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Date: Thu, 9 Nov 2023 21:18:48 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>, Florent Revest
 <revest@chromium.org>, linux-trace-kernel@vger.kernel.org, LKML
 <linux-kernel@vger.kernel.org>, Martin KaFai Lau <martin.lau@linux.dev>,
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 Carvalho de Melo <acme@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>,
 Alan Maguire <alan.maguire@oracle.com>, Mark Rutland
 <mark.rutland@arm.com>, Peter Zijlstra <peterz@infradead.org>, Thomas
 Gleixner <tglx@linutronix.de>, Guo Ren <guoren@kernel.org>
Subject: Re: [RFC PATCH v2 12/31] function_graph: Have the instances use
 their own ftrace_ops for filtering
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On Fri, 10 Nov 2023 10:51:54 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> So this patch registers ftrace_ops for each fgraph_ops to ftrace.
> This means that the ftrace_graph_func() will be called twice or more
> on the same function.
> Thus should I call ftrace_startup() once when the first fgraph_ops
> is registered? 
> No, it's not enough. Actually each fgraph_ops can have different filters.
> We need to define a shared filter and combine new filters to one and
> use it. We also need to do it when a fgraph is unregistered.
> 
> Is there any function which makes a new filter from two (or more) filters?

So I'm guessing that we need to have a fgraph_set_filter*() operations?

When one gets added, it needs to update the ftrace_ops to include the added
functions. Or we need to have a way to create a new hash from all the
registered fgraph_ops, and have that for the ftrace_ops. Then when it gets
called, if it has more than one registered function, it needs to iterate
over the list?

-- Steve


> 
> Or, maybe we can make the common callback to find the previous ret entry on
> the ret_stack and reuse it. (In this case we don't need loop on each
> fgraph_array entry)