linux-kernel - Re: [PATCH v4 2/2] rust: add tracepoint support

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Message-ID: <20240731121539.0888738b@gandalf.local.home>
Date: Wed, 31 Jul 2024 12:15:39 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Gary Guo <gary@...yguo.net>
Cc: Alice Ryhl <aliceryhl@...gle.com>, Masami Hiramatsu
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Subject: Re: [PATCH v4 2/2] rust: add tracepoint support

On Tue, 30 Jul 2024 11:35:27 +0100
Gary Guo <gary@...yguo.net> wrote:

> > +/*
> > + * Declare an exported function that Rust code can call to trigger this
> > + * tracepoint. This function does not include the static branch; that is done
> > + * in Rust to avoid a function call when the tracepoint is disabled.
> > + */
> > +#define DEFINE_RUST_DO_TRACE(name, proto, args)
> > +#define DEFINE_RUST_DO_TRACE_REAL(name, proto, args)			\
> > +	notrace void rust_do_trace_##name(proto)			\
> > +	{								\
> > +		__DO_TRACE(name,					\
> > +			TP_ARGS(args),					\
> > +			cpu_online(raw_smp_processor_id()), 0);		\  
> 
> I guess this doesn't support conditions. Currently the conditions are
> specified during declaration and not during definition.
> 
> Would it make sense to have
> 
> 	static inline void do_trace_##name(proto)
> 	{
> 		__DO_TRACE(name, TP_ARGS(args), TP_CONDITION(cond), 0);

But where is the "cond" passed in from?

I guess in the future if you want to add conditions, you would then just
add:

#define DEFINE_RUST_DO_TRACE_REAL_CONDITION(name, proto, args, cond)			\
	notrace void rust_do_trace_##name(proto)			\
	{								\
		__DO_TRACE(name,					\
			TP_ARGS(args),					\
			cpu_online(raw_smp_processor_id()) &&		\
			TP_CONDITION(cond), 0);				\  

-- Steve

> 	}
> 
> in `__DECLARE_TRACE` and then simply call it in `rust_do_trace_##name`?
> 
> > +	}
> > +
> >  /*