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

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Message-ID: <c384c5ea0805231702x5c37cccawcfcdb800141c2aeb@mail.gmail.com>
Date:	Sat, 24 May 2008 02:02:12 +0200
From:	"Leon Woestenberg" <leon.woestenberg@...il.com>
To:	"Hans J. Koch" <hjk@...utronix.de>
Cc:	"Uwe Kleine-König" <Uwe.Kleine-Koenig@...i.com>,
	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

Hello,

On Sat, May 24, 2008 at 12:43 AM, Hans J. Koch <hjk@...utronix.de> wrote:
> On Fri, May 23, 2008 at 10:44:42PM +0200, Leon Woestenberg wrote:
>>
>> Shouldn't this be more future-proof, what if we need to abuse write()
>> for something else in the future?
>
> We don't. I'm thinking about letting the function fail if irq_on is not
> 0 or 1, just to stop any ideas of abusing write().
>
We don't want to be future-proof?

With kernel UIO and userspace driver in seperate source repositories,
expect serious API drift in the longer term. I.e. the UIO interface
must be backwards and forwards proof IMHO.

> read() and write() only deal with irq handling, all data exchange with the
> device is done through mapped memory.
>
*Currently*, read() and write() only deal with irq handling.

In the future you might want to add a second control. I cannot think
of what that should be now, much like it was not foreseen a write()
call was needed.

>> I would suggest a check for ppos to be 0 (zero) as well, just to be
>> sure and future-proof and backwards-safe.
>
> write() is only for enabling/disabling irqs, there's only one possible
> value of count, and we don't have a seek function. So why check ppos?
>
So that *if* we have a second write()able location (again, for
something I cannot foresee now), you at least check that the userspace
proper wants to enable/disable the interrupt.

AFAIK, POSIX pwrite() does not require a seek() implementation in the
driver, but will come in with a different ppos.

Idea and patch looks fine, I just wanted to bring this up so that it
is considered.

Regards,
-- 
Leon
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