linux-kernel - Re: [PATCH 1/2] ftrace/selftests: Return the skip code when tracing directory not configured in kernel

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Message-Id: <20190704104017.b90d34d78e8a9ebec73185f2@kernel.org>
Date:   Thu, 4 Jul 2019 10:40:17 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        shuah <shuah@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Po-Hsu Lin <po-hsu.lin@...onical.com>
Subject: Re: [PATCH 1/2] ftrace/selftests: Return the skip code when tracing
 directory not configured in kernel

On Wed, 03 Jul 2019 15:50:00 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> If the kernel is not configured with ftrace enabled, the ftracetest
> selftests should return the error code of "4" as that is the kselftests
> "skip" code, and not "1" which means an error.
> 
> To determine if ftrace is enabled, first the newer "tracefs" is searched for
> in /proc/mounts. If it is not found, then "debugfs" is searched for (as old
> kernels do not have tracefs). If that is not found, an attempt to mount the
> tracefs or debugfs is performed. This is done by seeing first if the
> /sys/kernel/tracing directory exists. If it does than tracefs is configured
> in the kernel and an attempt to mount it is performed.
> 
> If /sys/kernel/tracing does not exist, then /sys/kernel/debug is tested to
> see if that directory exists. If it does, then an attempt to mount debugfs
> on that directory is performed. If it does not exist, then debugfs is not
> configured in the running kernel and the test exits with the skip code.
> 
> If either mount fails, then a normal error is returned as they do exist in
> the kernel but something went wrong to mount them.
> 
> This changes the test to always try the tracefs file system first as it has
> been in the kernel for some time now and it is better to test it if it is
> available instead of always testing debugfs.
> 
> Link: http://lkml.kernel.org/r/20190702062358.7330-1-po-hsu.lin@canonical.com
> 
> Reported-by: Po-Hsu Lin <po-hsu.lin@...onical.com>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
>  tools/testing/selftests/ftrace/ftracetest | 38 +++++++++++++++++++----
>  1 file changed, 32 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/testing/selftests/ftrace/ftracetest b/tools/testing/selftests/ftrace/ftracetest
> index 136387422b00..edf5ea35d2a7 100755
> --- a/tools/testing/selftests/ftrace/ftracetest
> +++ b/tools/testing/selftests/ftrace/ftracetest
> @@ -23,9 +23,15 @@ echo "		            If <dir> is -, all logs output in console only"
>  exit $1
>  }
>  
> +# default error
> +err_ret=1
> +
> +# kselftest skip code is 4
> +err_skip=4
> +
>  errexit() { # message
>    echo "Error: $1" 1>&2
> -  exit 1
> +  exit $err_ret
>  }
>  
>  # Ensuring user privilege
> @@ -116,11 +122,31 @@ parse_opts() { # opts
>  }
>  
>  # Parameters
> -DEBUGFS_DIR=`grep debugfs /proc/mounts | cut -f2 -d' ' | head -1`
> -if [ -z "$DEBUGFS_DIR" ]; then
> -    TRACING_DIR=`grep tracefs /proc/mounts | cut -f2 -d' ' | head -1`
> -else
> -    TRACING_DIR=$DEBUGFS_DIR/tracing
> +TRACING_DIR=`grep tracefs /proc/mounts | cut -f2 -d' ' | head -1`
> +if [ -z "$TRACING_DIR" ]; then
> +    DEBUGFS_DIR=`grep debugfs /proc/mounts | cut -f2 -d' ' | head -1`
> +    if [ -z "$DEBUGFS_DIR" ]; then
> +	# If tracefs exists, then so does /sys/kernel/tracing

Ah, indeed. the mount point also may not exist on older kernel.

OK, this looks good to me.

Acked-by: Masami Hiramatsu <mhiramat@...nel.org>

Thank you!

> +	if [ -d "/sys/kernel/tracing" ]; then
> +	    mount -t tracefs nodev /sys/kernel/tracing ||
> +	      errexit "Failed to mount /sys/kernel/tracing"
> +	    TRACING_DIR="/sys/kernel/tracing"
> +	# If debugfs exists, then so does /sys/kernel/debug
> +	elif [ -d "/sys/kernel/debug" ]; then
> +	    mount -t debugfs nodev /sys/kernel/debug ||
> +	      errexit "Failed to mount /sys/kernel/debug"
> +	    TRACING_DIR="/sys/kernel/debug/tracing"
> +	else
> +	    err_ret=$err_skip
> +	    errexit "debugfs and tracefs are not configured in this kernel"
> +	fi
> +    else
> +	TRACING_DIR="$DEBUGFS_DIR/tracing"
> +    fi
> +fi
> +if [ ! -d "$TRACING_DIR" ]; then
> +    err_ret=$err_skip
> +    errexit "ftrace is not configured in this kernel"
>  fi
>  
>  TOP_DIR=`absdir $0`
> -- 
> 2.20.1
> 
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>