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

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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 ?