Date: Thu, 10 Nov 2005 11:59:41 -0800
From: Andrew Morton <akpm@osdl.org>
To: Arun Sharma <arun.sharma@google.com>
Cc: rohit.seth@intel.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Expose SHM_HUGETLB in shmctl(id, IPC_STAT, ...)
Message-Id: <20051110115941.1cbe1ae7.akpm@osdl.org>
In-Reply-To: <43739302.1080404@google.com>
References: <20051109184623.GA21636@sharma-home.net>
	<20051109222223.538309e4.akpm@osdl.org>
	<43739302.1080404@google.com>
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Arun Sharma <arun.sharma@google.com> wrote:
>
> Andrew Morton wrote:
> 
> >> +	shp->shm_flags = (shmflg & (S_IRWXUGO | SHM_HUGETLB));
> > [...]
> > I dunno.  The manpage says:
> > 
> >        The highlighted fields in the member shm_perm can be set:
> > 
> >            struct ipc_perm {
> >        ...
> >                ushort mode;  /* lower 9 bits of access modes */
> >        ...
> >            };
> > 
> > So if an application used to do:
> > 
> > 	if (perm.mode == 0666)
> > 
> > it will now break, because we've gone and set bit 9 on hugetlb segments.
> 
> The man page on my system says:
> 
>                unsigned short mode;  /* Permissions + SHM_DEST and
>                                          SHM_LOCKED flags */
> 
> I looked for a precendent before sending the patch and thought that 
> SHM_LOCKED was a good one.
> 

hm, OK.   But an app could still do

	if (mode == 0666|SHM_LOCKED)


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