[Click Modular Router] Protocol implementation tutorial - part 1 DummyProto

Adding a protocol structure to Click Modular Router is as simple as defining the structure in itself:

struct DummyProto {
#if CLICK_BYTE_ORDER == CLICK_BIG_ENDIAN
	unsigned int T : 1;
	unsigned int Len : 7;
#elif CLICK_BYTE_ORDER == CLICK_LITTLE_ENDIAN
	unsigned int Len : 7;
	unsigned int T : 1;
#endif
	char Data[DUMMYPROTO_DATA_LEN];
} CLICK_SIZE_PACKED_ATTRIBUTE;

If you are not familiar with the notation, unsigned int Len : 7; is called a bitfield and creates a int field of size 7 bits. Because of this notation, the compiler might be tempted to include padding between fields hence CLICK_SIZE_PACKED_ATTRIBUTE (defined as __attribute__((packed))). This simple line is very important because it forces the compiler to arrange the bitfields exactly as told, without padding. CLICK_BYTE_ORDER is used to adjust the fields position according to the byte order.

The above is the strict minimum to define a protocol structure but you may need some additional informations. Here is the final file with all you need: