Short version: I need to know how, from a USB device descriptor associated with a USB-serial device, I can get the USB-serial device's minor number. I'm using Ubuntu 9.10 and have libusb-1.0.0 available. I have successfully written code to walk the enumerated-devices list. Long version: I lead the GPSD project, which maintains a service daemon for managing GPS and AIS sensors. The daemon acts as a device multiplexer so multiple location-aware apps won't contend for the same serial GPS device, and also specializes in knowing about GPS reporting protocols far too various and horrible to be inflicted on application developers. Some of our supported device use USB. Most simulate a plain serial device over USB; GPSD handles those nicely, using hotplug and protocol autodetection to configure them in and out without user intervention. There is, however, one bizarre special case, which is Garmin GPSes identified as 091e:0003. This family of devices emits USB natively; packet boundaries are indicated to the software on the other end of the wire by zero-length reads. If one attempts to treat this as a normal USB-serial device, hilarity will ensue. There is a shim, a kernel module called garmin_gps, that handles the USB reading and pretends to be a plain serial device. It aggregates each packet, surrounds it with leading/trailing DLEs, DLE-stuffs the contant. This happens to match what an RS232 Garmin does. All this is relevant because, by design, gpsd has no prior knowledge about what is on the other end of a tty port when the hotplug system tells it one has gone live and might be GPS. The port could be connected to a conventional serial device, a USB-serial interface, or a Garmin GPS via the shim. These require slightly different initializations, so gpsd has to figure out what it's dealing with in order to proceed. To detect Garmin GPSes, we have a function that grovels through the deprecated /proc/bus/usb/devices interface. Today I replaced this with a simple device-list check using libusb. Both probes have the same drawback. They only can tell us if a Garmin USB GPS, 091e:0003, is connected to the host. They can't tell us if it's connected to *the /dev/tty/USB device we just opened*. So this probe will give good results only if there is exactly one USB GPS attached. So: I have the pathname of a USB-serial device, and thus its minor number. I have a list of USB device descriptors from libusb. How do I tell which device descriptor correspons to my /dev/ttyUSB*? -- <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a> The direct use of physical force is so poor a solution to the problem of limited resources that it is commonly employed only by small children and great nations. -- David Friedman -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
