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Date:   Wed, 25 Sep 2019 15:34:01 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     James Bottomley <James.Bottomley@HansenPartnership.com>
Cc:     linux-integrity@vger.kernel.org, linux-crypto@vger.kernel.org,
        linux-security-module@vger.kernel.org
Subject: Re: [PATCH v6 02/12] tpm-buf: add handling for TPM2B types
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On Tue, Sep 24, 2019 at 07:12:40AM -0400, James Bottomley wrote:
> I thought about that.  The main problem is that most of the
> construct/append functions use the header, and these are the functions
> most useful to the TPM2B operation.
> 
> The other thing that argues against this is that the TPM2B case would
> save nothing if we eliminated the header, because we allocate a page
> for all the data regardless.

It would be way more clean. There is absolutely nothing TPM2B specific.

> >  and also it makes sense to have a separate length field in the
> > struct to keep the code sane given that sometimes the buffer does not
> > store the length.
> 
> I'm really not sure about that one.  The header length has to be filled
> in for the non-TPM2B case but right at the moment we have no finish
> function for the buf where it could be, so we'd end up having to
> maintain two lengths in every update operation on non-TPM2B buffers. 
> That seems inefficient and the only slight efficiency we get in the
> TPM2B case is not having to do the big endian conversion from the
> header which doesn't seem to be worth the added complexity.

It would be way more clean and an insignificant concern when it comes
to performance. I don't see any problem updating two lengths.

/Jarkko