How the usb function device exist in android/LE build

Question:
How the usb function device exist in android/LE build, how can I find them?

Answer:
There are different device node exist for different usb function.

The usb function code and qualcomm controller driver is at linux kernel driver/usb/function
1. modem /dev/ttyHSUSB0
2. nmea /dev/ttyHSUSB1
3. diag usb diag does not create device node
the character device ddrivers/char/diag/ will create a diag device and sysfs entry sys/devices/virtual/diag/diag
4. adb
two MISC device will be crated
/dev/android_adb
/dev/android_adb_enable
5.mass_storage
Does not need a device node, it has a sysfs entry at /sys/devices/platform/usb_mass_storage