Re: [dpdk-dev] [PATCH v2 4/4] add ABI checks

[Thomas Monjalon <thomas@monjalon.net>]

16/03/2020 13:57, Trahe, Fiona:
> From: Kusztal, ArkadiuszX <arkadiuszx.kusztal@intel.com>
> > > > > The patch we're working on will provide two versions of
> > > > > rte_cryptodev_info_get(), both call the same PMD function from the
> > > dev_ops info_get fn ptr.
> > > > > The default version operates s as normal, the 19.11 version searches
> > > > > through the list returned by the PMD, looking for sym.aead.algo =
> > > > > ChaChaPoly, it needs to strip it from
> > > > the list.
> > > > > As PMDs just pass a ptr to their capabilities list ( it isn't a
> > > > > linked list, but an array with an end marker  =
> > > > > RTE_CRYPTODEV_END_OF_CAPABILITIES_LIST) if the API layer detects
> > > > > Chacha it must allocate some space and store a local copy of the trimmed
> > > list. This must be stored only once per device.
> > 
> > [Arek] The problem with this solution is that we need to allocate memory.
> > So the question is how to handle unlikely case of malloc error when we operate inside void function
> > rte_cryptodev_info_get?
> > And even if we would pass somehow error condition to the caller then what to do is another question.
> 
> [Fiona] Quick recap: To avoid breaking ABI, we must return a set of capabilities with/without ChaChaPoly
> depending on the appl version. To resolve this, within the rte_cryptodev layer, we propose to 
> inspect the capabilities returned by PMD and strip ChaCha if it exists.
> In that case memory for the new trimmed capabilities array has to be malloced by the lib.

What happens if the capability is removed from the original capabilities input?

> All good, except how to handle a malloc fail is yet another API breakage as rte_cryptodev_get_info() returns void.
> We propose to return an empty capability list, i.e. a list with only the END element (which can be done without malloc) 
> in this corner case of a corner case.
> Anyone see any issue with this?

How can we use the feature if it is not advertised in capabilities?