ksm: move pages_sharing updates

[linux-2.6/kvm.git] / drivers / virtio / virtio_pci.c

/*
 * Virtio PCI driver
 *
 * This module allows virtio devices to be used over a virtual PCI device.
 * This can be used with QEMU based VMMs like KVM or Xen.
 *
 * Copyright IBM Corp. 2007
 *
 * Authors:
 *  Anthony Liguori  <aliguori@us.ibm.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or later.
 * See the COPYING file in the top-level directory.
 *
 */

#include <linux/module.h>
#include <linux/list.h>
#include <linux/pci.h>
#include <linux/interrupt.h>
#include <linux/virtio.h>
#include <linux/virtio_config.h>
#include <linux/virtio_ring.h>
#include <linux/virtio_pci.h>
#include <linux/highmem.h>
#include <linux/spinlock.h>

MODULE_AUTHOR("Anthony Liguori <aliguori@us.ibm.com>");
MODULE_DESCRIPTION("virtio-pci");
MODULE_LICENSE("GPL");
MODULE_VERSION("1");

/* Our device structure */
struct virtio_pci_device
{
        struct virtio_device vdev;
        struct pci_dev *pci_dev;

        /* the IO mapping for the PCI config space */
        void __iomem *ioaddr;

        /* a list of queues so we can dispatch IRQs */
        spinlock_t lock;
        struct list_head virtqueues;

        /* MSI-X support */
        int msix_enabled;
        int intx_enabled;
        struct msix_entry *msix_entries;
        /* Name strings for interrupts. This size should be enough,
         * and I'm too lazy to allocate each name separately. */
        char (*msix_names)[256];
        /* Number of available vectors */
        unsigned msix_vectors;
        /* Vectors allocated, excluding per-vq vectors if any */
        unsigned msix_used_vectors;
        /* Whether we have vector per vq */
        bool per_vq_vectors;
};

/* Constants for MSI-X */
/* Use first vector for configuration changes, second and the rest for
 * virtqueues Thus, we need at least 2 vectors for MSI. */
enum {
        VP_MSIX_CONFIG_VECTOR = 0,
        VP_MSIX_VQ_VECTOR = 1,
};

struct virtio_pci_vq_info
{
        /* the actual virtqueue */
        struct virtqueue *vq;

        /* the number of entries in the queue */
        int num;

        /* the index of the queue */
        int queue_index;

        /* the virtual address of the ring queue */
        void *queue;

        /* the list node for the virtqueues list */
        struct list_head node;

        /* MSI-X vector (or none) */
        unsigned vector;
};

/* Qumranet donated their vendor ID for devices 0x1000 thru 0x10FF. */
static struct pci_device_id virtio_pci_id_table[] = {
        { 0x1af4, PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 },
        { 0 },
};

MODULE_DEVICE_TABLE(pci, virtio_pci_id_table);

/* A PCI device has it's own struct device and so does a virtio device so
 * we create a place for the virtio devices to show up in sysfs.  I think it
 * would make more sense for virtio to not insist on having it's own device. */
static struct device *virtio_pci_root;

/* Convert a generic virtio device to our structure */
static struct virtio_pci_device *to_vp_device(struct virtio_device *vdev)
{
        return container_of(vdev, struct virtio_pci_device, vdev);
}

/* virtio config->get_features() implementation */
static u32 vp_get_features(struct virtio_device *vdev)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);

        /* When someone needs more than 32 feature bits, we'll need to
         * steal a bit to indicate that the rest are somewhere else. */
        return ioread32(vp_dev->ioaddr + VIRTIO_PCI_HOST_FEATURES);
}

/* virtio config->finalize_features() implementation */
static void vp_finalize_features(struct virtio_device *vdev)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);

        /* Give virtio_ring a chance to accept features. */
        vring_transport_features(vdev);

        /* We only support 32 feature bits. */
        BUILD_BUG_ON(ARRAY_SIZE(vdev->features) != 1);
        iowrite32(vdev->features[0], vp_dev->ioaddr+VIRTIO_PCI_GUEST_FEATURES);
}

