tools lib traceevent: Add direct access to dynamic arrays

Jiri Olsa was writing a plugin for the cfg80211_tx_mlme_mgmt trace
event, and was not able to get the implemented function working.
The event's print fmt looks like:

   "netdev:%s(%d), ftype:0x%.2x", REC->name, REC->ifindex,
            __le16_to_cpup((__le16 *)__get_dynamic_array(frame))

As there's no helper function for __le16_to_cpup(), Jiri was creating one
with a plugin. But unfortunately, it would not work even though he set
up the plugin correctly.

The problem is that the function parameters do not handle the helper
function "__get_dynamic_array()", and that passes in a NULL pointer.

Adding PRINT_DYNAMIC_ARRAY direct support to eval_num_arg() allows the
use of __get_dynamic_array() in function parameters.
Reported-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Jiri Olsa <jolsa@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20131111160810.0ba9df7d@gandalf.local.homeSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/traceevent/event-parse.c

@@ -3435,6 +3435,19 @@ eval_num_arg(void *data, int size, struct event_format *event, struct print_arg
 			goto out_warning_op;
 		}
 		break;
+	case PRINT_DYNAMIC_ARRAY:
+		/* Without [], we pass the address to the dynamic data */
+		offset = pevent_read_number(pevent,
+					    data + arg->dynarray.field->offset,
+					    arg->dynarray.field->size);
+		/*
+		 * The actual length of the dynamic array is stored
+		 * in the top half of the field, and the offset
+		 * is in the bottom half of the 32 bit field.
+		 */
+		offset &= 0xffff;
+		val = (unsigned long long)(data + offset);
+		break;
 	default: /* not sure what to do there */
 		return 0;
 	}