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

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Date:	Mon, 15 Oct 2012 17:49:22 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Peter.Huewe@...ineon.com, key@...ux.vnet.ibm.com,
	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [tpmdd-devel] [PATCH] TPM: Let the tpm char device be openable
 multiple times

On Mon, 15 Oct 2012 10:39:45 -0600
Jason Gunthorpe <jgunthorpe@...idianresearch.com> wrote:

> On Mon, Oct 15, 2012 at 08:35:09AM +0000, Peter.Huewe@...ineon.com wrote:
> > > From: Jason Gunthorpe [mailto:jgunthorpe@...idianresearch.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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