We now have at least two dive computers that enumerate as USB storage
devices: the Uemis Zurich and the Garmin Descent Mk1.
The Uemis is handled purely inside of subsurface, with no
libdivecomputer support. That was likely a mistake, but it was not
practical to do a libdivecomputer backend for it at the time.
The Garmin Descent Mk1 support would be much nicer to have natively in
libdivecomputer, and looks much more relevant and practical than the
Uemis situation was.
So start off with defining a new transport type.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Add a function to query the underlying transport type. This allows the
dive computer backends to implement transport specific behaviour where
necessary.
For the built-in I/O implementations, the transport type is obviously
always hardcoded, but for a custom I/O implementation the application
needs to provide the correct type. Hence the transport type can't be
hardcoded in the vtable and needs to be passed as a parameter.
The purpose of the new I/O interface is to provide a common interface
for all existing I/O implementations (serial, IrDA, bluetooth and USB
HID). With a common interface the dive computer backends can more easily
use different I/O implementations at runtime, without needing
significant code changes. For example bluetooth enabled devices can
easily switch between native bluetooth communication and serial port
emulation mode.
The new interface is modelled after the existing serial communication
api. Implementations where some of those functions are meaningless (e.g.
IrDA, bluetooth and USB), can just leave those functions unimplemented
(causing the call to fail with DC_STATUS_UNSUPPORTED), or implement it
as a no-op (always return DC_STATUS_SUCCESS).
