linux-kernel - O_CAREFUL flag to disable open() side effects

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Message-ID: <44C8F8E3.1070306@zytor.com>
Date:	Thu, 27 Jul 2006 10:33:23 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Pekka J Enberg <penberg@...Helsinki.FI>,
	Ulrich Drepper <drepper@...il.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	akpm@...l.org, viro@...iv.linux.org.uk, tytso@....edu,
	tigran@...itas.com
Subject: O_CAREFUL flag to disable open() side effects

Alan Cox wrote:
> Ar Iau, 2006-07-27 am 20:05 +0300, ysgrifennodd Pekka J Enberg:
>> Sure. Though I wonder if sys_frevoke is enough for us and we can drop 
>> sys_revoke completely.
> 
> Alas not. Some Unix devices have side effects when you open() them. 
> 

Dumb thought: would it make sense to add an O_CAREFUL flag to open(), to 
disable side effects?  It seems that a number of devices have this issue 
and one have to jump through weird hoops to configure them.  Obviously, 
a file descriptor obtained with O_CAREFUL may not be fully functional, 
at the device driver's option.

For a conventional file, directory, or block device O_CAREFUL is a 
no-op.  For ttys it would typically behave similar to O_NONBLOCK 
followed immediately by a fcntl to clear the nonblock flag.

	-hpa
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