Issue retrieving serial number of USB devices on Mac OS X - macos

Question

I'm working with libusb 0.1 and Qt in a Mac OS X v10.10 (Yosemite) environment. My goal is to get the serial numbers of all connected USB keys (usbclass = 8).
Usually the first reading occur properly, and I cannot understand why, but sometimes from subsequent readings, the device is no longer detected. Sometimes I get -60 error code on the usb_get_string_simple(handle, device->descriptor.iSerialNumber) function. How can I fix this problem?
I've tried USB keys with FAT, FAT32 and NTFS file systems, but they all had the same issue.
In the same project, I use libusb to read/write with printer devices connected to the Mac, and read serialnumbers too. No issue with this type of devices. So strange.
In the .pro file:
INCLUDEPATH += /Users/sborfedor/Desktop/root/current/includes
DEPENDPATH += /Users/sborfedor/Desktop/root/current/includes
LIBS += -L/Users/sborfedor/Desktop/root/current/bin_osx/libs/ -lusb-legacy
DESTDIR = /Users/sborfedor/Desktop/root/current/bin_osx
This is my code:
void MainWindow::run() {
struct usb_bus* bus = NULL;
struct usb_device* device = NULL;
const int MASSSTORAGE_CLASS = 8;
usb_init();
usb_set_debug(3);
usb_find_busses();
usb_find_devices();
int ret;
for ( bus = usb_get_busses(); bus; bus = bus->next ) {
for ( device = bus->devices; device; device = device->next ) {
if (device->descriptor.bDeviceClass != MASSSTORAGE_CLASS && device->descriptor.bDeviceClass != 0) {
continue;
}
for ( int cid = 0; cid < device->descriptor.bNumConfigurations; ++cid ) {
struct usb_config_descriptor* config = &( device->config[cid] );
if (config == NULL)
continue;
for ( int iid = 0; iid < config->bNumInterfaces; ++iid ) {
struct usb_interface* interface = &( config->interface[iid] );
if (interface == NULL)
continue;
usb_dev_handle* handle = usb_open( device );
if (handle == NULL)
continue;
for ( int sid = 0; sid < interface->num_altsetting; sid++ ) {
struct usb_interface_descriptor* settings = &( interface->altsetting[sid] );
if (settings == NULL)
continue;
int usbClass = device->descriptor.bDeviceClass;
if (usbClass == 0) {
usbClass = settings->bInterfaceClass;
}
if (usbClass != MASSSTORAGE_CLASS)
continue;
char device_serial_number[255];
ret = usb_get_string_simple( handle, device->descriptor.iSerialNumber, device_serial_number, sizeof(device_serial_number) );
if (ret > 0 ) {
qDebug() << "SERIAL_NUMBER="<<QString(device_serial_number);
} else {
qDebug() << "*** usb_get_string_simple( handle, device->descriptor.iSerialNumber, device_serial_number, USBX_DEVICE_SERIAL_NUMBER_MAX_SIZE ) RET="<<ret;
}
}
usb_close( handle );
}
}
}
}
}

Answer 1

I'm not especially familiar with libusb, but OSX already reads out serial numbers and stores them in the relevant property on IOKit device nubs. So there is no need to send requests to hardware, which might be confusing the active driver? (Libusb presumably creates a user client driver instance on the device)
The Disk Arbitration Framework is a good way of enumerating disks in the system and querying their properties - this is a bit easier than using IOKit directly.