From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Monjalon <thomas.monjalon@6wind.com>
Subject: Re: [PATCH v2 1/2] virtio: fix queue size and number of
	descriptors
Date: Wed, 22 Jul 2015 10:55:11 +0200
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To: Stephen Hemminger <stephen@networkplumber.org>
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2015-07-20 11:40, Stephen Hemminger:
> The number of descriptors can be either zero to use the whole
> available ring, or some value smaller. This is used to limit
> the number of mbufs allocated for the receive ring. If more
> descriptors are requested than available the size is silently
> truncated.
[...]
> +	if (nb_desc == 0 || nb_desc > vq_size)
> +		nb_desc = vq_size;

This behaviour should be common to every drivers and explained in the API doxygen:
http://dpdk.org/browse/dpdk/tree/lib/librte_ether/rte_ethdev.h?id=v2.1.0-rc1#n1843