Subject: Re: Right location in sysfs for dlpar file

From: Nathan Fontenot <[email-masked]>
Date: Wed, 03 Dec 2014 21:07:27 -0600

On 12/01/2014 10:26 PM, Greg KH wrote:
> On Mon, Dec 01, 2014 at 09:41:03AM -0600, Nathan Fontenot wrote:
>> On 11/26/2014 09:12 PM, Benjamin Herrenschmidt wrote:
>>> Hi Greg,
>>>
>>> So Nathan is working on a patch series to cleanup and improve our
>>> "DLPAR" infrastructure which is basically our hotplug mechanism when
>>> running under the PowerVM (aka pHyp) and KVM hypervisors.
>>
>> The cleanup to the dlpar infrastructure will move the entire operation
>> of hotplugging a device to the kernel instead of doing it partially in
>> userspace and partially in the kernel as is currently done.
>>
>>>
>>> I'll let Nathan give you a bit more details/background and answer
>>> subsequent question you might have as this is really his area of
>>> expertise.
>>>
>>> To cut a long story short, we need a sysfs file that allows our
>>> userspace tools to notify the kernel of hotplug events coming from
>>> the management console (which talks to userspace daemons using a
>>> proprietary protocol) to "initiate" the hotplug operations, which in
>>> turn get dispatched internally in the kernel to the right subsystem
>>> (memory, cpu, pci, ...) based on the resource type.
>>>
>>> On IRC, Greg suggested /sys/firmware and /sys/hypervisor which both
>>> look like a reasonable option to me, probably better than dlpar...
>>
>> For PowerVM systems we need this sysfs file to deliver what is
>> essentially a binary blob (specifically a rtas error log) to the
>> kernel. The current patch set is creating /sys/kernel/dlpar. As Ben
>> mentioned we would like your input on what would be the proper place
>> to create this file.
> 
> And what is the kernel supposed to do with such a binary blob?  Parse
> it?  Or pass it to something else?

The kernel will parse it and perform the requested hotplug operation.

> 
> Anyway, let's see the patches before I guess anything else, that will
> determine how things work out best.

I'll cc you on the next version of the patch set.

-Nathan