perf trace/scripting: Add support for script args

One oversight of the original scripting_ops patch was a lack of
support for passing args to handler scripts.  This adds
argc/argv to the start_script() scripting_op, and changes the
rw-by-file script to take 'comm' arg rather than the 'perf'
value currently hard-coded.  It also takes the opportunity to do
some related minor cleanup.

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: fweisbec@gmail.com
Cc: rostedt@goodmis.org
LKML-Reference: <1260867220-15699-2-git-send-email-tzanussi@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/scripts/perl/rw-by-file.pl

@@ -18,8 +18,9 @@ use lib "./Perf-Trace-Util/lib";
 use Perf::Trace::Core;
 use Perf::Trace::Util;
 
-# change this to the comm of the program you're interested in
-my $for_comm = "perf";
+my $usage = "perf trace -s rw-by-file.pl <comm>\n";
+
+my $for_comm = shift or die $usage;
 
 my %reads;
 my %writes;