linux-ext4 - About BUFFER_TRACE macro in include/linux/jbd2.h

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Message-Id: <20200106083020.2EF41AE064@d06av26.portsmouth.uk.ibm.com>
Date:   Mon, 6 Jan 2020 14:00:19 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     linux-ext4@...r.kernel.org
Subject: About BUFFER_TRACE macro in include/linux/jbd2.h

Hello Community,

A very happy new year to all of you!! :)

Had some query on BUFFER_TRACE macro. Here it goes:-

While debugging some issue w.r.t jbd2/bh I came across this empty macro
definition of BUFFER_TRACE in include/linux/jbd2.h.
Though this is called from multiple places, but I could not find any
definition of this as such.

I could see some patches on mailing list which are still calling this
macro. So that means I am definitely missing something here.

Could you please help me understand how can one use this "BUFFER_TRACE"
macro for debugging? I could not find any ftrace event related
to this macro.

For my debugging as of now I ended up creating a file in
include/trace/events/buffer_debug.h and added the definition
of BUFFER_TRACE macro there.

On more googling I did find some old patch which enabled 
CONFIG_BUFFER_DEBUG.
http://people.redhat.com/sct/patches/ext3-2.4/for-2.4.19/98-debug/00-ext3-debug.patch
But this seemed pretty old and I could not find anything latest on this
which is related to above patch.

Any pointers pls?

-ritesh