/* virtio config->get() implementation */
static void vp_get(struct virtio_device *vdev, unsigned offset,
                   void *buf, unsigned len)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        void __iomem *ioaddr = vp_dev->ioaddr +
                                VIRTIO_PCI_CONFIG(vp_dev) + offset;
        u8 *ptr = buf;
        int i;

        for (i = 0; i < len; i++)
                ptr[i] = ioread8(ioaddr + i);
}

/* the config->set() implementation.  it's symmetric to the config->get()
 * implementation */
static void vp_set(struct virtio_device *vdev, unsigned offset,
                   const void *buf, unsigned len)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        void __iomem *ioaddr = vp_dev->ioaddr +
                                VIRTIO_PCI_CONFIG(vp_dev) + offset;
        const u8 *ptr = buf;
        int i;

        for (i = 0; i < len; i++)
                iowrite8(ptr[i], ioaddr + i);
}

/* config->{get,set}_status() implementations */
static u8 vp_get_status(struct virtio_device *vdev)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        return ioread8(vp_dev->ioaddr + VIRTIO_PCI_STATUS);
}

static void vp_set_status(struct virtio_device *vdev, u8 status)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        /* We should never be setting status to 0. */
        BUG_ON(status == 0);
        iowrite8(status, vp_dev->ioaddr + VIRTIO_PCI_STATUS);
}

static void vp_reset(struct virtio_device *vdev)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        /* 0 status means a reset. */
        iowrite8(0, vp_dev->ioaddr + VIRTIO_PCI_STATUS);
}

/* the notify function used when creating a virt queue */
static void vp_notify(struct virtqueue *vq)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vq->vdev);
        struct virtio_pci_vq_info *info = vq->priv;

        /* we write the queue's selector into the notification register to
         * signal the other end */
        iowrite16(info->queue_index, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_NOTIFY);
}

/* Handle a configuration change: Tell driver if it wants to know. */
static irqreturn_t vp_config_changed(int irq, void *opaque)
{
        struct virtio_pci_device *vp_dev = opaque;
        struct virtio_driver *drv;
        drv = container_of(vp_dev->vdev.dev.driver,
                           struct virtio_driver, driver);

        if (drv && drv->config_changed)
                drv->config_changed(&vp_dev->vdev);
        return IRQ_HANDLED;
}

/* Notify all virtqueues on an interrupt. */
static irqreturn_t vp_vring_interrupt(int irq, void *opaque)
{
        struct virtio_pci_device *vp_dev = opaque;
        struct virtio_pci_vq_info *info;
        irqreturn_t ret = IRQ_NONE;
        unsigned long flags;

        spin_lock_irqsave(&vp_dev->lock, flags);
        list_for_each_entry(info, &vp_dev->virtqueues, node) {
                if (vring_interrupt(irq, info->vq) == IRQ_HANDLED)
                        ret = IRQ_HANDLED;
        }
        spin_unlock_irqrestore(&vp_dev->lock, flags);

        return ret;
}

/* A small wrapper to also acknowledge the interrupt when it's handled.
 * I really need an EIO hook for the vring so I can ack the interrupt once we
 * know that we'll be handling the IRQ but before we invoke the callback since
 * the callback may notify the host which results in the host attempting to
 * raise an interrupt that we would then mask once we acknowledged the
 * interrupt. */
static irqreturn_t vp_interrupt(int irq, void *opaque)
{
        struct virtio_pci_device *vp_dev = opaque;
        u8 isr;

        /* reading the ISR has the effect of also clearing it so it's very
         * important to save off the value. */
        isr = ioread8(vp_dev->ioaddr + VIRTIO_PCI_ISR);

        /* It's definitely not us if the ISR was not high */
        if (!isr)
                return IRQ_NONE;

