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QEMU直接从tap/tun取数据
QEMU tap数据接收步骤:
- qemu从tun取数据包
- qemu将数据包放入virtio硬件网卡。
- qemu触发中断。
- 虚拟机收到中断,从virtio读取数据。
在qemu中步骤1(tap_read_packet)和步骤2(qemu_send_packet_async)都是在tap_send中完成的,其中步骤2是异步流程。- qemu/net/tap.c
- static void tap_send(void *opaque)
- {
- TAPState *s = opaque;
- int size;
- int packets = 0;
- while (true) {
- uint8_t *buf = s->buf;
- uint8_t min_pkt[ETH_ZLEN];
- size_t min_pktsz = sizeof(min_pkt);
- size = tap_read_packet(s->fd, s->buf, sizeof(s->buf));
- if (size <= 0) {
- break;
- }
-
- if (s->host_vnet_hdr_len && !s->using_vnet_hdr) {
- buf += s->host_vnet_hdr_len;
- size -= s->host_vnet_hdr_len;
- }
- if (net_peer_needs_padding(&s->nc)) {
- if (eth_pad_short_frame(min_pkt, &min_pktsz, buf, size)) {
- buf = min_pkt;
- size = min_pktsz;
- }
- }
-
- size = qemu_send_packet_async(&s->nc, buf, size, tap_send_completed);
- if (size == 0) {
- tap_read_poll(s, false);
- break;
- } else if (size < 0) {
- break;
- }
- /*
- * When the host keeps receiving more packets while tap_send() is
- * running we can hog the QEMU global mutex. Limit the number of
- * packets that are processed per tap_send() callback to prevent
- * stalling the guest.
- */
- packets++;
- if (packets >= 50) {
- break;
- }
- }
- }
复制代码
qemu通过qemu_net_queue_deliver将数据包发送到virtio_queue,在发送之前若delivering或!qemu_can_send_packet满足,则先将数据包加入packets队列,随后在qemu_net_queue_flush阶段将数据包发送到virtio_queue中,上图中virtio_net_receive就到达virtio虚拟硬件网卡了。
QEMU通过vhost-net从tap/tun取数据
vhost-net驱动加载时会生成/dev/vhost-net设备。
qemu-kvm启动时会open设备/dev/vhost-net,将调用vhost_net_open完成这个过程,vhost_net_open会进行handle_tx_net、handle_rx_net poll函数的初始化。
handle_tx_net、handle_rx_net最终会调用tun_recvmsg、tun_sendmsg进行数据收发。- /drivers/vhost/net.c:
- static int vhost_net_open(struct inode *inode, struct file *f)
- {
- ... ...
- vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, EPOLLOUT, dev);
- vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, EPOLLIN, dev);
- ... ...
- }
- static void handle_rx_net(struct vhost_work *work)
- {
- struct vhost_net *net = container_of(work, struct vhost_net,
- poll[VHOST_NET_VQ_RX].work);
- handle_rx(net);
- }
复制代码 handle_rx函数中recvmsg完成从tun取数据,通过copy_to_iter将msg放入virtio_queue,最后vhost_add_used_and_signal_n实现通知机制,qemu收到数据。- static void handle_rx(struct vhost_net *net)
- {
- ... ...
- err = sock->ops->recvmsg(sock, &msg,
- sock_len, MSG_DONTWAIT | MSG_TRUNC);
- ... ...
- num_buffers = cpu_to_vhost16(vq, headcount);
- if (likely(mergeable) &&
- copy_to_iter(&num_buffers, sizeof num_buffers,
- &fixup) != sizeof num_buffers) {
- vq_err(vq, "Failed num_buffers write");
- vhost_discard_vq_desc(vq, headcount);
- break;
- }
- vhost_add_used_and_signal_n(&net->dev, vq, vq->heads,
- headcount);
- ... ...
- }
复制代码 vhost_net通过vhost_worker内核线程进行工作队列的调度用于完成poll,vhost_worker内核线程是qemu通过vhost_dev_ioctl VHOST_SET_OWNER时创建的。- drivers/vhost/vhost.c:
- static int vhost_poll_wakeup(wait_queue_entry_t *wait, unsigned mode, int sync,
- void *key)
- {
- struct vhost_poll *poll = container_of(wait, struct vhost_poll, wait);
- if (!(key_to_poll(key) & poll->mask))
- return 0;
- vhost_poll_queue(poll);
- return 0;
- }
- void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn)
- {
- clear_bit(VHOST_WORK_QUEUED, &work->flags);
- work->fn = fn;
- }
- EXPORT_SYMBOL_GPL(vhost_work_init);
- /* Init poll structure */
- void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
- __poll_t mask, struct vhost_dev *dev)
- {
- init_waitqueue_func_entry(&poll->wait, vhost_poll_wakeup);
- init_poll_funcptr(&poll->table, vhost_poll_func);
- poll->mask = mask;
- poll->dev = dev;
- poll->wqh = NULL;
- vhost_work_init(&poll->work, fn);
- }
- EXPORT_SYMBOL_GPL(vhost_poll_init);
- static int vhost_worker(void *data)
- {
- ... ...
