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In USB, the interface and endpoint descriptors, and possibly other vendor-specific descriptors, are nested inside the configuration descriptors. This makes it possible to retrieve the complete information about a configuration in one single call. Our drivers do this, and so does libusb (the Device Kit doesn't, it only cares about individual descriptors and does not provide access to the vendor-specific ones). The driver did not expose the full descriptor, only the part that belongs strictly to the configuration. libusb worked around this by getting the descriptor from the device directly, using a control transfer. This should be ok, but apparently some devices get confused when you do this too often or at unexpected times. These changes introduce a variation of the GET_CONFIGURATION_DESCRIPTOR ioctl that allows the caller to specify a size. This way, one can get the complete descriptor (after getting the configuration-only part to figure out the size needed, most likely). The data is copied from structures stored by the driver, so no further communication with the device is necessary, making this safe to the problems mentioned above, and faster. Change-Id: Id97e40ea0d45b8c051ae8548486c4751fc6aad2a Reviewed-on: https://review.haiku-os.org/453 Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>