Add the virtio-loopback-driver and .gitreview file

The virtio-loopback-driver is part of the Virtio Loopback
architecture detailed in the following link:
  https://git.virtualopensystems.com/virtio-loopback/docs

Change-Id: I4828f903f025966624396632a76a2debf6f958d4
Signed-off-by: Angelos Mouzakitis <a.mouzakitis@virtualopensystems.com>

5 files changed, 1708 insertions, 0 deletions

diff --git a/.gitreview b/.gitreview
new file mode 100644
index 0000000..2e563cd
--- /dev/null
+++ b/.gitreview
@@ -0,0 +1,5 @@
+[gerrit]
+host=gerrit.automotivelinux.org
+port=29418
+project=src/virtio/virtio-loopback-driver
+defaultbranch=master
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..0cbef1c
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,32 @@
+# Copyright (C) 2022 Virtual Open Systems SAS
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software Foundation,
+# Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+#
+
+NAME_C=loopback_driver
+
+LINUX_DIR ?= /lib/modules/$(shell uname -r)/build
+
+obj-m += $(NAME_C).o
+
+ifeq ($(DEBUG), 1)
+ ccflags-y += -DDEBUG
+endif
+
+all:
+	make -C $(LINUX_DIR) M=$(PWD) modules
+
+clean:
+	make -C $(LINUX_DIR) M=$(PWD) clean
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..70cc2d4
--- /dev/null
+++ b/README.md
@@ -0,0 +1,16 @@
+# virtio-loopback transport repository
+
+This repository includes the beta version of the "virtio_loopback_transport" driver which is part of the Virtio Loopback Design presented in this [document](https://git.virtualopensystems.com/virtio-loopback/docs/-/blob/master/design_docs). This work carried on by Virtual Open Systems in the [Automotive Grade Linux](https://www.automotivegradelinux.org) community.
+
+As described in the design document, the transport is only a part of a more complex architecture. If you want to see the implementation and build the other components, refer to the [virtio-loopback docs repository](https://git.virtualopensystems.com/virtio-loopback/docs/-/tree/beta-release).
+
+## Build the virtio-loopback transport
+
+In order to build this project the next commands need to be used:
+- `make` for x86
+- `make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-` for arm64
+
+**NOTE**: The `DEBUG=1` can be used in order to enable the driver's logs.
+
+This driver is tested with Linux v5.10 and it is NOT be compatible with newer versions ("fcheck_files" function is replaced by "files_lookup_fd_rcu".
+
diff --git a/loopback_driver.c b/loopback_driver.c
new file mode 100644
index 0000000..f271480
--- /dev/null
+++ b/loopback_driver.c
@@ -0,0 +1,1374 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Based on virtio_mmio.c
+ *   Copyright 2011-2014, ARM Ltd.
+ *
+ * Copyright 2022-2023 Virtual Open Systems SAS
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+
+#define pr_fmt(fmt) "virtio-loopback: " fmt
+
+#include <linux/cdev.h>
+#include <linux/eventfd.h>
+#include <linux/fdtable.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/of_address.h>
+#include <linux/cpumask.h>
+#include <linux/smp.h>
+
+/* MMIO includes */
+#include <linux/acpi.h>
+#include <linux/dma-mapping.h>
+#include <linux/highmem.h>
+#include <linux/io.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <uapi/linux/virtio_mmio.h>
+#include <linux/virtio_ring.h>
+
+#include <linux/kernel.h>
+#include <linux/pid.h>
+#include <linux/sched.h>
+#include <linux/rcupdate.h>
+#include <linux/kthread.h>
+
+/* mmap includes */
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/device.h>
+#include <linux/mutex.h>
+
+/* Loopback header file */
+#include "loopback_driver.h"
+
+#include <linux/pagemap.h>
+
+#include <linux/kfifo.h>
+
+/* Features */
+MODULE_LICENSE("GPL v2");
+
+/* function declaration */
+static uint64_t read_adapter(uint64_t fn_id, uint64_t size);
+static void write_adapter(uint64_t data, uint64_t fn_id, uint64_t size);
+
+struct mmap_info *info;
+int mmap_index;
+int page_fault_index;
+uint64_t sum_pgfaults;
+
+virtio_device_info_struct_t device_info;
+virtio_neg_t device_neg = {.done = ATOMIC_INIT(0)};
+
+/* Waitq */
+wait_queue_head_t wq;
+wait_queue_head_t wq_notify;
+
+/* Read write mutex */
+struct mutex read_write_lock;
+struct mutex notify_lock;
+struct mutex notify_q_lock;
+struct mutex interrupt_lock;
+
+bool share_communication_struct;
+uint32_t vq_index;
+uint64_t vq_pfns[16], vq_pfn;
+
+struct virtio_mmio_device *vm_dev_irq;
+
+struct virtqueue *global_vq;
+const struct vring *global_vring;
+
+/* counters */
+static int interrupt_cnt;
+static int notify_sent, notify_received;
+
+static struct platform_device virtio_loopback_device = {
+	.name = "loopback-transport",
+	.id = -1,
+	.num_resources = 2,
+	.resource = (struct resource []) {
+		{
+			.start = 0xa003e00,
+			.end = 0xa003fff,
+			.flags = 0x200 /* IORESOURCE_MEM, */
+		}, {
+			.start = 0x2c,
+			.end = 0x2c,
+			.flags = 0x401 /* IORESOURCE_IRQ, */
+		},
+	}
+};
+
+/* Virio-loopback device funcitonality */
+struct task_struct *userspace_task;
+struct file *efd_file;
+struct file *efd_file_notify;
+struct eventfd_ctx *efd_ctx;
+static struct task_struct *start_loopback_thread;
+
+/* global storage for device Major number */
+static int dev_major;
+/* sysfs class structure */
+static struct class *loopback_class;
+/* array of loopback_device_data for */
+static struct loopback_device_data loopback_data[MAX_DEV];
+
+/* Allow only one process to open the driver */
+unsigned long loopback_flags;
+#define IN_USE_BIT 0
+
+#define KFIFO_SIZE 1024
+static struct kfifo notify_queue;
+int32_t notified_vq_index;
+int notify_flag;
+int cur_ram_idx;
+
+/*
+ * If this variable is true then read/write should wait
+ * the adapter to unlock this opertion by sending an
+ * eventfd. If it's equal to "false" then the oparetion
+ * does not wait for adapter's confirmation.
