linux-kernel - Re: [PATCH] printk: ringbuffer: fix line counting

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Message-ID: <87r1mnei5g.fsf@jogness.linutronix.de>
Date:   Thu, 14 Jan 2021 15:02:43 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] printk: ringbuffer: fix line counting

On 2021-01-14, Petr Mladek <pmladek@...e.com> wrote:
>> --- a/kernel/printk/printk_ringbuffer.c
>> +++ b/kernel/printk/printk_ringbuffer.c
>> @@ -1718,7 +1718,7 @@ static bool copy_data(struct prb_data_ring *data_ring,
>>  
>>  	/* Caller interested in the line count? */
>>  	if (line_count)
>> -		*line_count = count_lines(data, data_size);
>> +		*line_count = count_lines(data, len);
>>  
>>  	/* Caller interested in the data content? */
>>  	if (!buf || !buf_size)
>
> Another question is what line count should be returned when
> the data are copied into the buffer. In this case, the text
> might get shrunken even more.

Good point. The code could look like this:

        if (!buf || !buf_size) {
                data_size = len;
        } else {
                data_size = min_t(u16, buf_size, len);
                memcpy(&buf[0], data, data_size);
        }

        if (line_count)
                *line_count = count_lines(data, data_size);
                
        return true;

John Ogness