| Linux Trace Toolkit Viewer Developer Guide | ||
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| Prev | Chapter 1. Linux Trace Toolkit Viewer Text Module Tutorial | Next |
A typical module must have a init() and destroy() function. Please refer to -lttv/modules/text/textDump.c for the detail of these functions. -
The init() function is called when the library is loaded and destroy() -inversely. It adds options to the command line by calling "lttv_option_add" from -option.h -
The module communicates with the main lttv program through the use of global -attributes. Use lttv/attribute.h, lttv/iattribute.h and lttv/lttv.h, and then -LTTV_IATTRIBUTE(lttv_global_attributes()) to get the pointer to these -global attributes. -
You can then add your hooks (functions that follows the prototype of a hook, as -defined in lttv/hook.h) in the different hook lists defined in lttv/lttv.h. Note -that hooks have an assigned priority. This is necessary to inform the trace -reader that a specific hook needs to be called, for example, before or after the -state update done for an event by the state module. For that specific example, a -hook could use the LTTV_PRIO_STATE-5 to get called before the state update and a -second hook could use the LTTV_PRIO_STATE+5 to get called after the state -update. This is especially important for graphical module, which is the subject -of a the chapter named "Linux Trace Toolkit Viewer Graphical Module Tutorial". -
You should also take a look at lttv/state.c, where by_id hooks are used. When -you only need some specific events, you should use this interface. It makes the -event filtering sooner in the dispatch chain : you hook doesn't have to be -called for each event, only the ones selected. That improves the performances a -lot! -
Note that you should use the lttv_trace_find_hook method from -lttv/tracecontext.h to connect the hook to the right facility/event type. See -state.c for an example. A problem that may arise is that the LttvTraceHook -structure must be passed as hook_data when registering the hook. In fact, it is -not necessary for it to be directly passed as the hook_data parameter. As long -as the hook function can access the LttvTraceHook fields necessary to parse the -LttEvent, there is no problem. In a complex viewer where you need a pointer to -your own data structure, just keep a pointer to the LttvTraceHook structure -inside your own data structure, and give to pointer to your data structure in -parameter as the hook_data. -
Then, you should use the macro LTTV_MODULE, defined in lttv/module.h. It allows -you to specify the module name, a short and a long description, the init and -destroy functions and the module dependencies. That permits to the module -backend to load the right dependencies when needed. -
A typical text module will depend on batchAnalysis for the batch computation of a -trace, and simply register before and after trace hooks, as weel as the most -important one : a event hook. -