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From:   Tiezhu Yang <yangtiezhu@loongson.cn>
To:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>
Cc:     linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Xuefeng Li <lixuefeng@loongson.cn>
Subject: [RFC PATCH 1/2] ftrace: Introduce cmdline argument ftrace_disabled
Date:   Sat, 19 Jun 2021 14:29:19 +0800
Message-Id: <1624084160-3342-2-git-send-email-yangtiezhu@loongson.cn>
In-Reply-To: <1624084160-3342-1-git-send-email-yangtiezhu@loongson.cn>
References: <1624084160-3342-1-git-send-email-yangtiezhu@loongson.cn>
Precedence: bulk

If set CONFIG_FUNCTION_TRACER=y, we can use the following command to
disable ftrace after boot up:
echo 0 > /proc/sys/kernel/ftrace_enabled

ftrace_disabled is much stronger than ftrace_enabled, introduce a new
cmdline argument ftrace_disabled for user to control whether to disable
ftrace when boot up.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 kernel/trace/ftrace.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 72ef4dc..a015699 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5517,6 +5517,14 @@ static char ftrace_filter_buf[FTRACE_FILTER_SIZE] __initdata;
 /* Used by function selftest to not test if filter is set */
 bool ftrace_filter_param __initdata;
 
+static int __init set_ftrace_disabled(char *str)
+{
+	pr_info("Set ftrace_disabled to disable ftrace\n");
+	ftrace_disabled = 1;
+	return 1;
+}
+__setup("ftrace_disabled", set_ftrace_disabled);
+
 static int __init set_ftrace_notrace(char *str)
 {
 	ftrace_filter_param = true;
-- 
2.1.0