+ */
+bool valid_eventfd = true;
+
+
+/* mmap functionality related structures */
+struct share_mmap {
+	uint64_t pfn;
+	uint64_t vm_start;
+	uint32_t size;
+	uint32_t uid;
+	struct page *page;
+};
+struct share_mmap share_mmap_list[MMAP_LIMIT];
+
+/* Configuration interface */
+
+static u64 vm_get_features(struct virtio_device *vdev)
+{
+	u64 features;
+
+	/* Take feature bits 0-31 */
+	write_adapter(1, VIRTIO_MMIO_DEVICE_FEATURES_SEL, 4);
+	features = read_adapter(VIRTIO_MMIO_DEVICE_FEATURES, 4);
+	features <<= 32;
+
+	/* Take feature bits 32-63 */
+	write_adapter(0, VIRTIO_MMIO_DEVICE_FEATURES_SEL, 4);
+	features |= read_adapter(VIRTIO_MMIO_DEVICE_FEATURES, 4);
+
+	return features;
+}
+
+static int vm_finalize_features(struct virtio_device *vdev)
+{
+	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+
+	/* Give virtio_ring a chance to accept features. */
+	vring_transport_features(vdev);
+
+	/* Make sure there are no mixed devices */
+	if (vm_dev->version == 2 &&
+		!__virtio_test_bit(vdev, VIRTIO_F_VERSION_1)) {
+		dev_err(&vdev->dev, "New virtio-mmio devices (version 2) "
+				"must provide VIRTIO_F_VERSION_1 feature!\n");
+		return -EINVAL;
+	}
+
+	write_adapter(1, VIRTIO_MMIO_DRIVER_FEATURES_SEL, 4);
+	write_adapter((u32)(vdev->features >> 32), VIRTIO_MMIO_DRIVER_FEATURES, 4);
+
+	write_adapter(0, VIRTIO_MMIO_DRIVER_FEATURES_SEL, 4);
+	write_adapter((u32)vdev->features, VIRTIO_MMIO_DRIVER_FEATURES, 4);
+
+	return 0;
+}
+
+static void vm_get(struct virtio_device *vdev, unsigned int offset,
+				   void *buf, unsigned int len)
+{
+	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+	u8 b;
+	__le16 w;
+	__le32 l;
+
+	if (vm_dev->version == 1) {
+		u8 *ptr = buf;
+		int i;
+
+		for (i = 0; i < len; i++)
+			ptr[i] = read_adapter(VIRTIO_MMIO_CONFIG + offset + i, 1);
+		return;
+	}
+
+	switch (len) {
+	case 1:
+		b = read_adapter(VIRTIO_MMIO_CONFIG + offset, 1);
+		memcpy(buf, &b, sizeof(b));
+		break;
+	case 2:
+		w = cpu_to_le16(read_adapter(VIRTIO_MMIO_CONFIG + offset, 2));
+		memcpy(buf, &w, sizeof(w));
+		break;
+	case 4:
+		l = cpu_to_le32(read_adapter(VIRTIO_MMIO_CONFIG + offset, 4));
+		memcpy(buf, &l, sizeof(l));
+		break;
+	case 8:
+		l = cpu_to_le32(read_adapter(VIRTIO_MMIO_CONFIG + offset, 4));
+		memcpy(buf, &l, sizeof(l));
+		l = cpu_to_le32(read_adapter(VIRTIO_MMIO_CONFIG + offset + sizeof(l), 4));
+		memcpy(buf + sizeof(l), &l, sizeof(l));
+		break;
+	default:
+		BUG();
+	}
+}
+
+static void vm_set(struct virtio_device *vdev, unsigned int offset,
+				   const void *buf, unsigned int len)
+{
+	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+	u8 b;
+	__le16 w;
+	__le32 l;
+
+	if (vm_dev->version == 1) {
+		const u8 *ptr = buf;
+		int i;
+
+		for (i = 0; i < len; i++)
+			write_adapter(ptr[i], VIRTIO_MMIO_CONFIG + offset + i, 1);
+
+		return;
+	}
+
+	switch (len) {
+	case 1:
+		memcpy(&b, buf, sizeof(b));
+		write_adapter(b, VIRTIO_MMIO_CONFIG + offset, 1);
+		break;
+	case 2:
+		memcpy(&w, buf, sizeof(w));
+		write_adapter(le16_to_cpu(w), VIRTIO_MMIO_CONFIG + offset, 2);
+		break;
+	case 4:
+		memcpy(&l, buf, sizeof(l));
+		write_adapter(le32_to_cpu(l), VIRTIO_MMIO_CONFIG + offset, 4);
+		break;
+	case 8:
+		memcpy(&l, buf, sizeof(l));
+		write_adapter(le32_to_cpu(l), VIRTIO_MMIO_CONFIG + offset, 4);
+		memcpy(&l, buf + sizeof(l), sizeof(l));
+		write_adapter(le32_to_cpu(l), VIRTIO_MMIO_CONFIG + offset + sizeof(l), 4);
+		break;
+	default:
+		BUG();
+	}
+}
+
+static u32 vm_generation(struct virtio_device *vdev)
+{
+	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+
+	if (vm_dev->version == 1)
+		return 0;
+	else
+		return read_adapter(VIRTIO_MMIO_CONFIG_GENERATION, 4);
+}
+
+static u8 vm_get_status(struct virtio_device *vdev)
+{
+	return read_adapter(VIRTIO_MMIO_STATUS, 4) & 0xff;
+}
+
+static void vm_set_status(struct virtio_device *vdev, u8 status)
+{
+	write_adapter(status, VIRTIO_MMIO_STATUS, 4);
+}
+
+static void vm_reset(struct virtio_device *vdev)
+{
+	/* 0 status means a reset. */
+	write_adapter(0, VIRTIO_MMIO_STATUS, 4);
+}
+
+static struct workqueue_struct *notify_workqueue, *interrupt_workqueue;
+static void async_work_handler(struct work_struct *work)
+{
+	int vq_index, ret;
+
+	mutex_lock(&notify_lock);
+
+	mutex_lock(&notify_q_lock);
+	ret = kfifo_get(&notify_queue, &vq_index);
+	if (ret == 0) {
+		DBG("fifo is empty\n");
+		DBG("kfifo_len -> %d\n", kfifo_len(&notify_queue));
+		mutex_unlock(&notify_q_lock);
+		mutex_unlock(&notify_lock);
+		return;
+	}
+	mutex_unlock(&notify_q_lock);
+
+	DBG("notify_received: %d, VQ: %d\n", notify_received++, vq_index);
+	write_adapter(vq_index, VIRTIO_MMIO_QUEUE_NOTIFY, 4);
+
+	mutex_unlock(&notify_lock);
+}
+
+DECLARE_WORK(async_work, async_work_handler);
+
+/* the notify function used when creating a virt queue */
+static bool vm_notify(struct virtqueue *vq)
+{
+	int ret, prev_len, vq_index;
+	/*
+	 * We write the queue's selector into
+	 * the notification register to signal
+	 * the other end
+	 */
+	mutex_lock(&notify_q_lock);
+
+	prev_len = kfifo_len(&notify_queue);
+	vq_index = vq->index;
+
+	ret = kfifo_put(&notify_queue, vq_index);
+	if (ret == 0) {
+			if (prev_len == kfifo_len(&notify_queue)) {
+			DBG("fifo is full: len = %d\n", kfifo_len(&notify_queue));
+			DBG("kfifo_put failed with error: %d\n", ret);
+			mutex_unlock(&notify_q_lock);
+			return false;
+			}
+	}
+
+	DBG("ADD in kfifo: %d, VQ: %d\n", notify_sent++, vq_index);
+
+	/* This doesn't make any difference in or out of the block */
+	queue_work(notify_workqueue, &async_work);
+	mutex_unlock(&notify_q_lock);
+
+	return true;
+}
+
+/* Notify all virtqueues on an interrupt. */
+static void vm_interrupt(struct work_struct *work)
+{
+	struct virtio_mmio_device *vm_dev = vm_dev_irq;
+	struct virtio_mmio_vq_info *info;
+	int irq = 44;
+	unsigned long status;
+
+	/* STATUS and ACK should ne done without any intermediate status change */
+	mutex_lock(&interrupt_lock);
+	DBG("interrupt_cnt: %d\n", interrupt_cnt++);
+
+	/* Read and acknowledge interrupts */
+	status = read_adapter(VIRTIO_MMIO_INTERRUPT_STATUS, 4);
+	write_adapter(status, VIRTIO_MMIO_INTERRUPT_ACK, 4);
+
+	if (unlikely(status & VIRTIO_MMIO_INT_CONFIG))
+		virtio_config_changed(&vm_dev->vdev);
+
+	if (likely(status & VIRTIO_MMIO_INT_VRING)) {
+		spin_lock(&vm_dev->lock);
+		list_for_each_entry(info, &vm_dev->virtqueues, node) {
+			(void)vring_interrupt(irq, info->vq);
+		}
+		spin_unlock(&vm_dev->lock);
+	}
+	mutex_unlock(&interrupt_lock);
+}
+DECLARE_WORK(async_interrupt, vm_interrupt);
+
+static void vm_del_vq(struct virtqueue *vq)
+{
+	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vq->vdev);
+	struct virtio_mmio_vq_info *info = vq->priv;
+	unsigned long flags;
+	unsigned int index = vq->index;
+
+	spin_lock_irqsave(&vm_dev->lock, flags);
+	list_del(&info->node);
+	spin_unlock_irqrestore(&vm_dev->lock, flags);
+
+	/* Select and deactivate the queue */
+	write_adapter(index, VIRTIO_MMIO_QUEUE_SEL, 4);
+
+	if (vm_dev->version == 1) {
+		write_adapter(0, VIRTIO_MMIO_QUEUE_PFN, 4);
+	} else {
+		write_adapter(0, VIRTIO_MMIO_QUEUE_READY, 4);
+		WARN_ON(read_adapter(VIRTIO_MMIO_QUEUE_READY, 4));
+	}
+
+	vring_del_virtqueue(vq);
+	kfree(info);
+}
+
+static void vm_del_vqs(struct virtio_device *vdev)
+{
+	struct virtqueue *vq, *n;
+
+	list_for_each_entry_safe(vq, n, &vdev->vqs, list)
+		vm_del_vq(vq);
+}
+
+static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned int index,
+				  void (*callback)(struct virtqueue *vq),
+				  const char *name, bool ctx)
+{
+	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+	struct virtio_mmio_vq_info *info;
+	struct virtqueue *vq;
+	unsigned long flags;
+	unsigned int num;
+	int err;
+
+	if (!name)
+		return NULL;
+
+	/* Select the queue we're interested in */
+	write_adapter(index, VIRTIO_MMIO_QUEUE_SEL, 4);
+
+	/* Queue shouldn't already be set up. */
+	if (read_adapter((vm_dev->version == 1 ?
