linux-kernel - Re: [PATCH] fs: O_* bit numbers uniqueness check

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Message-ID: <m2iqbfwq7h.fsf@whitebox.home>
Date:	Wed, 06 Jan 2010 10:13:54 +0100
From:	Andreas Schwab <schwab@...ux-m68k.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Eric Paris <eparis@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-fsdevel\@vger.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] fs: O_* bit numbers uniqueness check

Wu Fengguang <fengguang.wu@...el.com> writes:

> On Wed, Jan 06, 2010 at 03:07:01PM +0800, Eric Dumazet wrote:
>> Le 06/01/2010 07:55, Wu Fengguang a écrit :
>> > The O_* bit numbers are defined in 20+ arch/*, and hence can silently
>> > overlap. Add a boot time check to ensure the uniqueness as suggested
>> > by David Miller.
>> > 
>> > CC: David Miller <davem@...emloft.net>
>> > CC: Stephen Rothwell <sfr@...b.auug.org.au>
>> > CC: Al Viro <viro@...iv.linux.org.uk>
>> > CC: Christoph Hellwig <hch@...radead.org>
>> > CC: Eric Paris <eparis@...hat.com>
>> > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
>> > ---
>> >  {
>> > +	/* please add new bits here to ensure allocation uniqueness */
>> > +	BUG_ON(20 != hweight32(
>> > +		O_RDONLY	| O_WRONLY	| O_RDWR	|
>> > +		O_CREAT		| O_EXCL	| O_NOCTTY	|
>> > +		O_TRUNC		| O_APPEND	| O_NONBLOCK	|
>> > +		O_SYNC		| FASYNC	| O_DIRECT	|
>> > +		O_LARGEFILE	| O_DIRECTORY	| O_NOFOLLOW	|
>> > +		O_NOATIME	| O_CLOEXEC	| O_RANDOM	|
>> > +		FMODE_EXEC	| FMODE_NONOTIFY));
>> > +
>> 
>> I cannot test it, but given O_RDONLY is 0, are you sure 20 bits are actually set ?
>
> Yes, I tested it. The tricky one is O_SYNC, which actually has two bits..

What if a new architecture wants to use a single bit value (since it
does not need backwards compatibility)?

Andreas.

-- 
Andreas Schwab, schwab@...ux-m68k.org
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