linux-kernel - Re: [PATCH 1/1] UIO: Add a write() function to enable/disable interrupts

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Date:	Fri, 23 May 2008 12:48:46 +0100
From:	"Tom Spink" <tspink@...il.com>
To:	"Uwe Kleine-König" <Uwe.Kleine-Koenig@...i.com>
Cc:	"Hans J. Koch" <hjk@...utronix.de>, linux-kernel@...r.kernel.org,
	"Greg Kroah-Hartman" <gregkh@...e.de>,
	"Jan Altenberg" <jan.altenberg@...utronix.de>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Magnus Damm" <magnus.damm@...il.com>
Subject: Re: [PATCH 1/1] UIO: Add a write() function to enable/disable interrupts

2008/5/23 Uwe Kleine-König <Uwe.Kleine-Koenig@...i.com>:
> Hello Tom,

Hi Uwe,

> Tom Spink wrote:
>> The added benefit is that the code becomes less complex, as you don't
>> have to check buffer sizes and copy the integer from userspace.
> AFAIK this is wrong.  You need to copy the integer from userspace in
> uio_ioctl.  Actually it's a value coming from user space, so you need to
> do it somewhere.

Not really in this case.  It's not a *pointer* to a value in
userspace, so you don't need to copy anything.  If it was being used
to point to a memory location holding a value, then yes, it would need
to be copied across.  But in this case, it's just being used to pass
across 1 or 0.

For example, look at the drivers/char/tty_ioctl.c file, and see how
they use arg as a simple value.  arg doesn't have to be a pointer to
userspace.

> Best regards
> Uwe

-- 
Tom Spink
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