From: Roland Dreier <rdreier@cisco.com>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       David Miller <davem@davemloft.net>,
       Stephen Rothwell <sfr@canb.auug.org.au>,
       Al Viro <viro@zeniv.linux.org.uk>,
       Christoph Hellwig <hch@infradead.org>, Eric Paris <eparis@redhat.com>,
       LKML <linux-kernel@vger.kernel.org>, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] fs: O_* bit numbers uniqueness check
References: <20100106065526.GB11368@localhost>
Date: Tue, 05 Jan 2010 23:08:08 -0800
In-Reply-To: <20100106065526.GB11368@localhost> (Wu Fengguang's message of
	"Wed, 6 Jan 2010 14:55:26 +0800")
Message-ID: <adahbqzvhgn.fsf@roland-alpha.cisco.com>
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 > +	/* please add new bits here to ensure allocation uniqueness */
 > +	BUG_ON(20 != hweight32(
 > +		O_RDONLY	| O_WRONLY	| O_RDWR	|

I wonder if there's a way to make this BUILD_BUG_ON(), so the problem is
caught at compile time (a change like adding an O_ flag is often compile
tested only for obscure archs).  One could create a compile-time
macro-ized version of hweight32() and use that, I guess, although I'm
not sure it's worth the ugliness.

Failing that maybe this should be WARN_ON()?  I'd be annoyed if my arch
wouldn't boot because some strange new O_ flag happened to collide.

 - R.
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