        /* Configuration change?  Tell driver if it wants to know. */
        if (isr & VIRTIO_PCI_ISR_CONFIG)
                vp_config_changed(irq, opaque);

        return vp_vring_interrupt(irq, opaque);
}

static void vp_free_vectors(struct virtio_device *vdev)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        int i;

        if (vp_dev->intx_enabled) {
                free_irq(vp_dev->pci_dev->irq, vp_dev);
                vp_dev->intx_enabled = 0;
        }

        for (i = 0; i < vp_dev->msix_used_vectors; ++i)
                free_irq(vp_dev->msix_entries[i].vector, vp_dev);

        if (vp_dev->msix_enabled) {
                /* Disable the vector used for configuration */
                iowrite16(VIRTIO_MSI_NO_VECTOR,
                          vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
                /* Flush the write out to device */
                ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);

                pci_disable_msix(vp_dev->pci_dev);
                vp_dev->msix_enabled = 0;
                vp_dev->msix_vectors = 0;
        }

        vp_dev->msix_used_vectors = 0;
        kfree(vp_dev->msix_names);
        vp_dev->msix_names = NULL;
        kfree(vp_dev->msix_entries);
        vp_dev->msix_entries = NULL;
}

static int vp_request_vectors(struct virtio_device *vdev, int nvectors,
                              bool per_vq_vectors)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        const char *name = dev_name(&vp_dev->vdev.dev);
        unsigned i, v;
        int err = -ENOMEM;

        if (!nvectors) {
                /* Can't allocate MSI-X vectors, use regular interrupt */
                vp_dev->msix_vectors = 0;
                err = request_irq(vp_dev->pci_dev->irq, vp_interrupt,
                                  IRQF_SHARED, name, vp_dev);
                if (err)
                        return err;
                vp_dev->intx_enabled = 1;
                return 0;
        }

        vp_dev->msix_entries = kmalloc(nvectors * sizeof *vp_dev->msix_entries,
                                       GFP_KERNEL);
        if (!vp_dev->msix_entries)
                goto error;
        vp_dev->msix_names = kmalloc(nvectors * sizeof *vp_dev->msix_names,
                                     GFP_KERNEL);
        if (!vp_dev->msix_names)
                goto error;

        for (i = 0; i < nvectors; ++i)
                vp_dev->msix_entries[i].entry = i;

        err = pci_enable_msix(vp_dev->pci_dev, vp_dev->msix_entries, nvectors);
        if (err > 0)
                err = -ENOSPC;
        if (err)
                goto error;
        vp_dev->msix_vectors = nvectors;
        vp_dev->msix_enabled = 1;

        /* Set the vector used for configuration */
        v = vp_dev->msix_used_vectors;
        snprintf(vp_dev->msix_names[v], sizeof *vp_dev->msix_names,
                 "%s-config", name);
        err = request_irq(vp_dev->msix_entries[v].vector,
                          vp_config_changed, 0, vp_dev->msix_names[v],
                          vp_dev);
        if (err)
                goto error;
        ++vp_dev->msix_used_vectors;

        iowrite16(v, vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
        /* Verify we had enough resources to assign the vector */
        v = ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
        if (v == VIRTIO_MSI_NO_VECTOR) {
                err = -EBUSY;
                goto error;
        }

        if (!per_vq_vectors) {
                /* Shared vector for all VQs */
                v = vp_dev->msix_used_vectors;
                snprintf(vp_dev->msix_names[v], sizeof *vp_dev->msix_names,
                         "%s-virtqueues", name);
                err = request_irq(vp_dev->msix_entries[v].vector,
                                  vp_vring_interrupt, 0, vp_dev->msix_names[v],
                                  vp_dev);
                if (err)
                        goto error;
                ++vp_dev->msix_used_vectors;
        }
        return 0;
error:
        vp_free_vectors(vdev);
        return err;
}

static struct virtqueue *vp_find_vq(struct virtio_device *vdev, unsigned index,
                                    void (*callback)(struct virtqueue *vq),
                                    const char *name,
                                    u16 vector)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        struct virtio_pci_vq_info *info;
        struct virtqueue *vq;
        unsigned long flags, size;
        u16 num;
        int err;

