Re: [PATCHv2 2/2] vhost_net: a kernel-level virtio server

Gregory Haskins
2009-08-12T00:06:02Z

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Michael S. Tsirkin wrote:
> What it is: vhost net is a character device that can be used to reduce
> the number of system calls involved in virtio networking.
> Existing virtio net code is used in the guest without modification.
>
> There's similarity with vringfd, with some differences and reduced scope
> - uses eventfd for signalling
> - structures can be moved around in memory at any time (good for migration)
> - support memory table and not just an offset (needed for kvm)
>
> common virtio related code has been put in a separate file vhost.c and
> can be made into a separate module if/when more backends appear. I used
> Rusty's lguest.c as the source for developing this part : this supplied
> me with witty comments I wouldn't be able to write myself.
>
> What it is not: vhost net is not a bus, and not a generic new system
> call. No assumptions are made on how guest performs hypercalls.
> Userspace hypervisors are supported as well as kvm.
>
> How it works: Basically, we connect virtio frontend (configured by
> userspace) to a backend. The backend could be a network device, or a
> tun-like device. In this version I only support raw socket as a backend,
> which can be bound to e.g. SR IOV, or to macvlan device. Backend is
> also configured by userspace, including vlan/mac etc.
>
> Status:
> This works for me, and I haven't see any crashes.
> I have not run any benchmarks yet, compared to userspace, I expect to
> see improved latency (as I save up to 4 system calls per packet) but not
> bandwidth/CPU (as TSO and interrupt mitigation are not supported).
>
> Features that I plan to look at in the future:
> - TSO
> - interrupt mitigation
> - zero copy

Only a quick review for now. Will look closer later.

(see inline)

>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>
> v2
> ---
> MAINTAINERS | 10 +
> arch/x86/kvm/Kconfig | 1 +
> drivers/Makefile | 1 +
> drivers/vhost/Kconfig | 11 +
> drivers/vhost/Makefile | 2 +
> drivers/vhost/net.c | 411 +++++++++++++++++++++++++++
> drivers/vhost/vhost.c | 663 ++++++++++++++++++++++++++++++++++++++++++++
> drivers/vhost/vhost.h | 108 +++++++
> include/linux/Kbuild | 1 +
> include/linux/miscdevice.h | 1 +
> include/linux/vhost.h | 100 +++++++
> 11 files changed, 1309 insertions(+), 0 deletions(-)
> create mode 100644 drivers/vhost/Kconfig
> create mode 100644 drivers/vhost/Makefile
> create mode 100644 drivers/vhost/net.c
> create mode 100644 drivers/vhost/vhost.c
> create mode 100644 drivers/vhost/vhost.h
> create mode 100644 include/linux/vhost.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index ebc2691..eb0c1da 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -6312,6 +6312,16 @@ S: Maintained
> F: Documentation/filesystems/vfat.txt
> F: fs/fat/
>
> +VIRTIO HOST (VHOST)
> +P: Michael S. Tsirkin
> +M: mst@redhat.com
> +L: kvm@vger.kernel.org
> +L: virtualization@lists.osdl.org
> +L: netdev@vger.kernel.org
> +S: Maintained
> +F: drivers/vhost/
> +F: include/linux/vhost.h
> +
> VIA RHINE NETWORK DRIVER
> P: Roger Luethi
> M: rl@hellgate.ch
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index b84e571..94f44d9 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -64,6 +64,7 @@ config KVM_AMD
>
> # OK, it's a little counter-intuitive to do this, but it puts it neatly under
> # the virtualization menu.
> +source drivers/vhost/Kconfig
> source drivers/lguest/Kconfig
> source drivers/virtio/Kconfig
>
> diff --git a/drivers/Makefile b/drivers/Makefile
> index bc4205d..1551ae1 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -105,6 +105,7 @@ obj-$(CONFIG_HID) += hid/
> obj-$(CONFIG_PPC_PS3) += ps3/
> obj-$(CONFIG_OF) += of/
> obj-$(CONFIG_SSB) += ssb/
> +obj-$(CONFIG_VHOST_NET) += vhost/
> obj-$(CONFIG_VIRTIO) += virtio/
> obj-$(CONFIG_VLYNQ) += vlynq/
> obj-$(CONFIG_STAGING) += staging/
> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> new file mode 100644
> index 0000000..d955406
> --- /dev/null
> +++ b/drivers/vhost/Kconfig
> @@ -0,0 +1,11 @@
> +config VHOST_NET
> + tristate "Host kernel accelerator for virtio net"
> + depends on NET && EVENTFD
> + ---help---
> + This kernel module can be loaded in host kernel to accelerate
> + guest networking with virtio_net. Not to be confused with virtio_net
> + module itself which needs to be loaded in guest kernel.
> +
> + To compile this driver as a module, choose M here: the module will
> + be called vhost_net.
> +
> diff --git a/drivers/vhost/Makefile b/drivers/vhost/Makefile
> new file mode 100644
> index 0000000..72dd020
> --- /dev/null
> +++ b/drivers/vhost/Makefile
> @@ -0,0 +1,2 @@
> +obj-$(CONFIG_VHOST_NET) += vhost_net.o
> +vhost_net-y := vhost.o net.o
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> new file mode 100644
> index 0000000..a04ffd0
> --- /dev/null
> +++ b/drivers/vhost/net.c
> @@ -0,0 +1,411 @@
> +/* Copyright (C) 2009 Red Hat, Inc.
> + * Author: Michael S. Tsirkin <mst@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.
> + *
> + * virtio-net server in host kernel.
> + */
> +
> +#include <linux/eventfd.h>
> +#include <linux/vhost.h>
> +#include <linux/virtio_net.h>
> +#include <linux/mmu_context.h>
> +#include <linux/miscdevice.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/workqueue.h>
> +#include <linux/rcupdate.h>
> +#include <linux/file.h>
> +
> +#include <linux/net.h>
> +#include <linux/if_packet.h>
> +#include <linux/if_arp.h>
> +
> +#include <net/sock.h>
> +
> +#include <asm/mmu_context.h>
> +
> +#include "vhost.h"
> +
> +enum {
> + VHOST_NET_VQ_RX = 0,
> + VHOST_NET_VQ_TX = 1,
> + VHOST_NET_VQ_MAX = 2,
> +};
> +
> +struct vhost_net {
> + struct vhost_dev dev;
> + struct vhost_virtqueue vqs[VHOST_NET_VQ_MAX];
> + /* We use a kind of RCU to access sock pointer.
