Re: [PATCH] crypto: remove unused digest-appended feature

["Trahe, Fiona" <fiona.trahe@intel.com>]

Note, this is a cover letter - see important clarification below.
Sorry, I missed adding the [PATCH 0/1] and [PATCH 1/1] to the email subject.

> -----Original Message-----
> From: Trahe, Fiona
> Sent: Thursday, November 17, 2016 5:33 PM
> To: dev@dpdk.org
> Cc: De Lara Guarch, Pablo <pablo.de.lara.guarch@intel.com>; Trahe, Fiona
> <fiona.trahe@intel.com>; Griffin, John <john.griffin@intel.com>; Jastrzebski,
> MichalX K <michalx.k.jastrzebski@intel.com>; Kusztal, ArkadiuszX
> <arkadiuszx.kusztal@intel.com>
> Subject: [PATCH] crypto: remove unused digest-appended feature
> 
> The cryptodev API had specified that if the digest address field was
> left empty on an authentication operation, then the PMD would assume
> the digest was appended to the source or destination data.
> This case was not handled at all by most PMDs and incorrectly handled
> by the QAT PMD.
> As no bugs were raised, it is assumed to be not needed, so this patch
> removes it, rather than add handling for the case on all PMDs.
> The digest can still be appended to the data, but its
> address must now be provided in the op.
> 
> I've added this cover letter to pre-empt the question which will arise
> in chained-mbuf case.
> (Chained-mbuf support will be added in next few weeks for 17.02)
> In a chained-mbuf case, if the digest is appended to the data, it could
> in theory end up split across the last 2 mbufs. Using the digest address
> field only works for the case where the digest is in a flat buffer. The
> digest-appended feature would have provided one way of handling this,
> pushing the responsibility down to the PMD to follow the chain to find
> the digest address and handle it whether in 1 or 2 mbufs.
> However, this is adding extra cycles on the data path in all PMDs
> to handle a case which may not arise in many applications.
> The alternative is to give the application the responsibility
> to make sure the digest is in a flat buffer.
> Specifically if an application knows cases of a digest spanning
> buffers can arise, then it can check for this case and memcpy the partial
> start of the digest from the second last buffer into the last buffer
> so it's no longer split.
> Does anyone see a problem with this?
> 
> 
> Fiona Trahe (1):
>   crypto: remove unused digest-appended feature
> 
>  drivers/crypto/qat/qat_adf/qat_algs_build_desc.c |  2 ++
>  drivers/crypto/qat/qat_crypto.c                  | 18 +-----------------
>  lib/librte_cryptodev/rte_crypto_sym.h            | 10 +---------
>  3 files changed, 4 insertions(+), 26 deletions(-)
> 
> --
> 2.5.0