        /* Select the queue we're interested in */
        iowrite16(index, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_SEL);

        /* Check if queue is either not available or already active. */
        num = ioread16(vp_dev->ioaddr + VIRTIO_PCI_QUEUE_NUM);
        if (!num || ioread32(vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN))
                return ERR_PTR(-ENOENT);

        /* allocate and fill out our structure the represents an active
         * queue */
        info = kmalloc(sizeof(struct virtio_pci_vq_info), GFP_KERNEL);
        if (!info)
                return ERR_PTR(-ENOMEM);

        info->queue_index = index;
        info->num = num;
        info->vector = vector;

        size = PAGE_ALIGN(vring_size(num, VIRTIO_PCI_VRING_ALIGN));
        info->queue = alloc_pages_exact(size, GFP_KERNEL|__GFP_ZERO);
        if (info->queue == NULL) {
                err = -ENOMEM;
                goto out_info;
        }

        /* activate the queue */
        iowrite32(virt_to_phys(info->queue) >> VIRTIO_PCI_QUEUE_ADDR_SHIFT,
                  vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);

        /* create the vring */
        vq = vring_new_virtqueue(info->num, VIRTIO_PCI_VRING_ALIGN,
                                 vdev, info->queue, vp_notify, callback, name);
        if (!vq) {
                err = -ENOMEM;
                goto out_activate_queue;
        }

        vq->priv = info;
        info->vq = vq;

         if (vector != VIRTIO_MSI_NO_VECTOR) {
                iowrite16(vector, vp_dev->ioaddr + VIRTIO_MSI_QUEUE_VECTOR);
                vector = ioread16(vp_dev->ioaddr + VIRTIO_MSI_QUEUE_VECTOR);
                if (vector == VIRTIO_MSI_NO_VECTOR) {
                        err = -EBUSY;
                        goto out_assign;
                }
        }

        spin_lock_irqsave(&vp_dev->lock, flags);
        list_add(&info->node, &vp_dev->virtqueues);
        spin_unlock_irqrestore(&vp_dev->lock, flags);

        return vq;

out_assign:
        vring_del_virtqueue(vq);
out_activate_queue:
        iowrite32(0, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);
        free_pages_exact(info->queue, size);
out_info:
        kfree(info);
        return ERR_PTR(err);
}

static void vp_del_vq(struct virtqueue *vq)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vq->vdev);
        struct virtio_pci_vq_info *info = vq->priv;
        unsigned long flags, size;

        spin_lock_irqsave(&vp_dev->lock, flags);
        list_del(&info->node);
        spin_unlock_irqrestore(&vp_dev->lock, flags);

        iowrite16(info->queue_index, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_SEL);

        if (vp_dev->msix_enabled) {
                iowrite16(VIRTIO_MSI_NO_VECTOR,
                          vp_dev->ioaddr + VIRTIO_MSI_QUEUE_VECTOR);
                /* Flush the write out to device */
                ioread8(vp_dev->ioaddr + VIRTIO_PCI_ISR);
        }

        vring_del_virtqueue(vq);

        /* Select and deactivate the queue */
        iowrite32(0, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);

        size = PAGE_ALIGN(vring_size(info->num, VIRTIO_PCI_VRING_ALIGN));
        free_pages_exact(info->queue, size);
        kfree(info);
}

