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From:   John Ogness <john.ogness@linutronix.de>
To:     lijiang <lijiang@redhat.com>
Cc:     Petr Mladek <pmladek@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrea Parri <parri.andrea@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        kexec@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] printk: use the lockless ringbuffer
References: <20200128161948.8524-1-john.ogness@linutronix.de>
        <20200128161948.8524-3-john.ogness@linutronix.de>
        <ccbe1383-a4a4-41f8-3330-972f03c97429@redhat.com>
Date:   Fri, 14 Feb 2020 14:50:02 +0100
In-Reply-To: <ccbe1383-a4a4-41f8-3330-972f03c97429@redhat.com>
        (lijiang@redhat.com's message of "Fri, 14 Feb 2020 21:29:23 +0800")
Message-ID: <87zhdle0s5.fsf@linutronix.de>
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Hi Lianbo,

On 2020-02-14, lijiang <lijiang@redhat.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