net/tap: fix support for large Rx queues

Rx queues configured with more than 1023 descriptors cause readv() calls to
fail due to more iovec entries than permitted by the kernel. As a result,
no packets can be received.

Quietly limit internal Rx queue size to the maximum number of iovec entries
to fix this issue.

Fixes: 0781f5762cfe ("net/tap: support segmented mbufs")

Signed-off-by: Pascal Mazon <pascal.mazon@6wind.com>

diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
index d9ec14d..e44de02 100644 (file)
--- a/drivers/net/tap/rte_eth_tap.c
+++ b/drivers/net/tap/rte_eth_tap.c
@@ -875,7 +875,9 @@ tap_rx_queue_setup(struct rte_eth_dev *dev,
        struct pmd_internals *internals = dev->data->dev_private;
        struct rx_queue *rxq = &internals->rxq[rx_queue_id];
        struct rte_mbuf **tmp = &rxq->pool;
-       struct iovec (*iovecs)[nb_rx_desc + 1];
+       long iov_max = sysconf(_SC_IOV_MAX);
+       uint16_t nb_desc = RTE_MIN(nb_rx_desc, iov_max - 1);
+       struct iovec (*iovecs)[nb_desc + 1];
        int data_off = RTE_PKTMBUF_HEADROOM;
        int ret = 0;
        int fd;
@@ -891,13 +893,13 @@ tap_rx_queue_setup(struct rte_eth_dev *dev,
        rxq->mp = mp;
        rxq->trigger_seen = 1; /* force initial burst */
        rxq->in_port = dev->data->port_id;
-       rxq->nb_rx_desc = nb_rx_desc;
+       rxq->nb_rx_desc = nb_desc;
        iovecs = rte_zmalloc_socket(dev->data->name, sizeof(*iovecs), 0,
                                    socket_id);
        if (!iovecs) {
                RTE_LOG(WARNING, PMD,
                        "%s: Couldn't allocate %d RX descriptors\n",
-                       dev->data->name, nb_rx_desc);
+                       dev->data->name, nb_desc);
                return -ENOMEM;
        }
        rxq->iovecs = iovecs;
@@ -911,7 +913,7 @@ tap_rx_queue_setup(struct rte_eth_dev *dev,
        (*rxq->iovecs)[0].iov_len = sizeof(struct tun_pi);
        (*rxq->iovecs)[0].iov_base = &rxq->pi;
 
-       for (i = 1; i <= nb_rx_desc; i++) {
+       for (i = 1; i <= nb_desc; i++) {
                *tmp = rte_pktmbuf_alloc(rxq->mp);
                if (!*tmp) {
                        RTE_LOG(WARNING, PMD,