linux-kernel - Re: [PATCH] tracing/ring-buffer: hide unused last_boot

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Message-ID: <20240719095608.31e4c67f@rorschach.local.home>
Date: Fri, 19 Jul 2024 09:56:08 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Zheng Yejian
 <zhengyejian1@...wei.com>, Vincent Donnefort <vdonnefort@...gle.com>, Huang
 Yiwei <quic_hyiwei@...cinc.com>, "Tzvetomir Stoyanov (VMware)"
 <tz.stoyanov@...il.com>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing/ring-buffer: hide unused last_boot_fops

On Fri, 19 Jul 2024 12:26:33 +0200
Arnd Bergmann <arnd@...nel.org> wrote:

> From: Arnd Bergmann <arnd@...db.de>
> 
> This variable is used only in an #ifdef, which causes a W=1 warning
> with some compilers:
> 
> kernel/trace/trace.c:7570:37: error: 'last_boot_fops' defined but not used [-Werror=unused-const-variable=]
>  7570 | static const struct file_operations last_boot_fops = {
> 
> Guard this one with the same #ifdef.
> 
> Fixes: 7a1d1e4b9639 ("tracing/ring-buffer: Add last_boot_info file to boot instance")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Actually "last_boot_info" and snapshot should be mutually exclusive.
That is, an instance can have a snapshot or the "last_boot_info" but not
both. The real fix is:

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5462fb10ff64..0d1841b3363e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9828,15 +9828,15 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
 	if (ftrace_create_function_files(tr, d_tracer))
 		MEM_FAIL(1, "Could not allocate function filter files");
 
-#ifdef CONFIG_TRACER_SNAPSHOT
 	if (tr->range_addr_start) {
 		trace_create_file("last_boot_info", TRACE_MODE_READ, d_tracer,
 				  tr, &last_boot_fops);
+#ifdef CONFIG_TRACER_SNAPSHOT
 	} else {
 		trace_create_file("snapshot", TRACE_MODE_WRITE, d_tracer,
 				  tr, &snapshot_fops);
-	}
 #endif
+	}
 
 	trace_create_file("error_log", TRACE_MODE_WRITE, d_tracer,
 			  tr, &tracing_err_log_fops);


I'll write up a patch and give you the "reported-by".

Thanks!

-- Steve