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>1.2. A typical module</A
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><P
> A typical module must have a init() and destroy() function. Please refer to
lttv/modules/text/textDump.c for the detail of these functions.
</P
><P
> 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
</P
><P
> 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.
</P
><P
> 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".
</P
><P
> 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!
</P
><P
> 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.
</P
><P
> 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.
</P
><P
> 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.
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