[dpdk-dev] [PATCH] crypto: remove unused digest-appended feature

Fiona Trahe fiona.trahe at intel.com
Thu Nov 17 18:33:16 CET 2016

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(-)


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