> + * All readers access it from workqueue,
> + * which makes it possible to flush the workqueue
> + * instead of synchronize_rcu. Therefore readers
> + * do not need rcu_read_lock/rcu_read_unlock.
> + * Writers use device mutex. */

This seems odd. If you have the flush to act as a sync-barrier, why do
you also need rcu_dereference(sock)? At first blush, it seems
gratuitous. Can you talk about this aspect of the design in more detail?

> + struct socket *sock;
> + struct vhost_poll poll[VHOST_NET_VQ_MAX];
> +};
> +
> +static void handle_tx(struct vhost_net *net)
> +{
> + struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
> + unsigned head, out, in;
> + struct msghdr msg = {
> + .msg_name = NULL,
> + .msg_namelen = 0,
> + .msg_control = NULL,
> + .msg_controllen = 0,
> + .msg_iov = (struct iovec *)vq->iov + 1,
> + .msg_flags = MSG_DONTWAIT,
> + };
> + size_t len;
> + int err;
> + struct socket *sock = rcu_dereference(net->sock);
> + if (!sock || !sock_writeable(sock->sk))
> + return;
> +
> + use_mm(net->dev.mm);
> + mutex_lock(&vq->mutex);
> + for (;;) {
> + head = vhost_get_vq_desc(&net->dev, vq, vq->iov, &out, &in);
> + if (head == vq->num)
> + break;
> + if (out <= 1 || in) {
> + vq_err(vq, "Unexpected descriptor format for TX: "
> + "out %d, int %d\n", out, in);
> + break;
> + }
> + /* Sanity check */
> + if (vq->iov->iov_len != sizeof(struct virtio_net_hdr)) {
> + vq_err(vq, "Unexpected header len for TX: "
> + "%ld expected %zd\n", vq->iov->iov_len,
> + sizeof(struct virtio_net_hdr));
> + break;
> + }
> + /* Skip header. TODO: support TSO. */
> + msg.msg_iovlen = out - 1;
> + len = iov_length(vq->iov + 1, out - 1);
> + /* TODO: Check specific error and bomb out unless ENOBUFS? */
> + err = sock->ops->sendmsg(NULL, sock, &msg, len);
> + if (err < 0) {
> + vhost_discard_vq_desc(vq);
> + break;
> + }
> + if (err != len)
> + pr_err("Truncated TX packet: "
> + " len %d != %zd\n", err, len);
> + vhost_add_used_and_trigger(vq, head,
> + len + sizeof(struct virtio_net_hdr));
> + }
> +
> + mutex_unlock(&vq->mutex);
> + unuse_mm(net->dev.mm);
> +}
> +
> +static void handle_rx(struct vhost_net *net)
> +{
> + struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_RX];
> + unsigned head, out, in;
> + struct msghdr msg = {
> + .msg_name = NULL,
> + .msg_namelen = 0,
> + .msg_control = NULL, /* FIXME: get and handle RX aux data. */
> + .msg_controllen = 0,
> + .msg_iov = vq->iov + 1,
> + .msg_flags = MSG_DONTWAIT,
> + };
> +
> + struct virtio_net_hdr hdr = {
> + .flags = 0,
> + .gso_type = VIRTIO_NET_HDR_GSO_NONE
> + };
> +
> + size_t len;
> + int err;
> + struct socket *sock = rcu_dereference(net->sock);
> + if (!sock || skb_queue_empty(&sock->sk->sk_receive_queue))
> + return;
> +
> + use_mm(net->dev.mm);
> + mutex_lock(&vq->mutex);
> +
> + for (;;) {
> + head = vhost_get_vq_desc(&net->dev, vq, vq->iov, &out, &in);
> + if (head == vq->num)
> + break;
> + if (in <= 1 || out) {
> + vq_err(vq, "Unexpected descriptor format for RX: out %d, int %d\n",
> + out, in);
> + break;
> + }
> + /* Sanity check */
> + if (vq->iov->iov_len != sizeof(struct virtio_net_hdr)) {
> + vq_err(vq, "Unexpected header len for RX: %ld expected %zd\n",
> + vq->iov->iov_len, sizeof(struct virtio_net_hdr));
> + break;
> + }
> + /* Skip header. TODO: support TSO/mergeable rx buffers. */
> + msg.msg_iovlen = in - 1;
> + len = iov_length(vq->iov + 1, in - 1);
> + err = sock->ops->recvmsg(NULL, sock, &msg,
> + len, MSG_DONTWAIT | MSG_TRUNC);
> + /* TODO: Check specific error and bomb out unless EAGAIN? */
> + if (err < 0) {
> + vhost_discard_vq_desc(vq);
> + break;
> + }
> + /* TODO: Should check and handle checksum. */
> + if (err > len) {
> + pr_err("Discarded truncated rx packet: "
> + " len %d > %zd\n", err, len);
> + vhost_discard_vq_desc(vq);
> + continue;
> + }
> + len = err;
> + err = copy_to_user(vq->iov->iov_base, &hdr, sizeof hdr);
> + if (err) {
> + vq_err(vq, "Unable to write vnet_hdr at addr %p: %d\n",
> + vq->iov->iov_base, err);
> + break;
> + }
> + vhost_add_used_and_trigger(vq, head, len + sizeof hdr);
> + }
> +
> + mutex_unlock(&vq->mutex);
> + unuse_mm(net->dev.mm);
> +}
> +
> +static void handle_tx_kick(struct work_struct *work)
> +{
> + struct vhost_virtqueue *vq;
> + struct vhost_net *net;
> + vq = container_of(work, struct vhost_virtqueue, poll.work);
> + net = container_of(vq->dev, struct vhost_net, dev);
> + handle_tx(net);
> +}
> +
> +static void handle_rx_kick(struct work_struct *work)
> +{
> + struct vhost_virtqueue *vq;
> + struct vhost_net *net;
> + vq = container_of(work, struct vhost_virtqueue, poll.work);
> + net = container_of(vq->dev, struct vhost_net, dev);
> + handle_rx(net);
> +}
> +
> +static void handle_tx_net(struct work_struct *work)
> +{
> + struct vhost_net *net;
> + net = container_of(work, struct vhost_net, poll[VHOST_NET_VQ_TX].work);
> + handle_tx(net);
> +}
> +
> +static void handle_rx_net(struct work_struct *work)
> +{
> + struct vhost_net *net;
> + net = container_of(work, struct vhost_net, poll[VHOST_NET_VQ_RX].work);
> + handle_rx(net);
> +}
