linux-kernel - Re: [PATCH v2 5/6] printk: insert newline in devkmsg

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Date:	Fri, 18 Jul 2014 13:45:06 +0200
From:	Petr Mládek <pmladek@...e.cz>
To:	Alex Elder <elder@...aro.org>
Cc:	akpm@...ux-foundation.org, bp@...e.de, john.stultz@...aro.org,
	jack@...e.cz, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/6] printk: insert newline in devkmsg_read()

On Thu 2014-07-17 09:09:10, Alex Elder wrote:
> If a log record has LOG_PREFIX set, its predecessor record should be
> terminated if it was marked LOG_CONT.  In devkmsg_read(), this
> condition was being ignored, which would lead to such records
> showing up combined when reading /dev/kmsg.  Fix this oversight.
>
> Reported-by: Petr Mládek <pmladek@...e.cz>
> Signed-off-by: Alex Elder <elder@...aro.org>
> ---
>  kernel/printk/printk.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index e5ee1cb..3174ba9 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -575,6 +575,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
>  	char cont;
>  	size_t len;
>  	ssize_t ret;
> +	bool insert_newline;
>  
>  	if (!user)
>  		return -EBADF;
> @@ -626,7 +627,10 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
>  	else
>  		cont = '-';
>  
> -	len = sprintf(user->buf, "%u,%llu,%llu,%c;",
> +	/* Insert a newline if we're terminating the previous record
> early */

More correct description would be:

	/* Insert a newline if the previous line was not terminated properly */

> +	insert_newline = (user->prev & LOG_CONT) && (msg->flags & LOG_PREFIX);
> +	len = sprintf(user->buf, "%s%u,%llu,%llu,%c;",
> +		      insert_newline ? "\n" : "",
>  		      (msg->facility << 3) | msg->level,
>  		      user->seq, ts_usec, cont);
>  	user->prev = msg->flags;

Please, do similar change also in msg_print_text() that would fix also
syslog(). Note that syslog is the place where we stopped to disable
prefix when there was continuous line before.

Best Regards.
Petr
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