linux-kernel - RE: [Xen-devel] [PATCH 1/3] xen/mce: Add mcelog support for Xen platform (v2)

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Message-ID: <DE8DF0795D48FD4CA783C40EC82923351F0C4E@SHSMSX101.ccr.corp.intel.com>
Date:	Fri, 25 May 2012 17:56:56 +0000
From:	"Liu, Jinsong" <jinsong.liu@...el.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Borislav Petkov <bp@...64.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: RE: [Xen-devel] [PATCH 1/3] xen/mce: Add mcelog support for Xen
 platform (v2)

Konrad Rzeszutek Wilk wrote:
>>>>>> -static struct miscdevice mce_chrdev_device = {
>>>>>> +struct miscdevice mce_chrdev_device = {
>>>>>>  	MISC_MCELOG_MINOR,
>>>>>>  	"mcelog",
>>>>>>  	&mce_chrdev_ops,
>>>>> 
>>>>> You're still reusing those - pls, define your own 'struct
>>>>> miscdevice mce_chrdev_device' in drivers/xen/ or somewhere
>>>>> convenient and 
>>>>> your own mce_chrdev_ops. The only thing you should be touching in
>>>>> arch/x86/.../mcheck/ is the export of MISC_MCELOG_MINOR.
>>>>> 
>>>>> Thanks.
>>>> 
>>>> I'm *not* reuse native code.
>>>> I have defined 'struct miscdevice xen_mce_chrdev_device' in
>>>> drivers/xen, and I also implement xen_mce_chrdev_ops, they are all
>>>> xen-self-contained. 
>>>> 
>>>> The patch just redirect native mce_chrdev_device to
>>>> xen_mce_chrdev_device when running under xen environment.
>>>> It didn't change any native code (except just cancel
>>>> mce_chrdev_device 'static'), and will not break native logic.
>>> 
>>> Why are you doing that?
>>> 
>>> Why don't you do
>>> 
>>> 	misc_register(&xen_mce_chrdev_device);
>>> 
>>> in xen_early_init_mcelog() ?
>>> 
>>> This way there'll be no arch/x86/ dependencies at all.
>> 
>> The reason is, if we do so, it would be covered by native
>> misc_register(&mce_chrdev_device) later when native kernel init (xen
>> init first and then start native kernel).  
> 
> Won't the second registration (so the original one) of the major
> fail? So the mce_log would just error out since somebody already
> registered? 

No, that would be device confliction, the 2nd register return as -EBUSY and un-predicetable result.
I test it in your way, mcelog fail to fetch any error log.

Thanks,
Jinsong--
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