[PATCH v5 02/10] net/rtap: add TAP device creation and queue management

Stephen Hemminger
2026-02-09T18:41:06Z

Add TAP device creation using the Linux TUN/TAP interface with
IFF_MULTI_QUEUE, IFF_NO_PI, and IFF_VNET_HDR flags. Enable NAPI
mode when the kernel supports it.

The driver maintains a keep-alive file descriptor to the TAP device
and opens additional per-queue file descriptors for data path I/O.
This mirrors the multi-queue TAP architecture where each queue pair
(rx + tx) shares a single TAP fd.

Add the rtap_create() function that:
- Opens the TAP device with configurable interface name
- Configures the virtio-net header size
- Reads the kernel-assigned MAC address
- Supports the 'persist' option to keep the interface after exit
- Detaches the keep-alive queue from data traffic

Add rtap_queue_open() and rtap_queue_close() for per-queue fd
management used during queue setup and teardown.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
drivers/net/rtap/rtap.h | 4 +
drivers/net/rtap/rtap_ethdev.c | 216 ++++++++++++++++++++++++++++++++-
2 files changed, 219 insertions(+), 1 deletion(-)

diff --git a/drivers/net/rtap/rtap.h b/drivers/net/rtap/rtap.h
index 507ab000f3..39a3188a7b 100644
--- a/drivers/net/rtap/rtap.h
+++ b/drivers/net/rtap/rtap.h
@@ -66,4 +66,8 @@ struct rtap_pmd {
struct rte_ether_addr eth_addr; /* address assigned by kernel */
};

+/* rtap_ethdev.c */
+int rtap_queue_open(struct rte_eth_dev *dev, uint16_t queue_id);
+void rtap_queue_close(struct rte_eth_dev *dev, uint16_t queue_id);
+
#endif /* _RTAP_H_ */
diff --git a/drivers/net/rtap/rtap_ethdev.c b/drivers/net/rtap/rtap_ethdev.c
index ee5b5bad1b..4e7847ff8d 100644
--- a/drivers/net/rtap/rtap_ethdev.c
+++ b/drivers/net/rtap/rtap_ethdev.c
@@ -39,13 +39,140 @@ static const char * const valid_arguments[] = {
NULL
};