+			VIRTIO_MMIO_QUEUE_PFN : VIRTIO_MMIO_QUEUE_READY), 4)) {
+		err = -ENOENT;
+		goto error_available;
+	}
+
+	/* Allocate and fill out our active queue description */
+	info = kmalloc(sizeof(*info), GFP_KERNEL);
+	if (!info) {
+		err = -ENOMEM;
+		goto error_kmalloc;
+	}
+
+	num = read_adapter(VIRTIO_MMIO_QUEUE_NUM_MAX, 4);
+	if (num == 0) {
+		err = -ENOENT;
+		goto error_new_virtqueue;
+	}
+
+	/* Create the vring */
+	vq = vring_create_virtqueue(index, num, VIRTIO_MMIO_VRING_ALIGN, vdev,
+					 true, true, ctx, vm_notify, callback, name);
+	if (!vq) {
+		err = -ENOMEM;
+		goto error_new_virtqueue;
+	}
+
+	/* Activate the queue */
+	write_adapter(virtqueue_get_vring_size(vq), VIRTIO_MMIO_QUEUE_NUM, 4);
+	if (vm_dev->version == 1) {
+		u64 q_pfn = virtqueue_get_desc_addr(vq);
+
+		q_pfn = q_pfn >> PAGE_SHIFT;
+
+		/* Copy the physical address and enable the mmap */
+		vq_pfn = q_pfn;
+		vq_pfns[vq_index++] = q_pfn;
+
+		/* Save the virtqueue in a global variable */
+		global_vq = vq;
+		global_vring = virtqueue_get_vring(vq);
+
+		/*
+		 * virtio-mmio v1 uses a 32bit QUEUE PFN. If we have something
+		 * that doesn't fit in 32bit, fail the setup rather than
+		 * pretending to be successful.
+		 */
+		if (q_pfn >> 32) {
+			dev_err(&vdev->dev,
+				"platform bug: legacy virtio-mmio must not "
+				"be used with RAM above 0x%llxGB\n",
+				0x1ULL << (32 + PAGE_SHIFT - 30));
+			err = -E2BIG;
+			goto error_bad_pfn;
+		}
+
+		write_adapter(PAGE_SIZE, VIRTIO_MMIO_QUEUE_ALIGN, 4);
+		write_adapter(q_pfn, VIRTIO_MMIO_QUEUE_PFN, 4);
+	} else {
+		u64 addr;
+
+		addr = virtqueue_get_desc_addr(vq);
+		write_adapter((u32)addr, VIRTIO_MMIO_QUEUE_DESC_LOW, 4);
+		write_adapter((u32)(addr >> 32), VIRTIO_MMIO_QUEUE_DESC_HIGH, 4);
+
+		addr = virtqueue_get_avail_addr(vq);
+		write_adapter((u32)addr, VIRTIO_MMIO_QUEUE_AVAIL_LOW, 4);
+		write_adapter((u32)(addr >> 32), VIRTIO_MMIO_QUEUE_AVAIL_HIGH, 4);
+
+		addr = virtqueue_get_used_addr(vq);
+		write_adapter((u32)addr, VIRTIO_MMIO_QUEUE_USED_LOW, 4);
+		write_adapter((u32)(addr >> 32), VIRTIO_MMIO_QUEUE_USED_HIGH, 4);
+
+		write_adapter(1, VIRTIO_MMIO_QUEUE_READY, 4);
+	}
+
+	vq->priv = info;
+	info->vq = vq;
+
+	spin_lock_irqsave(&vm_dev->lock, flags);
+	list_add(&info->node, &vm_dev->virtqueues);
+	spin_unlock_irqrestore(&vm_dev->lock, flags);
+
+	return vq;
+
+error_bad_pfn:
+	vring_del_virtqueue(vq);
+error_new_virtqueue:
+	if (vm_dev->version == 1) {
+		write_adapter(0, VIRTIO_MMIO_QUEUE_PFN, 4);
+	} else {
+		write_adapter(0, VIRTIO_MMIO_QUEUE_READY, 4);
+		WARN_ON(read_adapter(VIRTIO_MMIO_QUEUE_READY, 4));
+	}
+	kfree(info);
+error_kmalloc:
+error_available:
+	return ERR_PTR(err);
+}
+
+static int vm_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
+					   struct virtqueue *vqs[],
+					   vq_callback_t *callbacks[],
+					   const char * const names[],
+					   const bool *ctx,
+					   struct irq_affinity *desc)
+{
+	int i, queue_idx = 0;
+
+	for (i = 0; i < nvqs; ++i) {
+		if (!names[i]) {
+			vqs[i] = NULL;
+			continue;
+		}
+
+		vqs[i] = vm_setup_vq(vdev, queue_idx++, callbacks[i], names[i],
+							 ctx ? ctx[i] : false);
+		if (IS_ERR(vqs[i])) {
+			vm_del_vqs(vdev);
+			return PTR_ERR(vqs[i]);
+		}
+	}
+
+	return 0;
+}
+
+static const char *vm_bus_name(struct virtio_device *vdev)
+{
+	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+
+	return vm_dev->pdev->name;
+}
+
+static bool vm_get_shm_region(struct virtio_device *vdev,
+				  struct virtio_shm_region *region, u8 id)
+{
+	u64 len, addr;
+
+	/* Select the region we're interested in */
+	write_adapter(id, VIRTIO_MMIO_SHM_SEL, 4);
+
+	/* Read the region size */
+	len = (u64) read_adapter(VIRTIO_MMIO_SHM_LEN_LOW, 4);
+	len |= (u64) read_adapter(VIRTIO_MMIO_SHM_LEN_HIGH, 4) << 32;
+
+	region->len = len;
+
+	/* Check if region length is -1. If that's the case, the shared memory
+	 * region does not exist and there is no need to proceed further.
+	 */
+	if (len == ~(u64)0)
+		return false;
+
+	/* Read the region base address */
+	addr = (u64) read_adapter(VIRTIO_MMIO_SHM_BASE_LOW, 4);
+	addr |= (u64) read_adapter(VIRTIO_MMIO_SHM_BASE_HIGH, 4) << 32;
+
+	region->addr = addr;
+
+	return true;
+}
+
+static const struct virtio_config_ops virtio_mmio_config_ops = {
+	.get			= vm_get,
+	.set			= vm_set,
+	.generation		= vm_generation,
+	.get_status		= vm_get_status,
+	.set_status		= vm_set_status,
+	.reset			= vm_reset,
+	.find_vqs		= vm_find_vqs,
+	.del_vqs		= vm_del_vqs,
+	.get_features		= vm_get_features,
+	.finalize_features	= vm_finalize_features,
+	.bus_name		= vm_bus_name,
+	.get_shm_region		= vm_get_shm_region,
+};
+
+static void virtio_mmio_release_dev(struct device *_d)
+{
+	struct virtio_device *vdev = container_of(_d, struct virtio_device, dev);
+	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+	struct platform_device *pdev = vm_dev->pdev;
+
+	devm_kfree(&pdev->dev, vm_dev);
+}
+
+static int virtio_mmio_probe(struct platform_device *pdev)
+{
+	struct virtio_mmio_device *vm_dev;
+	unsigned long magic;
+	int rc;
+
+	vm_dev = devm_kzalloc(&pdev->dev, sizeof(*vm_dev), GFP_KERNEL);
+	if (!vm_dev)
+		return -ENOMEM;
+
+	/* Save the device pointer globally */
+	vm_dev_irq = vm_dev;
+
+	vm_dev->vdev.dev.parent = &pdev->dev;
+	vm_dev->vdev.dev.release = virtio_mmio_release_dev;
+	vm_dev->vdev.config = &virtio_mmio_config_ops;
+	vm_dev->pdev = pdev;
+	INIT_LIST_HEAD(&vm_dev->virtqueues);
+	spin_lock_init(&vm_dev->lock);
+
+	/* Check magic value */
+	magic = read_adapter(VIRTIO_MMIO_MAGIC_VALUE, 4);
+
+	if (magic != ('v' | 'i' << 8 | 'r' << 16 | 't' << 24)) {
+		dev_warn(&pdev->dev, "Wrong magic value 0x%08lx!\n", magic);
+		return -ENODEV;
+	}
+
+	/* Check device version */
+	vm_dev->version = read_adapter(VIRTIO_MMIO_VERSION, 4);
+
+	if (vm_dev->version < 1 || vm_dev->version > 2) {
+		dev_err(&pdev->dev, "Version %ld not supported!\n",
+							vm_dev->version);
+		return -ENXIO;
+	}
+
+	vm_dev->vdev.id.device = read_adapter(VIRTIO_MMIO_DEVICE_ID, 4);
+
+	if (vm_dev->vdev.id.device == 0) {
+		/*
+		 * virtio-mmio device with an ID 0 is a (dummy) placeholder
+		 * with no function. End probing now with no error reported.
+		 */
+		return -ENODEV;
+	}
+
+	vm_dev->vdev.id.vendor = read_adapter(VIRTIO_MMIO_VENDOR_ID, 4);
+
+	if (vm_dev->version == 1) {
+		write_adapter(PAGE_SIZE, VIRTIO_MMIO_GUEST_PAGE_SIZE, 4);
+
+		rc = dma_set_mask(&pdev->dev, DMA_BIT_MASK(64));
+		/*
+		 * In the legacy case, ensure our coherently-allocated virtio
+		 * ring will be at an address expressable as a 32-bit PFN.
+		 */
+		if (!rc)
+			dma_set_coherent_mask(&pdev->dev,
+				  DMA_BIT_MASK(32 + PAGE_SHIFT));
+	} else {
+		rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
+	}
+	if (rc)
+		rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
+	if (rc)
+		dev_warn(&pdev->dev, "Failed to enable 64-bit or 32-bit DMA."
+				"Trying to continue, but this might not work.\n");
+
+	platform_set_drvdata(pdev, vm_dev);
+
+	rc = register_virtio_device(&vm_dev->vdev);
+
+	if (rc)
+		put_device(&vm_dev->vdev.dev);
+
+	return rc;
+}
+
+static int virtio_mmio_remove(struct platform_device *pdev)
+{
+	struct virtio_mmio_device *vm_dev = platform_get_drvdata(pdev);
+
+	unregister_virtio_device(&vm_dev->vdev);
+	DBG("unregister_virtio_device!\n");
+	return 0;
+}
+
+/* Not need of DTS and ACPI */
+static struct platform_driver virtio_mmio_driver = {
+	.probe	 = virtio_mmio_probe,
+	.remove	 = virtio_mmio_remove,
+	.driver	 = {
+		.name   = "loopback-transport",
+	},
+};
+
+/*
+ * This functions registers all mmap calls done by the user-space into an array
+ */
+void add_share_mmap(struct file *filp, uint64_t pfn, uint64_t vm_start, uint64_t size)
+{
+	DBG("Add new mmaping! index: %d\n", mmap_index);
+	DBG("pfn: 0x%llx", pfn);
+	DBG("vm_start: 0x%llx", vm_start);
+	DBG("size: 0x%llx", size);
+
+	share_mmap_list[mmap_index].pfn = pfn;
+	share_mmap_list[mmap_index].vm_start = vm_start;
+	share_mmap_list[mmap_index].size = size;
+	share_mmap_list[mmap_index].uid = task_pid_nr(current);
+	mmap_index++;
+}
+
+/*
+ * This functions removes a record from mmap array
+ */
+void share_mmap_rem(struct vm_area_struct *vma)
+{
+	int i;
+
+	for (i = 0; i < MMAP_LIMIT; i++) {
+		if (share_mmap_list[i].vm_start == vma->vm_start) {
+			DBG("share_mmap with pa: 0x%llx and size: %x is deleted from the list\n",
+					 share_mmap_list[i].pfn, share_mmap_list[i].size);
+			share_mmap_list[i].uid = 0;
+			share_mmap_list[i].pfn = 0;
+			share_mmap_list[i].vm_start = 0;
+			share_mmap_list[i].size = 0;
+		}
+	}
+}
+
+void print_mmap_idx(int i)
+{
+	DBG("share_mmap_list[%d].uid %x\n", i, share_mmap_list[i].uid);
+	DBG("share_mmap_list[%d].pfn %llx\n", i, share_mmap_list[i].pfn);
+	DBG("share_mmap_list[%d].vm_start %llx\n", i, share_mmap_list[i].vm_start);
+	DBG("share_mmap_list[%d].size %x\n", i, share_mmap_list[i].size);
+}
+
+void print_mmaps(void)
+{
+	int i;
+	int limit = mmap_index == 0 ? MMAP_LIMIT : mmap_index;
+
+	for (i = 0; i < limit; i++)
+		print_mmap_idx(i);
+
+}
+
+/*
+ * This function return the corresponding pfn of a user-space address
+ * based on the mapping done during the initialization
+ */
+uint64_t share_mmap_exist_vma_return_correct_addr(uint64_t pfn)
+{
+	int i;
+	uint64_t corrected_addr;
+
+	for (i = 0; i < MMAP_LIMIT; i++) {
+		if ((share_mmap_list[i].pfn <= pfn) &&
+			(pfn < share_mmap_list[i].pfn + (share_mmap_list[i].size >> PAGE_SHIFT)) &&
+			(share_mmap_list[i].uid == task_pid_nr(current))) {
+			DBG("pfn (0x%llx) exist in: 0x%llx - 0x%llx\n", pfn, share_mmap_list[i].pfn,
+				share_mmap_list[i].pfn + (share_mmap_list[i].size >> PAGE_SHIFT));
+			corrected_addr = ((pfn - share_mmap_list[i].pfn) << PAGE_SHIFT) + share_mmap_list[i].vm_start;
+			DBG("The return addr is: 0x%llx\n", corrected_addr);
+			return corrected_addr;
+		}
+	}
+	return 0;
+}
+
+/*
+ * This function return the corresponding user-space address of a pfn
+ * based on the mapping done during the initialization
+ */
+uint64_t share_mmap_exist_vma_return_correct_pfn(uint64_t addr)
+{
+	int i;
+	uint64_t corrected_pfn;
+
+	for (i = 0; i < MMAP_LIMIT; i++) {
+		if ((share_mmap_list[i].vm_start <= addr) &&
+			(addr < share_mmap_list[i].vm_start + share_mmap_list[i].size)) {
+			DBG("addr (0x%llx) exist in: 0x%llx - 0x%llx\n", addr, share_mmap_list[i].vm_start,
+				share_mmap_list[i].vm_start + share_mmap_list[i].size);
+			DBG("((addr - share_mmap_list[i].vm_start) / PAGE_SIZE): 0x%llx\n",
+											((addr - share_mmap_list[i].vm_start) / PAGE_SIZE));
+			DBG("share_mmap_list[i].pfn: 0x%llx\n", share_mmap_list[i].pfn);
+			corrected_pfn = ((addr - share_mmap_list[i].vm_start) / PAGE_SIZE) + share_mmap_list[i].pfn;
+			return corrected_pfn;
+		}
+	}
+	return 0;
+}
+
+/*
+ * This function returns the size of memory block area referrenced by the vrings
+ */
+uint64_t share_mmap_exist_vma_vring_size(uint64_t insert_pfn)
+{
+	int i = 0;
+	uint64_t next_pfn, mem_blk_size;
+
+	while (((vring_desc_t)global_vring->desc[i]).addr != 0) {
+
+		/* Get the current value of pfn and its size */
+		next_pfn = ((vring_desc_t)global_vring->desc[i]).addr >> PAGE_SHIFT;
+		mem_blk_size = ((vring_desc_t)global_vring->desc[i]).len;
+
+		/* Check if the insert_pfn is found */
+		if (insert_pfn == next_pfn) {
+
+			DBG("Found 0x%llx into the vring\n", insert_pfn);
+			/* Formalize the mem_blk_size to be multiple of PAGE_SIZE */
+			mem_blk_size = mem_blk_size % PAGE_SIZE ?
+					(mem_blk_size & PAGE_MASK) + PAGE_SIZE : mem_blk_size;
+			DBG("The formalized size is %llu\n", mem_blk_size);
+
+			return mem_blk_size;
+		}
+
+		/* Go to next element into the vring array */
+		i++;
+	}
+
+	return PAGE_SIZE;
+}
+
+/*
+ * This function tries to insert multiple PFNs into the user-space process.
+ * The pfn of the starting page is given as an argument and the number of
+ * pages to be inserted is calculated based on the memory block length found into
+ * the vrings.
+ */
+void vmf_insert_vring_pfns(struct vm_area_struct *vma, uint64_t vaddr, uint64_t insert_pfn)
+{
+	int i, page_num, ret;
+	uint64_t mem_blk_size;
+
+	/* Formalize the mem_blk_size to be multiple of PAGE_SIZE */
+	mem_blk_size = share_mmap_exist_vma_vring_size(insert_pfn);
+
+	page_num = mem_blk_size / PAGE_SIZE;
+	DBG("page_num: %u, need to be inserted\n", page_num);
+
+	for (i = 0; i < page_num; i++) {
+		DBG("\tTry to insert 0x%llx pfn into vaddr: 0x%llx with size of 0x%llx\n", insert_pfn, vaddr, mem_blk_size);
+		if (!pfn_valid(insert_pfn))
+			break;
+
+		ret = vmf_insert_pfn(vma, vaddr, insert_pfn);
+		DBG("vmf_insert_pfn returns: 0x%x\n", ret);
+
+		/* Go to the next page of the memory block */
+		vaddr += PAGE_SIZE;
+		insert_pfn++;
+	}
+}
+
+void pf_mmap_close(struct vm_area_struct *vma)
+{
+	DBG("unmap\t-> vma->vm_start: 0x%lx\n", vma->vm_start);
+	DBG("unmap\t-> size: %lu\n", vma->vm_end - vma->vm_start);
+	share_mmap_rem(vma);
+}
+
+vm_fault_t pf_mmap_fault(struct vm_fault *vmf)
+{
+	uint64_t corrected_pfn;
+	pfn_t corr_pfn_struct;
+	struct page *page;
+	int ret = 0;
+
+	DBG("----- Page fault: %lld -----\n", sum_pgfaults++);
+
+	/* Find the corrected pfn */
+	corrected_pfn = share_mmap_exist_vma_return_correct_pfn(vmf->address);
+	corr_pfn_struct.val = corrected_pfn;
+
+	/* Some debug prints */
+	DBG("vma->vm_start: 0x%lx\n", vmf->vma->vm_start);
+	DBG("vma->vm_pgoff: 0x%lx\n", vmf->vma->vm_pgoff);
+	DBG("vmf->address: 0x%lx\n", vmf->address);
+	DBG("corrected_pfn: 0x%llx\n", corrected_pfn);
+	DBG("pfn_valid(corrected_pfn): 0x%x\n", pfn_valid(corrected_pfn));
+
+	BUG_ON(!pfn_valid(corrected_pfn));
+
+	/* After finding the page, correct the vmf->page */
+	page = pfn_to_page(corrected_pfn);
+	BUG_ON(!virt_addr_valid(page_address(page)));
+
+	/* Insert the correct page */
+	ret = vmf_insert_pfn(vmf->vma, vmf->address, corrected_pfn);
+	DBG("vmf_insert_pfn -> ret: %d\n", ret);
+
+	return ret;
+}
+
+const struct vm_operations_struct pf_mmap_ops = {
+	.close = pf_mmap_close,
+	.fault = pf_mmap_fault,
+};
+
+int pf_mmap_vm_page(struct file *filp, struct vm_area_struct *vma)
+{
+	uint64_t size = (unsigned long)(vma->vm_end - vma->vm_start);
+	uint64_t pfn = ((cur_ram_idx++) * 0x40000);
+
+	vma->vm_flags |= VM_PFNMAP;
+
+	add_share_mmap(filp, pfn, vma->vm_start, size);
+	return 0;
+}
+
+int mmap_mix(struct file *filp, struct vm_area_struct *vma)
+{
+	int ret = 0;
+	unsigned long size = (unsigned long)(vma->vm_end - vma->vm_start);
+
+	ret = remap_pfn_range(vma, vma->vm_start, vq_pfn, size, vma->vm_page_prot);
+	if (ret != 0) {
+		DBG("Mmap error\n");
+		print_mmaps();
+		goto out;
+	}
+
+	add_share_mmap(filp, vq_pfn, vma->vm_start, size);
+
+out:
+	return ret;
+}
+
+int mmap_communication_shared_space(struct file *filp, struct vm_area_struct *vma)
+{
+	unsigned long size = (unsigned long)(vma->vm_end - vma->vm_start);
+	struct mmap_info *com_mmap_virt = ((struct mmap_info *)(filp->private_data))->data;
+	uint64_t com_mmap_pfn = ((uint64_t)virt_to_phys(com_mmap_virt)) >> PAGE_SHIFT;
+	int ret;
+
+	vma->vm_flags |= VM_RESERVED;
+	ret = remap_pfn_range(vma, vma->vm_start, com_mmap_pfn, size, vma->vm_page_prot);
+
+	if (ret != 0)
+		DBG("Error to mmap communication shared space\n");
+
+	return ret;
+}
+
+int op_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	int ret = 0;
+	uint64_t size = (unsigned long)(vma->vm_end - vma->vm_start);
+
+	DBG("op_mmap -> vma->vm_pgoff: 0x%lx", vma->vm_pgoff);
+
+	if (share_communication_struct) {
+		DBG("MMAP communication struct\n");
+		ret = mmap_communication_shared_space(filp, vma);
+		share_communication_struct = false;
+		goto out;
+	}
+
+	if (size > PAGE_SIZE * 100) {
+		vma->vm_ops = &pf_mmap_ops;
+		ret = pf_mmap_vm_page(filp, vma);
+		goto out;
+	}
+
+	vma->vm_ops = &pf_mmap_ops;
+	ret = mmap_mix(filp, vma);
+
+out:
+	return ret;
+
+}
+
+static uint64_t read_adapter(uint64_t fn_id, uint64_t size)
+{
+	uint64_t result;
+
+	mutex_lock(&read_write_lock);
+
+	/*
+	 * By enabling the following line all
+	 * read messages will be printed:
+	 *
+	 * print_neg_flag(fn_id, 1);
+	 */
+	print_neg_flag(fn_id, 1);
+
+	((virtio_neg_t *)(info->data))->notification = fn_id;
+	((virtio_neg_t *)(info->data))->data = 0;
+	((virtio_neg_t *)(info->data))->size = size;
+	((virtio_neg_t *)(info->data))->read = true;
+
+	atomic_set(&((virtio_neg_t *)(info->data))->done, 0);
+
+	eventfd_signal(efd_ctx, 1);
+
+	/*
+	 * There is a chance virtio-loopback adapter to call "wake_up"
+	 * before the current thread sleep. This is the reason that
+	 * "wait_event_timeout" is used instead of "wait_event". In this
+	 * way, virtio-loopback driver will wake up even if has missed the
+	 * "wake_up" kick, check the updated "done" value and return.
+	 */
+
+	while (valid_eventfd && atomic_read(&((virtio_neg_t *)(info->data))->done) != 1)
+		wait_event_timeout(wq, atomic_read(&((virtio_neg_t *)(info->data))->done) == 1, 1 * HZ);
+
+	result = ((virtio_neg_t *)(info->data))->data;
+
+	mutex_unlock(&read_write_lock);
+
+	return result;
+}
+
+static void write_adapter(uint64_t data, uint64_t fn_id, uint64_t size)
+{
+
+	mutex_lock(&read_write_lock);
+
+	/*
+	 * By enabling the following line all
+	 * write messages will be printed:
+	 *
+	 * print_neg_flag(fn_id, 1);
+	 */
+	print_neg_flag(fn_id, 0);
+
+	((virtio_neg_t *)(info->data))->notification = fn_id;
+	((virtio_neg_t *)(info->data))->data = data;
+	((virtio_neg_t *)(info->data))->size = size;
+	((virtio_neg_t *)(info->data))->read = false;
+
+	atomic_set(&((virtio_neg_t *)(info->data))->done, 0);
+
+	eventfd_signal(efd_ctx, 1);
+
+	/*
+	 * There is a chance virtio-loopback adapter to call "wake_up"
+	 * before the current thread sleep. This is the reason that
+	 * "wait_event_timeout" is used instead of "wait_event". In this
+	 * way, virtio-loopback driver will wake up even if has missed the
+	 * "wake_up" kick, check the updated "done" value and return.
+	 */
+	while (valid_eventfd && atomic_read(&((virtio_neg_t *)(info->data))->done) != 1)
+		wait_event_timeout(wq, atomic_read(&((virtio_neg_t *)(info->data))->done) == 1, 1 * HZ);
+
+	mutex_unlock(&read_write_lock);
+}
+
+/* Defined for future work */
+static ssize_t loopback_write(struct file *file,
+				   const char __user *user_buffer,
+				   size_t size,
+				   loff_t *offset)
+{
+	ssize_t len = sizeof(int);
+
+	DBG("loopback write function is called\n");
+	if (len <= 0)
+		return 0;
+
+	return len;
+}
+
+/* Defined for future work */
+static ssize_t loopback_read(struct file *file,
+				 char __user *user_buffer,
+				 size_t size, loff_t *offset)
+{
+	DBG("loopback read function is called\n");
+	return 0;
+}
+
+loff_t loopback_seek(struct file *file, loff_t offset, int whence)
+{
+	loff_t new_pos;
+
+	DBG("loopback seek function!\n");
+	switch (whence) {
+	case SEEK_SET:
+		DBG("SEEK_SET\n");
+		new_pos = offset;
+		break;
+	case SEEK_CUR:
+		DBG("SEEK_CUR\n");
+		new_pos = file->f_pos + offset;
+		break;
+	case SEEK_END:
+		DBG("SEEK_END\n");
+		new_pos = file->f_inode->i_size;
+		break;
+	default:
+		return -EINVAL; // Invalid whence value
+	}
+
+	if (new_pos < 0 || new_pos > file->f_inode->i_size)
+		return -EINVAL;
+
+	return new_pos;
+}
+
+int start_loopback(void *data)
+{
+	(void)data;
+	/* Register mmio_trasmport */
+	(void)platform_driver_register(&virtio_mmio_driver);
+	(void)platform_device_register(&virtio_loopback_device);
+	return 0;
+}
+
+static long loopback_ioctl(struct file *file,
+				unsigned int cmd, unsigned long arg)
+{
+	efd_data_t efd_data;
+	int irq;
+	uint32_t queue_sel;
+
+	switch (cmd) {
+	case EFD_INIT:
+		if (copy_from_user(&efd_data, (efd_data_t *) arg,
+						   sizeof(efd_data_t)))
+			return -EFAULT;
+
+		userspace_task = pid_task(find_vpid(efd_data.pid), PIDTYPE_PID);
+
+		rcu_read_lock();
+		efd_file = fcheck_files(userspace_task->files, efd_data.efd[0]);
+		rcu_read_unlock();
+
+		efd_ctx = eventfd_ctx_fileget(efd_file);
+		if (!efd_ctx)
+			return -1;
+
+		break;
+	case WAKEUP:
+		atomic_set(&((virtio_neg_t *)(info->data))->done, 1);
+		wake_up(&wq);
+		break;
+	case START_LOOPBACK:
+		if (copy_from_user(&device_info, (virtio_device_info_struct_t *) arg,
+						   sizeof(virtio_device_info_struct_t)))
+			return -EFAULT;
+		start_loopback_thread = kthread_run(start_loopback, NULL, "start_loopback");
+		break;
+	case IRQ:
+		if (copy_from_user(&irq, (int *) arg, sizeof(int)))
+			return -EFAULT;
+		DBG("\nIRQ\n");
+		/*
+		 * Both ot the interrupt ways work but b) has better performance
+		 * a) vm_interrupt(NULL);
+		 * b) queue_work(interrupt_workqueue, &async_interrupt);
+		 */
+		queue_work(interrupt_workqueue, &async_interrupt);
+		break;
+	case SHARE_VQS:
+		if (copy_from_user(&queue_sel, (uint32_t *) arg, sizeof(uint32_t)))
+			return -EFAULT;
+		DBG("\n\nSHARE_VQS: %u\n\n", queue_sel);
+		vq_pfn = vq_pfns[queue_sel];
+		DBG("Selected pfn is: 0x%llx", vq_pfn);
+		break;
+	case SHARE_BUF:
+		if (copy_from_user(&vq_pfn, (uint64_t *) arg, sizeof(uint64_t)))
+			return -EFAULT;
+		DBG("\n\nSHARE_BUF -> vq_pfn: 0x%llx\n", vq_pfn);
+		vq_pfn = vq_pfn >> PAGE_SHIFT;
+		break;
+	case SHARE_COM_STRUCT:
+		share_communication_struct = true;
+		break;
+	default:
+		DBG("loopback ioctl: default, %u\n", cmd);
+		return -ENOTTY;
+	}
+
+	return 0;
+}
+
+/*
+ * The current implementation of the driver supports
+ * exclusive access to one user-space thread. Multi-device
+ * support will be added in future implementation.
+ */
+static int loopback_open(struct inode *inode, struct file *file)
+{
+		uint32_t val_1gb = 1024 * 1024 * 1024; // 1GB
+
+		int ret;
+	/* Update the global variable, the driver is in use */
+	if (test_and_set_bit(IN_USE_BIT, &loopback_flags)) {
+		DBG("Driver is busy\n");
+		return -EBUSY;
+	}
+
+		/* Set the i_size for the stat SYS_CALL*/
+		file->f_inode->i_size = 10 * val_1gb;
+
+	/* Init mmap funcitonality */
+	info = kmalloc(sizeof(struct mmap_info), GFP_KERNEL);
+	info->data = (void *)get_zeroed_page(GFP_KERNEL);
+
+	memcpy(info->data, &device_neg, sizeof(virtio_neg_t));
+
+	/* assign this info struct to the file */
+	file->private_data = info;
+
+	/* Init wq */
+	init_waitqueue_head(&wq);
+	init_waitqueue_head(&wq_notify);
+
+	/* Create a workqueue for our char device */
+	notify_workqueue = create_singlethread_workqueue("notify_workqueue");
+	interrupt_workqueue = create_singlethread_workqueue("interrupt_workqueue");
+
+	/* Init mutex */
+	mutex_init(&read_write_lock);
+	mutex_init(&notify_lock);
+	mutex_init(&notify_q_lock);
+	mutex_init(&interrupt_lock);
+
+	/* Allocate memory for the FIFO using kfifo_alloc */
+	ret = kfifo_alloc(&notify_queue, KFIFO_SIZE, GFP_KERNEL);
+	if (ret) {
+		printk(KERN_ERR "Failed to allocate memory for kfifo\n");
+		return ret;
+	}
+
+	/* Init global variables */
+	mmap_index = 0;
+	page_fault_index = 0;
+	sum_pgfaults = 0;
+	share_communication_struct = false;
+	vq_index = 0;
+	notify_flag = 0;
+	cur_ram_idx = 0;
+	interrupt_cnt = 0;
+	notify_sent = 0;
+	notify_received = 0;
+
+	return 0;
+}
+
+static int loopback_release(struct inode *inode, struct file *file)
+{
+	/* TODO:
+	 * struct mmap_info *info = file->private_data;
+	 * free_page((unsigned long)info->data);
+	 * kfree(info);
+	 * file->private_data = NULL;
+	 */
+	DBG("Release the device\n");
+
+	/* Update the global variable, the driver is not in use */
+	smp_mb__before_atomic();
+	clear_bit(IN_USE_BIT, &loopback_flags);
+	DBG("clear_bit!\n");
+
+	/*
+	 * This make the read/write do not wait
+	 * for the virtio-loopback-adapter if
+	 * the last has closed the fd
+	 */
+	valid_eventfd = false;
+
+	return 0;
+}
+
+static const struct file_operations fops = {
+	.owner		= THIS_MODULE,
+	.read		= loopback_read,
+	.write		= loopback_write,
+	.open		= loopback_open,
+	.unlocked_ioctl = loopback_ioctl,
+	.mmap		= op_mmap,
+	.llseek = loopback_seek,
+	.release	= loopback_release
+};
+
+static int __init loopback_init(void)
+{
+	int err, i;
+	dev_t dev;
+
+	err = alloc_chrdev_region(&dev, 0, MAX_DEV, "loopback");
+	dev_major = MAJOR(dev);
+	loopback_class = class_create(THIS_MODULE, "loopback");
+
+	for (i = 0; i < MAX_DEV; i++) {
+		cdev_init(&loopback_data[i].cdev, &fops);
+		loopback_data[i].cdev.owner = THIS_MODULE;
+		cdev_add(&loopback_data[i].cdev, MKDEV(dev_major, i), 1);
+		device_create(loopback_class, NULL, MKDEV(dev_major, i), NULL, "loopback");
+	}
+
+	return 0;
+}
+
+void __exit loopback_exit(void)
+{
+	int i;
+
+	DBG("Exit driver!\n");
+
+	/* Unegister loopback device */
+	platform_device_del(&virtio_loopback_device);
+
+	DBG("platform_device_del!\n");
+	/* Unegister mmio_trasmport */
+	platform_driver_unregister(&virtio_mmio_driver);
+	DBG("platform_driver_unregister!\n");
+
+	for (i = 0; i < MAX_DEV; i++) {
+		device_destroy(loopback_class, MKDEV(dev_major, i));
+		cdev_del(&loopback_data[i].cdev);
+	}
+	DBG("device_destroy!\n");
+
+	class_destroy(loopback_class);
+	DBG("class_destroy!\n");
+}
+
+module_init(loopback_init);
+module_exit(loopback_exit);
diff --git a/loopback_driver.h b/loopback_driver.h
new file mode 100644
index 0000000..0a27382
--- /dev/null
+++ b/loopback_driver.h
@@ -0,0 +1,281 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Based on virtio_mmio.c
+ *   Copyright 2011-2014, ARM Ltd.
+ *
+ * Copyright 2022-2023 Virtual Open Systems SAS.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+#ifndef __LOOPBACK_H__
+#define __LOOPBACK_H__
+
+#define DRIVER	"LOOPBACK"
+
+/* max Minor devices */
+#define MAX_DEV	1
+
+/* Define mmap elements limit */
+#define MMAP_LIMIT	200
+
+#ifdef DEBUG
+#define DBG(...) pr_crit(__VA_ARGS__)
+#else
+#define DBG(...)
+#endif /* DEBUG */
+
+/*
+ * The alignment to use between consumer and producer parts of vring.
+ * Currently hardcoded to the page size.
