Date: Mon, 15 Oct 2012 17:49:22 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Cc: Peter.Huewe@infineon.com, key@linux.vnet.ibm.com,
        tpmdd-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
Subject: Re: [tpmdd-devel] [PATCH] TPM: Let the tpm char device be openable
 multiple times
Message-ID: <20121015174922.31fbadd9@pyramind.ukuu.org.uk>
In-Reply-To: <20121015163945.GA32563@obsidianresearch.com>
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	<20121012205658.GM4124@obsidianresearch.com>
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	<20121015163945.GA32563@obsidianresearch.com>
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On Mon, 15 Oct 2012 10:39:45 -0600
Jason Gunthorpe <jgunthorpe@obsidianresearch.com> wrote:

> On Mon, Oct 15, 2012 at 08:35:09AM +0000, Peter.Huewe@infineon.com wrote:
> > > From: Jason Gunthorpe [mailto:jgunthorpe@obsidianresearch.com] 
> > 
> > > Using open/close is an interesting idea, but it wouldn't work. open()
> > > is coded to return EBUSY if another process has it open, rather than
> > > block, and spinning on open would be unacceptable.
> > 
> > Hmm, maybe write a small pass through program which opens /dev/tpm
> > once and accepts its data via a socket or pipe?
> 
> I believe the kernel should not be enforcing this kind of policy into
> userspace. Plus, some of our embedded system are memory constrained
> so an unnecessary process is not welcome..

Sane device drivers for devices where contention is meaningful block on
an open that is busy, or return an error if the O_NONBLOCK option is
specified. That's the normal case.

Alan
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