how to add a struct in wireshark?

["??????????" <237825552 () qq com>]

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 ?

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