linux-kernel - Re: [PATCH 2/2] uio: do not expose inode to uio open/release hooks

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Date:	Wed, 12 Dec 2012 02:42:22 +0100
From:	"Hans J. Koch" <hjk@...sjkoch.de>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Benedikt Spranger <b.spranger@...utronix.de>,
	linux-kernel@...r.kernel.org, hjk@...sjkoch.de,
	Alexander.Frank@...rspaecher.com
Subject: Re: [PATCH 2/2] uio: do not expose inode to uio open/release hooks

On Tue, Dec 11, 2012 at 03:20:32PM -0800, Greg KH wrote:
> On Wed, Dec 12, 2012 at 12:12:02AM +0100, Benedikt Spranger wrote:
> > The inode parameter is unused by in kernel users of UIO.
> 
> Ok.
> 
> > Also the inode parameter makes it hard to resolve the existing open(),
> > mmap() and close() difficulty.
> 
> I don't understand, what do you mean by this?  What is this parameter
> causing problems with?

The problem is that according to POSIX, it is guaranteed that in userspace
you can do

fd = open("/dev/uio0", ...)
ptr = mmap(...fd...)
close(fd)

with ptr still being valid and useable after that.

Thanks,
Hans
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