsdb_jsonrpc_session *s,
     return NULL;
 }
 
-static void
-ovsdb_monitor_add_column(struct ovsdb_monitor *dbmon,
-                         const struct ovsdb_table *table,
-                         const struct ovsdb_column *column,
-                         enum ovsdb_monitor_selection select,
-                         size_t *allocated_columns)
-{
-    struct ovsdb_monitor_table *mt;
-    struct ovsdb_monitor_column *c;
-
-    mt = shash_find_data(&dbmon->tables, table->schema->name);
-
-    if (mt->n_columns >= *allocated_columns) {
-        mt->columns = x2nrealloc(mt->columns, allocated_columns,
-                                 sizeof *mt->columns);
-    }
-
-    c = &mt->columns[mt->n_columns++];
-    c->column = column;
-    c->select = select;
-}
-
-static int
-compare_ovsdb_monitor_column(const void *a_, const void *b_)
+static bool
+parse_bool(struct ovsdb_parser *parser, const char *name, bool default_value)
 {
-    const struct ovsdb_monitor_column *a = a_;
-    const struct ovsdb_monitor_column *b = b_;
-
-    return a->column < b->column ? -1 : a->column > b->column;
-}
+    const struct json *json;
 
-static void
-ovsdb_monitor_table_add_select(struct ovsdb_monitor *dbmon,
-                               const struct ovsdb_table *table,
-                               enum ovsdb_monitor_selection select)
-{
-    struct ovsdb_monitor_table * mt;
-    mt = shash_find_data(&dbmon->tables, table->schema->name);
-    mt->select |= select;
+    json = ovsdb_parser_member(parser, name, OP_BOOLEAN | OP_OPTIONAL);
+    return json ? json_boolean(json) : default_value;
 }
 
 static struct ovsdb_error * OVS_WARN_UNUSED_RESULT
@@ -1249,61 +1146,6 @@ ovsdb_jsonrpc_parse_monitor_request(struct ovsdb_monitor *dbmon,
     return NULL;
 }
 
-static struct ovsdb_monitor *
-ovsdb_monitor_create(struct ovsdb *db,
-                     struct ovsdb_jsonrpc_monitor *jsonrpc_monitor,
-                     const struct ovsdb_replica_class *replica_class)
-{
-    struct ovsdb_monitor *dbmon;
-
-    dbmon = xzalloc(sizeof *dbmon);
-
-    ovsdb_replica_init(&dbmon->replica, replica_class);
-    ovsdb_add_replica(db, &dbmon->replica);
-    dbmon->jsonrpc_monitor = jsonrpc_monitor;
-    shash_init(&dbmon->tables);
-
-    return dbmon;
-}
-
-static void
-ovsdb_monitor_add_table(struct ovsdb_monitor *m,
-                        const struct ovsdb_table *table)
-{
-    struct ovsdb_monitor_table *mt;
-
-    mt = xzalloc(sizeof *mt);
-    mt->table = table;
-    hmap_init(&mt->changes);
-    shash_add(&m->tables, table->schema->name, mt);
-}
-
-/* Check for duplicated column names. Return the first
- * duplicated column's name if found. Otherwise return
- * NULL.  */
-static const char * OVS_WARN_UNUSED_RESULT
-ovsdb_monitor_table_check_duplicates(struct ovsdb_monitor *m,
-                          const struct ovsdb_table *table)
-{
-    struct ovsdb_monitor_table *mt;
-    int i;
-
-    mt = shash_find_data(&m->tables, table->schema->name);
-
-    if (mt) {
-        /* Check for duplicate columns. */
-        qsort(mt->columns, mt->n_columns, sizeof *mt->columns,
-              compare_ovsdb_monitor_column);
-        for (i = 1; i < mt->n_columns; i++) {
-            if (mt->columns[i].column == mt->columns[i - 1].column) {
-                return mt->columns[i].column->name;
-            }
-        }
-    }
-
-    return NULL;
-}
-
 static struct jsonrpc_msg *
 ovsdb_jsonrpc_monitor_create(struct ovsdb_jsonrpc_session *s, struct ovsdb *db,
                              struct json *params,
@@ -1335,7 +1177,7 @@ ovsdb_jsonrpc_monitor_create(struct ovsdb_jsonrpc_session *s, struct ovsdb *db,
     m = xzalloc(sizeof *m);
     m->session = s;
     m->db = db;
-    m->dbmon = ovsdb_monitor_create(db, m, &ovsdb_jsonrpc_replica_class);
+    m->dbmon = ovsdb_monitor_create(db, m);
     hmap_insert(&s->monitors, &m->node, json_hash(monitor_id, 0));
     m->monitor_id = json_clone(monitor_id);
 
@@ -1431,309 +1273,6 @@ ovsdb_jsonrpc_monitor_remove_all(struct ovsdb_jsonrpc_session *s)
     }
 }
 
-static struct ovsdb_monitor *
-ovsdb_monitor_cast(struct ovsdb_replica *replica)
-{
-    ovs_assert(replica->class == &ovsdb_jsonrpc_replica_class);
-    return CONTAINER_OF(replica, struct ovsdb_monitor, replica);
-}
-
-struct ovsdb_monitor_aux {
-    const struct ovsdb_monitor *monitor;
-    struct ovsdb_monitor_table *mt;
-};
-
-/* Finds and returns the ovsdb_monitor_row in 'mt->changes' for the
- * given 'uuid', or NULL if there is no such row. */
-static struct ovsdb_monitor_row *
-ovsdb_monitor_row_find(const struct ovsdb_monitor_table *mt,
-                       const struct uuid *uuid)
-{
-    struct ovsdb_monitor_row *row;
-
-    HMAP_FOR_EACH_WITH_HASH (row, hmap_node, uuid_hash(uuid), &mt->changes) {
-        if (uuid_equals(uuid, &row->uuid)) {
-            return row;
-        }
-    }
-    return NULL;
-}
-
-/* Allocates an array of 'mt->n_columns' ovsdb_datums and initializes them as
- * copies of the data in 'row' drawn from the columns represented by
- * mt->columns[].  Returns the array.
