linux-kernel - Re: [PATCH 2/2] printk: use the lockless ringbuffer

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Date:   Fri, 14 Feb 2020 14:50:02 +0100
From:   John Ogness <john.ogness@...utronix.de>
To:     lijiang <lijiang@...hat.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        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>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] printk: use the lockless ringbuffer

Hi Lianbo,

On 2020-02-14, lijiang <lijiang@...hat.com> wrote:
>> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
>> index 1ef6f75d92f1..d0d24ee1d1f4 100644
>> --- a/kernel/printk/printk.c
>> +++ b/kernel/printk/printk.c
>> @@ -1062,21 +928,16 @@ void log_buf_vmcoreinfo_setup(void)
>>  {
>>  	VMCOREINFO_SYMBOL(log_buf);
>>  	VMCOREINFO_SYMBOL(log_buf_len);
>
> I notice that the "prb"(printk tb static) symbol is not exported into
> vmcoreinfo as follows:
>
> +	VMCOREINFO_SYMBOL(prb);
>
> Should the "prb"(printk tb static) symbol be exported into vmcoreinfo?
> Otherwise, do you happen to know how to walk through the log_buf and
> get all kernel logs from vmcore?

You are correct. This will need to be exported as well so that the
descriptors can be accessed. (log_buf is only the pure human-readable
text.) I am currently hacking the crash tool to see exactly what needs
to be made available in order to access all the data of the ringbuffer.

John Ogness