Wireshark-dev: [Wireshark-dev] how to add a struct in wireshark?

From: "??????????" <237825552@xxxxxx>
Date: Sat, 29 Mar 2014 17:54:53 +0800
I need to define a struct in wireshark,so i create a file named performance.h in wireshark main directory,

//performance.h
struct pefroamce_s{
XXXXXXXX
guint index;
}performance;

extern performance * performance_test;

then i define the  performance_test in file wiretap/libpcap.c, then i want to use the pointer in epan/dissectors/packet-ieee80211.c
//epan/dissectors/packet-ieee80211.c
performance_test->index=0;

it came up with an error:undefined reference to 'performance_test'

what should i do to create a struct and use it in different files,it looks like we can only  define an use the struct in the same file ?