- *
- * If 'row' is NULL, returns NULL. */
-static struct ovsdb_datum *
-clone_monitor_row_data(const struct ovsdb_monitor_table *mt,
-                       const struct ovsdb_row *row)
-{
-    struct ovsdb_datum *data;
-    size_t i;
-
-    if (!row) {
-        return NULL;
-    }
-
-    data = xmalloc(mt->n_columns * sizeof *data);
-    for (i = 0; i < mt->n_columns; i++) {
-        const struct ovsdb_column *c = mt->columns[i].column;
-        const struct ovsdb_datum *src = &row->fields[c->index];
-        struct ovsdb_datum *dst = &data[i];
-        const struct ovsdb_type *type = &c->type;
-
-        ovsdb_datum_clone(dst, src, type);
-    }
-    return data;
-}
-
-/* Replaces the mt->n_columns ovsdb_datums in row[] by copies of the data from
- * in 'row' drawn from the columns represented by mt->columns[]. */
-static void
-update_monitor_row_data(const struct ovsdb_monitor_table *mt,
-                        const struct ovsdb_row *row,
-                        struct ovsdb_datum *data)
-{
-    size_t i;
-
-    for (i = 0; i < mt->n_columns; i++) {
-        const struct ovsdb_column *c = mt->columns[i].column;
-        const struct ovsdb_datum *src = &row->fields[c->index];
-        struct ovsdb_datum *dst = &data[i];
-        const struct ovsdb_type *type = &c->type;
-
-        if (!ovsdb_datum_equals(src, dst, type)) {
-            ovsdb_datum_destroy(dst, type);
-            ovsdb_datum_clone(dst, src, type);
-        }
-    }
-}
-
-/* Frees all of the mt->n_columns ovsdb_datums in data[], using the types taken
- * from mt->columns[], plus 'data' itself. */
-static void
-free_monitor_row_data(const struct ovsdb_monitor_table *mt,
-                      struct ovsdb_datum *data)
-{
-    if (data) {
-        size_t i;
-
-        for (i = 0; i < mt->n_columns; i++) {
-            const struct ovsdb_column *c = mt->columns[i].column;
-
-            ovsdb_datum_destroy(&data[i], &c->type);
-        }
-        free(data);
-    }
-}
-
-/* Frees 'row', which must have been created from 'mt'. */
-static void
-ovsdb_monitor_row_destroy(const struct ovsdb_monitor_table *mt,
-                          struct ovsdb_monitor_row *row)
-{
-    if (row) {
-        free_monitor_row_data(mt, row->old);
-        free_monitor_row_data(mt, row->new);
-        free(row);
-    }
-}
-
-static bool
-ovsdb_monitor_change_cb(const struct ovsdb_row *old,
-                        const struct ovsdb_row *new,
-                        const unsigned long int *changed OVS_UNUSED,
-                        void *aux_)
-{
-    struct ovsdb_monitor_aux *aux = aux_;
-    const struct ovsdb_monitor *m = aux->monitor;
-    struct ovsdb_table *table = new ? new->table : old->table;
-    const struct uuid *uuid = ovsdb_row_get_uuid(new ? new : old);
-    struct ovsdb_monitor_row *change;
-    struct ovsdb_monitor_table *mt;
-
-    if (!aux->mt || table != aux->mt->table) {
-        aux->mt = shash_find_data(&m->tables, table->schema->name);
-        if (!aux->mt) {
-            /* We don't care about rows in this table at all.  Tell the caller
-             * to skip it.  */
-            return false;
-        }
-    }
-    mt = aux->mt;
-
-    change = ovsdb_monitor_row_find(mt, uuid);
-    if (!change) {
-        change = xmalloc(sizeof *change);
-        hmap_insert(&mt->changes, &change->hmap_node, uuid_hash(uuid));
-        change->uuid = *uuid;
-        change->old = clone_monitor_row_data(mt, old);
-        change->new = clone_monitor_row_data(mt, new);
-    } else {
-        if (new) {
-            update_monitor_row_data(mt, new, change->new);
-        } else {
-            free_monitor_row_data(mt, change->new);
-            change->new = NULL;
-
-            if (!change->old) {
-                /* This row was added then deleted.  Forget about it. */
-                hmap_remove(&mt->changes, &change->hmap_node);
-                free(change);
-            }
-        }
-    }
-    return true;
-}
-
-/* Returns JSON for a <row-update> (as described in RFC 7047) for 'row' within
- * 'mt', or NULL if no row update should be sent.
- *
- * The caller should specify 'initial' as true if the returned JSON is going to
- * be used as part of the initial reply to a "monitor" request, false if it is
- * going to be used as part of an "update" notification.
