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Subject: Re: [PATCH v3 07/18] nitro_enclaves: Init misc device providing the
 ioctl interface
From:   Benjamin Herrenschmidt <benh@kernel.crashing.org>
To:     Greg KH <gregkh@linuxfoundation.org>,
        Alexander Graf <graf@amazon.de>
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Date:   Mon, 01 Jun 2020 13:01:52 +1000
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On Wed, 2020-05-27 at 00:24 +0200, Greg KH wrote:
> > Would you want random users to get the ability to hot unplug CPUs from your
> > system? At unlimited quantity? I don't :).
> 
> A random user, no, but one with admin rights, why not?  They can do that
> already today on your system, this isn't new.

So I agree with you that a module parameter sucks. I disagree on the
ioctl :)

This is the kind of setup task that will probably end up being done by
some shell script at boot time based on some config file. Being able to
echo something in a sysfs file which will parse the standard-format CPU
list using the existing kernel functions to turn that into a cpu_mask
makes a lot more sense than having a binary interface via an ioctl
which will require an extra userspace program for use by the admin for
that one single task.

So sysfs is my preference here.

Another approach would be configfs, which would provide a more flexible
interface to potentially create multiple "CPU sets" that could be given
to different users or classes of users etc... but that might be pushing
it, I don't know.

Cheers,
Ben.