linux-kernel - Re: [tpmdd-devel] [PATCH] TPM: Let the tpm char device be openable multiple times

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Message-ID: <20091103224157.GA20963@obsidianresearch.com>
Date:	Tue, 3 Nov 2009 15:41:58 -0700
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Valdis.Kletnieks@...edu
Cc:	Hal Finney <hal.finney@...il.com>,
	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	srajiv@...ux.vnet.ibm.com
Subject: Re: [tpmdd-devel] [PATCH] TPM: Let the tpm char device be openable
	multiple times

On Tue, Nov 03, 2009 at 01:14:28PM -0500, Valdis.Kletnieks@...edu wrote:
> On Tue, 03 Nov 2009 09:31:55 PST, Hal Finney said:
> > What if you don't want it accessible by user mode apps, you only want
> > your middleware (ie tcs daemon, tcsd) to open it? Will this still
> > allow that to be enforced, so nobody can interfere with tcsd's
> > exclusive access to the device?
> 
> Couldn't tcsd just open the device with O_EXCL? Or am I missing something
> subtle here?

O_EXCL isn't a locking flag...

       O_EXCL Ensure  that  this  call  creates  the file: if this flag is specified in conjunction with O_CREAT, and
              pathname already exists, then open() will fail.  The behavior of O_EXCL is undefined if O_CREAT is  not
              specified.

Jason
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