- *
- * 'changed' must be a scratch buffer for internal use that is at least
- * bitmap_n_bytes(mt->n_columns) bytes long. */
-static struct json *
-ovsdb_monitor_compose_row_update(
-    const struct ovsdb_monitor_table *mt,
-    const struct ovsdb_monitor_row *row,
-    bool initial, unsigned long int *changed)
-{
-    enum ovsdb_monitor_selection type;
-    struct json *old_json, *new_json;
-    struct json *row_json;
-    size_t i;
-
-    type = (initial ? OJMS_INITIAL
-            : !row->old ? OJMS_INSERT
-            : !row->new ? OJMS_DELETE
-            : OJMS_MODIFY);
-    if (!(mt->select & type)) {
-        return NULL;
-    }
-
-    if (type == OJMS_MODIFY) {
-        size_t n_changes;
-
-        n_changes = 0;
-        memset(changed, 0, bitmap_n_bytes(mt->n_columns));
-        for (i = 0; i < mt->n_columns; i++) {
-            const struct ovsdb_column *c = mt->columns[i].column;
-            if (!ovsdb_datum_equals(&row->old[i], &row->new[i], &c->type)) {
-                bitmap_set1(changed, i);
-                n_changes++;
-            }
-        }
-        if (!n_changes) {
-            /* No actual changes: presumably a row changed and then
-             * changed back later. */
-            return NULL;
-        }
-    }
-
-    row_json = json_object_create();
-    old_json = new_json = NULL;
-    if (type & (OJMS_DELETE | OJMS_MODIFY)) {
-        old_json = json_object_create();
-        json_object_put(row_json, "old", old_json);
-    }
-    if (type & (OJMS_INITIAL | OJMS_INSERT | OJMS_MODIFY)) {
-        new_json = json_object_create();
-        json_object_put(row_json, "new", new_json);
-    }
-    for (i = 0; i < mt->n_columns; i++) {
-        const struct ovsdb_monitor_column *c = &mt->columns[i];
-
-        if (!(type & c->select)) {
-            /* We don't care about this type of change for this
-             * particular column (but we will care about it for some
-             * other column). */
-            continue;
-        }
-
-        if ((type == OJMS_MODIFY && bitmap_is_set(changed, i))
-            || type == OJMS_DELETE) {
-            json_object_put(old_json, c->column->name,
-                            ovsdb_datum_to_json(&row->old[i],
-                                                &c->column->type));
-        }
-        if (type & (OJMS_INITIAL | OJMS_INSERT | OJMS_MODIFY)) {
-            json_object_put(new_json, c->column->name,
-                            ovsdb_datum_to_json(&row->new[i],
-                                                &c->column->type));
-        }
-    }
-
-    return row_json;
-}
-
-/* Constructs and returns JSON for a <table-updates> object (as described in
- * RFC 7047) for all the outstanding changes within 'monitor', and deletes all
- * the outstanding changes from 'monitor'.  Returns NULL if no update needs to
- * be sent.
- *
- * The caller should specify 'initial' as true if the returned JSON is going to
- * be used as part of the initial reply to a "monitor" request, false if it is
- * going to be used as part of an "update" notification. */
-static struct json *
-ovsdb_monitor_compose_table_update(
-    const struct ovsdb_monitor *dbmon, bool initial)
-{
-    struct shash_node *node;
-    unsigned long int *changed;
-    struct json *json;
-    size_t max_columns;
-
-    max_columns = 0;
-    SHASH_FOR_EACH (node, &dbmon->tables) {
-        struct ovsdb_monitor_table *mt = node->data;
-
-        max_columns = MAX(max_columns, mt->n_columns);
-    }
-    changed = xmalloc(bitmap_n_bytes(max_columns));
-
-    json = NULL;
-    SHASH_FOR_EACH (node, &dbmon->tables) {
-        struct ovsdb_monitor_table *mt = node->data;
-        struct ovsdb_monitor_row *row, *next;
-        struct json *table_json = NULL;
-
-        HMAP_FOR_EACH_SAFE (row, next, hmap_node, &mt->changes) {
-            struct json *row_json;
-
-            row_json = ovsdb_monitor_compose_row_update(
-                mt, row, initial, changed);
-            if (row_json) {
-                char uuid[UUID_LEN + 1];
-
-                /* Create JSON object for transaction overall. */
-                if (!json) {
-                    json = json_object_create();
-                }
-
-                /* Create JSON object for transaction on this table. */
-                if (!table_json) {
-                    table_json = json_object_create();
-                    json_object_put(json, mt->table->schema->name, table_json);
-                }
-
-                /* Add JSON row to JSON table. */
-                snprintf(uuid, sizeof uuid, UUID_FMT, UUID_ARGS(&row->uuid));
-                json_object_put(table_json, uuid, row_json);
-            }
-
-            hmap_remove(&mt->changes, &row->hmap_node);
-            ovsdb_monitor_row_destroy(mt, row);
-        }
-    }
-
-    free(changed);
-
-    return json;
-}
-
 static struct json *
