linux-kernel - Re: [PATCH v5 2/4] tracing: Make the backup instance non-reusable

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Message-ID: <20260130102133.2ab84911@gandalf.local.home>
Date: Fri, 30 Jan 2026 10:21:33 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/4] tracing: Make the backup instance non-reusable

On Fri, 30 Jan 2026 18:20:58 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> > > -	trace_create_file("free_buffer", 0200, d_tracer,
> > > -			  tr, &tracing_free_buffer_fops);
> > > +	if (!readonly) {
> > > +		trace_create_file("free_buffer", 0200, d_tracer,
> > > +				tr, &tracing_free_buffer_fops);  
> > 
> > Hmm, why remove the free_buffer. It just shrinks the buffer down to a
> > minimum. Perhaps its useless, but I it doesn't write to the buffer. Sure it
> > removes data but so does trace_pipe.  
> 
> I can keep it but free_buffer and free instance is a bit different on
> the persistent ring buffer and its backup. For both cases, since the
> scratch area needs to be kept, it does not free the reserved memory.
> (but the minimum ring buffer is dynamically allocated.)
> IMHO, the buffer resize interfaces are not useful for persistent ring
> buffer.

Ah yeah. OK, lets not add free_buffer to read only instances.

-- Steve