From: John Ogness <john.ogness@linutronix.de>
To: Dave Young <dyoung@redhat.com>
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>,
Petr Mladek <pmladek@suse.com>,
Kazuhito Hagio <k-hagio@ab.jp.nec.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Brendan Higgins <brendanhiggins@google.com>,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Simon Horman <horms@verge.net.au>,
Thomas Gleixner <tglx@linutronix.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
kexec@lists.infradead.org
Subject: Re: [RFC PATCH v4 9/9] printk: use a new ringbuffer implementation
Date: Fri, 16 Aug 2019 11:40:54 +0200 [thread overview]
Message-ID: <87y2ztwiqh.fsf@linutronix.de> (raw)
In-Reply-To: <20190816054651.GA4403@dhcp-128-65.nay.redhat.com> (Dave Young's message of "Fri, 16 Aug 2019 13:46:51 +0800")
On 2019-08-16, Dave Young <dyoung@redhat.com> wrote:
> John, can you cc kexec list for your later series?
Sure.
> On 08/08/19 at 12:32am, John Ogness wrote:
>> This is a major change because the API (and underlying workings) of
>> the new ringbuffer are completely different than the previous
>> ringbuffer. Since there are several components of the printk
>> infrastructure that use the ringbuffer API (console, /dev/kmsg,
>> syslog, kmsg_dump), there are quite a few changes throughout the
>> printk implementation.
>>
>> This is also a conservative change because it continues to use the
>> logbuf_lock raw spinlock even though the new ringbuffer is lockless.
>>
>> The externally visible changes are:
>>
>> 1. The exported vmcore info has changed:
>>
>> - VMCOREINFO_SYMBOL(log_buf);
>> - VMCOREINFO_SYMBOL(log_buf_len);
>> - VMCOREINFO_SYMBOL(log_first_idx);
>> - VMCOREINFO_SYMBOL(clear_idx);
>> - VMCOREINFO_SYMBOL(log_next_idx);
>> + VMCOREINFO_SYMBOL(printk_rb_static);
>> + VMCOREINFO_SYMBOL(printk_rb_dynamic);
>
> I assumed this needs some userspace work in kexec, how did you test
> them?
I did not test any direct userspace access to the ringbuffer structures.
> makedumpfile should need changes to dump the kernel log.
>
> Also kexec-tools includes a vmcore-dmesg.c to extrace dmesg from
> /proc/vmcore.
Thanks for the heads up. I'll take a look at it. The code changes should
be straight forward. I expect there will need to be backwards
compatibility. Perhaps it would check first for "printk_rb_*" then
fallback to "log_*"?
John Ogness
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prev parent reply other threads:[~2019-08-16 9:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190807222634.1723-1-john.ogness@linutronix.de>
[not found] ` <20190807222634.1723-10-john.ogness@linutronix.de>
2019-08-16 5:46 ` [RFC PATCH v4 9/9] printk: use a new ringbuffer implementation Dave Young
2019-08-16 5:54 ` Dave Young
2019-08-16 9:40 ` John Ogness [this message]
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