linux-kernel - Re: [PATCH 1/4] tracing: Add creation of instances at boot command line

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Message-ID: <Y8CWodcFALp3MEBM@google.com>
Date:   Thu, 12 Jan 2023 16:24:17 -0700
From:   Ross Zwisler <zwisler@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/4] tracing: Add creation of instances at boot command
 line

On Wed, Jan 11, 2023 at 09:56:37AM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> Add kernel command line to add tracing instances. This only creates
> instances at boot but still does not enable any events to them. Later
> changes will extend this command line to add enabling of events, filters,
> and triggers. As well as possibly redirecting trace_printk()!
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  .../admin-guide/kernel-parameters.txt         |  6 +++
>  kernel/trace/trace.c                          | 51 +++++++++++++++++++
>  2 files changed, 57 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 6cfa6e3996cf..cec486217ccc 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -6272,6 +6272,12 @@
>  			comma-separated list of trace events to enable. See
>  			also Documentation/trace/events.rst
>  
> +	trace_instance=[instance-info]
> +			[FTRACE] Create an ring buffer instance early in boot up.
> +			This will be listed in:
> +
> +				/sys/kernel/tracing/instances

Should this be "/sys/kernel/debug/tracing/instances"?

Ditto for the text for 'ftrace_boot_snapshot':

	ftrace_boot_snapshot
			[FTRACE] On boot up, a snapshot will be taken of the
			ftrace ring buffer that can be read at:
			/sys/kernel/tracing/snapshot.

Everywhere else we use /sys/kernel/debug/tracing, though we do use
/sys/kernel/tracing in Documentation/trace/ftrace.txt ?

I guess either works, but having just 1 or the other will help us not confuse
users.

> +
>  	trace_options=[option-list]
>  			[FTRACE] Enable or disable tracer options at boot.
>  			The option-list is a comma delimited list of options
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index a555a861b978..34ed504ffca9 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -48,6 +48,9 @@
>  #include <linux/fsnotify.h>
>  #include <linux/irq_work.h>
>  #include <linux/workqueue.h>
> +#include <linux/workqueue.h>

Duplicate include 1 line above.

> +
> +#include <asm/setup.h> /* COMMAND_LINE_SIZE */
>  
>  #include "trace.h"
>  #include "trace_output.h"
> @@ -186,6 +189,9 @@ static char *default_bootup_tracer;
>  static bool allocate_snapshot;
>  static bool snapshot_at_boot;
>  
> +static char boot_instance_info[COMMAND_LINE_SIZE] __initdata;
> +static int boot_instance_index;
> +
>  static int __init set_cmdline_ftrace(char *str)
>  {
>  	strlcpy(bootup_tracer_buf, str, MAX_TRACER_SIZE);
> @@ -239,6 +245,23 @@ static int __init boot_snapshot(char *str)
>  __setup("ftrace_boot_snapshot", boot_snapshot);
>  
>  
> +static int __init boot_instance(char *str)
> +{
> +	char *slot = boot_instance_info + boot_instance_index;
> +	int left = COMMAND_LINE_SIZE - boot_instance_index;

A bit safer to use sizeof(boot_instance_info) instead of COMMAND_LINE_SIZE,
so we can change the allocation size of boot_instance_info without having to
keep them in sync.

These are mostly nits, you can add:

Reviewed-by: Ross Zwisler <zwisler@...gle.com>