DFU (Device Firmware Upgrade) is the standard method to upload paparazzi code to the stm32fx MCU via usb.
The native dfu bootloader is already embedded in the ROM of the MCU. The MCU will not go automatically in dfu mode, so either Luftboot is needed or it is done on hardware side (e.g. stm32f4-discovery).
Entering dfu mode
With extra bootloader
with native dfu bootloader
This can be used on the stm32f4-discovery board e.g. Provide the board with power and connect the usb cable for dfu upload (stm32f4-discovery can bot be powred through micro usb ab port) Connect BOOT0 pin with 3V pin(BOOT1 with GND ?), press reset button , disconnect BOOT0 and 3V
this will list all devices in dfu-mode
dfu-util is needed and must be installed
sudo apt-get install dfu-util
More information about dfu-util can be found at their Homepage http://dfu-util.gnumonks.org
At least Luftboot (does dfu-util need extra udev rules?) needs acsess to the USB ports via "stm32_mem.py", just copy the paparazzi udev rules into your system.