[dpdk-dev] [PATCH 4/5] virtio: fix ring size negotiation

[Stephen Hemminger <stephen@networkplumber.org>]

This fixes another of the issues with running virtio on non-KVM
envirionments. For example, Google Compute Engine reports a
ring size of 16K.

If guest virtio requests more slots than available then
the queue should just be initialized to the smaller value.

Conversely, if the number of descriptors requested exceeds the virtio
host queue size, then just silently use the smaller host size.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 lib/librte_pmd_virtio/virtio_ethdev.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/lib/librte_pmd_virtio/virtio_ethdev.c b/lib/librte_pmd_virtio/virtio_ethdev.c
index 3cb9c6a..db0232e 100644
--- a/lib/librte_pmd_virtio/virtio_ethdev.c
+++ b/lib/librte_pmd_virtio/virtio_ethdev.c
@@ -267,13 +267,21 @@ int virtio_dev_queue_setup(struct rte_eth_dev *dev,
 	if (vq_size == 0) {
 		PMD_INIT_LOG(ERR, "%s: virtqueue does not exist", __func__);
 		return -EINVAL;
-	} else if (!rte_is_power_of_2(vq_size)) {
+	}
+
+	if (!rte_is_power_of_2(vq_size)) {
 		PMD_INIT_LOG(ERR, "%s: virtqueue size is not powerof 2", __func__);
 		return -EINVAL;
-	} else if (nb_desc != vq_size) {
-		PMD_INIT_LOG(ERR, "Warning: nb_desc(%d) is not equal to vq size (%d), fall to vq size",
-			nb_desc, vq_size);
-		nb_desc = vq_size;
+	}
+
+	if (nb_desc < vq_size) {
+		if (!rte_is_power_of_2(nb_desc)) {
+			PMD_INIT_LOG(ERR,
+				     "nb_desc(%u) size is not powerof 2",
+				     nb_desc);
+			return -EINVAL;
+		}
+		vq_size = nb_desc;
 	}
 
 	if (queue_type == VTNET_RQ) {
-- 
2.1.4