 ovsdb_jsonrpc_monitor_compose_table_update(
     const struct ovsdb_jsonrpc_monitor *monitor, bool initial)
@@ -1742,21 +1281,6 @@ ovsdb_jsonrpc_monitor_compose_table_update(
 }
 
 static bool
-ovsdb_monitor_needs_flush(struct ovsdb_monitor *dbmon)
-{
-    struct shash_node *node;
-
-    SHASH_FOR_EACH (node, &dbmon->tables) {
-        struct ovsdb_monitor_table *mt = node->data;
-
-        if (!hmap_is_empty(&mt->changes)) {
-            return true;
-        }
-    }
-    return false;
-}
-
-static bool
 ovsdb_jsonrpc_monitor_needs_flush(struct ovsdb_jsonrpc_session *s)
 {
     struct ovsdb_jsonrpc_monitor *m;
@@ -1770,6 +1294,15 @@ ovsdb_jsonrpc_monitor_needs_flush(struct ovsdb_jsonrpc_session *s)
     return false;
 }
 
+void
+ovsdb_jsonrpc_monitor_destroy(struct ovsdb_jsonrpc_monitor *m)
+{
+    json_destroy(m->monitor_id);
+    hmap_remove(&m->session->monitors, &m->node);
+    ovsdb_monitor_destroy(m->dbmon);
+    free(m);
+}
+
 static void
 ovsdb_jsonrpc_monitor_flush_all(struct ovsdb_jsonrpc_session *s)
 {
@@ -1789,95 +1322,3 @@ ovsdb_jsonrpc_monitor_flush_all(struct ovsdb_jsonrpc_session *s)
         }
     }
 }
-
-static void
-ovsdb_monitor_init_aux(struct ovsdb_monitor_aux *aux,
-                       const struct ovsdb_monitor *m)
-{
-    aux->monitor = m;
-    aux->mt = NULL;
-}
-
-static struct ovsdb_error *
-ovsdb_monitor_commit(struct ovsdb_replica *replica,
-                     const struct ovsdb_txn *txn,
-                     bool durable OVS_UNUSED)
-{
-    struct ovsdb_monitor *m = ovsdb_monitor_cast(replica);
-    struct ovsdb_monitor_aux aux;
-
-    ovsdb_monitor_init_aux(&aux, m);
-    ovsdb_txn_for_each_change(txn, ovsdb_monitor_change_cb, &aux);
-
-    return NULL;
-}
-
-static struct json *
-ovsdb_monitor_get_initial(const struct ovsdb_monitor *dbmon)
-{
-    struct ovsdb_monitor_aux aux;
-    struct shash_node *node;
-    struct json *json;
-
-    ovsdb_monitor_init_aux(&aux, dbmon);
-    SHASH_FOR_EACH (node, &dbmon->tables) {
-        struct ovsdb_monitor_table *mt = node->data;
-
-        if (mt->select & OJMS_INITIAL) {
-            struct ovsdb_row *row;
-
-            HMAP_FOR_EACH (row, hmap_node, &mt->table->rows) {
-                ovsdb_monitor_change_cb(NULL, row, NULL, &aux);
-            }
-        }
-    }
-    json = ovsdb_monitor_compose_table_update(dbmon, true);
-    return json ? json : json_object_create();
-}
-
-static void
-ovsdb_jsonrpc_monitor_destroy(struct ovsdb_jsonrpc_monitor *m)
-{
-    json_destroy(m->monitor_id);
-    hmap_remove(&m->session->monitors, &m->node);
-    ovsdb_monitor_destroy(m->dbmon);
-    free(m);
-}
-
-static void
-ovsdb_monitor_destroy(struct ovsdb_monitor *dbmon)
-{
-    struct shash_node *node;
-
-    list_remove(&dbmon->replica.node);
-
-    SHASH_FOR_EACH (node, &dbmon->tables) {
-        struct ovsdb_monitor_table *mt = node->data;
-        struct ovsdb_monitor_row *row, *next;
-
-        HMAP_FOR_EACH_SAFE (row, next, hmap_node, &mt->changes) {
-            hmap_remove(&mt->changes, &row->hmap_node);
-            ovsdb_monitor_row_destroy(mt, row);
-        }
-        hmap_destroy(&mt->changes);
-
-        free(mt->columns);
-        free(mt);
-    }
-    shash_destroy(&dbmon->tables);
-    free(dbmon);
-}
-
-static void
-ovsdb_monitor_destroy_callback(struct ovsdb_replica *replica)
-{
-    struct ovsdb_monitor *dbmon = ovsdb_monitor_cast(replica);
-    struct ovsdb_jsonrpc_monitor *m = dbmon->jsonrpc_monitor;
-
-    ovsdb_jsonrpc_monitor_destroy(m);
-}
-
-static const struct ovsdb_replica_class ovsdb_jsonrpc_replica_class = {
-    ovsdb_monitor_commit,
-    ovsdb_monitor_destroy_callback,
-};
diff --git a/ovsdb/jsonrpc-server.h b/ovsdb/jsonrpc-server.h
index e6a1642a5..fce8b7bd0 100644
--- a/ovsdb/jsonrpc-server.h
+++ b/ovsdb/jsonrpc-server.h
@@ -69,4 +69,7 @@ void ovsdb_jsonrpc_server_wait(struct ovsdb_jsonrpc_server *);
 void ovsdb_jsonrpc_server_get_memory_usage(const struct ovsdb_jsonrpc_server *,
                                            struct simap *usage);
 
+struct ovsdb_jsonrpc_monitor;
+void ovsdb_jsonrpc_monitor_destroy(struct ovsdb_jsonrpc_monitor *);
+
 #endif /* ovsdb/jsonrpc-server.h */
diff --git a/ovsdb/monitor.c b/ovsdb/monitor.c
new file mode 100644
index 000000000..a1aeb5f51
--- /dev/null
+++ b/ovsdb/monitor.c
@@ -0,0 +1,581 @@
+/*
+ * Copyright (c) 2015 Nicira, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+
+#include <errno.h>
+
+#include "bitmap.h"
+#include "column.h"
+#include "dynamic-string.h"
+#include "json.h"
+#include "jsonrpc.h"
+#include "ovsdb-error.h"
+#include "ovsdb-parser.h"
+#include "ovsdb.h"
+#include "row.h"
+#include "simap.h"
+#include "table.h"
+#include "timeval.h"
+#include "transaction.h"
+#include "jsonrpc-server.h"
+#include "monitor.h"
+#include "openvswitch/vlog.h"
+
+
+static const struct ovsdb_replica_class ovsdb_jsonrpc_replica_class;
+
+/*  Backend monitor.
