linux-kernel - Re: [PATCH v4] printk: Add monotonic, boottime, and realtime timestamps

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Date:   Tue, 8 Aug 2017 09:19:08 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Mark Salyzyn <salyzyn@...roid.com>,
        Jonathan Corbet <corbet@....net>,
        Petr Mladek <pmladek@...e.com>,
        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 v4] printk: Add monotonic, boottime, and realtime
 timestamps

On (08/07/17 11:52), Prarit Bhargava wrote:
[..]
> +/**
> + * enum printk_time_type - Timestamp types for printk() messages.
> + * @PRINTK_TIME_DISABLE: No time stamp.
> + * @PRINTK_TIME_LOCAL: Local hardware clock timestamp.
> + * @PRINTK_TIME_BOOT: Boottime clock timestamp.
> + * @PRINTK_TIME_MONO: Monotonic clock timestamp.
> + * @PRINTK_TIME_REAL: Realtime clock timestamp.  On 32-bit
> + * systems selecting the real clock printk timestamp may lead to unlikely
> + * situations where a timestamp is wrong because the real time offset is read
> + * without the protection of a sequence lock in the call to ktime_get_log_ts()
> + * in printk_get_ts() below.
> + */
> +enum printk_time_type {
> +	PRINTK_TIME_DISABLE = 0,
> +	PRINTK_TIME_LOCAL = 1,
> +	PRINTK_TIME_BOOT = 2,
> +	PRINTK_TIME_MONO = 3,
> +	PRINTK_TIME_REAL = 4,
> +};

may be call the entire thing 'timestamp surces' or something?

[..]
> +	if (strlen(param) == 1) {
> +		/* Preserve legacy boolean settings */
> +		if (!strcmp("0", param) || !strcmp("n", param) ||
> +		    !strcmp("N", param))
> +			_printk_time = PRINTK_TIME_DISABLE;
> +		if (!strcmp("1", param) || !strcmp("y", param) ||
> +		    !strcmp("Y", param))
> +			_printk_time = PRINTK_TIME_LOCAL;
> +	}
> +	if (_printk_time == -1) {
> +		for (stamp = 0; stamp <= 4; stamp++) {
> +			if (!strncmp(printk_time_str[stamp], param,
> +				     strlen(param))) {
> +				_printk_time = stamp;
> +				break;
> +			}
> +		}
> +	}

	you can use match_string() here.

> +	if (_printk_time == -1) {
> +		pr_warn("printk: invalid timestamp value %s\n", param);
> +		return -EINVAL;
> +	}

`invalid timestamp value' is confusing.


> +	} else if ((printk_time_setting != _printk_time) &&
> +		   (_printk_time != 0)) {
> +		pr_warn("printk: timestamp can only be set to 0(disabled) or %s\n",
> +			printk_time_str[printk_time_setting]);

ditto.


> +		return -EINVAL;
> +	}
> +
> +	printk_time = _printk_time;
> +	pr_info("printk: timestamp set to %s\n", printk_time_str[printk_time]);

ditto.


[..]

> +static u64 printk_get_ts(void)
> +{
> +	u64 mono, offset_real;
> +
> +	if (printk_time <= PRINTK_TIME_LOCAL)
> +		return local_clock();
> +
> +	if (printk_time == PRINTK_TIME_BOOT)
> +		return ktime_get_boot_log_ts();
> +
> +	mono = ktime_get_real_log_ts(&offset_real);
> +
> +	if (printk_time == PRINTK_TIME_MONO)
> +		return mono;
> +
> +	return mono + offset_real;
> +}

this looks hard...

> +static int printk_time;
> +static int printk_time_setting;

how about s/printk_time_setting/printk_time_source/? or something similar?

	-ss