[PATCH] Don't trace if all tracepoints disabled

[Joel Brobecker]

> This patch simply requires that there be at least one enabled
> tracepoint before a trace run will start.  While it's not
> necessarily wrong to have a tracepoint-less trace run, this could
> save a user or two from massive puzzlement as to why there are no
> trace frames accumulating. :-)  While this seems uncontroversial,
> I'm going to hold off commit to allow comments.

It seems to me that, from a user's perspective, a trace run without
tracepoints would be pointless, right? So, if a user request a trace
run without any tracepoint, he most likely made a mistake somewhere
(wrong command or forgot to create the tracepoints). So I agree with
your suggestion (FWIW).

-- 
Joel