ovsdb: Add unixctl command to show storage status.

If a database enters an error state, e.g., in case of RAFT when reading
the DB file contents if applying the RAFT records triggers constraint
violations, there's no way to determine this unless a client generates a
write transaction. Such write transactions would fail with "ovsdb-error:
inconsistent data".

This commit adds a new command to show the status of the storage that's
backing a database.

Example, on an inconsistent database:
$ ovs-appctl -t /tmp/test.ctl ovsdb-server/get-db-storage-status DB
status: ovsdb error: inconsistent data

Example, on a consistent database:
$ ovs-appctl -t /tmp/test.ctl ovsdb-server/get-db-storage-status DB
status: ok

Signed-off-by: Dumitru Ceara <dceara@redhat.com>
Acked-by: Han Zhou <hzhou@ovn.org>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

NEWS

@@ -1,5 +1,8 @@
 Post-v2.14.0
 ---------------------
+   - OVSDB:
+     * New unixctl command 'ovsdb-server/get-db-storage-status' to show the
+       status of the storage that's backing a database.
 
 
 v2.14.0 - 17 Aug 2020

ovsdb/ovsdb-server.c

@@ -90,6 +90,7 @@ static unixctl_cb_func ovsdb_server_set_active_ovsdb_server_probe_interval;
 static unixctl_cb_func ovsdb_server_set_sync_exclude_tables;
 static unixctl_cb_func ovsdb_server_get_sync_exclude_tables;
 static unixctl_cb_func ovsdb_server_get_sync_status;
+static unixctl_cb_func ovsdb_server_get_db_storage_status;
 
 struct server_config {
     struct sset *remotes;
@@ -453,6 +454,9 @@ main(int argc, char *argv[])
     unixctl_command_register("ovsdb-server/sync-status", "",
                              0, 0, ovsdb_server_get_sync_status,
                              &server_config);
+    unixctl_command_register("ovsdb-server/get-db-storage-status", "DB", 1, 1,
+                             ovsdb_server_get_db_storage_status,
+                             &server_config);
 
     /* Simulate the behavior of OVS release prior to version 2.5 that
      * does not support the monitor_cond method.  */
@@ -1701,6 +1705,41 @@ ovsdb_server_get_sync_status(struct unixctl_conn *conn, int argc OVS_UNUSED,
     ds_destroy(&ds);
 }
 
+static void
+ovsdb_server_get_db_storage_status(struct unixctl_conn *conn,
+                                   int argc OVS_UNUSED,
+                                   const char *argv[],
+                                   void *config_)
+{
+    struct server_config *config = config_;
+    struct shash_node *node;
+
+    node = shash_find(config->all_dbs, argv[1]);
+    if (!node) {
+        unixctl_command_reply_error(conn, "Failed to find the database.");
+        return;
+    }
+
+    struct db *db = node->data;
+
+    if (!db->db) {
+        unixctl_command_reply_error(conn, "Failed to find the database.");
+        return;
+    }
+
+    struct ds ds = DS_EMPTY_INITIALIZER;
+    char *error = ovsdb_storage_get_error(db->db->storage);
+
+    if (!error) {
+        ds_put_cstr(&ds, "status: ok");
+    } else {
+        ds_put_format(&ds, "status: %s", error);
+        free(error);
+    }
+    unixctl_command_reply(conn, ds_cstr(&ds));
+    ds_destroy(&ds);
+}
+
 static void
 parse_options(int argc, char *argv[],
               struct sset *db_filenames, struct sset *remotes,

ovsdb/storage.c

@@ -198,6 +198,16 @@ ovsdb_storage_get_memory_usage(const struct ovsdb_storage *storage,
     }
 }
 
+char *
+ovsdb_storage_get_error(const struct ovsdb_storage *storage)
+{
+    if (storage->error) {
+        return ovsdb_error_to_string(storage->error);
+    }
+
+    return NULL;
+}
+
 void
 ovsdb_storage_run(struct ovsdb_storage *storage)
 {

ovsdb/storage.h

@@ -42,6 +42,7 @@ const struct uuid *ovsdb_storage_get_sid(const struct ovsdb_storage *);
 uint64_t ovsdb_storage_get_applied_index(const struct ovsdb_storage *);
 void ovsdb_storage_get_memory_usage(const struct ovsdb_storage *,
                                     struct simap *usage);
+char *ovsdb_storage_get_error(const struct ovsdb_storage *);
 
 void ovsdb_storage_run(struct ovsdb_storage *);
 void ovsdb_storage_wait(struct ovsdb_storage *);