linux-kernel - Re: truncate dict: was: Re: [PATCH v3 3/3] printk: use the lockless ringbuffer

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Date:   Fri, 26 Jun 2020 15:48:42 +0200
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul McKenney <paulmck@...nel.org>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: truncate dict: was: Re: [PATCH v3 3/3] printk: use the lockless ringbuffer

On 2020-06-25, Petr Mladek <pmladek@...e.com> wrote:
>> --- a/kernel/printk/printk.c
>> +++ b/kernel/printk/printk.c
>> @@ -594,22 +473,26 @@ static u32 msg_used_size(u16 text_len, u16 dict_len, u32 *pad_len)
>>  #define MAX_LOG_TAKE_PART 4
>>  static const char trunc_msg[] = "<truncated>";
>>  
>> -static u32 truncate_msg(u16 *text_len, u16 *trunc_msg_len,
>> -			u16 *dict_len, u32 *pad_len)
>> +static void truncate_msg(u16 *text_len, u16 *trunc_msg_len, u16 *dict_len)
>>  {
>>  	/*
>>  	 * The message should not take the whole buffer. Otherwise, it might
>>  	 * get removed too soon.
>>  	 */
>>  	u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
>> +
>>  	if (*text_len > max_text_len)
>>  		*text_len = max_text_len;
>> -	/* enable the warning message */
>> +
>> +	/* enable the warning message (if there is room) */
>>  	*trunc_msg_len = strlen(trunc_msg);
>> +	if (*text_len >= *trunc_msg_len)
>> +		*text_len -= *trunc_msg_len;
>> +	else
>> +		*trunc_msg_len = 0;
>> +
>>  	/* disable the "dict" completely */
>>  	*dict_len = 0;
>
> The dictionary does not longer need to be removed at this point.
> It is stored in a separate buffer. It is ignored by prb_reserve()
> when there is not enough space for it.

Agreed. @dict_len argument will also be dropped from the function.

John Ogness