半虚拟化下网络数据包的处理过程
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http://hi.baidu.com/%B0%B5%D4%C2%C1%F7%B9%E2/blog/item/2c21d0231c03dbffd7cae2eb.html
（Note: 先要理解Xen的split driver model，之后再看这篇文章）
（1）网络设备后端代码分析
linux中网络数据包处理流程：
R3 应用程序数据包发送
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
. TCP/IP协议栈处理
. v
R0 sk_buff格式数据
. v
. 网络设备发包函数完成发包过程
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
. 硬 件
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
xen半虚拟化下网络数据包处理过程：
------------------------------------------ ---------------------------------------------
. R3 R3
. 应用程序发送数据包
. v
-Dom0---------------------------------- --DomU------------------------------------
. R1 R1
. ----------------TCP/IP TCP/IP
. v ^ v
真实设备驱动 后端设备驱动 前端设备驱动
. | ^ |
------ ---------------------------------------------------------------------------------------------
. | R0 | ------------------------- |
. | -------| 发送数据 |<---
. | | (共享内存方式) |
. | -------------------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
. v 硬 件
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
由于DomU可以有多个，因此设备后端需要为多个设备前端提供服务，具有网桥的功能。借两张图来说明下：
网络设备后端初始化：
/linux-2.6.18-xen.hg/drivers/xen/netback/netback.c
1659 module_init(netback_init); // 定义设备后端模块初始化函数
/linux-2.6.18-xen.hg/drivers/xen/netback/netback.c
1591 static int __init netback_init(void)
1592 {
.....................
// skb队列初始化
1602 skb_queue_head_init(&rx_queue);
1603 skb_queue_head_init(&tx_queue);
......................
// xenbus初始化（下次找时间把整个xenbus的代码分析给补上）
1645 netif_xenbus_init();
......................
1656 return 0;
1657 }
/linux-2.6.18-xen.hg/drivers/xen/netback/netback.c
451 void netif_xenbus_init(void)
452 {
// 网络后端设备注册
453 xenbus_register_backend(&netback);
454 }
/linux-2.6.18-xen.hg/drivers/xen/netback/xenbus.c
440 static struct xenbus_driver netback = {
441 .name = "vif",
442 .owner = THIS_MODULE,
443 .ids = netback_ids,
444 .probe = netback_probe, // 后端设备回调函数
445 .remove = netback_remove,
446 .uevent = netback_uevent,
447 .otherend_changed = frontend_changed, // 前端状态发生改变时调用
448 };
/linux-2.6.18-xen.hg/drivers/xen/xenbus/xenbus_probe_backend.c
175 int xenbus_register_backend(struct xenbus_driver *drv)
176 {
177 drv->read_otherend_details = read_frontend_details;
178
179 return xenbus_register_driver_common(drv, &xenbus_backend);
180 }
181 EXPORT_SYMBOL_GPL(xenbus_register_backend);
/linux-2.6.18-xen.hg/drivers/xen/xenbus/xenbus_probe_backend.c
112 static struct xen_bus_type xenbus_backend = {
113 .root = "backend",
114 .levels = 3, /* backend/type/<frontend>/<id> */
115 .get_bus_id = backend_bus_id,
116 .probe = xenbus_probe_backend,
117 .error = -ENODEV,
118 .bus = {
119 .name = "xen-backend",
120 .match = xenbus_match,
121 .probe = xenbus_dev_probe,
122 .remove = xenbus_dev_remove,
123 // .shutdown = xenbus_dev_shutdown,
124 .uevent = xenbus_uevent_backend,
125 },
126 .dev = {
127 .bus_id = "xen-backend",
128 },
129 };
/linux-2.6.18-xen.hg/drivers/xen/xenbus/xenbus_probe_backend.c
373 int xenbus_register_driver_common(struct xenbus_driver *drv,
374 struct xen_bus_type *bus)
375 {
............................
381 drv->driver.name = drv->name;
382 drv->driver.bus = &bus->bus;
.............................
392 mutex_lock(&xenwatch_mutex);
393 ret = driver_register(&drv->driver); //注册后端设备driver
394 mutex_unlock(&xenwatch_mutex);
395 return ret;
396 }
/linux-2.6.18-xen.hg/drivers/base/driver.c
171 int driver_register(struct device_driver * drv)
172 {
.................
180 return bus_add_driver(drv); // - - 后面就出了xen目录了，不分析了
181 }
下面来分析下注册的后端设备回调函数 netback_probe
/linux-2.6.18-xen.hg/drivers/xen/netback/xenbus.c
53 /**
54 * Entry point to this code when a new device is created. Allocate the basic
55 * structures and switch to InitWait.
