Re: [PATCH v2 6/7] tpm: expose spaces via a device link /dev/tpms<n>

[Jarkko Sakkinen]

On Fri, Feb 24, 2017 at 08:02:08AM -0500, James Bottomley wrote:
> On Thu, 2017-02-23 at 11:09 +0200, Jarkko Sakkinen wrote:
> > On Thu, Feb 16, 2017 at 09:25:19PM +0200, Jarkko Sakkinen wrote:
> > > From: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
> > > 
> > > Currently the tpm spaces are not exposed to userspace.  Make this
> > > exposure via a separate device, which can now be opened multiple 
> > > times because each read/write transaction goes separately via the
> > > space.
> > > 
> > > Concurrency is protected by the chip->tpm_mutex for each read/write
> > > transaction separately.  The TPM is cleared of all transient 
> > > objects by the time the mutex is dropped, so there should be no
> > > interference between the kernel and userspace.
> > > Signed-off-by: James Bottomley <
> > > 
> > > James.Bottomley@xxxxxxxxxxxxxxxxxxxx>
> 
> > Reviewed-by: Jarkko Sakkinen <jarkko.sakkine@xxxxxxxxxxxxxxx>
> > Tested-by: Jarkko Sakkinen <jarkko.sakkine@xxxxxxxxxxxxxxx>
> 
> Thanks!
> 
> > Nitpicking but I've been thinking about naming. What about calling 
> > the device as tpmrc0 as in resource context. I think that would be a
> > better name than TPM space.
> 
> Well the original name was tpmrm<n> for TPM with Resource Manager.  You
> wanted it to be tpms<n> for TPM with Spaces.
> 
> I'm not entirely sold on the Resource Context name ... I think
> Resource Manager (because it's what the TCG calls it) or Spaces
> (because it's what all the code comments call it) are better.
> Resource Context sounds like what TPM2_SaveContext() creates for you
> rather than the interface.
> 
> >  You do not mix it up with namespaces and/or virtualization. With
> > resource in front it cannot be easily mixed up with TPM contexts
> > either.
> 
> I'm a containers person.  What this set of patches does is precisely OS
> level virtualization in my book, so I don't think you need to pretend
> it is't; and OS level virtualization is what a namespace does.  The
> only difference between this and the other kernel namespaces is that
> you get a new namespace automatically when you open the device and you
> can't enter an existing namespace.
> 
> I think therefore that tpmns<n> for TPM Namespace would be very
> appropriate.

Sorry for going back and forth with this but I turn it back to your
original tpmrm. It's in the end of the day the least confusing option. I
think this has been anyway useful to trip a bit around the options
because it is hard to rollback API...

> > This does not equire any effort from your side. I could do the
> > renaming.
> >
> > PS. Could you go through my commits and test and review them at some
> > point so we would have the whole patch set peer tested?
> 
> Already reviewed, just doing a test build (I'm travelling, so it
> actually has to be on my physical laptop).
> 
> James

There's now tabrm-v3 branch. I had to tweak error handling in your
device adding patch because of b4e9d7561a70. I hope I didn't break
anything.

/Jarkko