linux-kernel - Re: [tpmdd-devel] [PATCH RFC v4 4/5] tpm: split out tpm-dev.c into tpm-dev.c and tpm-common-dev.c

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Date:   Mon, 23 Jan 2017 15:20:12 -0800
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     linux-security-module@...r.kernel.org,
        tpmdd-devel@...ts.sourceforge.net,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [tpmdd-devel] [PATCH RFC v4 4/5] tpm: split out tpm-dev.c into
 tpm-dev.c and tpm-common-dev.c

On Mon, 2017-01-23 at 16:04 -0700, Jason Gunthorpe wrote:
> On Mon, Jan 23, 2017 at 02:57:11PM -0800, James Bottomley wrote:
> > On Mon, 2017-01-23 at 15:49 -0700, Jason Gunthorpe wrote:
> > > On Mon, Jan 23, 2017 at 02:28:23PM -0800, James Bottomley wrote:
> > > > On Mon, 2017-01-23 at 09:47 -0700, Jason Gunthorpe wrote:
> > > > > On Mon, Jan 23, 2017 at 01:44:32AM +0200, Jarkko Sakkinen
> > > > > wrote:
> > > > > > From: James Bottomley <
> > > > > > James.Bottomley@...senPartnership.com>
> > > > > > 
> > > > > > Signed-off-by: James Bottomley
> > > > > > <James.Bottomley@...senPartnership.com>
> > > > > 
> > > > > I really think we should not use the ugly read/write 
> > > > > interface for any new things.
> > > > 
> > > > The R/W interface is needed for backward compat,
> > > 
> > > With what? This is a new cdev with different semantics.
> > 
> > If you set TPM_DEVICE=/dev/tpms0 the old software just works.  If 
> > we remove the R/W interface, nothing will work.  The point being 
> > the new cdev has the same interface semantics, it just has 
> > different global behavour.
> 
> So you are saying there is so much already deployed TPM2 software 
> that has this TPM_DEVICE env var convention that we need to support 
> it with compat?
> 
> I'm really surprised by that.. But OK.
> 
> Can you at least remove the 'user_read_timer' junk from the new cdev?

What's the problem with it?  Can we not just fix whatever the issue is?

I'd rather reuse all the R/W machinery as is.  If I start trying to
special case it so that we only use some parts on some control flows,
the chances are I'll introduce additional bugs as well.

James