/* the config->del_vqs() implementation */
static void vp_del_vqs(struct virtio_device *vdev)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        struct virtqueue *vq, *n;
        struct virtio_pci_vq_info *info;

        list_for_each_entry_safe(vq, n, &vdev->vqs, list) {
                info = vq->priv;
                if (vp_dev->per_vq_vectors)
                        free_irq(vp_dev->msix_entries[info->vector].vector, vq);
                vp_del_vq(vq);
        }
        vp_dev->per_vq_vectors = false;

        vp_free_vectors(vdev);
}

static int vp_try_to_find_vqs(struct virtio_device *vdev, unsigned nvqs,
                              struct virtqueue *vqs[],
                              vq_callback_t *callbacks[],
                              const char *names[],
                              int nvectors,
                              bool per_vq_vectors)
{
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        u16 vector;
        int i, err, allocated_vectors;

        err = vp_request_vectors(vdev, nvectors, per_vq_vectors);
        if (err)
                goto error_request;

        vp_dev->per_vq_vectors = per_vq_vectors;
        allocated_vectors = vp_dev->msix_used_vectors;
        for (i = 0; i < nvqs; ++i) {
                if (!callbacks[i] || !vp_dev->msix_enabled)
                        vector = VIRTIO_MSI_NO_VECTOR;
                else if (vp_dev->per_vq_vectors)
                        vector = allocated_vectors++;
                else
                        vector = VP_MSIX_VQ_VECTOR;
                vqs[i] = vp_find_vq(vdev, i, callbacks[i], names[i], vector);
                if (IS_ERR(vqs[i])) {
                        err = PTR_ERR(vqs[i]);
                        goto error_find;
                }
                /* allocate per-vq irq if available and necessary */
                if (vp_dev->per_vq_vectors && vector != VIRTIO_MSI_NO_VECTOR) {
                        snprintf(vp_dev->msix_names[vector], sizeof *vp_dev->msix_names,
                                 "%s-%s", dev_name(&vp_dev->vdev.dev), names[i]);
                        err = request_irq(vp_dev->msix_entries[vector].vector,
                                          vring_interrupt, 0,
                                          vp_dev->msix_names[vector], vqs[i]);
                        if (err) {
                                vp_del_vq(vqs[i]);
                                goto error_find;
                        }
                }
        }
        return 0;

error_find:
        vp_del_vqs(vdev);

error_request:
        return err;
}

/* the config->find_vqs() implementation */
static int vp_find_vqs(struct virtio_device *vdev, unsigned nvqs,
                       struct virtqueue *vqs[],
                       vq_callback_t *callbacks[],
                       const char *names[])
{
        int vectors = 0;
        int i, uninitialized_var(err);

        /* How many vectors would we like? */
        for (i = 0; i < nvqs; ++i)
                if (callbacks[i])
                        ++vectors;

        /* We want at most one vector per queue and one for config changes. */
        err = vp_try_to_find_vqs(vdev, nvqs, vqs, callbacks, names,
                                 vectors + 1, true);
        if (!err)
                return 0;
        /* Fallback to separate vectors for config and a shared for queues. */
        err = vp_try_to_find_vqs(vdev, nvqs, vqs, callbacks, names,
                                 2, false);
        if (!err)
                return 0;
        /* Finally fall back to regular interrupts. */
        err = vp_try_to_find_vqs(vdev, nvqs, vqs, callbacks, names,
                                 0, false);
        return err;
}

static struct virtio_config_ops virtio_pci_config_ops = {
        .get            = vp_get,
        .set            = vp_set,
        .get_status     = vp_get_status,
        .set_status     = vp_set_status,
        .reset          = vp_reset,
        .find_vqs       = vp_find_vqs,
        .del_vqs        = vp_del_vqs,
        .get_features   = vp_get_features,
        .finalize_features = vp_finalize_features,
};

static void virtio_pci_release_dev(struct device *_d)
{
        struct virtio_device *dev = container_of(_d, struct virtio_device, dev);
        struct virtio_pci_device *vp_dev = to_vp_device(dev);
        struct pci_dev *pci_dev = vp_dev->pci_dev;

        vp_del_vqs(dev);
        pci_set_drvdata(pci_dev, NULL);
        pci_iounmap(pci_dev, vp_dev->ioaddr);
        pci_release_regions(pci_dev);
        pci_disable_device(pci_dev);
        kfree(vp_dev);
}

/* the PCI probing function */
static int __devinit virtio_pci_probe(struct pci_dev *pci_dev,
                                      const struct pci_device_id *id)
{
        struct virtio_pci_device *vp_dev;
        int err;