+/* Creates a new tap device, name returned in ifr */
+static int
+rtap_tap_open(const char *name, struct ifreq *ifr, uint8_t persist)
+{
+ static const char tun_dev[] = "/dev/net/tun";
+ int tap_fd;
+
+ tap_fd = open(tun_dev, O_RDWR | O_CLOEXEC | O_NONBLOCK);
+ if (tap_fd < 0) {
+ PMD_LOG_ERRNO(ERR, "Open %s failed", tun_dev);
+ return -1;
+ }
+
+ int features = 0;
+ if (ioctl(tap_fd, TUNGETFEATURES, &features) < 0) {
+ PMD_LOG_ERRNO(ERR, "ioctl(TUNGETFEATURES): %s", tun_dev);
+ goto error;
+ }
+
+ int flags = IFF_TAP | IFF_MULTI_QUEUE | IFF_NO_PI | IFF_VNET_HDR;
+ if ((features & flags) != flags) {
+ PMD_LOG(ERR, "TUN features %#x missing support for %#x",
+ features, features & flags);
+ goto error;
+ }
+
+#ifdef IFF_NAPI
+ /* If kernel supports using NAPI enable it */
+ if (features & IFF_NAPI)
+ flags |= IFF_NAPI;
+#endif
+ /*
+ * Sets the device name and packet format.
+ * Do not want the protocol information (PI)
+ */
+ strlcpy(ifr->ifr_name, name, IFNAMSIZ);
+ ifr->ifr_flags = flags;
+ if (ioctl(tap_fd, TUNSETIFF, ifr) < 0) {
+ PMD_LOG_ERRNO(ERR, "ioctl(TUNSETIFF) %s", ifr->ifr_name);
+ goto error;
+ }
+
+ /* (Optional) keep the device after application exit */
+ if (persist && ioctl(tap_fd, TUNSETPERSIST, 1) < 0) {
+ PMD_LOG_ERRNO(ERR, "ioctl(TUNSETPERSIST) %s", ifr->ifr_name);
+ goto error;
+ }
+
+ int hdr_size = sizeof(struct virtio_net_hdr);
+ if (ioctl(tap_fd, TUNSETVNETHDRSZ, &hdr_size) < 0) {
+ PMD_LOG(ERR, "ioctl(TUNSETVNETHDRSZ) %s", strerror(errno));
+ goto error;
+ }
+
+ return tap_fd;
+error:
+ close(tap_fd);
+ return -1;
+}
+
+static int
+rtap_dev_start(struct rte_eth_dev *dev)
+{
+ dev->data->dev_link.link_status = RTE_ETH_LINK_UP;
+ for (uint16_t i = 0; i < dev->data->nb_rx_queues; i++) {
+ dev->data->rx_queue_state[i] = RTE_ETH_QUEUE_STATE_STARTED;
+ dev->data->tx_queue_state[i] = RTE_ETH_QUEUE_STATE_STARTED;
+ }
+
+ return 0;
+}
+
+static int
+rtap_dev_stop(struct rte_eth_dev *dev)
+{
+ int *fds = dev->process_private;
+
+ dev->data->dev_link.link_status = RTE_ETH_LINK_DOWN;
+
+ for (uint16_t i = 0; i < dev->data->nb_rx_queues; i++) {
+ dev->data->rx_queue_state[i] = RTE_ETH_QUEUE_STATE_STOPPED;
+ dev->data->tx_queue_state[i] = RTE_ETH_QUEUE_STATE_STOPPED;
+ }
+
+ if (rte_eal_process_type() == RTE_PROC_PRIMARY) {
+ for (uint16_t i = 0; i < RTE_MAX_QUEUES_PER_PORT; i++) {
+ if (fds[i] == -1)
+ continue;
+
+ close(fds[i]);
+ fds[i] = -1;
+ }
+ }
+
+ return 0;
+}
+
+static int
+rtap_dev_configure(struct rte_eth_dev *dev)
+{
+ struct rtap_pmd *pmd = dev->data->dev_private;
+
+ /* rx/tx must be paired */
+ if (dev->data->nb_rx_queues != dev->data->nb_tx_queues)
+ return -EINVAL;
+
+ if (ioctl(pmd->keep_fd, TUNSETOFFLOAD, 0) != 0) {
+ PMD_LOG(ERR, "ioctl(TUNSETOFFLOAD) failed: %s", strerror(errno));
+ return -1;
+ }
+
+ return 0;
+}
+
static int
rtap_dev_close(struct rte_eth_dev *dev)
{
struct rtap_pmd *pmd = dev->data->dev_private;
+ int *fds = dev->process_private;

PMD_LOG(INFO, "Closing %s", pmd->ifname);

+ /* Release all io_uring queues (calls rx/tx_queue_release for each) */
+ rte_eth_dev_internal_reset(dev);
+
+ /* Close any remaining queue fds (each process owns its own set) */
+ for (uint16_t i = 0; i < RTE_MAX_QUEUES_PER_PORT; i++) {
+ if (fds[i] == -1)
+ continue;
+ PMD_LOG(DEBUG, "Closed queue %u fd %d", i, fds[i]);
+ close(fds[i]);
+ fds[i] = -1;
+ }
+
if (rte_eal_process_type() == RTE_PROC_PRIMARY) {
/* mac_addrs must not be freed alone because part of dev_private */
dev->data->mac_addrs = NULL;
@@ -63,10 +190,96 @@ rtap_dev_close(struct rte_eth_dev *dev)
return 0;
}

