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77 | >1.2. A typical module</A |
78 | ></H1 |
79 | ><P |
80 | > A typical module must have a init() and destroy() function. Please refer to |
81 | lttv/modules/text/textDump.c for the detail of these functions. |
82 | </P |
83 | ><P |
84 | > The init() function is called when the library is loaded and destroy() |
85 | inversely. It adds options to the command line by calling "lttv_option_add" from |
86 | option.h |
87 | </P |
88 | ><P |
89 | > The module communicates with the main lttv program through the use of global |
90 | attributes. Use lttv/attribute.h, lttv/iattribute.h and lttv/lttv.h, and then |
91 | LTTV_IATTRIBUTE(lttv_global_attributes()) to get the pointer to these |
92 | global attributes. |
93 | </P |
94 | ><P |
95 | > You can then add your hooks (functions that follows the prototype of a hook, as |
96 | defined in lttv/hook.h) in the different hook lists defined in lttv/lttv.h. Note |
97 | that hooks have an assigned priority. This is necessary to inform the trace |
98 | reader that a specific hook needs to be called, for example, before or after the |
99 | state update done for an event by the state module. For that specific example, a |
100 | hook could use the LTTV_PRIO_STATE-5 to get called before the state update and a |
101 | second hook could use the LTTV_PRIO_STATE+5 to get called after the state |
102 | update. This is especially important for graphical module, which is the subject |
103 | of a the chapter named "Linux Trace Toolkit Viewer Graphical Module Tutorial". |
104 | </P |
105 | ><P |
106 | > You should also take a look at lttv/state.c, where by_id hooks are used. When |
107 | you only need some specific events, you should use this interface. It makes the |
108 | event filtering sooner in the dispatch chain : you hook doesn't have to be |
109 | called for each event, only the ones selected. That improves the performances a |
110 | lot! |
111 | </P |
112 | ><P |
113 | > Note that you should use the lttv_trace_find_hook method from |
114 | lttv/tracecontext.h to connect the hook to the right facility/event type. See |
115 | state.c for an example. A problem that may arise is that the LttvTraceHook |
116 | structure must be passed as hook_data when registering the hook. In fact, it is |
117 | not necessary for it to be directly passed as the hook_data parameter. As long |
118 | as the hook function can access the LttvTraceHook fields necessary to parse the |
119 | LttEvent, there is no problem. In a complex viewer where you need a pointer to |
120 | your own data structure, just keep a pointer to the LttvTraceHook structure |
121 | inside your own data structure, and give to pointer to your data structure in |
122 | parameter as the hook_data. |
123 | </P |
124 | ><P |
125 | > Then, you should use the macro LTTV_MODULE, defined in lttv/module.h. It allows |
126 | you to specify the module name, a short and a long description, the init and |
127 | destroy functions and the module dependencies. That permits to the module |
128 | backend to load the right dependencies when needed. |
129 | </P |
130 | ><P |
131 | > A typical text module will depend on batchAnalysis for the batch computation of a |
132 | trace, and simply register before and after trace hooks, as weel as the most |
133 | important one : a event hook. |
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