Add support for opening a DC_TRANSPORT_USBSTORAGE stream

This is part of the whole "let's support the notion of dive computers
being exported as USB storage devices" push.

With an older libdivecomputer, we'll just fall back on failing the
operation, but we still want to support the generic notion of
DC_TRANSPORT_USBSTORAGE since we have our own internal Uemis downloader.
That one won't ever get to the open phase, since it's caught earlier.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

core/libdivecomputer.c

@@ -1342,6 +1342,12 @@ dc_status_t divecomputer_device_open(device_data_t *data)
 			return rc;
 	}
 
+	if (transports & DC_TRANSPORT_USBSTORAGE) {
+		rc = dc_usb_storage_open(&data->iostream, context, data->devname);
+		if (rc == DC_STATUS_SUCCESS)
+			return rc;
+	}
+
 	return DC_STATUS_UNSUPPORTED;
 }
 

core/libdivecomputer.h

@@ -15,6 +15,7 @@
 // Even if we have an old libdivecomputer, Uemis uses this
 #ifndef DC_TRANSPORT_USBSTORAGE
 #define DC_TRANSPORT_USBSTORAGE (1 << 6)
+#define dc_usb_storage_open(stream, context, devname) (DC_STATUS_UNSUPPORTED)
 #endif
 
 #include "dive.h"