From mboxrd@z Thu Jan  1 00:00:00 1970
From: Olivier Matz <olivier.matz@6wind.com>
Subject: Re: [PATCH v1 2/6] mempool: implement abstract mempool
	info API
Date: Wed, 25 Apr 2018 12:26:18 +0200
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Cc: dev@dpdk.org, "Artem V. Andreev" <Artem.Andreev@oktetlabs.ru>
To: Andrew Rybchenko <arybchenko@solarflare.com>
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Hi Andrew,

> > > + * @warning
> > > + * @b EXPERIMENTAL: this API may change without prior notice.
> > > + *
> > > + * Additional information about the mempool
> > > + */
> > > +struct rte_mempool_info;
> > > +
> > [...]
> > 
> > > +/* wrapper to get additional mempool info */
> > > +int
> > > +rte_mempool_ops_get_info(const struct rte_mempool *mp,
> > > +			 struct rte_mempool_info *info)
> > > +{
> > > +	struct rte_mempool_ops *ops;
> > > +
> > > +	ops = rte_mempool_get_ops(mp->ops_index);
> > > +
> > > +	RTE_FUNC_PTR_OR_ERR_RET(ops->get_info, -ENOTSUP);
> > > +	return ops->get_info(mp, info);
> > > +}
> > Thinking in terms of ABI compatibility, it looks that each time we will
> > add or remove a field, it will break the ABI because the info structure
> > will change.
> > 
> > Well, it's maybe nitpicking, because most of the time adding a field in
> > info structure goes with adding a field in the mempool struct, which
> > will anyway break the ABI.
> > 
> > Another approach is to have a function
> > rte_mempool_info_contig_block_size(mp) whose ABI can be more easily
> > wrapped with VERSION_SYMBOL().
> > 
> > On my side I'm fine with your current approach, especially given how few
> > usages of VERSION_SYMBOL() we can find in DPDK. But in case you feel
> > it's better to have a function...
> 
> I'd prefer to keep current solution. Otherwise it could result in too many
> different functions to get various information about mempool driver
> features/characteristics. Also it could be not very convenient to get
> many parameters.
> 
> May be we should align info structure size to cache line to avoid size
> changes in many cases? Typically it will be used on slow path and
> located on caller stack and adding some bytes more should not
> be a problem.

Yes, that could be a good thing to do.

Thanks,
Olivier