> +
> +static int vhost_net_open(struct inode *inode, struct file *f)
> +{
> + struct vhost_net *n = kzalloc(sizeof *n, GFP_KERNEL);
> + int r;
> + if (!n)
> + return -ENOMEM;
> + f->private_data = n;
> + n->vqs[VHOST_NET_VQ_TX].handle_kick = handle_tx_kick;
> + n->vqs[VHOST_NET_VQ_RX].handle_kick = handle_rx_kick;
> + r = vhost_dev_init(&n->dev, n->vqs, VHOST_NET_VQ_MAX);
> + if (r < 0) {
> + kfree(n);
> + return r;
> + }
> +
> + vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT);
> + vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN);
> + return 0;
> +}
> +
> +static struct socket *vhost_net_stop(struct vhost_net *n)
> +{
> + struct socket *sock = n->sock;
> + rcu_assign_pointer(n->sock, NULL);
> + if (sock) {
> + vhost_poll_flush(n->poll + VHOST_NET_VQ_TX);
> + vhost_poll_flush(n->poll + VHOST_NET_VQ_RX);
> + }
> + return sock;
> +}
> +
> +static int vhost_net_release(struct inode *inode, struct file *f)
> +{
> + struct vhost_net *n = f->private_data;
> + struct socket *sock;
> +
> + sock = vhost_net_stop(n);
> + vhost_dev_cleanup(&n->dev);
> + if (sock)
> + fput(sock->file);
> + kfree(n);
> + return 0;
> +}
> +
> +static long vhost_net_set_socket(struct vhost_net *n, int fd)
> +{
> + struct {
> + struct sockaddr_ll sa;
> + char buf[MAX_ADDR_LEN];
> + } uaddr;
> + struct socket *sock, *oldsock = NULL;
> + int uaddr_len = sizeof uaddr, r;
> +
> + mutex_lock(&n->dev.mutex);
> + r = vhost_dev_check_owner(&n->dev);
> + if (r)
> + goto done;
> +
> + if (fd == -1) {
> + /* Disconnect from socket and device. */
> + oldsock = vhost_net_stop(n);
> + goto done;
> + }
> +
> + sock = sockfd_lookup(fd, &r);
> + if (!sock) {
> + r = -ENOTSOCK;
> + goto done;
> + }
> +
> + /* Parameter checking */
> + if (sock->sk->sk_type != SOCK_RAW) {
> + r = -ESOCKTNOSUPPORT;
> + goto done;
> + }
> +
> + r = sock->ops->getname(sock, (struct sockaddr *)&uaddr.sa,
> + &uaddr_len, 0);
> + if (r)
> + goto done;
> +
> + if (uaddr.sa.sll_family != AF_PACKET) {
> + r = -EPFNOSUPPORT;
> + goto done;
> + }
> +
> + /* start polling new socket */
> + if (sock == oldsock)
> + goto done;
> +
> + if (oldsock) {
> + vhost_poll_stop(n->poll + VHOST_NET_VQ_TX);
> + vhost_poll_stop(n->poll + VHOST_NET_VQ_RX);
> + }
> + oldsock = n->sock;
> + rcu_assign_pointer(n->sock, sock);
> + vhost_poll_start(n->poll + VHOST_NET_VQ_TX, sock->file);
> + vhost_poll_start(n->poll + VHOST_NET_VQ_RX, sock->file);
> +done:
> + mutex_unlock(&n->dev.mutex);
> + if (oldsock) {
> + vhost_poll_flush(n->poll + VHOST_NET_VQ_TX);
> + vhost_poll_flush(n->poll + VHOST_NET_VQ_RX);
> + vhost_poll_flush(&n->dev.vqs[VHOST_NET_VQ_TX].poll);
> + vhost_poll_flush(&n->dev.vqs[VHOST_NET_VQ_RX].poll);
> + fput(oldsock->file);
> + }
> + return r;
> +}
> +
> +static long vhost_net_reset_owner(struct vhost_net *n)
> +{
> + struct socket *sock = NULL;
> + long r;
> + mutex_lock(&n->dev.mutex);
> + r = vhost_dev_check_owner(&n->dev);
> + if (r)
> + goto done;
> + sock = vhost_net_stop(n);
> + r = vhost_dev_reset_owner(&n->dev);
> +done:
> + mutex_unlock(&n->dev.mutex);
> + if (sock)
> + fput(sock->file);
> + return r;
> +}
> +
> +static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
> + unsigned long arg)
> +{
> + struct vhost_net *n = f->private_data;
> + void __user *argp = (void __user *)arg;
> + u32 __user *featurep = argp;
> + int __user *fdp = argp;
> + u32 features;
> + int fd, r;
> + switch (ioctl) {
> + case VHOST_NET_SET_SOCKET:
> + r = get_user(fd, fdp);
> + if (r < 0)
> + return r;
> + return vhost_net_set_socket(n, fd);
> + case VHOST_GET_FEATURES:
> + /* No features for now */
> + features = 0;
> + return put_user(features, featurep);
> + case VHOST_ACK_FEATURES:
> + r = get_user(features, featurep);
> + /* No features for now */
> + if (r < 0)
> + return r;
> + if (features)
> + return -EOPNOTSUPP;
> + return 0;
> + case VHOST_RESET_OWNER:
> + return vhost_net_reset_owner(n);
> + default:
> + return vhost_dev_ioctl(&n->dev, ioctl, arg);
> + }
> +}
> +
> +static struct file_operations vhost_net_fops = {
> + .owner = THIS_MODULE,
> + .release = vhost_net_release,
> + .unlocked_ioctl = vhost_net_ioctl,
> + .open = vhost_net_open,
> +};
> +
> +static struct miscdevice vhost_net_misc = {
> + VHOST_NET_MINOR,
> + "vhost-net",
> + &vhost_net_fops,
> +};
> +
> +int vhost_net_init(void)
> +{
> + int r = vhost_init();
> + if (r)
> + goto err_init;
> + r = misc_register(&vhost_net_misc);
> + if (r)
> + goto err_reg;
> + return 0;
> +err_reg:
> + vhost_cleanup();
> +err_init:
> + return r;
> +
> +}
> +module_init(vhost_net_init);
> +
> +void vhost_net_exit(void)
> +{
> + misc_deregister(&vhost_net_misc);
> + vhost_cleanup();
> +}
> +module_exit(vhost_net_exit);
> +
> +MODULE_VERSION("0.0.1");
> +MODULE_LICENSE("GPL v2");
> +MODULE_AUTHOR("Michael S. Tsirkin");
> +MODULE_DESCRIPTION("Host kernel accelerator for virtio net");
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> new file mode 100644
> index 0000000..6178ec1
> --- /dev/null
> +++ b/drivers/vhost/vhost.c
> @@ -0,0 +1,663 @@
> +/* Copyright (C) 2009 Red Hat, Inc.
