linux-kernel - Re: [RESEND PATCH 3.18-rc3] kdb: Avoid printing KERN

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Message-ID: <545C9791.7050608@linaro.org>
Date:	Fri, 07 Nov 2014 09:57:37 +0000
From:	Daniel Thompson <daniel.thompson@...aro.org>
To:	Joe Perches <joe@...ches.com>
CC:	Jason Wessel <jason.wessel@...driver.com>,
	linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>, patches@...aro.org,
	linaro-kernel@...ts.linaro.org,
	John Stultz <john.stultz@...aro.org>,
	Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [RESEND PATCH 3.18-rc3] kdb: Avoid printing KERN_ levels to consoles

On 06/11/14 17:43, Joe Perches wrote:
> On Thu, 2014-11-06 at 17:22 +0000, Daniel Thompson wrote:
>> On 06/11/14 16:13, Joe Perches wrote:
>>> On Thu, 2014-11-06 at 15:27 +0000, Daniel Thompson wrote:
>>>> Currently when kdb traps printk messages then the raw log level prefix
>>>> (consisting of '\001' followed by a numeral) does not get stripped off
>>>> before the message is issued to the various I/O handlers supported by
>>>> kdb. This causes annoying visual noise as well as causing problems
>>>> grepping for ^. It is also a change of behaviour compared to normal usage
>>>> of printk() usage. For example <SysRq>-h ends up with different to that of
>>>> kdb's "sr h".
>>>>
>>>> This patch addresses the problem by stripping log levels from messages
>>>> before they are issued to the I/O handlers.
>>>
>>> Perhaps instead of stripping the logging level,
>>> maybe a KERN_SOH_ASCII 'char' sequence should be
>>> emitted as '<' 'char' '>' (see: printk:print_prefix)
>>>
>>> Maybe this should be added to stable from v3.6
>>> when KERN_SOH_ASCII was first added.
>>
>> You mean call the problem a regression and try to restore the original
>> 3.5 behaviour?
> 
> Yes.
> 
> I added KERN_SOH_ASCII so to me it's a regression.
> 
>> However I have to confess that I don't really like the old behaviour.
>> I'd view it as contradicting the normal behaviours of consoles
>> (including the kgdbcon console). Why should printk() inside kdb show
>> different text to printk() outside kdb? For me, having <5> and <c>
>> scribbled all over the output of an "sr" command (which I think is
>> probably the heaviest user of printk() inside kdb) never struck me as
>> adding much value.
>>
>> Is the above paragraph convincing?
> 
> I don't use it so I have a useful opinion.
> 
> I don't recall that anyone has reported it in the 
> 2+ years since so it doesn't seem widely used.

Does that arguing against Cc:ing stable@ or you think I should just put
that on anyway and leave it for the stable committee?


> But then again, this is a resend and I don't recall
> seeing it the first time either.
>
>> On the other hand if you really mean "perhaps and maybe" then I'd prefer
>> to leave it as it it.
> 
> Your choice.
> 
> btw: in the patch I suggest using printk_skip_level
> instead of the direct test here:
> 
> +       cp = kdb_buffer;
> +       if (cp[0] == KERN_SOH_ASCII && cp[1] != '\0')
> +               cp += 2;
> 
> so this could be
> 
> 	cp = printk_skip_level(kdb_buffer);

Excellent. I'll do that.

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