- for (;;) {
- ... ...
- node = llist_del_all(&dev->work_list);
- if (!node)
- schedule();
- node = llist_reverse_order(node);
- /* make sure flag is seen after deletion */
- smp_wmb();
- llist_for_each_entry_safe(work, work_next, node, node) {
- clear_bit(VHOST_WORK_QUEUED, &work->flags);
- __set_current_state(TASK_RUNNING);
- work->fn(work);
- if (need_resched())
- schedule();
- }
- ... ...
- }
- ... ...
- }
- long vhost_dev_set_owner(struct vhost_dev *dev)
- {
- ... ...
- worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid);
- ... ...
- }
- long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
- {
- ... ...
- if (ioctl == VHOST_SET_OWNER) {
- r = vhost_dev_set_owner(d);
- goto done;
- }
- ... ...
- }
复制代码- drivers/vhost/net.c:
- static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
- unsigned long arg)
- {
- ... ...
- switch (ioctl) {
- ... ...
- case VHOST_RESET_OWNER:
- return vhost_net_reset_owner(n);
- case VHOST_SET_OWNER:
- return vhost_net_set_owner(n);
- default:
- mutex_lock(&n->dev.mutex);
- r = vhost_dev_ioctl(&n->dev, ioctl, argp);
- if (r == -ENOIOCTLCMD)
- r = vhost_vring_ioctl(&n->dev, ioctl, argp);
- else
- vhost_net_flush(n);
- mutex_unlock(&n->dev.mutex);
- return r;
- }
- }
- static long vhost_net_set_owner(struct vhost_net *n)
- {
- ... ...
- r = vhost_dev_set_owner(&n->dev);
- ... ...
- return r;
- }
- static const struct file_operations vhost_net_fops = {
- .owner = THIS_MODULE,
- .release = vhost_net_release,
- .read_iter = vhost_net_chr_read_iter,
- .write_iter = vhost_net_chr_write_iter,
- .poll = vhost_net_chr_poll,
- .unlocked_ioctl = vhost_net_ioctl,
- #ifdef CONFIG_COMPAT
- .compat_ioctl = vhost_net_compat_ioctl,
- #endif
- .open = vhost_net_open,
- .llseek = noop_llseek,
- };
- static struct miscdevice vhost_net_misc = {
- .minor = VHOST_NET_MINOR,
- .name = "vhost-net",
- .fops = &vhost_net_fops,
- };
- static int vhost_net_init(void)
- {
- if (experimental_zcopytx)
- vhost_net_enable_zcopy(VHOST_NET_VQ_TX);
- return misc_register(&vhost_net_misc);
- }
复制代码 附
主机vhost驱动加载时调用vhost_net_init注册一个MISC驱动,生成/dev/vhost-net的设备文件。
主机qemu-kvm启动时调用open对应的vhost_net_open做主要创建队列和收发函数的挂载,接着调用ioctl启动内核线程vhost,做收发包的处理。
主机qemu通过ioctl配置kvm模块,主要设置通信方式,因为主机vhost和virtio只进行报文的传输,kvm进行提醒。
虚拟机virtio模块注册,生成虚拟机的网络设备,配置中断和NAPI。
虚拟机发包流程如下:
直接从应用层走协议栈最后调用发送接口ndo_start_xmit对应的start_xmit,将报文放入发送队列,vp_notify通知kvm。
kvm通过vmx_handle_exit一系列调用到wake_up_process唤醒vhost线程。
vhost模块的线程激活并且拿到报文,在通过之前绑定的发送接口handle_tx_kick进行发送,调用虚拟网卡的tun_sendmsg最终到netif_rx接口进入主机内核协议栈。
虚拟机收包流程如下:
tap设备的ndo_start_xmit对应的tun_net_xmit最终调用到wake_up_process激活vhost线程,调用handle_rx_kick,将报文放入接收队列。
通过一系列的调用到kvm模块的接口kvm_vcpu_kick,向qemu虚拟机注入中断。
虚拟机virtio模块中断调用接口vp_interrupt,调用virtnet_poll,再调用到netif_receive_skb进入虚拟机的协议栈。
资料来源:https://blog.csdn.net/qq_20817327/article/details/106838029
来源:https://www.cnblogs.com/forwards/p/17514221.html
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