> + * Copyright (C) 2006 Rusty Russell IBM Corporation
> + *
> + * Author: Michael S. Tsirkin <mst@redhat.com>
> + *
> + * Inspiration, some code, and most witty comments come from
> + * Documentation/lguest/lguest.c, by Rusty Russell
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.
> + *
> + * Generic code for virtio server in host kernel.
> + */
> +
> +#include <linux/eventfd.h>
> +#include <linux/vhost.h>
> +#include <linux/virtio_net.h>
> +#include <linux/mm.h>
> +#include <linux/miscdevice.h>
> +#include <linux/mutex.h>
> +#include <linux/workqueue.h>
> +#include <linux/rcupdate.h>
> +#include <linux/poll.h>
> +#include <linux/file.h>
> +
> +#include <linux/net.h>
> +#include <linux/if_packet.h>
> +#include <linux/if_arp.h>
> +
> +#include <net/sock.h>
> +
> +#include <asm/mmu_context.h>
> +
> +#include "vhost.h"
> +
> +enum {
> + VHOST_MEMORY_MAX_NREGIONS = 64,
> +};
> +
> +struct workqueue_struct *vhost_workqueue;
> +
> +static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
> + poll_table *pt)
> +{
> + struct vhost_poll *poll;
> + poll = container_of(pt, struct vhost_poll, table);
> +
> + poll->wqh = wqh;
> + add_wait_queue(wqh, &poll->wait);
> +}
> +
> +static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
> +{
> + struct vhost_poll *poll;
> + poll = container_of(wait, struct vhost_poll, wait);
> + if (!((unsigned long)key & poll->mask))
> + return 0;
> +
> + queue_work(vhost_workqueue, &poll->work);
> + return 0;
> +}
> +
> +/* Init poll structure */
> +void vhost_poll_init(struct vhost_poll *poll, work_func_t func,
> + unsigned long mask)
> +{
> + INIT_WORK(&poll->work, func);
> + init_waitqueue_func_entry(&poll->wait, vhost_poll_wakeup);
> + init_poll_funcptr(&poll->table, vhost_poll_func);
> + poll->mask = mask;
> +}
> +
> +/* Start polling a file. We add ourselves to file's wait queue. The user must
> + * keep a reference to a file until after vhost_poll_stop is called. */
> +void vhost_poll_start(struct vhost_poll *poll, struct file *file)
> +{
> + unsigned long mask;
> + mask = file->f_op->poll(file, &poll->table);
> + if (mask)
> + vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask);
> +}
> +
> +/* Stop polling a file. After this function returns, it becomes safe to drop the
> + * file reference. You must also flush afterwards. */
> +void vhost_poll_stop(struct vhost_poll *poll)
> +{
> + remove_wait_queue(poll->wqh, &poll->wait);
> +}
> +
> +/* Flush any work that has been scheduled. When calling this, don't hold any
> + * locks that are also used by the callback. */
> +void vhost_poll_flush(struct vhost_poll *poll)
> +{
> + flush_work(&poll->work);
> +}
> +
> +long vhost_dev_init(struct vhost_dev *dev, struct vhost_virtqueue *vqs, int nvqs)
> +{
> + int i;
> + dev->vqs = vqs;
> + dev->nvqs = nvqs;
> + mutex_init(&dev->mutex);
> +
> + for(i = 0; i < dev->nvqs; ++i) {
> + dev->vqs[i].dev = dev;
> + mutex_init(&dev->vqs[i].mutex);
> + if (dev->vqs[i].handle_kick)
> + vhost_poll_init(&dev->vqs[i].poll,
> + dev->vqs[i].handle_kick,
> + POLLIN);
> + }
> + return 0;
> +}
> +
> +/* User should have device mutex */
> +long vhost_dev_check_owner(struct vhost_dev *dev)
> +{
> + return dev->mm == current->mm ? 0 : -EPERM;
> +}
> +
> +/* User should have device mutex */
> +static long vhost_dev_set_owner(struct vhost_dev *dev)
> +{
> + if (dev->mm)
> + return -EBUSY;
> + dev->mm = get_task_mm(current);
> + return 0;
> +}
> +
> +/* User should have device mutex */
> +long vhost_dev_reset_owner(struct vhost_dev *dev)
> +{
> + struct vhost_memory *memory;
> +
> + /* Restore memory to default 1:1 mapping. */
> + memory = kmalloc(offsetof(struct vhost_memory, regions) +
> + 2 * sizeof *memory->regions, GFP_KERNEL);
> + if (!memory)
> + return -ENOMEM;
> +
> + vhost_dev_cleanup(dev);
> +
> + memory->nregions = 2;
> + memory->regions[0].guest_phys_addr = 1;
> + memory->regions[0].userspace_addr = 1;
> + memory->regions[0].memory_size = ~0ULL;
> + memory->regions[1].guest_phys_addr = 0;
> + memory->regions[1].userspace_addr = 0;
> + memory->regions[1].memory_size = 1;
> + dev->memory = memory;
> + return 0;
> +}
> +
> +/* User should have device mutex */
> +void vhost_dev_cleanup(struct vhost_dev *dev)
> +{
> + int i;
> + for(i = 0; i < dev->nvqs; ++i) {
> + if (dev->vqs[i].kick && dev->vqs[i].handle_kick) {
> + vhost_poll_stop(&dev->vqs[i].poll);
> + vhost_poll_flush(&dev->vqs[i].poll);
> + }
> + if (dev->vqs[i].error_ctx)
> + eventfd_ctx_put(dev->vqs[i].error_ctx);
> + if (dev->vqs[i].error)
> + fput(dev->vqs[i].error);
> + if (dev->vqs[i].kick)
> + fput(dev->vqs[i].kick);
> + if (dev->vqs[i].call_ctx)
