Re: [PATCH v4 1/1] tpm: add sysfs exports for all banks of PCR registers

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Thu, Aug 20, 2020 at 09:14:44AM -0700, James Bottomley wrote:
> On Wed, 2020-08-19 at 20:21 -0300, Jason Gunthorpe wrote:
> > On Wed, Aug 19, 2020 at 01:09:16PM -0700, James Bottomley wrote:
> > > On Wed, 2020-08-19 at 14:17 -0300, Jason Gunthorpe wrote:
> > > > On Wed, Aug 19, 2020 at 12:57:42PM -0400, Mimi Zohar wrote:
> > > > > On Wed, 2020-08-19 at 13:18 -0300, Jason Gunthorpe wrote:
> > > > > > Yes - it was dropped because TPM 2 was a *complete ABI break*
> > > > > > for everything. The kernel was reset to a uABI that matches
> > > > > > current uABI standards starting TPM 2.
> > > > > > 
> > > > > > The whole userspace needed to be redone anyhow, and certainly
> > > > > > nobody objected at the time.
> > > > > > 
> > > > > > At least my expecation was that a sensible userspace for TPM
> > > > > > (for administrator user) would be built, like we see in other
> > > > > > subsystems eg 'ip' for netdev.
> > > > > 
> > > > > "Because TPM 2 was a complete ABI break for everything" could
> > > > > be reason for upstreaming a minimal subset of functionality
> > > > > initially, which could be expanded over time.  I don't recall a
> > > > > discussion about limting features in the future.
> > > > 
> > > > All new uAPI additions need to pass the usual uAPI hurdles.
> > > > 
> > > > As James outlined, justify why the kernel must present a
> > > > duplicated uAPI between sysfs and /dev/tpm. 
> > > > 
> > > > There have been good reasons in the past, eg SCSI inquiry.
> > > 
> > > First, can we please agree /dev/tpm does not substitute as a
> > > "duplicate API". 
> > 
> > Er? Huh? How so?
> 
> Because like the SCSI command interface it's a binary marshalled
> protocol we want to abstract for users.  We can still argue whether the
> kernel or a toolkit should do the abstraction but it's not one we want
> to dump on users and say "this is it, what do you mean you don't like
> it?"

No we don't. On the contrary, we expose the protocol through /dev/tpm0.

/Jarkko