linux-kernel - Re: [PATCH RFC] x86/mce: Move MCE sysfs attributes out of the per-cpu location

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Message-ID: <503F36C4.50004@linux.vnet.ibm.com>
Date:	Thu, 30 Aug 2012 15:17:48 +0530
From:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:	"Luck, Tony" <tony.luck@...el.com>, Borislav Petkov <bp@...64.org>
CC:	"andi@...stfloor.org" <andi@...stfloor.org>,
	"ananth@...ibm.com" <ananth@...ibm.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>
Subject: Re: [PATCH RFC] x86/mce: Move MCE sysfs attributes out of the per-cpu
 location

On 08/29/2012 08:13 PM, Luck, Tony wrote:
>> Note: I'm not sure if it's ok to change sysfs entries and this does break
>> userspace tools that depend on the current path for some of these attributes.
>> So, they will need to be updated to use the new path. However, if we ever get
>> to a point where cpu0 can be offlined, these tools will need to be updated
>> anyway (as they mostly hardcode machinecheck0 currently)
>
> Linus' clarified his "never break user space" edict at the kernel summit
> on Monday. Paraphrasing:
>
>    If nobody notices, or nobody complains, then we can make changes. But
>    if anyone does complain, then the patch gets reverted.
>
> So if you want to do this, the right approach would be to change the
> utilities that use this to look in the new location for these sysfs files
> first, and fall back to looking in the old per-cpu place.
>
> Next (or in parallel) have the kernel provide both interfaces.
>
> Wait a long[1] time so that most people have updated utilities.
>
> Delete the per-cpu interfaces from the kernel.
>
> Delete the per-cpu references from the utilities.
>
> -Tony
>
> [1] Long enough that there are no complaints. At least a year, probably two or more.
>

Makes sense. Thanks for the explanation. I will send a new patch for this.


Thanks,
Naveen

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