linux-kernel - RE: [PATCH 00/14] Introduce cpu_enabled

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Date:	Tue, 15 Jul 2008 13:10:14 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Alex Chiang <achiang@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
CC:	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: RE: [PATCH 00/14] Introduce cpu_enabled_map and friends

> Patch 14 is the money patch. It demonstrates why we might
> want to go through all these gyrations. Now that ia64 presents
> *all* physically present CPUs in sysfs, even if they have been
> disabled by firmware, we give userspace a way to poke at those
> CPUs.

There's only the one bit for "disabled by firmware" ... no extra
space for any extra information.  How would userspace know that
it was safe to poke at a disabled cpu?  Perhaps firmware disabled
it for some very good reason, and poking at it could cause system
instability.

-Tony