+ *
+ *  ovsdb_monitor keep track of the ovsdb changes.
+ */
+
+/* A collection of tables being monitored. */
+struct ovsdb_monitor {
+    struct ovsdb_replica replica;
+    struct shash tables;     /* Holds "struct ovsdb_monitor_table"s. */
+    struct ovsdb_jsonrpc_monitor *jsonrpc_monitor;
+    struct ovsdb *db;
+};
+
+/* A particular column being monitored. */
+struct ovsdb_monitor_column {
+    const struct ovsdb_column *column;
+    enum ovsdb_monitor_selection select;
+};
+
+/* A row that has changed in a monitored table. */
+struct ovsdb_monitor_row {
+    struct hmap_node hmap_node; /* In ovsdb_jsonrpc_monitor_table.changes. */
+    struct uuid uuid;           /* UUID of row that changed. */
+    struct ovsdb_datum *old;    /* Old data, NULL for an inserted row. */
+    struct ovsdb_datum *new;    /* New data, NULL for a deleted row. */
+};
+
+/* A particular table being monitored. */
+struct ovsdb_monitor_table {
+    const struct ovsdb_table *table;
+
+    /* This is the union (bitwise-OR) of the 'select' values in all of the
+     * members of 'columns' below. */
+    enum ovsdb_monitor_selection select;
+
+    /* Columns being monitored. */
+    struct ovsdb_monitor_column *columns;
+    size_t n_columns;
+
+    /* Contains 'struct ovsdb_monitor_row's for rows that have been
+     * updated but not yet flushed to the jsonrpc connection. */
+    struct hmap changes;
+};
+
+static int
+compare_ovsdb_monitor_column(const void *a_, const void *b_)
+{
+    const struct ovsdb_monitor_column *a = a_;
+    const struct ovsdb_monitor_column *b = b_;
+
+    return a->column < b->column ? -1 : a->column > b->column;
+}
+
+static struct ovsdb_monitor *
+ovsdb_monitor_cast(struct ovsdb_replica *replica)
+{
+    ovs_assert(replica->class == &ovsdb_jsonrpc_replica_class);
+    return CONTAINER_OF(replica, struct ovsdb_monitor, replica);
+}
+
+/* Finds and returns the ovsdb_monitor_row in 'mt->changes' for the
+ * given 'uuid', or NULL if there is no such row. */
+static struct ovsdb_monitor_row *
+ovsdb_monitor_row_find(const struct ovsdb_monitor_table *mt,
+                       const struct uuid *uuid)
+{
+    struct ovsdb_monitor_row *row;
+
+    HMAP_FOR_EACH_WITH_HASH (row, hmap_node, uuid_hash(uuid), &mt->changes) {
+        if (uuid_equals(uuid, &row->uuid)) {
+            return row;
+        }
+    }
+    return NULL;
+}
+
+/* Allocates an array of 'mt->n_columns' ovsdb_datums and initializes them as
+ * copies of the data in 'row' drawn from the columns represented by
+ * mt->columns[].  Returns the array.
+ *
+ * If 'row' is NULL, returns NULL. */
+static struct ovsdb_datum *
+clone_monitor_row_data(const struct ovsdb_monitor_table *mt,
+                       const struct ovsdb_row *row)
+{
+    struct ovsdb_datum *data;
+    size_t i;
+
+    if (!row) {
+        return NULL;
+    }
+
+    data = xmalloc(mt->n_columns * sizeof *data);
+    for (i = 0; i < mt->n_columns; i++) {
+        const struct ovsdb_column *c = mt->columns[i].column;
+        const struct ovsdb_datum *src = &row->fields[c->index];
+        struct ovsdb_datum *dst = &data[i];
+        const struct ovsdb_type *type = &c->type;
+
+        ovsdb_datum_clone(dst, src, type);
+    }
+    return data;
+}
+
+/* Replaces the mt->n_columns ovsdb_datums in row[] by copies of the data from
+ * in 'row' drawn from the columns represented by mt->columns[]. */
+static void
+update_monitor_row_data(const struct ovsdb_monitor_table *mt,
+                        const struct ovsdb_row *row,
+                        struct ovsdb_datum *data)
+{
+    size_t i;
+
+    for (i = 0; i < mt->n_columns; i++) {
+        const struct ovsdb_column *c = mt->columns[i].column;
+        const struct ovsdb_datum *src = &row->fields[c->index];
+        struct ovsdb_datum *dst = &data[i];
+        const struct ovsdb_type *type = &c->type;
+
+        if (!ovsdb_datum_equals(src, dst, type)) {
+            ovsdb_datum_destroy(dst, type);
+            ovsdb_datum_clone(dst, src, type);
+        }
+    }
+}
+
+/* Frees all of the mt->n_columns ovsdb_datums in data[], using the types taken
+ * from mt->columns[], plus 'data' itself. */
+static void
+free_monitor_row_data(const struct ovsdb_monitor_table *mt,
+                      struct ovsdb_datum *data)
+{
+    if (data) {
+        size_t i;
+
+        for (i = 0; i < mt->n_columns; i++) {
+            const struct ovsdb_column *c = mt->columns[i].column;
+
+            ovsdb_datum_destroy(&data[i], &c->type);
+        }
+        free(data);
+    }
+}
+
+/* Frees 'row', which must have been created from 'mt'. */
+static void
+ovsdb_monitor_row_destroy(const struct ovsdb_monitor_table *mt,
+                          struct ovsdb_monitor_row *row)
+{
+    if (row) {
+        free_monitor_row_data(mt, row->old);
+        free_monitor_row_data(mt, row->new);
+        free(row);
+    }
+}
+
+struct ovsdb_monitor *
+ovsdb_monitor_create(struct ovsdb *db,
+                     struct ovsdb_jsonrpc_monitor *jsonrpc_monitor)
+{
+    struct ovsdb_monitor *dbmon;
+
+    dbmon = xzalloc(sizeof *dbmon);
+
+    ovsdb_replica_init(&dbmon->replica, &ovsdb_jsonrpc_replica_class);
+    ovsdb_add_replica(db, &dbmon->replica);
