StorageSettings.bundle is the preference bundle used to view storage information as of iOS 11.0. The class prefix used by StorageSettings is ST
Getting the disk usage as reported by the Settings app
To get the disk usage that is reported in the Storage settings, one can use this code snippet (note: this won't work in the sandbox):
NSBundle *storageSettingsBundle = [NSBundle bundleWithPath:@"/System/Library/PreferenceBundles/StorageSettings.bundle"];
[storageSettingsBundle load];
STStorageDiskMonitor *monitor = [objc_getClass("STStorageDiskMonitor") sharedMonitor];
[monitor updateDiskSpace];
long long totalDiskSpace = monitor.deviceSize;
long long usedDiskSpace = totalDiskSpace - monitor.lastFree;
// Do stuff with totalDiskSpace and usedDiskSpace