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Date: Thu, 19 Apr 2018 18:42:40 +0200
From: Olivier Matz <olivier.matz@6wind.com>
To: Andrew Rybchenko <arybchenko@solarflare.com>
Cc: dev@dpdk.org, "Artem V. Andreev" <Artem.Andreev@oktetlabs.ru>
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Subject: Re: [dpdk-dev] [PATCH v1 2/6] mempool: implement abstract mempool
	info API
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On Mon, Mar 26, 2018 at 05:12:55PM +0100, Andrew Rybchenko wrote:
> From: "Artem V. Andreev" <Artem.Andreev@oktetlabs.ru>
> 
> Primarily, it is intended as a way for the mempool driver to provide
> additional information on how it lays up objects inside the mempool.
> 
> Signed-off-by: Artem V. Andreev <Artem.Andreev@oktetlabs.ru>
> Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>

I think it's a good idea to have a way to query mempool features
or parameters. The approach chosen in this patch looks similar
to what we have with ethdev devinfo, right?

[...]

>  /**
> + * @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...