> + eventfd_ctx_put(dev->vqs[i].call_ctx);
> + if (dev->vqs[i].call)
> + fput(dev->vqs[i].call);
> + dev->vqs[i].error_ctx = NULL;
> + dev->vqs[i].error = NULL;
> + dev->vqs[i].kick = NULL;
> + dev->vqs[i].call_ctx = NULL;
> + dev->vqs[i].call = NULL;
> + }
> + /* No one will access memory at this point */
> + kfree(dev->memory);
> + dev->memory = NULL;
> + if (dev->mm)
> + mmput(dev->mm);
> + dev->mm = NULL;
> +}
> +
> +static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
> +{
> + struct vhost_memory mem, *newmem, *oldmem;
> + unsigned long size = offsetof(struct vhost_memory, regions);
> + long r;
> + r = copy_from_user(&mem, m, size);
> + if (r)
> + return r;
> + if (mem.padding)
> + return -EOPNOTSUPP;
> + if (mem.nregions > VHOST_MEMORY_MAX_NREGIONS)
> + return -E2BIG;
> + newmem = kmalloc(size + mem.nregions * sizeof *m->regions, GFP_KERNEL);
> + if (!newmem)
> + return -ENOMEM;
> +
> + memcpy(newmem, &mem, size);
> + r = copy_from_user(newmem->regions, m->regions,
> + mem.nregions * sizeof *m->regions);
> + if (r) {
> + kfree(newmem);
> + return r;
> + }
> + oldmem = d->memory;
> + rcu_assign_pointer(d->memory, newmem);
> + synchronize_rcu();
> + kfree(oldmem);
> + return 0;
> +}
> +
> +static int init_used(struct vhost_virtqueue *vq)
> +{
> + u16 flags = 0;
> + int r = put_user(flags, &vq->used->flags);
> + if (r)
> + return r;
> + return get_user(vq->last_used_idx, &vq->used->idx);
> +}
> +
> +static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
> +{
> + struct file *eventfp, *filep = NULL, *pollstart = NULL, *pollstop = NULL;
> + struct eventfd_ctx *ctx = NULL;
> + u32 __user *idxp = argp;
> + struct vhost_virtqueue *vq;
> + struct vhost_vring_state s;
> + struct vhost_vring_file f;
> + struct vhost_vring_addr a;
> + u32 idx;
> + long r;
> +
> + r = get_user(idx, idxp);
> + if (r < 0)
> + return r;
> + if (idx > d->nvqs)
> + return -ENOBUFS;
> +
> + vq = d->vqs + idx;
> +
> + mutex_lock(&vq->mutex);
> +
> + switch (ioctl) {
> + case VHOST_SET_VRING_NUM:
> + r = copy_from_user(&s, argp, sizeof s);
> + if (r < 0)
> + break;
> + if (s.num > 0xffff) {
> + r = -EINVAL;
> + break;
> + }
> + vq->num = s.num;
> + break;
> + case VHOST_SET_VRING_BASE:
> + r = copy_from_user(&s, argp, sizeof s);
> + if (r < 0)
> + break;
> + if (s.num > 0xffff) {
> + r = -EINVAL;
> + break;
> + }
> + vq->last_avail_idx = s.num;
> + break;
> + case VHOST_GET_VRING_BASE:
> + s.index = idx;
> + s.num = vq->last_avail_idx;
> + r = copy_to_user(argp, &s, sizeof s);
> + break;
> + case VHOST_SET_VRING_DESC:
> + r = copy_from_user(&a, argp, sizeof a);
> + if (r < 0)
> + break;
> + if (a.padding) {
> + r = -EOPNOTSUPP;
> + break;
> + }
> + if ((u64)(long)a.user_addr != a.user_addr) {
> + r = -EFAULT;
> + break;
> + }
> + vq->desc = (void __user *)(long)a.user_addr;
> + break;
> + case VHOST_SET_VRING_AVAIL:
> + r = copy_from_user(&a, argp, sizeof a);
> + if (r < 0)
> + break;
> + if (a.padding) {
> + r = -EOPNOTSUPP;
> + break;
> + }
> + if ((u64)(long)a.user_addr != a.user_addr) {
> + r = -EFAULT;
> + break;
> + }
> + vq->avail = (void __user *)(long)a.user_addr;
> + break;
> + case VHOST_SET_VRING_USED:
> + r = copy_from_user(&a, argp, sizeof a);
> + if (r < 0)
> + break;
> + if (a.padding) {
> + r = -EOPNOTSUPP;
> + break;
> + }
> + if ((u64)(long)a.user_addr != a.user_addr) {
> + r = -EFAULT;
> + break;
> + }
> + vq->used = (void __user *)(long)a.user_addr;
> + r = init_used(vq);
> + if (r)
> + break;
> + break;
> + case VHOST_SET_VRING_KICK:
> + r = copy_from_user(&f, argp, sizeof f);
> + if (r < 0)
> + break;
> + eventfp = f.fd == -1 ? NULL: eventfd_fget(f.fd);
> + if (IS_ERR(eventfp))
> + return PTR_ERR(eventfp);
> + if (eventfp != vq->kick) {
> + pollstop = filep = vq->kick;
> + pollstart = vq->kick = eventfp;
> + } else
> + filep = eventfp;
> + break;
> + case VHOST_SET_VRING_CALL:
> + r = copy_from_user(&f, argp, sizeof f);
> + if (r < 0)
> + break;
> + eventfp = f.fd == -1 ? NULL: eventfd_fget(f.fd);
> + if (IS_ERR(eventfp))
> + return PTR_ERR(eventfp);
> + if (eventfp != vq->call) {
> + filep = vq->call;
> + ctx = vq->call_ctx;
> + vq->call = eventfp;
> + vq->call_ctx = eventfp ?
> + eventfd_ctx_fileget(eventfp) : NULL;
> + } else
> + filep = eventfp;
> + break;
> + case VHOST_SET_VRING_ERR:
> + r = copy_from_user(&f, argp, sizeof f);
> + if (r < 0)
> + break;
> + eventfp = f.fd == -1 ? NULL: eventfd_fget(f.fd);
> + if (IS_ERR(eventfp))
> + return PTR_ERR(eventfp);
> + if (eventfp != vq->error) {
> + filep = vq->error;
> + vq->error = eventfp;
> + ctx = vq->error_ctx;
> + vq->error_ctx = eventfp ?
> + eventfd_ctx_fileget(eventfp) : NULL;
> + } else
> + filep = eventfp;
> + break;
> + default:
> + r = -ENOTTY;
> + }
> +
> + if (pollstop && vq->handle_kick)
> + vhost_poll_stop(&vq->poll);
> +
> + if (ctx)
> + eventfd_ctx_put(ctx);
> + if (filep)
> + fput(filep);
> +
> + if (pollstart && vq->handle_kick)
> + vhost_poll_start(&vq->poll, vq->kick);
> +
> + mutex_unlock(&vq->mutex);
> +
> + if (pollstop && vq->handle_kick)
> + vhost_poll_flush(&vq->poll);
> + return 0;
> +}
> +
> +long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, unsigned long arg)
> +{
> + void __user *argp = (void __user *)arg;
> + long r;
> +
> + mutex_lock(&d->mutex);
> + if (ioctl == VHOST_SET_OWNER) {
> + r = vhost_dev_set_owner(d);
> + goto done;
> + }
> +
> + r = vhost_dev_check_owner(d);
> + if (r)
> + goto done;
> +
> + switch (ioctl) {
> + case VHOST_SET_MEM_TABLE:
> + r = vhost_set_memory(d, argp);
> + break;
> + default:
> + r = vhost_set_vring(d, ioctl, argp);
> + break;
> + }
> +done:
> + mutex_unlock(&d->mutex);
> + return r;
> +}
> +
> +static const struct vhost_memory_region *find_region(struct vhost_memory *mem,
> + __u64 addr, __u32 len)
> +{
> + struct vhost_memory_region *reg;
> + int i;
> + /* linear search is not brilliant, but we really have on the order of 6
> + * regions in practice */
> + for (i = 0; i < mem->nregions; ++i) {
> + reg = mem->regions + i;
> + if (reg->guest_phys_addr <= addr &&
> + reg->guest_phys_addr + reg->memory_size - 1 >= addr)
> + return reg;
> + }
> + return NULL;
> +}
> +
> +/* FIXME: this does not handle a region that spans multiple
> + * address/len pairs */
> +int translate_desc(struct vhost_dev *dev, u64 addr, u32 len,
> + struct iovec iov[], int iov_count, int iov_size,
> + unsigned *num)
> +{
> + const struct vhost_memory_region *reg;
> + struct vhost_memory *mem;
> + struct iovec *_iov;
> + u64 s = 0;
> + int ret = 0;
> +
> + rcu_read_lock();
> +
> + mem = rcu_dereference(dev->memory);
> + while ((u64)len > s) {
> + u64 size;
> + if (*num + iov_count >= iov_size) {
> + ret = -ENOBUFS;
> + break;
> + }
> + reg = find_region(mem, addr, len);
> + if (!reg) {
> + ret = -EFAULT;
> + break;
> + }
> + _iov = iov + iov_count + *num;
> + size = reg->memory_size - addr + reg->guest_phys_addr;
> + _iov->iov_len = min((u64)len, size);
> + _iov->iov_base = (void *)
> + (reg->userspace_addr + addr - reg->guest_phys_addr);
> + s += size;
> + addr += size;
> + ++*num;
> + }
> +
> + rcu_read_unlock();
> + return ret;
> +}
> +
> +/* Each buffer in the virtqueues is actually a chain of descriptors. This
> + * function returns the next descriptor in the chain, or vq->vring.num if we're
> + * at the end. */
> +static unsigned next_desc(struct vhost_virtqueue *vq, struct vring_desc *desc)
> +{
> + unsigned int next;
> +
> + /* If this descriptor says it doesn't chain, we're done. */
> + if (!(desc->flags & VRING_DESC_F_NEXT))
> + return vq->num;
> +
> + /* Check they're not leading us off end of descriptors. */
> + next = desc->next;
> + /* Make sure compiler knows to grab that: we don't want it changing! */
> + /* We will use the result as an index in an array, so most
> + * architectures only need a compiler barrier here. */
> + read_barrier_depends();
> +
> + if (next >= vq->num) {
> + vq_err(vq, "Desc next is %u > %u", next, vq->num);
> + return vq->num;
> + }
> +
> + return next;
> +}
> +
> +/* This looks in the virtqueue and for the first available buffer, and converts
> + * it to an iovec for convenient access. Since descriptors consist of some
> + * number of output then some number of input descriptors, it's actually two
> + * iovecs, but we pack them into one and note how many of each there were.
> + *
> + * This function returns the descriptor number found, or vq->num (which
> + * is never a valid descriptor number) if none was found. */
> +unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
> + struct iovec iov[],
> + unsigned int *out_num, unsigned int *in_num)
> +{
> + struct vring_desc desc;
> + unsigned int i, head;
> + u16 last_avail_idx, idx;
> +
> + /* Check it isn't doing very strange things with descriptor numbers. */
> + last_avail_idx = vq->last_avail_idx;
> + if (get_user(idx, &vq->avail->idx)) {
> + vq_err(vq, "Failed to access avail idx at %p\n",
> + &vq->avail->idx);
> + return vq->num;
> + }
> +
> + if ((u16)(idx - last_avail_idx) > vq->num) {
> + vq_err(vq, "Guest moved used index from %u to %u",
> + last_avail_idx, idx);
> + return vq->num;
> + }
> +
> + /* If there's nothing new since last we looked, return invalid. */
> + if (idx == last_avail_idx)
> + return vq->num;
> +
> + /* Grab the next descriptor number they're advertising, and increment
> + * the index we've seen. */
> + if (get_user(head, &vq->avail->ring[last_avail_idx % vq->num])) {
> + vq_err(vq, "Failed to read head: idx %d address %p\n",
> + idx, &vq->avail->ring[last_avail_idx % vq->num]);
> + return vq->num;
> + }
> +
> + /* If their number is silly, that's a fatal mistake. */
> + if (head >= vq->num) {
> + vq_err(vq, "Guest says index %u > %u is available",
> + head, vq->num);
> + return vq->num;
> + }
> +
> + vq->last_avail_idx++;
> +
> + /* When we start there are none of either input nor output. */
> + *out_num = *in_num = 0;
> +
> + i = head;
> + do {
> + unsigned *num;
> + unsigned iov_count;
> + if (copy_from_user(&desc, vq->desc + i, sizeof desc)) {
> + vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
> + i, vq->desc + i);
> + return vq->num;
> + }
> + /* If this is an input descriptor, increment that count. */
> + if (desc.flags & VRING_DESC_F_WRITE) {
> + num = in_num;
> + iov_count = *out_num;
> + } else {
> + /* If it's an output descriptor, they're all supposed
> + * to come before any input descriptors. */
> + if (*in_num) {
> + vq_err(vq, "Descriptor has out after in: "
> + "idx %d\n", i);
> + return vq->num;
> + }
> + num = out_num;
> + iov_count = *in_num;
> + }
> + if (translate_desc(dev, desc.addr, desc.len, iov, iov_count,
> + VHOST_NET_MAX_SG, num)) {
> + vq_err(vq, "Failed to translate descriptor: idx %d\n",
> + i);
> + return vq->num;
> + }
> +
> + /* If we've got too many, that implies a descriptor loop. */
> + if (*out_num + *in_num > vq->num) {
> + vq_err(vq, "Looped descriptor: idx %d\n", i);
> + return vq->num;
> + }
> + } while ((i = next_desc(vq, &desc)) != vq->num);
> +
> + vq->inflight++;
> + return head;
> +}
> +
> +/* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
> +void vhost_discard_vq_desc(struct vhost_virtqueue *vq)
> +{
> + vq->last_avail_idx--;
> + vq->inflight--;
> +}
> +
> +/* After we've used one of their buffers, we tell them about it. We'll then
> + * want to send them an interrupt, using vq->call. */
> +int vhost_add_used(struct vhost_virtqueue *vq,
> + unsigned int head, int len)
> +{
> + struct vring_used_elem *used;
> +
> + /* The virtqueue contains a ring of used buffers. Get a pointer to the
> + * next entry in that used ring. */
> + used = &vq->used->ring[vq->last_used_idx % vq->num];
> + if (put_user(head, &used->id)) {
> + vq_err(vq, "Failed to write used id");
> + return -EFAULT;
> + }
> + if (put_user(len, &used->len)) {
> + vq_err(vq, "Failed to write used len");
> + return -EFAULT;
> + }
> + /* Make sure buffer is written before we update index. */
> + wmb();
> + if (put_user(vq->last_used_idx + 1, &vq->used->idx)) {
> + vq_err(vq, "Failed to increment used idx");
> + return -EFAULT;
> + }
> + vq->last_used_idx++;
> + vq->inflight--;
> + return 0;
> +}
> +
> +/* This actually sends the interrupt for this virtqueue */
> +void vhost_trigger_irq(struct vhost_virtqueue *vq)
> +{
> + __u16 flags = 0;
> + if (get_user(flags, &vq->avail->flags)) {
> + vq_err(vq, "Failed to get flags");
> + return;
> + }
> +
> + /* If they don't want an interrupt, don't send one, unless empty. */
> + if ((flags & VRING_AVAIL_F_NO_INTERRUPT) && vq->inflight)
> + return;
> +
> + /* Send the Guest an interrupt tell them we used something up. */
> + if (vq->call_ctx)
> + eventfd_signal(vq->call_ctx, 1);
> +}
> +
> +/* And here's the combo meal deal. Supersize me! */
> +void vhost_add_used_and_trigger(struct vhost_virtqueue *vq,
> + unsigned int head, int len)
> +{
> + vhost_add_used(vq, head, len);
> + vhost_trigger_irq(vq);
> +}
> +
> +int vhost_init(void)
> +{
> + vhost_workqueue = create_workqueue("vhost");
> + if (!vhost_workqueue)
> + return -ENOMEM;
> + return 0;
> +}
> +
> +void vhost_cleanup(void)
> +{
> + destroy_workqueue(vhost_workqueue);
> +}
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> new file mode 100644
> index 0000000..7f7ffcd
> --- /dev/null
> +++ b/drivers/vhost/vhost.h
> @@ -0,0 +1,108 @@
> +#ifndef _VHOST_H
> +#define _VHOST_H
> +
> +#include <linux/eventfd.h>
> +#include <linux/vhost.h>
> +#include <linux/mm.h>
> +#include <linux/mutex.h>
> +#include <linux/workqueue.h>
> +#include <linux/poll.h>
> +#include <linux/file.h>
> +#include <linux/skbuff.h>
> +
> +struct vhost_device;
> +
> +enum {
> + VHOST_NET_MAX_SG = MAX_SKB_FRAGS + 2,
> +};
> +
> +/* Poll a file (eventfd or socket) */
> +/* Note: there's nothing vhost specific about this structure. */
> +struct vhost_poll {
> + poll_table table;
> + wait_queue_head_t *wqh;
> + wait_queue_t wait;
> + /* struct which will handle all actual work. */
> + struct work_struct work;
> + unsigned long mask;
> +};
> +
> +void vhost_poll_init(struct vhost_poll *poll, work_func_t func,
> + unsigned long mask);
> +void vhost_poll_start(struct vhost_poll *poll, struct file *file);
> +void vhost_poll_stop(struct vhost_poll *poll);
> +void vhost_poll_flush(struct vhost_poll *poll);
> +
> +/* The virtqueue structure describes a queue attached to a device. */
> +struct vhost_virtqueue {
> + struct vhost_dev *dev;
> +
> + /* The actual ring of buffers. */
> + struct mutex mutex;
> + unsigned int num;
> + struct vring_desc __user *desc;
> + struct vring_avail __user *avail;
> + struct vring_used __user *used;
> + struct file *kick;
> + struct file *call;
> + struct file *error;
> + struct eventfd_ctx *call_ctx;
> + struct eventfd_ctx *error_ctx;
> +
> + struct vhost_poll poll;
> +
> + /* The routine to call when the Guest pings us, or timeout. */
> + work_func_t handle_kick;
> +
> + /* Last available index we saw. */
> + u16 last_avail_idx;
> +
> + /* Last index we used. */
> + u16 last_used_idx;
> +
> + /* Outstanding buffers */
> + unsigned int inflight;
> +
> + /* Is this blocked? */
> + bool blocked;
> +
> + struct iovec iov[VHOST_NET_MAX_SG];
> +
> +} ____cacheline_aligned;
> +
> +struct vhost_dev {
> + /* Readers use RCU to access memory table pointer.
> + * Writers use mutex below.*/
> + struct vhost_memory *memory;
> + struct mm_struct *mm;
> + struct vhost_virtqueue *vqs;
> + int nvqs;
> + struct mutex mutex;
> +};
> +
> +long vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue *vqs, int nvqs);
> +long vhost_dev_check_owner(struct vhost_dev *);
> +long vhost_dev_reset_owner(struct vhost_dev *);
> +void vhost_dev_cleanup(struct vhost_dev *);
> +long vhost_dev_ioctl(struct vhost_dev *, unsigned int ioctl, unsigned long arg);
> +
> +unsigned vhost_get_vq_desc(struct vhost_dev *, struct vhost_virtqueue *,
> + struct iovec iov[],
> + unsigned int *out_num, unsigned int *in_num);
> +void vhost_discard_vq_desc(struct vhost_virtqueue *);
> +
> +int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
> +void vhost_trigger_irq(struct vhost_virtqueue *);
> +void vhost_add_used_and_trigger(struct vhost_virtqueue *,
> + unsigned int head, int len);
> +
> +int vhost_init(void);
> +void vhost_cleanup(void);
> +
> +#define vq_err(vq, fmt, ...) do { \
> + printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__); \
> + if ((vq)->error_ctx) \
> + eventfd_signal((vq)->error_ctx, 1);\
> + } while (0)
> +
> +#endif
> diff --git a/include/linux/Kbuild b/include/linux/Kbuild
> index dec2f18..975df9a 100644
> --- a/include/linux/Kbuild
> +++ b/include/linux/Kbuild
> @@ -360,6 +360,7 @@ unifdef-y += uio.h
> unifdef-y += unistd.h
> unifdef-y += usbdevice_fs.h
> unifdef-y += utsname.h
> +unifdef-y += vhost.h
> unifdef-y += videodev2.h
> unifdef-y += videodev.h
> unifdef-y += virtio_config.h
> diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h
> index 0521177..781a8bb 100644
> --- a/include/linux/miscdevice.h
> +++ b/include/linux/miscdevice.h
> @@ -30,6 +30,7 @@
> #define HPET_MINOR 228
> #define FUSE_MINOR 229
> #define KVM_MINOR 232
> +#define VHOST_NET_MINOR 233

Would recommend using DYNAMIC-MINOR.

> #define MISC_DYNAMIC_MINOR 255
>
> struct device;
> diff --git a/include/linux/vhost.h b/include/linux/vhost.h
> new file mode 100644
> index 0000000..9ec6d5f
> --- /dev/null
> +++ b/include/linux/vhost.h
> @@ -0,0 +1,100 @@
> +#ifndef _LINUX_VHOST_H
> +#define _LINUX_VHOST_H
> +/* Userspace interface for in-kernel virtio accelerators. */
> +
> +/* vhost is used to reduce the number of system calls involved in virtio.
> + *
> + * Existing virtio net code is used in the guest without modification.
> + *
> + * This header includes interface used by userspace hypervisor for
> + * device configuration.
> + */
> +
> +#include <linux/types.h>
> +#include <linux/compiler.h>
> +#include <linux/ioctl.h>
> +#include <linux/virtio_config.h>
> +#include <linux/virtio_ring.h>
> +
> +struct vhost_vring_state {
> + unsigned int index;
> + unsigned int num;
> +};
> +
> +struct vhost_vring_file {
> + unsigned int index;
> + int fd;
> +};
> +
> +struct vhost_vring_addr {
> + unsigned int index;
> + unsigned int padding;
> + __u64 user_addr;
> +};
> +
> +struct vhost_memory_region {
> + __u64 guest_phys_addr;
> + __u64 memory_size; /* bytes */
> + __u64 userspace_addr;
> + __u64 padding; /* read/write protection? */
> +};
> +
> +struct vhost_memory {
> + __u32 nregions;
> + __u32 padding;
> + struct vhost_memory_region regions[0];
> +};
> +
> +/* ioctls */
> +
> +#define VHOST_VIRTIO 0xAF
> +
> +/* Features bitmask for forward compatibility. Transport bits must be zero. */
> +#define VHOST_GET_FEATURES _IOR(VHOST_VIRTIO, 0x00, __u32)
> +#define VHOST_ACK_FEATURES _IOW(VHOST_VIRTIO, 0x00, __u32)
> +
> +/* Set current process as the (exclusive) owner of this file descriptor. This
> + * must be called before any other vhost command. Further calls to
> + * VHOST_OWNER_SET fail until VHOST_OWNER_RESET is called. */
> +#define VHOST_SET_OWNER _IO(VHOST_VIRTIO, 0x01)
> +/* Give up ownership, and reset the device to default values.
> + * Allows subsequent call to VHOST_OWNER_SET to succeed. */
> +#define VHOST_RESET_OWNER _IO(VHOST_VIRTIO, 0x02)
> +
> +/* Set up/modify memory layout */
> +#define VHOST_SET_MEM_TABLE _IOW(VHOST_VIRTIO, 0x03, struct vhost_memory)
> +
> +/* Ring setup. These parameters can not be modified while ring is running
> + * (bound to a device). */
> +/* Set number of descriptors in ring */
> +#define VHOST_SET_VRING_NUM _IOW(VHOST_VIRTIO, 0x10, struct vhost_vring_state)
> +/* Start of array of descriptors (virtually contiguous) */
> +#define VHOST_SET_VRING_DESC _IOW(VHOST_VIRTIO, 0x11, struct vhost_vring_addr)
> +/* Used structure address */
> +#define VHOST_SET_VRING_USED _IOW(VHOST_VIRTIO, 0x12, struct vhost_vring_addr)
> +/* Available structure address */
> +#define VHOST_SET_VRING_AVAIL _IOW(VHOST_VIRTIO, 0x13, struct vhost_vring_addr)
> +/* Base value where queue looks for available descriptors */
> +#define VHOST_SET_VRING_BASE _IOW(VHOST_VIRTIO, 0x14, struct vhost_vring_state)
> +/* Get accessor: reads index, writes value in num */
> +#define VHOST_GET_VRING_BASE _IOWR(VHOST_VIRTIO, 0x14, struct vhost_vring_state)
> +
> +/* The following ioctls use eventfd file descriptors to signal and poll
> + * for events. */
> +
> +/* Set eventfd to poll for added buffers */
> +#define VHOST_SET_VRING_KICK _IOW(VHOST_VIRTIO, 0x20, struct vhost_vring_file)
> +/* Set eventfd to signal when buffers have beed used */
> +#define VHOST_SET_VRING_CALL _IOW(VHOST_VIRTIO, 0x21, struct vhost_vring_file)
> +/* Set eventfd to signal an error */
> +#define VHOST_SET_VRING_ERR _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file)
> +
> +/* VHOST_NET specific defines */
> +
> +/* Attach virtio net device to a raw socket. The socket must be already
> + * bound to an ethernet device, this device will be used for transmit.
> + * Pass -1 to unbind from the socket and the transmit device.
> + * This can be used to stop the device (e.g. for migration). */
> +#define VHOST_NET_SET_SOCKET _IOW(VHOST_VIRTIO, 0x30, int)
> +
> +#endif

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