+    dbmon->jsonrpc_monitor = jsonrpc_monitor;
+    dbmon->db = db;
+    shash_init(&dbmon->tables);
+
+    return dbmon;
+}
+
+void
+ovsdb_monitor_add_table(struct ovsdb_monitor *m,
+                        const struct ovsdb_table *table)
+{
+    struct ovsdb_monitor_table *mt;
+
+    mt = xzalloc(sizeof *mt);
+    mt->table = table;
+    hmap_init(&mt->changes);
+    shash_add(&m->tables, table->schema->name, mt);
+}
+
+void
+ovsdb_monitor_add_column(struct ovsdb_monitor *dbmon,
+                         const struct ovsdb_table *table,
+                         const struct ovsdb_column *column,
+                         enum ovsdb_monitor_selection select,
+                         size_t *allocated_columns)
+{
+    struct ovsdb_monitor_table *mt;
+    struct ovsdb_monitor_column *c;
+
+    mt = shash_find_data(&dbmon->tables, table->schema->name);
+
+    if (mt->n_columns >= *allocated_columns) {
+        mt->columns = x2nrealloc(mt->columns, allocated_columns,
+                                 sizeof *mt->columns);
+    }
+
+    mt->select |= select;
+    c = &mt->columns[mt->n_columns++];
+    c->column = column;
+    c->select = select;
+}
+
+/* Check for duplicated column names. Return the first
+ * duplicated column's name if found. Otherwise return
+ * NULL.  */
+const char * OVS_WARN_UNUSED_RESULT
+ovsdb_monitor_table_check_duplicates(struct ovsdb_monitor *m,
+                                     const struct ovsdb_table *table)
+{
+    struct ovsdb_monitor_table *mt;
+    int i;
+
+    mt = shash_find_data(&m->tables, table->schema->name);
+
+    if (mt) {
+        /* Check for duplicate columns. */
+        qsort(mt->columns, mt->n_columns, sizeof *mt->columns,
+              compare_ovsdb_monitor_column);
+        for (i = 1; i < mt->n_columns; i++) {
+            if (mt->columns[i].column == mt->columns[i - 1].column) {
+                return mt->columns[i].column->name;
+            }
+        }
+    }
+
+    return NULL;
+}
+
+/* Returns JSON for a <row-update> (as described in RFC 7047) for 'row' within
+ * 'mt', or NULL if no row update should be sent.
+ *
+ * The caller should specify 'initial' as true if the returned JSON is going to
+ * be used as part of the initial reply to a "monitor" request, false if it is
+ * going to be used as part of an "update" notification.
+ *
+ * 'changed' must be a scratch buffer for internal use that is at least
+ * bitmap_n_bytes(mt->n_columns) bytes long. */
+static struct json *
+ovsdb_monitor_compose_row_update(
+    const struct ovsdb_monitor_table *mt,
+    const struct ovsdb_monitor_row *row,
+    bool initial, unsigned long int *changed)
+{
+    enum ovsdb_monitor_selection type;
+    struct json *old_json, *new_json;
+    struct json *row_json;
+    size_t i;
+
+    type = (initial ? OJMS_INITIAL
+            : !row->old ? OJMS_INSERT
+            : !row->new ? OJMS_DELETE
+            : OJMS_MODIFY);
+    if (!(mt->select & type)) {
+        return NULL;
+    }
+
+    if (type == OJMS_MODIFY) {
+        size_t n_changes;
+
+        n_changes = 0;
+        memset(changed, 0, bitmap_n_bytes(mt->n_columns));
+        for (i = 0; i < mt->n_columns; i++) {
+            const struct ovsdb_column *c = mt->columns[i].column;
+            if (!ovsdb_datum_equals(&row->old[i], &row->new[i], &c->type)) {
+                bitmap_set1(changed, i);
+                n_changes++;
+            }
+        }
+        if (!n_changes) {
+            /* No actual changes: presumably a row changed and then
+             * changed back later. */
+            return NULL;
+        }
+    }
+
+    row_json = json_object_create();
+    old_json = new_json = NULL;
+    if (type & (OJMS_DELETE | OJMS_MODIFY)) {
+        old_json = json_object_create();
+        json_object_put(row_json, "old", old_json);
+    }
+    if (type & (OJMS_INITIAL | OJMS_INSERT | OJMS_MODIFY)) {
+        new_json = json_object_create();
+        json_object_put(row_json, "new", new_json);
+    }
+    for (i = 0; i < mt->n_columns; i++) {
+        const struct ovsdb_monitor_column *c = &mt->columns[i];
+
+        if (!(type & c->select)) {
+            /* We don't care about this type of change for this
+             * particular column (but we will care about it for some
+             * other column). */
+            continue;
+        }
+
+        if ((type == OJMS_MODIFY && bitmap_is_set(changed, i))
+            || type == OJMS_DELETE) {
+            json_object_put(old_json, c->column->name,
+                            ovsdb_datum_to_json(&row->old[i],
+                                                &c->column->type));
+        }
+        if (type & (OJMS_INITIAL | OJMS_INSERT | OJMS_MODIFY)) {
+            json_object_put(new_json, c->column->name,
+                            ovsdb_datum_to_json(&row->new[i],
+                                                &c->column->type));
+        }
+    }
+
+    return row_json;
+}
+
+/* Constructs and returns JSON for a <table-updates> object (as described in
+ * RFC 7047) for all the outstanding changes within 'monitor', and deletes all
+ * the outstanding changes from 'monitor'.  Returns NULL if no update needs to
+ * be sent.
