Allow an optional readonly base database (minetest#7544)

* Allow an optional readonly base database

* Added basic documentation

doc/world_format.txt

@@ -98,8 +98,15 @@ See Player File Format below.
 world.mt
 ---------
 World metadata.
-Example content (added indentation):
- gameid = mesetint
+Example content (added indentation and - explanations):
+ gameid = mesetint - name of the game
+ enable_damage = true - whether damage is enabled or not
+ creative_mode = false - whether creative mode is enabled or not
+ backend = sqlite3 - which DB backend to use for blocks (sqlite3, dummy, leveldb, redis, postgresql)
+ player_backend = sqlite3 - which DB backend to use for player data
+ readonly_backend = sqlite3 - optionally readonly seed DB (DB file _must_ be located in "readonly" subfolder)
+ server_announce = false - whether the server is publicly announced or not
+ load_mod_<mod> = false - whether <mod> is to be loaded in this world
 
 Player File Format
 ===================

src/map.cpp

@@ -1159,7 +1159,10 @@ ServerMap::ServerMap(const std::string &savedir, IGameDef *gamedef,
  }
  std::string backend = conf.get("backend");
  dbase = createDatabase(backend, savedir, conf);
-
+ if (conf.exists("readonly_backend")) {
+ std::string readonly_dir = savedir + DIR_DELIM + "readonly";
+ dbase_ro = createDatabase(conf.get("readonly_backend"), readonly_dir, conf);
+ }
  if (!conf.updateConfigFile(conf_path.c_str()))
  errorstream << "ServerMap::ServerMap(): Failed to update world.mt!" << std::endl;
 
@@ -1230,6 +1233,8 @@ ServerMap::~ServerMap()
  Close database if it was opened
  */
  delete dbase;
+ if (dbase_ro)
+ delete dbase_ro;
 
 #if 0
  /*
@@ -1869,6 +1874,8 @@ void ServerMap::listAllLoadableBlocks(std::vector<v3s16> &dst)
  << "all blocks that are stored in flat files." << std::endl;
  }
  dbase->listAllLoadableBlocks(dst);
+ if (dbase_ro)
+ dbase_ro->listAllLoadableBlocks(dst);
 }
 
 void ServerMap::listAllLoadedBlocks(std::vector<v3s16> &dst)
@@ -2107,6 +2114,11 @@ MapBlock* ServerMap::loadBlock(v3s16 blockpos)
  dbase->loadBlock(blockpos, &ret);
  if (!ret.empty()) {
  loadBlock(&ret, blockpos, createSector(p2d), false);
+ } else if (dbase_ro) {
+ dbase_ro->loadBlock(blockpos, &ret);
+ if (!ret.empty()) {
+ loadBlock(&ret, blockpos, createSector(p2d), false);
+ }
  } else {
  // Not found in database, try the files
 

src/map.h

@@ -469,6 +469,7 @@ class ServerMap : public Map
  */
  bool m_map_metadata_changed = true;
  MapDatabase *dbase = nullptr;
+ MapDatabase *dbase_ro = nullptr;
 };