get disk number(s) before getting bsdName - usb-flash-drive

Question

I have just encountered one problem, I can get the bsdName with below code lines but if there are two partitions in a USB flash disk, then I can only get the last bsdName, can someone tell me how do I get all the bsdName from the USB drive? actually I would like to get the volume name of each partition... thanks in advance
CFStringRef bsdName = ( CFStringRef ) IORegistryEntrySearchCFProperty ( usbDevice,
kIOServicePlane,
CFSTR ( kIOBSDNameKey ),
kCFAllocatorDefault,
kIORegistryIterateRecursively );
NSLog(#"bsdName=%#",bsdName);
volumeName = deviceNameWithMountPath((NSString*)bsdName);
//find_hid_device(usbDevice);
NSLog(#"volume Name=%#",volumeName);
NSString *mediaType = FindWholeMedia(usbDevice);
NSLog(#"media type = %#",mediaType);
//CFRelease(bsdName);
// Done with this USB device; release the reference added by IOIteratorNext
kr = IOObjectRelease(usbDevice);
}
}
NSString *deviceNameWithMountPath(NSString *mountPath)
{
DASessionRef session = NULL;
DADiskRef disk = NULL;
CFDictionaryRef dd = NULL;
CFTypeRef val = nil;
session = DASessionCreate(kCFAllocatorDefault);
if (!session) {
NSLog(#"Can't create DiskArb session");
return nil;
}
// DASessionScheduleWithRunLoop(session,
// CFRunLoopGetCurrent(),
// kCFRunLoopDefaultMode);
//
// DARegisterDiskAppearedCallback(session, NULL, DiskAppeared, NULL);
disk = DADiskCreateFromBSDName(kCFAllocatorDefault, session, [mountPath UTF8String]);
if (!disk) {
NSLog(#"DADiskCreateFromBSDName(%s) failed", [mountPath UTF8String]);
return nil;
}
dd = DADiskCopyDescription(disk);
if (!dd) {
NSLog(#"DADiskCopyDescription(%s) failed", [mountPath UTF8String]);
return nil;
}
CFDictionaryGetValueIfPresent(dd, (kDADiskDescriptionVolumeNameKey), &val);
DiskAppeared(disk, NULL);
CFRelease(disk);
CFRelease(session);
return (NSString *)val;
}