linux-kernel - Re: [PATCH] VFS: Sanity check mount flags passed to change_mnt

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Message-ID: <20100828105707.GD3521@parisc-linux.org>
Date:	Sat, 28 Aug 2010 04:57:07 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Bob Copeland <me@...copeland.com>
Cc:	Valerie Aurora <vaurora@...hat.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Karel Zak <kzak@...hat.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] VFS: Sanity check mount flags passed to
	change_mnt_propagation()

On Fri, Aug 27, 2010 at 01:51:06PM -0400, Bob Copeland wrote:
> On Fri, Aug 27, 2010 at 1:43 PM, Valerie Aurora <vaurora@...hat.com> wrote:
> > On Thu, Aug 26, 2010 at 07:14:36PM -0600, Matthew Wilcox wrote:
> >> 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?
> >
> > I was hoping someone would go find the best bitop for me, thanks. :)
> > hweight32() is an awkward name but the comment makes it clear. ?I'm
> > happy with either.
> >
> > Thanks for the help,
> 
> Didn't read surrounding code, but is that supposed to be '||'?
> 
> Otherwise the case where only a single non-propagation flag is
> set no longer returns 0...

Val's original code returned 0 as failure.  So a single non-propagation
flag set shouldn't return 0.

-- 
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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