+/* Setup another fd to TAP device for the queue */
+int
+rtap_queue_open(struct rte_eth_dev *dev, uint16_t queue_id)
+{
+ struct rtap_pmd *pmd = dev->data->dev_private;
+ int *fds = dev->process_private;
+
+ if (fds[queue_id] != -1) {
+ PMD_LOG(DEBUG, "queue %u already has fd %d", queue_id, fds[queue_id]);
+ return 0; /* already setup */
+ }
+
+ struct ifreq ifr = { 0 };
+ int tap_fd = rtap_tap_open(pmd->ifname, &ifr, 0);
+ if (tap_fd < 0) {
+ PMD_LOG(ERR, "tap_open failed");
+ return -1;
+ }
+
+ PMD_LOG(DEBUG, "Opened %d for queue %u", tap_fd, queue_id);
+ fds[queue_id] = tap_fd;
+ return 0;
+}
+
+void
+rtap_queue_close(struct rte_eth_dev *dev, uint16_t queue_id)
+{
+ int *fds = dev->process_private;
+ int tap_fd = fds[queue_id];
+
+ if (tap_fd == -1)
+ return; /* already closed */
+ PMD_LOG(DEBUG, "Closed queue %u fd %d", queue_id, tap_fd);
+ close(tap_fd);
+ fds[queue_id] = -1;
+}
+
static const struct eth_dev_ops rtap_ops = {
+ .dev_start = rtap_dev_start,
+ .dev_stop = rtap_dev_stop,
+ .dev_configure = rtap_dev_configure,
.dev_close = rtap_dev_close,
};

+static int
+rtap_create(struct rte_eth_dev *dev, const char *tap_name, uint8_t persist)
+{
+ struct rte_eth_dev_data *data = dev->data;
+ struct rtap_pmd *pmd = data->dev_private;
+
+ pmd->keep_fd = -1;
+
+ dev->dev_ops = &rtap_ops;
+
+ /* Get the initial fd used to keep the tap device around */
+ struct ifreq ifr = { 0 };
+ pmd->keep_fd = rtap_tap_open(tap_name, &ifr, persist);
+ if (pmd->keep_fd < 0)
+ goto error;
+
+ PMD_LOG(DEBUG, "Created %s keep_fd %d", ifr.ifr_name, pmd->keep_fd);
+
+ /* Use name returned by kernel i.e if tap_name is rtap%d this will be rtap0 */
+ strlcpy(pmd->ifname, ifr.ifr_name, IFNAMSIZ);
+
+ /* Read the MAC address assigned by the kernel */
+ if (ioctl(pmd->keep_fd, SIOCGIFHWADDR, &ifr) < 0) {
+ PMD_LOG_ERRNO(ERR, "Unable to get MAC address for %s", ifr.ifr_name);
+ goto error;
+ }
+ memcpy(&pmd->eth_addr, &ifr.ifr_hwaddr.sa_data, RTE_ETHER_ADDR_LEN);
+ data->mac_addrs = &pmd->eth_addr;
+
+ /* Detach this instance, not used for traffic */
+ ifr.ifr_flags = IFF_DETACH_QUEUE;
+ if (ioctl(pmd->keep_fd, TUNSETQUEUE, &ifr) < 0) {
+ PMD_LOG_ERRNO(ERR, "Unable to detach keep-alive queue for %s", ifr.ifr_name);
+ goto error;
+ }
+
+ PMD_LOG(DEBUG, "%s setup", ifr.ifr_name);
+
+ return 0;
+
+error:
+ if (pmd->keep_fd != -1)
+ close(pmd->keep_fd);
+ return -1;
+}
+
static int
rtap_parse_iface(const char *key __rte_unused, const char *value, void *extra_args)
{
@@ -129,7 +342,8 @@ rtap_probe(struct rte_vdev_device *vdev)
eth_dev->process_private = fds;
eth_dev->data->dev_flags |= RTE_ETH_DEV_AUTOFILL_QUEUE_XSTATS;

- RTE_SET_USED(persist); /* used in later patches */
+ if (rtap_create(eth_dev, tap_name, persist) < 0)
+ goto error;

rte_eth_dev_probing_finish(eth_dev);
rte_kvargs_free(kvlist);
--
2.51.0