linux-kernel - Re: [PATCH] tty add compat

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Message-ID: <463A8FF9.3080607@microgate.com>
Date:	Thu, 03 May 2007 19:44:25 -0600
From:	Paul Fulghum <paulkf@...rogate.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] tty add compat_ioctl

Arnd Bergmann wrote:
> - The return value of the new compat_ioctl methods should probably
> 'int', not 'long'. We've had the discussion before and then
> decided not to change the existing compat_ioctl and 
> unlocked_ioctl functions -- even though int is more appropriate,
> but having the same prototype has the advantage that a driver
> can use the same function for both ->ioctl and ->compat_ioctl
> if all calls are compatible.

I noticed that but thought the change in return value type
had some higher purpose I had not perceived. If it can be int
that would be the way to go.

> - In your driver you don't get the big kernel lock in the 
> compat_ioctl function. I assume that this is correct for
> the particular driver, but it may be nice if you could
> consequently also add an unlocked_ioctl function that can
> be used without the BKL for native ioctls. It would be good
> to hear an opinon on this from someone who has an insight
> in tty locking issues though, so I'm Cc:ing some people
> who have touched that recently.

I don't count on higher level locking for
synchronization issues specific to the driver.

I thought the current compat_ioctl() was already
meant to *not* have the BKL just like unlocked_ioctl.
My thought was that any driver getting a recent update
like compat_ioctl() would need to be reviewed for BKL
safety and take the lock manually if necessary.

Drivers that are falling behind wont have a compat_ioctl
defined at all.

--
Paul

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