Add comments for touched functions

fdbbackup/backup.actor.cpp

@@ -2236,6 +2236,8 @@ Reference<IBackupContainer> openBackupContainer(const char* name, std::string de
 	return c;
 }
 
+// Submit the restore request to the database if "performRestore" is true. Otherwise,
+// check if the restore can be performed.
 ACTOR Future<Void> runRestore(Database db,
                               std::string originalClusterFile,
                               std::string tagName,

fdbclient/BackupContainerFileSystem.actor.cpp

@@ -891,6 +891,13 @@ public:
 		return Optional<RestorableFileSet>();
 	}
 
+	// Get a set of files that can restore the given "keyRangesFilter" to the "targetVersion".
+	// If "keyRangesFilter" is empty, the restore will recover the whole database. It's generally
+	// a good idea to specify "keyRangesFilter" to reduce the number of files for restore times.
+	//
+	// If "logsOnly" is true, then only log files are returned and "keyRangesFilter" is ignored,
+	// because the log can contain mutations of the whole key space, unlike range files that each
+	// is limited to a smaller key range.
 	ACTOR static Future<Optional<RestorableFileSet>> getRestoreSet(Reference<BackupContainerFileSystem> bc,
 	                                                               Version targetVersion,
 	                                                               VectorRef<KeyRangeRef> keyRangesFilter,

fdbclient/FileBackupAgent.actor.cpp

@@ -4001,6 +4001,8 @@ struct StartFullRestoreTaskFunc : RestoreTaskFuncBase {
 		static TaskParam<Version> firstVersion() { return LiteralStringRef(__FUNCTION__); }
 	} Params;
 
+	// Find all files needed for the restore and save them in the RestoreConfig for the task.
+	// Update the total number of files and blocks and change state to starting.
 	ACTOR static Future<Void> _execute(Database cx,
 	                                   Reference<TaskBucket> taskBucket,
 	                                   Reference<FutureBucket> futureBucket,
@@ -5198,6 +5200,24 @@ public:
 		return r;
 	}
 
+	// Submits the restore request to the database and throws "restore_invalid_version" error if
+	// restore is not possible. Parameters:
+	//   cx: the database to be restored to
+	//   cxOrig: if present, is used to resolve the restore timestamp into a version.
+	//   tagName: restore tag
+	//   url: the backup container's URL that contains all backup files
+	//   ranges: the restored key ranges; if empty, restore the whole database
+	//   waitForComplete: if set, wait until the restore is completed before returning; otherwise,
+	//                    return when the request is submitted to the database.
+	//   targetVersion: the version to be restored.
+	//   verbose: print verbose information.
+	//   addPrefix: each key is added this prefix during restore.
+	//   removePrefix: for each key to be restored, remove this prefix first.
+	//   lockDB: if set lock the database with randomUid before performing restore;
+	//           otherwise, check database is locked with the randomUid
+	//   incrementalBackupOnly: only perform incremental backup
+	//   beginVersion: restore's begin version
+	//   randomUid: the UID for lock the database
 	ACTOR static Future<Version> restore(FileBackupAgent* backupAgent,
 	                                     Database cx,
 	                                     Optional<Database> cxOrig,