Lots of libusb apps I write are simple test apps not intended to be real
apps. Having a function available to quickly locate my device will be
handy in such situations.
libusb_find_devices and libusb_get_devices are no more
libusb_get_device_list obtains a list of libusb_device structures for all
known devices in the system.
Each libusb_device now has a reference count, defaulting to 1 on
instantiation. The reference count of 1 refers to the fact that it is
present in the list in this scenario.
Opening a device adds a pointer to the libusb_device structure in the
handle, so that also adds a reference. Closing the device removes that
reference.
The function to free the device list can optionally unref all the devices
inside.
In future we will make the libusb_device instances all "global" so that if
the app calls get_device_list twice it actually gets the same libusb_device
structure references back. This way we can start to track disconnects, and
we can investigate adding a unique "session ID" to each libusb_device, an
identifier guaranteed to be unique to that device until reboot.
Instead of timers, add a mechanism for informing the parent app when the
next timeout is due to happen, so that it can call us at that time.
As we no longer use signals, signalfd has also been removed.
fpi changed to usbi.
We should not expose structures with prefix "usb_" in the public
namespace as it is quite likely there will be some conflict somewhere.
Instead, using "libusb_" should be safer.
These are easiest to construct on the stack, but in the async case it is
likely that the submitting function returns (hence stack is destroyed)
before URB completion.
