linux-kernel - Re: [PATCH 3/3 v12] printk: Add monotonic, boottime, and realtime timestamps

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Message-ID: <20170926114842.GB13820@pathway.suse.cz>
Date:   Tue, 26 Sep 2017 13:48:42 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Mark Salyzyn <salyzyn@...roid.com>,
        Jonathan Corbet <corbet@....net>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Christoffer Dall <cdall@...aro.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Olof Johansson <olof@...om.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH 3/3 v12] printk: Add monotonic, boottime, and realtime
 timestamps

On Mon 2017-09-18 13:51:00, Prarit Bhargava wrote:
> printk.time=1/CONFIG_PRINTK_TIME=1 adds a unmodified local hardware clock
> timestamp to printk messages.  The local hardware clock loses time each
> day making it difficult to determine exactly when an issue has occurred in
> the kernel log, and making it difficult to determine how kernel and
> hardware issues relate to each other in real time.
> 
> Make printk output different timestamps by adding options for no
> timestamp, the local hardware clock, the monotonic clock, the boottime
> clock, and the real clock.  Allow a user to pick one of the clocks by
> using the printk.time kernel parameter.  Output the type of clock in
> /sys/module/printk/parameters/time so userspace programs can interpret the
> timestamp.
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 512f7c2baedd..5e0bf2ef02f7 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1201,14 +1204,130 @@ static inline void boot_delay_msec(int level)
> +static int printk_time = CONFIG_PRINTK_TIME_TYPE;
> +
> +static int printk_set_ts_source(enum timestamp_sources ts_source)
> +{
> +	int err = 0;


> @@ -1861,6 +1980,7 @@ static size_t msg_print_text(const struct printk_log *msg,
>  			     bool syslog, char *buf, size_t size) { return 0; }
>  static bool suppress_message_printing(int level) { return false; }
>  
> +static int printk_time;

I worried if the variable should have got initialized. But it seems to
be a relic from an older version. The variable is not longer used and
needed when CONFIG_PRINTK is not defined. It is proved by gcc:

  CC      kernel/printk/printk.o
kernel/printk/printk.c:1983:12: warning: ‘printk_time’ defined but not used [-Wunused-variable]
 static int printk_time;


>  #endif /* CONFIG_PRINTK */
>  
>  #ifdef CONFIG_EARLY_PRINTK

Otherwise that patch looks fine. With the unused variable removed,
feel free to use:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr