Imported Upstream version 16.04

Change-Id: I77eadcd8538a9122e4773cbe55b24033dc451757
Signed-off-by: C.J. Collier <cjcollier@linuxfoundation.org>

1 files changed, 772 insertions, 0 deletions

diff --git a/lib/librte_vhost/virtio-net.c b/lib/librte_vhost/virtio-net.c
new file mode 100644
index 00000000..d870ad97
--- /dev/null
+++ b/lib/librte_vhost/virtio-net.c
@@ -0,0 +1,772 @@
+/*-
+ *   BSD LICENSE
+ *
+ *   Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
+ *   All rights reserved.
+ *
+ *   Redistribution and use in source and binary forms, with or without
+ *   modification, are permitted provided that the following conditions
+ *   are met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in
+ *       the documentation and/or other materials provided with the
+ *       distribution.
+ *     * Neither the name of Intel Corporation nor the names of its
+ *       contributors may be used to endorse or promote products derived
+ *       from this software without specific prior written permission.
+ *
+ *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <linux/vhost.h>
+#include <linux/virtio_net.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <sys/mman.h>
+#include <unistd.h>
+#ifdef RTE_LIBRTE_VHOST_NUMA
+#include <numaif.h>
+#endif
+
+#include <sys/socket.h>
+
+#include <rte_ethdev.h>
+#include <rte_log.h>
+#include <rte_string_fns.h>
+#include <rte_memory.h>
+#include <rte_malloc.h>
+#include <rte_virtio_net.h>
+
+#include "vhost-net.h"
+#include "virtio-net.h"
+
+#define MAX_VHOST_DEVICE	1024
+static struct virtio_net *vhost_devices[MAX_VHOST_DEVICE];
+
+/* device ops to add/remove device to/from data core. */
+struct virtio_net_device_ops const *notify_ops;
+
+#define VHOST_USER_F_PROTOCOL_FEATURES	30
+
+/* Features supported by this lib. */
+#define VHOST_SUPPORTED_FEATURES ((1ULL << VIRTIO_NET_F_MRG_RXBUF) | \
+				(1ULL << VIRTIO_NET_F_CTRL_VQ) | \
+				(1ULL << VIRTIO_NET_F_CTRL_RX) | \
+				(1ULL << VIRTIO_NET_F_GUEST_ANNOUNCE) | \
+				(VHOST_SUPPORTS_MQ)            | \
+				(1ULL << VIRTIO_F_VERSION_1)   | \
+				(1ULL << VHOST_F_LOG_ALL)      | \
+				(1ULL << VHOST_USER_F_PROTOCOL_FEATURES) | \
+				(1ULL << VIRTIO_NET_F_HOST_TSO4) | \
+				(1ULL << VIRTIO_NET_F_HOST_TSO6) | \
+				(1ULL << VIRTIO_NET_F_CSUM)    | \
+				(1ULL << VIRTIO_NET_F_GUEST_CSUM) | \
+				(1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
+				(1ULL << VIRTIO_NET_F_GUEST_TSO6))
+
+static uint64_t VHOST_FEATURES = VHOST_SUPPORTED_FEATURES;
+
+
+/*
+ * Converts QEMU virtual address to Vhost virtual address. This function is
+ * used to convert the ring addresses to our address space.
+ */
+static uint64_t
+qva_to_vva(struct virtio_net *dev, uint64_t qemu_va)
+{
+	struct virtio_memory_regions *region;
+	uint64_t vhost_va = 0;
+	uint32_t regionidx = 0;
+
+	/* Find the region where the address lives. */
+	for (regionidx = 0; regionidx < dev->mem->nregions; regionidx++) {
+		region = &dev->mem->regions[regionidx];
+		if ((qemu_va >= region->userspace_address) &&
+			(qemu_va <= region->userspace_address +
+			region->memory_size)) {
+			vhost_va = qemu_va + region->guest_phys_address +
+				region->address_offset -
+				region->userspace_address;
+			break;
+		}
+	}
+	return vhost_va;
+}
+
+
+struct virtio_net *
+get_device(struct vhost_device_ctx ctx)
+{
+	struct virtio_net *dev = vhost_devices[ctx.fh];
+
+	if (unlikely(!dev)) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"(%"PRIu64") device not found.\n", ctx.fh);
+	}
+
+	return dev;
+}
+
+static void
+cleanup_vq(struct vhost_virtqueue *vq, int destroy)
+{
+	if ((vq->callfd >= 0) && (destroy != 0))
+		close(vq->callfd);
+	if (vq->kickfd >= 0)
+		close(vq->kickfd);
+}
+
+/*
+ * Unmap any memory, close any file descriptors and
+ * free any memory owned by a device.
+ */
+static void
+cleanup_device(struct virtio_net *dev, int destroy)
+{
+	uint32_t i;
+
+	vhost_backend_cleanup(dev);
+
+	for (i = 0; i < dev->virt_qp_nb; i++) {
+		cleanup_vq(dev->virtqueue[i * VIRTIO_QNUM + VIRTIO_RXQ], destroy);
+		cleanup_vq(dev->virtqueue[i * VIRTIO_QNUM + VIRTIO_TXQ], destroy);
+	}
+}
+
+/*
+ * Release virtqueues and device memory.
+ */
+static void
+free_device(struct virtio_net *dev)
+{
+	uint32_t i;
+
+	for (i = 0; i < dev->virt_qp_nb; i++)
+		rte_free(dev->virtqueue[i * VIRTIO_QNUM]);
+
+	rte_free(dev);
+}
+
+static void
+init_vring_queue(struct vhost_virtqueue *vq, int qp_idx)
+{
+	memset(vq, 0, sizeof(struct vhost_virtqueue));
+
+	vq->kickfd = VIRTIO_UNINITIALIZED_EVENTFD;
+	vq->callfd = VIRTIO_UNINITIALIZED_EVENTFD;
+
+	/* Backends are set to -1 indicating an inactive device. */
+	vq->backend = -1;
+
+	/* always set the default vq pair to enabled */
+	if (qp_idx == 0)
+		vq->enabled = 1;
+}
+
+static void
+init_vring_queue_pair(struct virtio_net *dev, uint32_t qp_idx)
+{
+	uint32_t base_idx = qp_idx * VIRTIO_QNUM;
+
+	init_vring_queue(dev->virtqueue[base_idx + VIRTIO_RXQ], qp_idx);
+	init_vring_queue(dev->virtqueue[base_idx + VIRTIO_TXQ], qp_idx);
+}
+
+static void
+reset_vring_queue(struct vhost_virtqueue *vq, int qp_idx)
+{
+	int callfd;
+
+	callfd = vq->callfd;
+	init_vring_queue(vq, qp_idx);
+	vq->callfd = callfd;
+}
+
+static void
+reset_vring_queue_pair(struct virtio_net *dev, uint32_t qp_idx)
+{
+	uint32_t base_idx = qp_idx * VIRTIO_QNUM;
+
+	reset_vring_queue(dev->virtqueue[base_idx + VIRTIO_RXQ], qp_idx);
+	reset_vring_queue(dev->virtqueue[base_idx + VIRTIO_TXQ], qp_idx);
+}
+
+static int
+alloc_vring_queue_pair(struct virtio_net *dev, uint32_t qp_idx)
+{
+	struct vhost_virtqueue *virtqueue = NULL;
+	uint32_t virt_rx_q_idx = qp_idx * VIRTIO_QNUM + VIRTIO_RXQ;
+	uint32_t virt_tx_q_idx = qp_idx * VIRTIO_QNUM + VIRTIO_TXQ;
+
+	virtqueue = rte_malloc(NULL,
+			       sizeof(struct vhost_virtqueue) * VIRTIO_QNUM, 0);
+	if (virtqueue == NULL) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"Failed to allocate memory for virt qp:%d.\n", qp_idx);
+		return -1;
+	}
+
+	dev->virtqueue[virt_rx_q_idx] = virtqueue;
+	dev->virtqueue[virt_tx_q_idx] = virtqueue + VIRTIO_TXQ;
+
+	init_vring_queue_pair(dev, qp_idx);
+
+	dev->virt_qp_nb += 1;
+
+	return 0;
+}
+
+/*
+ * Reset some variables in device structure, while keeping few
+ * others untouched, such as device_fh, ifname, virt_qp_nb: they
+ * should be same unless the device is removed.
+ */
+static void
+reset_device(struct virtio_net *dev)
+{
+	uint32_t i;
+
+	dev->features = 0;
+	dev->protocol_features = 0;
+	dev->flags = 0;
+
+	for (i = 0; i < dev->virt_qp_nb; i++)
+		reset_vring_queue_pair(dev, i);
+}
+
+/*
+ * Function is called from the CUSE open function. The device structure is
+ * initialised and a new entry is added to the device configuration linked
+ * list.
+ */
+int
+vhost_new_device(struct vhost_device_ctx ctx)
+{
+	struct virtio_net *dev;
+	int i;
+
+	dev = rte_zmalloc(NULL, sizeof(struct virtio_net), 0);
+	if (dev == NULL) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"(%"PRIu64") Failed to allocate memory for dev.\n",
+			ctx.fh);
+		return -1;
+	}
+
+	for (i = 0; i < MAX_VHOST_DEVICE; i++) {
+		if (vhost_devices[i] == NULL)
+			break;
+	}
+	if (i == MAX_VHOST_DEVICE) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"Failed to find a free slot for new device.\n");
+		return -1;
+	}
+
+	vhost_devices[i] = dev;
+	dev->device_fh   = i;
+
+	return i;
+}
+
+/*
+ * Function is called from the CUSE release function. This function will
+ * cleanup the device and remove it from device configuration linked list.
+ */
+void
+vhost_destroy_device(struct vhost_device_ctx ctx)
+{
+	struct virtio_net *dev = get_device(ctx);
+
+	if (dev == NULL)
+		return;
+
+	if (dev->flags & VIRTIO_DEV_RUNNING)
+		notify_ops->destroy_device(dev);
+
+	cleanup_device(dev, 1);
+	free_device(dev);
+
+	vhost_devices[ctx.fh] = NULL;
+}
+
+void
+vhost_set_ifname(struct vhost_device_ctx ctx,
+	const char *if_name, unsigned int if_len)
+{
+	struct virtio_net *dev;
+	unsigned int len;
+
+	dev = get_device(ctx);
+	if (dev == NULL)
+		return;
+
+	len = if_len > sizeof(dev->ifname) ?
+		sizeof(dev->ifname) : if_len;
+
+	strncpy(dev->ifname, if_name, len);
+}
+
+
+/*
+ * Called from CUSE IOCTL: VHOST_SET_OWNER
+ * This function just returns success at the moment unless
+ * the device hasn't been initialised.
+ */
+int
+vhost_set_owner(struct vhost_device_ctx ctx)
+{
+	struct virtio_net *dev;
+
+	dev = get_device(ctx);
+	if (dev == NULL)
+		return -1;
+
+	return 0;
+}
+
+/*
+ * Called from CUSE IOCTL: VHOST_RESET_OWNER
+ */
+int
+vhost_reset_owner(struct vhost_device_ctx ctx)
+{
+	struct virtio_net *dev;
+
+	dev = get_device(ctx);
+	if (dev == NULL)
+		return -1;
+
+	if (dev->flags & VIRTIO_DEV_RUNNING)
+		notify_ops->destroy_device(dev);
+
+	cleanup_device(dev, 0);
+	reset_device(dev);
+	return 0;
+}
+
+/*
+ * Called from CUSE IOCTL: VHOST_GET_FEATURES
+ * The features that we support are requested.
+ */
+int
+vhost_get_features(struct vhost_device_ctx ctx, uint64_t *pu)
+{
+	struct virtio_net *dev;
+
+	dev = get_device(ctx);
+	if (dev == NULL)
+		return -1;
+
+	/* Send our supported features. */
+	*pu = VHOST_FEATURES;
+	return 0;
+}
+
+/*
+ * Called from CUSE IOCTL: VHOST_SET_FEATURES
+ * We receive the negotiated features supported by us and the virtio device.
+ */
+int
+vhost_set_features(struct vhost_device_ctx ctx, uint64_t *pu)
+{
+	struct virtio_net *dev;
+	uint16_t vhost_hlen;
+	uint16_t i;
+
+	dev = get_device(ctx);
+	if (dev == NULL)
+		return -1;
+	if (*pu & ~VHOST_FEATURES)
+		return -1;
+
+	dev->features = *pu;
+	if (dev->features &
+		((1 << VIRTIO_NET_F_MRG_RXBUF) | (1ULL << VIRTIO_F_VERSION_1))) {
+		vhost_hlen = sizeof(struct virtio_net_hdr_mrg_rxbuf);
+	} else {
+		vhost_hlen = sizeof(struct virtio_net_hdr);
+	}
+	LOG_DEBUG(VHOST_CONFIG,
+		"(%"PRIu64") Mergeable RX buffers %s, virtio 1 %s\n",
+		dev->device_fh,
+		(dev->features & (1 << VIRTIO_NET_F_MRG_RXBUF)) ? "on" : "off",
+		(dev->features & (1ULL << VIRTIO_F_VERSION_1)) ? "on" : "off");
+
+	for (i = 0; i < dev->virt_qp_nb; i++) {
+		uint16_t base_idx = i * VIRTIO_QNUM;
+
+		dev->virtqueue[base_idx + VIRTIO_RXQ]->vhost_hlen = vhost_hlen;
+		dev->virtqueue[base_idx + VIRTIO_TXQ]->vhost_hlen = vhost_hlen;
+	}
+
+	return 0;
+}
+
+/*
+ * Called from CUSE IOCTL: VHOST_SET_VRING_NUM
+ * The virtio device sends us the size of the descriptor ring.
+ */
+int
+vhost_set_vring_num(struct vhost_device_ctx ctx,
+	struct vhost_vring_state *state)
+{
+	struct virtio_net *dev;
+
+	dev = get_device(ctx);
+	if (dev == NULL)
+		return -1;
+
+	/* State->index refers to the queue index. The txq is 1, rxq is 0. */
+	dev->virtqueue[state->index]->size = state->num;
+
+	return 0;
+}
+
+/*
+ * Reallocate virtio_dev and vhost_virtqueue data structure to make them on the
+ * same numa node as the memory of vring descriptor.
+ */
+#ifdef RTE_LIBRTE_VHOST_NUMA
+static struct virtio_net*
+numa_realloc(struct virtio_net *dev, int index)
+{
+	int oldnode, newnode;
+	struct virtio_net *old_dev;
+	struct vhost_virtqueue *old_vq, *vq;
+	int ret;
+
+	/*
+	 * vq is allocated on pairs, we should try to do realloc
+	 * on first queue of one queue pair only.
+	 */
+	if (index % VIRTIO_QNUM != 0)
+		return dev;
+
+	old_dev = dev;
+	vq = old_vq = dev->virtqueue[index];
+
+	ret = get_mempolicy(&newnode, NULL, 0, old_vq->desc,
+			    MPOL_F_NODE | MPOL_F_ADDR);
+
+	/* check if we need to reallocate vq */
+	ret |= get_mempolicy(&oldnode, NULL, 0, old_vq,
+			     MPOL_F_NODE | MPOL_F_ADDR);
+	if (ret) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"Unable to get vq numa information.\n");
+		return dev;
+	}
+	if (oldnode != newnode) {
+		RTE_LOG(INFO, VHOST_CONFIG,
+			"reallocate vq from %d to %d node\n", oldnode, newnode);
+		vq = rte_malloc_socket(NULL, sizeof(*vq) * VIRTIO_QNUM, 0,
+				       newnode);
+		if (!vq)
+			return dev;
+
+		memcpy(vq, old_vq, sizeof(*vq) * VIRTIO_QNUM);
+		rte_free(old_vq);
+	}
+
+	/* check if we need to reallocate dev */
+	ret = get_mempolicy(&oldnode, NULL, 0, old_dev,
+			    MPOL_F_NODE | MPOL_F_ADDR);
+	if (ret) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"Unable to get dev numa information.\n");
+		goto out;
+	}
+	if (oldnode != newnode) {
+		RTE_LOG(INFO, VHOST_CONFIG,
+			"reallocate dev from %d to %d node\n",
+			oldnode, newnode);
+		dev = rte_malloc_socket(NULL, sizeof(*dev), 0, newnode);
+		if (!dev) {
+			dev = old_dev;
+			goto out;
+		}
+
+		memcpy(dev, old_dev, sizeof(*dev));
+		rte_free(old_dev);
+	}
+
+out:
+	dev->virtqueue[index] = vq;
+	dev->virtqueue[index + 1] = vq + 1;
+	vhost_devices[dev->device_fh] = dev;
+
+	return dev;
+}
+#else
+static struct virtio_net*
+numa_realloc(struct virtio_net *dev, int index __rte_unused)
+{
+	return dev;
+}
+#endif
+
+/*
+ * Called from CUSE IOCTL: VHOST_SET_VRING_ADDR
+ * The virtio device sends us the desc, used and avail ring addresses.
+ * This function then converts these to our address space.
+ */
+int
+vhost_set_vring_addr(struct vhost_device_ctx ctx, struct vhost_vring_addr *addr)
+{
+	struct virtio_net *dev;
+	struct vhost_virtqueue *vq;
+
+	dev = get_device(ctx);
+	if ((dev == NULL) || (dev->mem == NULL))
+		return -1;
+
+	/* addr->index refers to the queue index. The txq 1, rxq is 0. */
+	vq = dev->virtqueue[addr->index];
+
+	/* The addresses are converted from QEMU virtual to Vhost virtual. */
+	vq->desc = (struct vring_desc *)(uintptr_t)qva_to_vva(dev,
+			addr->desc_user_addr);
+	if (vq->desc == 0) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"(%"PRIu64") Failed to find desc ring address.\n",
+			dev->device_fh);
+		return -1;
+	}
+
+	dev = numa_realloc(dev, addr->index);
+	vq = dev->virtqueue[addr->index];
+
+	vq->avail = (struct vring_avail *)(uintptr_t)qva_to_vva(dev,
+			addr->avail_user_addr);
+	if (vq->avail == 0) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"(%"PRIu64") Failed to find avail ring address.\n",
+			dev->device_fh);
+		return -1;
+	}
+
+	vq->used = (struct vring_used *)(uintptr_t)qva_to_vva(dev,
+			addr->used_user_addr);
+	if (vq->used == 0) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"(%"PRIu64") Failed to find used ring address.\n",
+			dev->device_fh);
+		return -1;
+	}
+
+	vq->log_guest_addr = addr->log_guest_addr;
+
+	LOG_DEBUG(VHOST_CONFIG, "(%"PRIu64") mapped address desc: %p\n",
+			dev->device_fh, vq->desc);
+	LOG_DEBUG(VHOST_CONFIG, "(%"PRIu64") mapped address avail: %p\n",
+			dev->device_fh, vq->avail);
+	LOG_DEBUG(VHOST_CONFIG, "(%"PRIu64") mapped address used: %p\n",
+			dev->device_fh, vq->used);
+	LOG_DEBUG(VHOST_CONFIG, "(%"PRIu64") log_guest_addr: %"PRIx64"\n",
+			dev->device_fh, vq->log_guest_addr);
+
+	return 0;
+}
+
+/*
+ * Called from CUSE IOCTL: VHOST_SET_VRING_BASE
+ * The virtio device sends us the available ring last used index.
+ */
+int
+vhost_set_vring_base(struct vhost_device_ctx ctx,
+	struct vhost_vring_state *state)
+{
+	struct virtio_net *dev;
+
+	dev = get_device(ctx);
+	if (dev == NULL)
+		return -1;
+
+	/* State->index refers to the queue index. The txq is 1, rxq is 0. */
+	dev->virtqueue[state->index]->last_used_idx = state->num;
+	dev->virtqueue[state->index]->last_used_idx_res = state->num;
+
+	return 0;
+}
+
+/*
+ * Called from CUSE IOCTL: VHOST_GET_VRING_BASE
+ * We send the virtio device our available ring last used index.
+ */
+int
+vhost_get_vring_base(struct vhost_device_ctx ctx, uint32_t index,
+	struct vhost_vring_state *state)
+{
+	struct virtio_net *dev;
+
+	dev = get_device(ctx);
+	if (dev == NULL)
+		return -1;
+
+	state->index = index;
+	/* State->index refers to the queue index. The txq is 1, rxq is 0. */
+	state->num = dev->virtqueue[state->index]->last_used_idx;
+
+	return 0;
+}
+
+
+/*
+ * Called from CUSE IOCTL: VHOST_SET_VRING_CALL
+ * The virtio device sends an eventfd to interrupt the guest. This fd gets
+ * copied into our process space.
+ */
+int
+vhost_set_vring_call(struct vhost_device_ctx ctx, struct vhost_vring_file *file)
+{
+	struct virtio_net *dev;
+	struct vhost_virtqueue *vq;
+	uint32_t cur_qp_idx = file->index / VIRTIO_QNUM;
+
+	dev = get_device(ctx);
+	if (dev == NULL)
+		return -1;
+
+	/*
+	 * FIXME: VHOST_SET_VRING_CALL is the first per-vring message
+	 * we get, so we do vring queue pair allocation here.
+	 */
+	if (cur_qp_idx + 1 > dev->virt_qp_nb) {
+		if (alloc_vring_queue_pair(dev, cur_qp_idx) < 0)
+			return -1;
+	}
+
+	/* file->index refers to the queue index. The txq is 1, rxq is 0. */
+	vq = dev->virtqueue[file->index];
+	assert(vq != NULL);
+
+	if (vq->callfd >= 0)
+		close(vq->callfd);
+
+	vq->callfd = file->fd;
+
+	return 0;
+}
+
+/*
+ * Called from CUSE IOCTL: VHOST_SET_VRING_KICK
+ * The virtio device sends an eventfd that it can use to notify us.
+ * This fd gets copied into our process space.
+ */
+int
+vhost_set_vring_kick(struct vhost_device_ctx ctx, struct vhost_vring_file *file)
+{
+	struct virtio_net *dev;
+	struct vhost_virtqueue *vq;
+
+	dev = get_device(ctx);
+	if (dev == NULL)
+		return -1;
+
+	/* file->index refers to the queue index. The txq is 1, rxq is 0. */
+	vq = dev->virtqueue[file->index];
+
+	if (vq->kickfd >= 0)
+		close(vq->kickfd);
+
+	vq->kickfd = file->fd;
+
+	return 0;
+}
+
+/*
+ * Called from CUSE IOCTL: VHOST_NET_SET_BACKEND
+ * To complete device initialisation when the virtio driver is loaded,
+ * we are provided with a valid fd for a tap device (not used by us).
+ * If this happens then we can add the device to a data core.
+ * When the virtio driver is removed we get fd=-1.
+ * At that point we remove the device from the data core.
+ * The device will still exist in the device configuration linked list.
+ */
+int
+vhost_set_backend(struct vhost_device_ctx ctx, struct vhost_vring_file *file)
+{
+	struct virtio_net *dev;
+
+	dev = get_device(ctx);
+	if (dev == NULL)
+		return -1;
+
+	/* file->index refers to the queue index. The txq is 1, rxq is 0. */
+	dev->virtqueue[file->index]->backend = file->fd;
+
+	/*
+	 * If the device isn't already running and both backend fds are set,
+	 * we add the device.
+	 */
+	if (!(dev->flags & VIRTIO_DEV_RUNNING)) {
+		if (((int)dev->virtqueue[VIRTIO_TXQ]->backend != VIRTIO_DEV_STOPPED) &&
+			((int)dev->virtqueue[VIRTIO_RXQ]->backend != VIRTIO_DEV_STOPPED)) {
+			return notify_ops->new_device(dev);
+		}
+	/* Otherwise we remove it. */
+	} else
+		if (file->fd == VIRTIO_DEV_STOPPED)
+			notify_ops->destroy_device(dev);
+	return 0;
+}
+
+int rte_vhost_enable_guest_notification(struct virtio_net *dev,
+	uint16_t queue_id, int enable)
+{
+	if (enable) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"guest notification isn't supported.\n");
+		return -1;
+	}
+
+	dev->virtqueue[queue_id]->used->flags = VRING_USED_F_NO_NOTIFY;
+	return 0;
+}
+
+uint64_t rte_vhost_feature_get(void)
+{
+	return VHOST_FEATURES;
+}
+
+int rte_vhost_feature_disable(uint64_t feature_mask)
+{
+	VHOST_FEATURES = VHOST_FEATURES & ~feature_mask;
+	return 0;
+}
+
+int rte_vhost_feature_enable(uint64_t feature_mask)
+{
+	if ((feature_mask & VHOST_SUPPORTED_FEATURES) == feature_mask) {
+		VHOST_FEATURES = VHOST_FEATURES | feature_mask;
+		return 0;
+	}
+	return -1;
+}
+
+/*
+ * Register ops so that we can add/remove device to data core.
+ */
+int
+rte_vhost_driver_callback_register(struct virtio_net_device_ops const * const ops)
+{
+	notify_ops = ops;
+
+	return 0;
+}