linux-kernel - Re: [PATCH] Use userland-like functions for reading the ACPI table

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Date:	Sat, 23 Feb 2008 12:45:38 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Éric Piel <Eric.Piel@...mplin-utc.net>
cc:	len.brown@...el.com, Christoph Hellwig <hch@....de>,
	dsdt@...gusch.at,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	trenn@...e.de
Subject: Re: [PATCH] Use userland-like functions for reading the ACPI table

On Sat, 23 Feb 2008, Éric Piel wrote:
> 
> As recommended by Christoph Hellwig, even if we can't rely on the userspace
> firmware loader so early at boot, at least use normal syscall (as in
> init/do_mounts_*.c). Similarly, use kfree() instead of ACPI_FREE().

So I'm missing a lot of the background here.

I don't think "sys_open()" is in any way preferable to the alternatives, 
especially since it depends on thread-global state (the file descriptor 
table) rather than much more local state ("struct file" that you've 
opened).

I think the calls to sys_open() in init do_dounts etc are very different: 
they really are more about a real kernel-level almost-user-mode thread 
than a core driver. 

I *also* think this patch is just fundamentally broken regardless. You 
can't just cast a kernel pointer to (char __user *). The two can be in 
totally different address spaces. There's a reason why it used to do that 
whole dance with oldfs.

[ Of course, on platforms where ACPI actually runs this is not the case, 
  but that is not an excuse for doing things wrong ]

So I would NAK this patch - it looks buggy, and the reason for it is not 
sufficiently explained in the first place.

		Linus
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