linux-kernel - Re: [PATCH v5 3/7] printk: initialize syslog_prev and console

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Date:	Tue, 22 Jul 2014 06:48:22 -0500
From:	Alex Elder <elder@...aro.org>
To:	akpm@...ux-foundation.org
CC:	kay@...y.org, pmladek@...e.cz, bp@...e.de, john.stultz@...aro.org,
	jack@...e.cz, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/7] printk: initialize syslog_prev and console_prev

On 07/21/2014 08:02 AM, Alex Elder wrote:
> Two global variables, "syslog_prev" and "console_prev", maintain a
> copy of the flags value used in the log record most recently
> formatted for syslog or the console, respectively.
> 
> Initially there is no previous formatted log record, and these
> variables simply have an initial value 0.  And occasionally log
> records can get consumed at a rate such that syslog or the console
> can't keep up, in which case those variables (along with their
> corresponding position variables) must be reset.  Here too, they're
> reset to 0.
> 
> This patch changes it so the initial value used is LOG_NEWLINE.
> That is, if we know nothing about the prevously-formatted log
> record, we can assume it was complete, and ended with a newline.
> One exception is that occasionally we reset our syslog or console
> (etc.) position variables.  In that case the previously-formatted
> record flags value is still valid, so we preserve that information.
> 
> This is being done to support the next patch.  Initializing
> these variables this way makes LOG_NEWLINE and LOG_CONT be
> mutually exclusive, and the next patch uses that fact to simplify
> some logic.
> 
> Signed-off-by: Alex Elder <elder@...aro.org>
> Reviewed-by: Petr Mládek <pmladek@...e.cz>

I have one change I'd like to suggest on this one.

Petr, could you offer your opinion?


> ---
>  kernel/printk/printk.c | 44 ++++++++++++++++++++++++++++++--------------
>  1 file changed, 30 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 9f11eab..2f43116 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c


. . .

> @@ -2156,10 +2168,14 @@ again:
>  				      "%s** %u printk messages dropped **\n",
>  				      (console_prev & LOG_CONT) ? "\n" : "",
>  				      (unsigned)(log_first_seq - console_seq));
> -			/* messages are gone, move to first one */
> +			/*
> +			 * Messages are gone, move to first one.
> +			 * Don't discard what we know about the
> +			 * previously-formatted record.
> +			 */
>  			console_seq = log_first_seq;
>  			console_idx = log_first_idx;
> -			console_prev = 0;
> +			console_prev &= LOG_NEWLINE|LOG_CONT;

In this one spot, I think console_prev should simply be
initialized with LOG_NEWLINE.

The reason is that the "printk messages dropped" message will
be inserted into the formatted output, and is hence the last
formatted line.  And that message is (now) terminated with
a newline.

					-Alex

>  		} else {
>  			len = 0;
>  		}

. . .

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