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

[Jason Gunthorpe <jgg@nvidia.com>]

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.

But there are also bad reasons like "our userpsace is dysfunctional
and can't make a library or tool".

Jason