+ *
+ * The caller should specify 'initial' as true if the returned JSON is going to
+ * be used as part of the initial reply to a "monitor" request, false if it is
+ * going to be used as part of an "update" notification. */
+struct json *
+ovsdb_monitor_compose_table_update(
+    const struct ovsdb_monitor *dbmon, bool initial)
+{
+    struct shash_node *node;
+    unsigned long int *changed;
+    struct json *json;
+    size_t max_columns;
+
+    max_columns = 0;
+    SHASH_FOR_EACH (node, &dbmon->tables) {
+        struct ovsdb_monitor_table *mt = node->data;
+
+        max_columns = MAX(max_columns, mt->n_columns);
+    }
+    changed = xmalloc(bitmap_n_bytes(max_columns));
+
+    json = NULL;
+    SHASH_FOR_EACH (node, &dbmon->tables) {
+        struct ovsdb_monitor_table *mt = node->data;
+        struct ovsdb_monitor_row *row, *next;
+        struct json *table_json = NULL;
+
+        HMAP_FOR_EACH_SAFE (row, next, hmap_node, &mt->changes) {
+            struct json *row_json;
+
+            row_json = ovsdb_monitor_compose_row_update(
+                mt, row, initial, changed);
+            if (row_json) {
+                char uuid[UUID_LEN + 1];
+
+                /* Create JSON object for transaction overall. */
+                if (!json) {
+                    json = json_object_create();
+                }
+
+                /* Create JSON object for transaction on this table. */
+                if (!table_json) {
+                    table_json = json_object_create();
+                    json_object_put(json, mt->table->schema->name, table_json);
+                }
+
+                /* Add JSON row to JSON table. */
+                snprintf(uuid, sizeof uuid, UUID_FMT, UUID_ARGS(&row->uuid));
+                json_object_put(table_json, uuid, row_json);
+            }
+
+            hmap_remove(&mt->changes, &row->hmap_node);
+            ovsdb_monitor_row_destroy(mt, row);
+        }
+    }
+
+    free(changed);
+    return json;
+}
+
+bool
+ovsdb_monitor_needs_flush(struct ovsdb_monitor *dbmon)
+{
+    struct shash_node *node;
+
+    SHASH_FOR_EACH (node, &dbmon->tables) {
+        struct ovsdb_monitor_table *mt = node->data;
+
+        if (!hmap_is_empty(&mt->changes)) {
+            return true;
+        }
+    }
+    return false;
+}
+
+void
+ovsdb_monitor_table_add_select(struct ovsdb_monitor *dbmon,
+                               const struct ovsdb_table *table,
+                               enum ovsdb_monitor_selection select)
+{
+    struct ovsdb_monitor_table * mt;
+
+    mt = shash_find_data(&dbmon->tables, table->schema->name);
+    mt->select |= select;
+}
+
+struct ovsdb_monitor_aux {
+    const struct ovsdb_monitor *monitor;
+    struct ovsdb_monitor_table *mt;
+};
+
+static void
+ovsdb_monitor_init_aux(struct ovsdb_monitor_aux *aux,
+                       const struct ovsdb_monitor *m)
+{
+    aux->monitor = m;
+    aux->mt = NULL;
+}
+
+static bool
+ovsdb_monitor_change_cb(const struct ovsdb_row *old,
+                        const struct ovsdb_row *new,
+                        const unsigned long int *changed OVS_UNUSED,
+                        void *aux_)
+{
+    struct ovsdb_monitor_aux *aux = aux_;
+    const struct ovsdb_monitor *m = aux->monitor;
+    struct ovsdb_table *table = new ? new->table : old->table;
+    const struct uuid *uuid = ovsdb_row_get_uuid(new ? new : old);
+    struct ovsdb_monitor_row *change;
+    struct ovsdb_monitor_table *mt;
+
+    if (!aux->mt || table != aux->mt->table) {
+        aux->mt = shash_find_data(&m->tables, table->schema->name);
+        if (!aux->mt) {
+            /* We don't care about rows in this table at all.  Tell the caller
+             * to skip it.  */
+            return false;
+        }
+    }
+    mt = aux->mt;
+
+    change = ovsdb_monitor_row_find(mt, uuid);
+    if (!change) {
+        change = xmalloc(sizeof *change);
+        hmap_insert(&mt->changes, &change->hmap_node, uuid_hash(uuid));
+        change->uuid = *uuid;
+        change->old = clone_monitor_row_data(mt, old);
+        change->new = clone_monitor_row_data(mt, new);
+    } else {
+        if (new) {
+            update_monitor_row_data(mt, new, change->new);
+        } else {
+            free_monitor_row_data(mt, change->new);
