Re: [PATCH v2 4/5] tracing: Unify the logic for function tracing options

[Yordan Karadzhov (VMware)]

Hi Steven,

Hi Steven,

On 6.04.21 г. 1:15, Steven Rostedt wrote:
> >   
> > @@ -235,30 +248,31 @@ static struct tracer function_trace;
> >   static int
> >   func_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
> >   {
> > -	switch (bit) {
> > -	case TRACE_FUNC_OPT_STACK:
> > -		/* do nothing if already set */
> > -		if (!!set == !!(func_flags.val & TRACE_FUNC_OPT_STACK))
> > -			break;
> > +	ftrace_func_t func;
> > +	u32 new_flags_val;
> Nit, but the variable should just be "new_flags", which is consistent with
> old_flags. In the kernel we don't need to the variable names to be so
> verbose.
>
> >   
> > -		/* We can change this flag when not running. */
> > -		if (tr->current_trace != &function_trace)
> > -			break;
> > +	/* Do nothing if already set. */
> > +	if (!!set == !!(func_flags.val & bit))
> > +		return 0;
> >   
> > -		unregister_ftrace_function(tr->ops);
> > +	/* We can change this flag only when not running. */
> > +	if (tr->current_trace != &function_trace)
> > +		return 0;
> >   
> > -		if (set) {
> > -			tr->ops->func = function_stack_trace_call;
> > -			register_ftrace_function(tr->ops);
> > -		} else {
> > -			tr->ops->func = function_trace_call;
> > -			register_ftrace_function(tr->ops);
> > -		}
> > +	new_flags_val = (func_flags.val & ~(1UL << (bit - 1)));
> > +	new_flags_val |= (set << (bit - 1));
> bit is already the mask, no need to shift it, nor there's no reason for the
> extra set of parenthesis. And the above can be done in one line.
>
> 	new_flags = (func_flags.val & ~bit) | (set ? bit : 0);

OK, I totally misinterpreted the meaning of the "bit" argument of the 
function. I did not realized it is a mask. I was thinking the argument 
gives only the number of the bit that changes (like 5 for the 5-th bit 
inside the mask).

Thanks!
Yordan