[dpdk-stable] [PATCH v6] net/tap: fix missing _SC_IOV_MAX

[dpdk-stable] [PATCH v6] net/tap: fix missing _SC_IOV_MAX

[olegpoly123]

If the value _SC_IOV_MAX is missing, sysconf returns -1.
In this case, iov_max is set to a default value of 1024.

Fixes: ec12df9504fe ("net/tap: fix support for large Rx queues")
Cc: stable@dpdk.org

Signed-off-by: Oleg Polyakov <olegp123@walla.co.il>
Acked-by: Keith Wiles <keith.wiles@intel.com>
---
 drivers/net/tap/rte_eth_tap.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
index 6f5109fca..8f7c552b3 100644
--- a/drivers/net/tap/rte_eth_tap.c
+++ b/drivers/net/tap/rte_eth_tap.c
@@ -68,6 +68,8 @@
 /* IPC key for queue fds sync */
 #define TAP_MP_KEY "tap_mp_sync_queues"
 
+#define TAP_IOV_DEFAULT_MAX 1024
+
 static int tap_devices_count;
 static struct rte_vdev_driver pmd_tap_drv;
 static struct rte_vdev_driver pmd_tun_drv;
@@ -1326,6 +1328,13 @@ tap_rx_queue_setup(struct rte_eth_dev *dev,
 	struct rx_queue *rxq = &internals->rxq[rx_queue_id];
 	struct rte_mbuf **tmp = &rxq->pool;
 	long iov_max = sysconf(_SC_IOV_MAX);
+
+	if (iov_max <= 0) {
+		TAP_LOG(WARNING,
+			"_SC_IOV_MAX is not defined. Using %d as default\n",
+			TAP_IOV_DEFAULT_MAX);
+		iov_max = TAP_IOV_DEFAULT_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;
-- 
2.14.1

Re: [dpdk-stable] [dpdk-dev] [PATCH v6] net/tap: fix missing _SC_IOV_MAX

[Stephen Hemminger]

On Mon, 18 Mar 2019 12:55:23 -0400
olegpoly123 <olegp123@walla.co.il> wrote:

>  	long iov_max = sysconf(_SC_IOV_MAX);
> +
> +	if (iov_max <= 0) {
> +		TAP_LOG(WARNING,
> +			"_SC_IOV_MAX is not defined. Using %d as default\n",
> +			TAP_IOV_DEFAULT_MAX);
> +		iov_max = TAP_IOV_DEFAULT_MAX;
> +	}
>  	uint16_t nb_desc = RTE_MIN(nb_rx_desc, iov_max - 1);

Looking at this a little more carefully.

1. Trivial: TAP_LOG() already adds a newline.

2. TAP device should not be silently reducing the number of receive descriptors.

3. TAP device be using IOV_MAX to set rx_descriptor limit. (in dev_info)
   The ethdev would rx_queue_setup with any request for too large a value.