Some of the transport types have meaningful names.
The BLE transport has a device name that was exposed during device
discovery, for example, and some back-ends (ok, right now only the
Aqualung i300C and i770R) need to know what that device name was in
order to handshake with the device properly.
Other transports, like the USBSTORAGE one, could usefully use this to
get the basename of the path to the storage, although right now that
transport makes do with simply doing a "dc_iostream_read()" on the
transport instead.
For now, this is just the infrastructure, ready to get hooked into.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
For most I/O stream implementations the serial communication specific
functions are meaningless. Implementing them as no-ops allows the dive
computer backends the call the I/O stream functions unconditionally.
However, implementing the no-op with a dummy function returning
DC_STATUS_SUCCESS, does not only add some (small) overhead at runtime,
but also requires many such functions. This is inconvenient and the same
result can easily be obtained by using a NULL pointer instead.
The consequence is that the logic is reversed now. To obtain the
previous behaviour of returning the DC_STATUS_UNSUPPORTED error code
again, you'll need to implement a dummy function. But that's fine
because it's the less common case.
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.
Wih the custom I/O implementation, an application can use its own
low-level I/O layer instead of using one of the built-in ones. The
application only needs to provide a set of callback functions, and
libdivecomputer will wrap them into a I/O stream.