+            change->new = NULL;
+
+            if (!change->old) {
+                /* This row was added then deleted.  Forget about it. */
+                hmap_remove(&mt->changes, &change->hmap_node);
+                free(change);
+            }
+        }
+    }
+    return true;
+}
+
+struct json *
+ovsdb_monitor_get_initial(const struct ovsdb_monitor *dbmon)
+{
+    struct ovsdb_monitor_aux aux;
+    struct shash_node *node;
+    struct json *json;
+
+    ovsdb_monitor_init_aux(&aux, dbmon);
+    SHASH_FOR_EACH (node, &dbmon->tables) {
+        struct ovsdb_monitor_table *mt = node->data;
+
+        if (mt->select & OJMS_INITIAL) {
+            struct ovsdb_row *row;
+
+            HMAP_FOR_EACH (row, hmap_node, &mt->table->rows) {
+                ovsdb_monitor_change_cb(NULL, row, NULL, &aux);
+            }
+        }
+    }
+    json = ovsdb_monitor_compose_table_update(dbmon, true);
+    return json ? json : json_object_create();
+}
+
+void
+ovsdb_monitor_destroy(struct ovsdb_monitor *dbmon)
+{
+    struct shash_node *node;
+
+    list_remove(&dbmon->replica.node);
+
+    SHASH_FOR_EACH (node, &dbmon->tables) {
+        struct ovsdb_monitor_table *mt = node->data;
+        struct ovsdb_monitor_row *row, *next;
+
+        HMAP_FOR_EACH_SAFE (row, next, hmap_node, &mt->changes) {
+            hmap_remove(&mt->changes, &row->hmap_node);
+            ovsdb_monitor_row_destroy(mt, row);
+        }
+        hmap_destroy(&mt->changes);
+
+        free(mt->columns);
+        free(mt);
+    }
+    shash_destroy(&dbmon->tables);
+    free(dbmon);
+}
+
+static struct ovsdb_error *
+ovsdb_monitor_commit(struct ovsdb_replica *replica,
+                     const struct ovsdb_txn *txn,
+                     bool durable OVS_UNUSED)
+{
+    struct ovsdb_monitor *m = ovsdb_monitor_cast(replica);
+    struct ovsdb_monitor_aux aux;
+
+    ovsdb_monitor_init_aux(&aux, m);
+    ovsdb_txn_for_each_change(txn, ovsdb_monitor_change_cb, &aux);
+
+    return NULL;
+}
+
+static void
+ovsdb_monitor_destroy_callback(struct ovsdb_replica *replica)
+{
+    struct ovsdb_monitor *dbmon = ovsdb_monitor_cast(replica);
+    struct ovsdb_jsonrpc_monitor *m = dbmon->jsonrpc_monitor;
+
+    ovsdb_jsonrpc_monitor_destroy(m);
+}
+
+static const struct ovsdb_replica_class ovsdb_jsonrpc_replica_class = {
+    ovsdb_monitor_commit,
+    ovsdb_monitor_destroy_callback,
+};
diff --git a/ovsdb/monitor.h b/ovsdb/monitor.h
new file mode 100644
index 000000000..82c9a578b
--- /dev/null
+++ b/ovsdb/monitor.h
@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2015 Nicira, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef OVSDB_MONITOR_H
+#define OVSDB_MONITOR_H
+
+struct ovsdb_monitor;
+
+enum ovsdb_monitor_selection {
+    OJMS_INITIAL = 1 << 0,      /* All rows when monitor is created. */
+    OJMS_INSERT = 1 << 1,       /* New rows. */
+    OJMS_DELETE = 1 << 2,       /* Deleted rows. */
+    OJMS_MODIFY = 1 << 3        /* Modified rows. */
+};
+
+
+struct ovsdb_monitor *ovsdb_monitor_create(struct ovsdb *db,
+                        struct ovsdb_jsonrpc_monitor *jsonrpc_monitor);
+
+void ovsdb_monitor_add_table(struct ovsdb_monitor *m,
+                             const struct ovsdb_table *table);
+
+void ovsdb_monitor_add_column(struct ovsdb_monitor *dbmon,
+                              const struct ovsdb_table *table,
+                              const struct ovsdb_column *column,
+                              enum ovsdb_monitor_selection select,
+                              size_t *allocated_columns);
+
+const char * OVS_WARN_UNUSED_RESULT
+ovsdb_monitor_table_check_duplicates(struct ovsdb_monitor *,
+                          const struct ovsdb_table *);
+
+struct json *ovsdb_monitor_compose_table_update(
+    const struct ovsdb_monitor *dbmon, bool initial);
+
+void ovsdb_monitor_table_add_select(struct ovsdb_monitor *dbmon,
+                                    const struct ovsdb_table *table,
+                                    enum ovsdb_monitor_selection select);
+
+bool ovsdb_monitor_needs_flush(struct ovsdb_monitor *dbmon);
+
+struct json *ovsdb_monitor_get_initial(const struct ovsdb_monitor *dbmon);
+
+void ovsdb_monitor_destroy(struct ovsdb_monitor *dbmon);
+#endif