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+What: /sys/kernel/debug/tracing
+Date: May 2008
+KernelVersion: 2.6.27
+Contact: linux-trace-kernel@vger.kernel.org
+Description:
+
+ The ftrace was first added to the kernel, its interface was placed
+ into the debugfs file system under the "tracing" directory. Access
+ to the files were in /sys/kernel/debug/tracing. As systems wanted
+ access to the tracing interface without having to enable debugfs, a
+ new interface was created called "tracefs". This was a stand alone
+ file system and was usually mounted in /sys/kernel/tracing.
+
+ To allow older tooling to continue to operate, when mounting
+ debugfs, the tracefs file system would automatically get mounted in
+ the "tracing" directory of debugfs. The tracefs interface was added
+ in January 2015 in the v4.1 kernel.
+
+ All tooling should now be using tracefs directly and the "tracing"
+ directory in debugfs should be removed by January 2030.