Re: [PATCH v2 2/2] tracing: Allow execnames to be passed as args for synthetic events

[Masami Hiramatsu]

On Sun, 25 Jul 2021 11:18:30 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:

> Hi,
> 
> On Sat, 24 Jul 2021 19:31:45 +0900
> Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> 
> > Hi Steve,
> > 
> > On Thu, 22 Jul 2021 21:24:38 -0400
> > Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> > 
> > > On Fri, 23 Jul 2021 10:11:33 +0900
> > > Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> > > 
> > > > I understand. As far as I can see the code, it looks a bit complicated.
> > > > To simplify it, I need to understand the spec for "hist_field"
> > > > for keys and for vars. And maybe need to split both case.
> > > 
> > > I'll give you a hint that took me a bit to figure out.
> > > 
> > > 1) The execname is saved at the start of the histogram and not by one
> > > of the ->fn() functions.
> > > 
> > > It's saved by hist_trigger_elt_data_init() if the elt_data->comm is
> > > allocated. That function is part of the "tracing_map_ops" which gets
> > > assigned by tracing_map_create() (in tracing_map.c) as the "elt_init"
> > > function, which is called when getting a new elt element by
> > > get_free_elt().
> > > 
> > > 2) That elt_data->comm is only allocated if it finds a "hist_field"
> > > that has HIST_FIELD_FL_EXECNAME flag set. It currently only looks for
> > > that flag in the "keys" fields, which means that .execname is useless
> > > for everything else. This patch changed it to search all hist_fields so
> > > that it can find that flag if a variable has it set (which I added).
> > 
> > Thanks for the hints, but actually, that part looks good to me.
> > 
> > So, what I pointed was the part of update_var_execname(). Below diff
> > is what I intended.
> > This moves HIST_FIELD_FL_EXECNAME setup in the create_hist_field()
> > as same as other flags, and removed the add-hoc update_var_execname()
> > fixup function.
> > 
> > I confirmed it passed the ftracetest trigger testcases and your
> > example code.
> > 
> > Thank you,
> > 
> 
> I found a bug in this change.
> 
> [..]
> > @@ -1682,6 +1703,16 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
> >  		goto out;
> >  	}
> >  
> > +	if ((flags & HIST_FIELD_FL_EXECNAME) && var_name) {
> > +		flags |= HIST_FIELD_FL_STRING | HIST_FIELD_FL_VAR;
> 
> Here, we don't need to check 'var_name' and remove HIST_FIELD_FL_VAR, since it must be set in the flag.
> 
> 	if (flags & HIST_FIELD_FL_EXECNAME) {
> 		flags |= HIST_FIELD_FL_STRING;

And with this change, hist trigger can correctly detect a string type in
the operand in the expression and rejects it.

Thank you,