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

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Message-ID: <fade55ad-cefd-898b-6062-6fe45f17b94a@redhat.com>
Date:   Sat, 15 Feb 2020 12:15:34 +0800
From:   lijiang <lijiang@...hat.com>
To:     John Ogness <john.ogness@...utronix.de>
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

在 2020年02月14日 21:50, John Ogness 写道:
> 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

Really agree, and I guess that there may be more structures and their offsets
to be exported, for example: struct prb_desc_ring, struct prb_data_ring, and
struct prb_desc, etc.

This makes sure that tools(such as makedumpfile and crash) can appropriately
access them. 

> 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.
> 
It makes sense and avoids exporting unnecessary symbols and offsets.

Thanks.
Lianbo


> John Ogness
>