+ */
+#define VIRTIO_MMIO_VRING_ALIGN		 PAGE_SIZE
+
+#define to_virtio_mmio_device(_plat_dev) \
+	container_of(_plat_dev, struct virtio_mmio_device, vdev)
+
+typedef struct virtio_device_info_struct {
+	unsigned long magic;
+	unsigned long version;
+	unsigned long device_id;
+	unsigned long vendor;
+} virtio_device_info_struct_t;
+
+typedef struct virtio_neg {
+	uint64_t notification;
+	uint64_t data;
+	uint64_t size;
+	bool read;
+	atomic_t done;
+} virtio_neg_t;
+
+struct virtio_mmio_device {
+	struct virtio_device vdev;
+	struct platform_device *pdev;
+
+	void __iomem *base;
+	unsigned long version;
+
+	/* A list of queues so we can dispatch IRQs */
+	spinlock_t lock;
+	struct list_head virtqueues;
+};
+
+struct virtio_mmio_vq_info {
+	/* the actual virtqueue */
+	struct virtqueue *vq;
+
+	/* the list node for the virtqueues list */
+	struct list_head node;
+};
+
+
+/*
+ * Print the pdev:
+ *
+ *static void print_virtio_pdev(struct platform_device *pdev)
+ *{
+ *	int i;
+ *
+ *	pr_info("Print the pdev:\n");
+ *	pr_info("\t.name = %s\n", pdev->name);
+ *	pr_info("\t.id = %d\n", pdev->id);
+ *	pr_info("\t.num_resources = %d\n", pdev->num_resources);
+ *
+ *	for (i=0; i < pdev->num_resources; i++) {
+ *		pr_info("\t.num_resource = %d\n", i);
+ *		pr_info("\t\t.start = 0x%llx\n", pdev->resource[i].start);
+ *		pr_info("\t\t.end = 0x%llx\n", pdev->resource[i].end);
+ *		pr_info("\t\t.flags = 0x%lx\n", pdev->resource[i].flags);
+ *	}
+ *}
+ *
+ *Result:
+ *
+ *	.name = a003e00.virtio_mmio
+ *	.id = -1
+ *	.num_resources = 2
+ *	.num_resource = 0
+ *		.start = 0xa003e00
+ *		.end = 0xa003fff
+ *		.flags = 0x200
+ *	.num_resource = 1
+ *		.start = 0x2c
+ *		.end = 0x2c
+ *		.flags = 0x401
+ */
+
+/* mmap finctionality */
+#ifndef VM_RESERVED
+#define VM_RESERVED (VM_DONTEXPAND | VM_DONTDUMP)
+#endif
+
+struct mmap_info {
+	void *data;
+	int reference;
+};
+
+void print_neg_flag(uint64_t neg_flag, bool read)
+{
+	if (read)
+		DBG("Read:\n");
+	else
+		DBG("Write:\n");
+
+	switch (neg_flag) {
+	case VIRTIO_MMIO_MAGIC_VALUE:		//0x000
+		DBG("\tVIRTIO_MMIO_MAGIC_VALUE\n");
+		break;
+	case VIRTIO_MMIO_VERSION:		//0x004
+		DBG("\tVIRTIO_MMIO_VERSION\n");
+		break;
+	case VIRTIO_MMIO_DEVICE_ID:		//0x008
+		DBG("\tVIRTIO_MMIO_DEVICE_ID\n");
+		break;
+	case VIRTIO_MMIO_VENDOR_ID:		//0x00c
+		DBG("\tVIRTIO_MMIO_VENDOR_ID\n");
+		break;
+	case VIRTIO_MMIO_DEVICE_FEATURES:	//0x010
+		DBG("\tVIRTIO_MMIO_DEVICE_FEATURES\n");
+		break;
+	case VIRTIO_MMIO_DEVICE_FEATURES_SEL:	//0x014
+		DBG("\tVIRTIO_MMIO_DEVICE_FEATURES_SEL\n");
+		break;
+	case VIRTIO_MMIO_DRIVER_FEATURES:	//0x020
+		DBG("\tVIRTIO_MMIO_DRIVER_FEATURES\n");
+		break;
+	case VIRTIO_MMIO_DRIVER_FEATURES_SEL:	//0x024
+		DBG("\tVIRTIO_MMIO_DRIVER_FEATURES_SEL\n");
+		break;
+	case VIRTIO_MMIO_GUEST_PAGE_SIZE:	//0x028
+		DBG("\tVIRTIO_MMIO_GUEST_PAGE_SIZE\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_SEL:		//0x030
+		DBG("\tVIRTIO_MMIO_QUEUE_SEL\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_NUM_MAX:		//0x034
+		DBG("\tVIRTIO_MMIO_QUEUE_NUM_MAX\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_NUM:		//0x038
+		DBG("\tVIRTIO_MMIO_QUEUE_NUM\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_ALIGN:		//0x03c
+		DBG("\tVIRTIO_MMIO_QUEUE_ALIGN\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_PFN:		//0x040
+		DBG("\tVIRTIO_MMIO_QUEUE_PFN\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_READY:		//0x044
+		DBG("\tVIRTIO_MMIO_QUEUE_READY\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_NOTIFY:		//0x050
+		DBG("\tVIRTIO_MMIO_QUEUE_NOTIFY\n");
+		break;
+	case VIRTIO_MMIO_INTERRUPT_STATUS:	//0x060
+		DBG("\tVIRTIO_MMIO_INTERRUPT_STATUS\n");
+		break;
+	case VIRTIO_MMIO_INTERRUPT_ACK:		//0x064
+		DBG("\tVIRTIO_MMIO_INTERRUPT_ACK\n");
+		break;
+	case VIRTIO_MMIO_STATUS:		//0x070
+		DBG("\tVIRTIO_MMIO_STATUS\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_DESC_LOW:	//0x080
+		DBG("\tVIRTIO_MMIO_QUEUE_DESC_LOW\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_DESC_HIGH:	//0x084
+		DBG("\tVIRTIO_MMIO_QUEUE_DESC_HIGH\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_AVAIL_LOW:	//0x090
+		DBG("\tVIRTIO_MMIO_QUEUE_AVAIL_LOW\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_AVAIL_HIGH:	//0x094
+		DBG("\tVIRTIO_MMIO_QUEUE_AVAIL_HIGH\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_USED_LOW:	//0x0a0
+		DBG("\tVIRTIO_MMIO_QUEUE_USED_LOW\n");
+		break;
+	case VIRTIO_MMIO_QUEUE_USED_HIGH:	//0x0a4
+		DBG("\tVIRTIO_MMIO_QUEUE_USED_HIGH\n");
+		break;
+	case VIRTIO_MMIO_SHM_SEL:		//0x0ac
+		DBG("\tVIRTIO_MMIO_SHM_SEL\n");
+		break;
+	case VIRTIO_MMIO_SHM_LEN_LOW:		//0x0b0
+		DBG("\tVIRTIO_MMIO_SHM_LEN_LOW\n");
+		break;
+	case VIRTIO_MMIO_SHM_LEN_HIGH:		//0x0b4
+		DBG("\tVIRTIO_MMIO_SHM_LEN_HIGH\n");
+		break;
+	case VIRTIO_MMIO_SHM_BASE_LOW:		//0x0b8
+		DBG("\tVIRTIO_MMIO_SHM_BASE_LOW\n");
+		break;
+	case VIRTIO_MMIO_SHM_BASE_HIGH:		//0x0bc
+		DBG("\tVIRTIO_MMIO_SHM_BASE_HIGH\n");
+		break;
+	case VIRTIO_MMIO_CONFIG_GENERATION:	//0x0fc
+		DBG("\tVIRTIO_MMIO_CONFIG_GENERATION\n");
+		break;
+	default:
+		if (neg_flag >= VIRTIO_MMIO_CONFIG)
+			DBG("\tVIRTIO_MMIO_CONFIG\n");
+		else
+			DBG("\tNegotiation flag Unknown: %lld\n", neg_flag);
+		return;
+	}
+}
+
+void print_data(const void *buf, size_t size)
+{
+	int offset = 10;
+	int i, j;
+
+	DBG("Print data from linux virtio-rng side:\n");
+
+	printk(KERN_CRIT "");
+
+	for (i = 0; i < size; i += offset) {
+		printk(KERN_CONT "\t\t");
+
+		for (j = i; (j < i + offset) && (j < size); j++)
+			printk(KERN_CONT "%d, ", *((uint8_t *)(buf + j)));
+
+		printk(KERN_CRIT "");
+	}
+}
+
+typedef struct efd_data {
+	int efd[2];
+	int pid;
+} efd_data_t;
+
+/*
+ * ref: https://elixir.bootlin.com/linux/latest/source/arch/x86/mm/init_64.c#L1419
+ */
+
+/* IOCTL defines */
+#define EFD_INIT _IOC(_IOC_WRITE, 'k', 1, sizeof(efd_data))
+#define WAKEUP _IOC(_IOC_WRITE, 'k', 2, 0)
+#define START_LOOPBACK _IOC(_IOC_WRITE, 'k', 3, sizeof(virtio_device_info_struct_t))
+#define IRQ _IOC(_IOC_WRITE, 'k', 4, sizeof(int))
+#define SHARE_VQS _IOC(_IOC_WRITE, 'k', 5, sizeof(uint32_t))
+#define SHARE_BUF _IOC(_IOC_WRITE, 'k', 6, sizeof(uint64_t))
+#define SHARE_COM_STRUCT _IOC(_IOC_WRITE, 'k', 7, 0)
+
+/* device data holder, this structure may be extended to hold additional data */
+struct loopback_device_data {
+	struct cdev cdev;
+};
+
+#endif /* __VIRTUALNET_H__ */