om the event name it's meant to handle e.g.
'sched::sched_switch()'.  The 'format' information for trace
events can be used to parse the binary data and map it into a
form usable by a given scripting language; see the Perl
implemention in subsequent patches for one possible way to
leverage the existing trace format parsing code in perf and map
that info into specific scripting language types.

generate_script() should generate a ready-to-run script for the
current set of events in the trace, preferably with bodies that
print out every field for each event.  Again, look at the Perl
implementation for clues as to how that can be done.  This is an
optional, but very useful op.

Support for a given language should also add a language-specific
setup function and call it from setup_scripting().  The
language-specific setup function associates the the scripting
ops for that language with one or more 'language specifiers'
(see below) using script_spec_register().  When a script name is
specified on the command line, the scripting ops associated with
the specified language are used to instantiate and use the
appropriate interpreter to process the trace stream.

In general, it should be relatively easy to add support for a
new language, especially if the language implementation supports
an interface allowing an interpreter to be 'embedded' inside
another program (in this case the containing program will be
'perf trace'). If so, it should be relatively straightforward to
translate trace events into invocations of user-defined script
functions where e.g. the function name corresponds to the event
type and the function parameters correspond to the event fields.
 The event and field type information exported by the event
tracing infrastructure (via the event 'format' files) should be
enough to parse and send any piece of trace data to the user
script.  The easiest way to see how this can be done would be to
look at the Perl implementation contained in
perf/util/trace-event-perl.c/.h.

There are a couple of other things that aren't covered by the
scripting_ops or setup interface and are technically optional,
but should be implemented if possible.  One of these is support
for 'flag' and 'symbolic' fields e.g. being able to use more
human-readable values such as 'GFP_KERNEL' or
HI/BLOCK_IOPOLL/TASKLET in place of raw flag values.  See the
Perl implementation to see how this can be done. The other thing
is support for 'calling back' into the perf executable to access
e.g. uncommon fields not passed by default into handler
functions, or any metadata the implementation might want to make
available to users via the language interface.  Again, see the
Perl implementation for examples.

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: fweisbec@gmail.com
Cc: rostedt@goodmis.org
Cc: anton@samba.org
Cc: hch@infradead.org
LKML-Reference: <1259133352-23685-2-git-send-email-tzanussi@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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