Map USB disk BSD Name to actual mounted drive(s) in OSX - usb-drive

Question

I am trying to get from the USB device BSD Name to the actual mounted volume(s) for that device e.g. device has BSD name "disk2" and mounts a single volume with BSD name "disk2s1" at "/Volumes/USBSTICK".
Here is what I have been doing so far. Using
NSNotificationCenter NSWorkspaceDidMountNotification
I detect when a drive has been added. I then scan through all the USB devices and use
IORegistryEntrySearchCFProperty kIOBSDNameKey
to get the BSD name of the device.
For my USB stick this returns "disk2". Running
system_profiler SPUSBDataTypesystem_profiler SPUSBDataType
shows
Product ID: 0x5607
Vendor ID: 0x03f0 (Hewlett Packard)
Serial Number: AA04012700008687
Speed: Up to 480 Mb/sec
Manufacturer: HP
Location ID: 0x14200000 / 25
Current Available (mA): 500
Current Required (mA): 500
Capacity: 16.04 GB (16,039,018,496 bytes)
Removable Media: Yes
Detachable Drive: Yes
BSD Name: disk2
Partition Map Type: MBR (Master Boot Record)
S.M.A.R.T. status: Not Supported
Volumes:
USBSTICK:
Capacity: 16.04 GB (16,037,879,808 bytes)
Available: 5.22 GB (5,224,095,744 bytes)
Writable: Yes
File System: MS-DOS FAT32
BSD Name: disk2s1
Mount Point: /Volumes/USBSTICK
Content: Windows_FAT_32
which makes sense since there could be multiple volumes for a single USB device.
I assumed I could use DiskArbitration to find the actual volumes, but
DASessionRef session = DASessionCreate(NULL);
if (session)
{
DADiskRef disk = DADiskCreateFromBSDName(NULL,session,"disk2");
if (disk)
{
CFDictionaryRef dict = DADiskCopyDescription(disk);
if (dict)
always returns a NULL dictionary.
So, how do I get from the BSD name for a USB device to the actual mounted volume(s) for that device? I guess it should be possible to get iterate over all the volumes, get their BSD name and check if it starts with the string e.g. /Volumes/USBSTICK above is "disk2s1", but that's hacky and what if there is a disk20 etc.

Answer 1

Found a solution using IOBSDNameMatching will create a dictionary to match the service with a given BSD name. Then the children of that service can be searched for their BSD names.
NOTE: This is my first time doing anything on OSX. Also, the 'dict' in the above code was NULL because of bug, but that dictionary is of no use for this anyway.
Here's some cut down code with no error checking etc.
CFMutableDictionaryRef matchingDict;
matchingDict = IOBSDNameMatching(kIOMasterPortDefault, 0, "disk2");
io_iterator_t itr;
// Might only ever be one service so, MatchingService could be used. No sure though
IOServiceGetMatchingServices(kIOMasterPortDefault, matchingDict, &itr);
io_object_t service;
while ((service = IOIteratorNext(itr)))
{
io_iterator_t children;
io_registry_entry_t child;
// Obtain the service's children.
IORegistryEntryGetChildIterator(service, kIOServicePlane, &children);
while ((child = IOIteratorNext(children)))
{
CFTypeRef name = IORegistryEntrySearchCFProperty(child,
kIOServicePlane,
CFSTR(kIOBSDNameKey),
kCFAllocatorDefault,
kIORegistryIterateRecursively);
if (name)
{
// Got child BSD Name e.g. "disk2s1"
}
}
}