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