linux-kernel - Re: [PATCH 01/22] tools lib traceevent: Add plugin support

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Date:	Mon, 25 Nov 2013 16:33:39 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 01/22] tools lib traceevent: Add plugin support

On Sat, 23 Nov 2013 03:12:19 -0500, Steven Rostedt wrote:
> On Fri, 22 Nov 2013 23:17:06 +0900
> Namhyung Kim <namhyung@...nel.org> wrote:
>
>> > 
>> [SNIP[
>> > +static void
>> > +load_plugin(struct pevent *pevent, const char *path,
>> > +	    const char *file, void *data)
>> > +{
>> > +	struct plugin_list **plugin_list = data;
>> > +	pevent_plugin_load_func func;
>> > +	struct plugin_list *list;
>> > +	const char *alias;
>> > +	char *plugin;
>> > +	void *handle;
>> > +
>> > +	plugin = malloc_or_die(strlen(path) + strlen(file) + 2);
>> 
>> I'd like not to see this malloc_or_die() anymore in a new code.  Just
>> returning after showing a warning looks enough here.
>
> Yeah I agree. This is a relic from my code. I think it's OK to add
> here, as it is pretty much direct port of my code, and then we can just
> add a patch against it to remove it.

Okay.  I agree that it'd be better to make them separate patches.

>
>> 
>> > +
>> > +	strcpy(plugin, path);
>> > +	strcat(plugin, "/");
>> > +	strcat(plugin, file);
>> > +
>> > +	handle = dlopen(plugin, RTLD_NOW | RTLD_GLOBAL);
>> 
>> Why RTLD_NOW and RTLD_GLOBAL?  Hmm.. maybe using _NOW is needed to
>> prevent a runtime error, but not sure why _GLOBAL is needed.
>
> Yes, we want to make sure all symbols defined are available at time of
> load, otherwise bail out.
>
>> 
>> IIUC _GLOBAL is for exporting symbols to *other libraries*.  Is it
>> intended for this plugin support?
>
> That was the plan. To have one plugin supply a set of functions that
> other plugins may use. That is what GLOBAL is for, right?  I don't
> recall if I every did this, but it was something I wanted for future
> work.
>
> Now if we don't need it, we could remove it, but is it bad to have?

I might be slow down symbol resolution of new plugins tiny bit.  But I
don't think it's a real problem as its effect will be negligible.

I don't object the code but just want to know your intention. :)

Thanks,
Namhyung
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