linux-kernel - Re: [PATCH] FE_GET_PROPERTY should be _IOW, because the associated structure is transferred from userspace to kernelspace. Keep the old ioctl around for compatibility so that existing code is not broken.

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Message-ID: <4DE8D72E.7010300@linuxtv.org>
Date:	Fri, 03 Jun 2011 14:44:30 +0200
From:	Andreas Oberritter <obi@...uxtv.org>
To:	Mauro Carvalho Chehab <mchehab@...hat.com>
CC:	Hans Petter Selasky <hselasky@....net>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] FE_GET_PROPERTY should be _IOW, because the associated
 structure is transferred from userspace to kernelspace. Keep the old ioctl
 around for compatibility so that existing code is not broken.

On 06/01/2011 11:15 PM, Mauro Carvalho Chehab wrote:
> The dvb_usercopy will do the right thing, if we use _IOR or _IORW.

It only works, because _IOC_READ triggers a copy_from_user, as a
workaround for wrongly marked ioctls like this, according to a code
comment. It does not really do the right thing, because in this special
case the later call to copy_to_user isn't required. But it doesn't do
any real harm either.

> I prefer to not apply this patch, as it won't fix anything. Adding an _OLD means
> that we'll need later to remove it, causing a regression. Ok, we may do like we did
> with V4L _OLD ioctl's that were marked as _OLD at 2.6.5 and were removed on a late
> 2.6.3x.

Either way is fine for me.

Regards,
Andreas
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