The vs_alloc_slot function allocates a new slot for storing a pointer to data specific to a certain VirtualServer*. The returned slot number can be used in subsequent vs_set_data and vs_get_data calls. The returned slot number is valid for any VirtualServer*.
The value of the pointer, which may be returned by a call to vs_set_data , defaults to NULL for every VirtualServer*.
int vs_alloc_slot(void);
A slot number if the function succeeds, or -1 if fails.