linux-kernel - Re: [PATCH v2 5/6] tools/virtio: use canonical ftrace path

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Date:   Fri, 17 Feb 2023 21:16:03 +0530
From:   Mukesh Ojha <quic_mojha@...cinc.com>
To:     Ross Zwisler <zwisler@...omium.org>, <linux-kernel@...r.kernel.org>
CC:     Ross Zwisler <zwisler@...gle.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        <virtualization@...ts.linux-foundation.org>,
        <linux-trace-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2 5/6] tools/virtio: use canonical ftrace path



On 2/16/2023 4:03 AM, Ross Zwisler wrote:
> The canonical location for the tracefs filesystem is at /sys/kernel/tracing.
> 
> But, from Documentation/trace/ftrace.rst:
> 
>    Before 4.1, all ftrace tracing control files were within the debugfs
>    file system, which is typically located at /sys/kernel/debug/tracing.
>    For backward compatibility, when mounting the debugfs file system,
>    the tracefs file system will be automatically mounted at:
> 
>    /sys/kernel/debug/tracing
> 
> A few spots in tools/virtio still refer to this older debugfs
> path, so let's update them to avoid confusion.
> 
> Signed-off-by: Ross Zwisler <zwisler@...gle.com>
> ---
>   tools/virtio/virtio-trace/README        |  2 +-
>   tools/virtio/virtio-trace/trace-agent.c | 12 ++++++++----
>   2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/virtio/virtio-trace/README b/tools/virtio/virtio-trace/README
> index b64845b823ab..cea29a2a4c0a 100644
> --- a/tools/virtio/virtio-trace/README
> +++ b/tools/virtio/virtio-trace/README
> @@ -95,7 +95,7 @@ Run
>   
>   1) Enable ftrace in the guest
>    <Example>
> -	# echo 1 > /sys/kernel/debug/tracing/events/sched/enable
> +	# echo 1 > /sys/kernel/tracing/events/sched/enable
>   
>   2) Run trace agent in the guest
>    This agent must be operated as root.
> diff --git a/tools/virtio/virtio-trace/trace-agent.c b/tools/virtio/virtio-trace/trace-agent.c
> index cdfe77c2b4c8..7e2d9bbf0b84 100644
> --- a/tools/virtio/virtio-trace/trace-agent.c
> +++ b/tools/virtio/virtio-trace/trace-agent.c
> @@ -18,8 +18,9 @@
>   #define PIPE_DEF_BUFS		16
>   #define PIPE_MIN_SIZE		(PAGE_SIZE*PIPE_DEF_BUFS)
>   #define PIPE_MAX_SIZE		(1024*1024)
> -#define READ_PATH_FMT	\
> -		"/sys/kernel/debug/tracing/per_cpu/cpu%d/trace_pipe_raw"
> +#define TRACEFS 		"/sys/kernel/tracing"
> +#define DEBUGFS 		"/sys/kernel/debug/tracing"
> +#define READ_PATH_FMT		"%s/per_cpu/cpu%d/trace_pipe_raw"
>   #define WRITE_PATH_FMT		"/dev/virtio-ports/trace-path-cpu%d"
>   #define CTL_PATH		"/dev/virtio-ports/agent-ctl-path"
>   
> @@ -120,9 +121,12 @@ static const char *make_path(int cpu_num, bool this_is_write_path)
>   	if (this_is_write_path)
>   		/* write(output) path */
>   		ret = snprintf(buf, PATH_MAX, WRITE_PATH_FMT, cpu_num);
> -	else
> +	else {
>   		/* read(input) path */
> -		ret = snprintf(buf, PATH_MAX, READ_PATH_FMT, cpu_num);
> +		ret = snprintf(buf, PATH_MAX, READ_PATH_FMT, TRACEFS, cpu_num);
> +		if (ret > 0 && access(buf, F_OK) != 0)
> +			ret = snprintf(buf, PATH_MAX, READ_PATH_FMT, DEBUGFS, cpu_num);
> +	}
> 


Reviewed-by: Mukesh Ojha <quic_mojha@...cinc.com>

-Mukesh


>   	if (ret <= 0) {
>   		pr_err("Failed to generate %s path(CPU#%d):%d\n",