Date: Thu, 26 Aug 2010 19:14:36 -0600
From: Matthew Wilcox <matthew@wil.cx>
To: Valerie Aurora <vaurora@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>, Karel Zak <kzak@redhat.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] VFS: Sanity check mount flags passed to
	change_mnt_propagation()
Message-ID: <20100827011436.GB3521@parisc-linux.org>
References: <20100826200318.GA13636@shell>
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On Thu, Aug 26, 2010 at 04:03:18PM -0400, Valerie Aurora wrote:
> +	/* Fail if any non-propagation flags are set */
> +	if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
> +		return 0;
> +	/* Only one propagation flag should be set */
> +	if (((type & (MS_SHARED)) && (type & ~MS_SHARED)) ||
> +	    ((type & (MS_PRIVATE)) && (type & ~MS_PRIVATE)) ||
> +	    ((type & (MS_SLAVE)) && (type & ~MS_SLAVE)) ||
> +	    ((type & (MS_UNBINDABLE)) && (type & ~MS_UNBINDABLE)))
> +		return 0;

Hrm.  I think we can do this a bit more pithily.

	/* Only one propagation flag should be set, and no others */
	if (hweight32(type) != 1 &&
	    (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
		return 0;

Too clever?

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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