        /* We only own devices >= 0x1000 and <= 0x103f: leave the rest. */
        if (pci_dev->device < 0x1000 || pci_dev->device > 0x103f)
                return -ENODEV;

        if (pci_dev->revision != VIRTIO_PCI_ABI_VERSION) {
                printk(KERN_ERR "virtio_pci: expected ABI version %d, got %d\n",
                       VIRTIO_PCI_ABI_VERSION, pci_dev->revision);
                return -ENODEV;
        }

        /* allocate our structure and fill it out */
        vp_dev = kzalloc(sizeof(struct virtio_pci_device), GFP_KERNEL);
        if (vp_dev == NULL)
                return -ENOMEM;

        vp_dev->vdev.dev.parent = virtio_pci_root;
        vp_dev->vdev.dev.release = virtio_pci_release_dev;
        vp_dev->vdev.config = &virtio_pci_config_ops;
        vp_dev->pci_dev = pci_dev;
        INIT_LIST_HEAD(&vp_dev->virtqueues);
        spin_lock_init(&vp_dev->lock);

        /* enable the device */
        err = pci_enable_device(pci_dev);
        if (err)
                goto out;

        err = pci_request_regions(pci_dev, "virtio-pci");
        if (err)
                goto out_enable_device;

        vp_dev->ioaddr = pci_iomap(pci_dev, 0, 0);
        if (vp_dev->ioaddr == NULL)
                goto out_req_regions;

        pci_set_drvdata(pci_dev, vp_dev);

        /* we use the subsystem vendor/device id as the virtio vendor/device
         * id.  this allows us to use the same PCI vendor/device id for all
         * virtio devices and to identify the particular virtio driver by
         * the subsytem ids */
        vp_dev->vdev.id.vendor = pci_dev->subsystem_vendor;
        vp_dev->vdev.id.device = pci_dev->subsystem_device;

        /* finally register the virtio device */
        err = register_virtio_device(&vp_dev->vdev);
        if (err)
                goto out_set_drvdata;

        return 0;

out_set_drvdata:
        pci_set_drvdata(pci_dev, NULL);
        pci_iounmap(pci_dev, vp_dev->ioaddr);
out_req_regions:
        pci_release_regions(pci_dev);
out_enable_device:
        pci_disable_device(pci_dev);
out:
        kfree(vp_dev);
        return err;
}

static void __devexit virtio_pci_remove(struct pci_dev *pci_dev)
{
        struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);

        unregister_virtio_device(&vp_dev->vdev);
}

#ifdef CONFIG_PM
static int virtio_pci_suspend(struct pci_dev *pci_dev, pm_message_t state)
{
        pci_save_state(pci_dev);
        pci_set_power_state(pci_dev, PCI_D3hot);
        return 0;
}

static int virtio_pci_resume(struct pci_dev *pci_dev)
{
        pci_restore_state(pci_dev);
        pci_set_power_state(pci_dev, PCI_D0);
        return 0;
}
#endif

static struct pci_driver virtio_pci_driver = {
        .name           = "virtio-pci",
        .id_table       = virtio_pci_id_table,
        .probe          = virtio_pci_probe,
        .remove         = virtio_pci_remove,
#ifdef CONFIG_PM
        .suspend        = virtio_pci_suspend,
        .resume         = virtio_pci_resume,
#endif
};

static int __init virtio_pci_init(void)
{
        int err;

        virtio_pci_root = root_device_register("virtio-pci");
        if (IS_ERR(virtio_pci_root))
                return PTR_ERR(virtio_pci_root);

        err = pci_register_driver(&virtio_pci_driver);
        if (err)
                root_device_unregister(virtio_pci_root);

        return err;
}

module_init(virtio_pci_init);

static void __exit virtio_pci_exit(void)
{
        pci_unregister_driver(&virtio_pci_driver);
        root_device_unregister(virtio_pci_root);
}

module_exit(virtio_pci_exit);