56 */
// 当一个新设备被创建的时候会调用该函数
57 static int netback_probe(struct xenbus_device *dev,
58 const struct xenbus_device_id *id)
59 {
................
// 分配一个与新设备对应的backend
64 struct backend_info *be = kzalloc(sizeof(struct backend_info),
65 GFP_KERNEL);
................
72 be->dev = dev;
73 dev->dev.driver_data = be;
................
// 却换设备的状态为XenbusStateInitWait
128 err = xenbus_switch_state(dev, XenbusStateInitWait);
129 if (err)
130 goto fail;
131
132 /* This kicks hotplug scripts, so do it immediately. */
133 backend_create_netif(be);
.................
144 }
30 struct backend_info
31 {
32 struct xenbus_device *dev;
33 blkif_t *blkif;
34 struct xenbus_watch backend_watch;
35 unsigned major;
36 unsigned minor;
37 char *mode;
38 };
/linux-2.6.18-xen.hg/include/xen/interface/io/xenbus.h
36 enum xenbus_state {
37 XenbusStateUnknown = 0,
38
39 XenbusStateInitialising = 1,
40
41 /*
42 * InitWait: Finished early initialisation but waiting for information
43 * from the peer or hotplug scripts.
44 */
45 XenbusStateInitWait = 2,
46
47 /*
48 * Initialised: Waiting for a connection from the peer.
49 */
50 XenbusStateInitialised = 3,
51
52 XenbusStateConnected = 4,
53
54 /*
55 * Closing: The device is being closed due to an error or an unplug event.
56 */
57 XenbusStateClosing = 5,
58
59 XenbusStateClosed = 6,
60
61 /*
62 * Reconfiguring: The device is being reconfigured.
63 */
64 XenbusStateReconfiguring = 7,
65
66 XenbusStateReconfigured = 8
67 };
68 typedef enum xenbus_state XenbusState;
/linux-2.6.18-xen.hg/drivers/xen/netback/xenbus.c
183 static void backend_create_netif(struct backend_info *be)
184 {
185 int err;
186 long handle;
187 struct xenbus_device *dev = be->dev;
...............
//
198 be->netif = netif_alloc(&dev->dev, dev->otherend_id, handle);
...............
207 }
/linux-2.6.18-xen.hg/drivers/xen/netback/interface.c
178 netif_t *netif_alloc(struct device *parent, domid_t domid, unsigned int handle)
179 {
................
181 struct net_device *dev;
182 netif_t *netif;
183 char name[IFNAMSIZ] = {};
184
185 snprintf(name, IFNAMSIZ - 1, "vif%u.%u", domid, handle);
186 dev = alloc_netdev(sizeof(netif_t), name, ether_setup); // 创建网络设备
................
196 netif->domid = domid;
197 netif->handle = handle;
................
199 init_waitqueue_head(&netif->waiting_to_free);
200 netif->dev = dev;
201
202 netback_carrier_off(netif);
203
204 netif->credit_bytes = netif->remaining_credit = ~0UL;
205 netif->credit_usec = 0UL;
...................
207 /* Initialize 'expires' now: it's used to track the credit window. */
208 netif->credit_timeout.expires = jiffies;
...................
212 dev->hard_start_xmit = netif_be_start_xmit; // 定义后端发送函数
213 dev->get_stats = netif_be_get_stats;
214 dev->open = net_open;
215 dev->stop = net_close;
216 dev->change_mtu = netbk_change_mtu;
217 dev->features = NETIF_F_IP_CSUM;
.....................
232 rtnl_lock();
233 err = register_netdevice(dev); // 向内核注册设备
234 rtnl_unlock();
.....................
243 return netif;
244 }
下面来分析下frontend_changed函数，该函数在前端设备状态发生改变之后被调用
/linux-2.6.18-xen.hg/drivers/xen/netback/xenbus.c
210 /**
211 * Callback received when the frontend's state changes.
212 */
213 static void frontend_changed(struct xenbus_device *dev,
214 enum xenbus_state frontend_state)
215 {
.................
222 switch (frontend_state) { // 根据前端设备状态进行处理
.................
234 case XenbusStateConnected: // 前端设备连接
235 if (dev->state == XenbusStateConnected)
236 break;
237 backend_create_netif(be);
238 if (be->netif)
239 connect(be);
240 break;
.................
265 }
/linux-2.6.18-xen.hg/drivers/xen/netback/xenbus.c
326 static void connect(struct backend_info *be)
327 {
.................
331 err = connect_rings(be);
.................
345 xenbus_switch_state(dev, XenbusStateConnected); // 更改设备状态
.................
347 netif_wake_queue(be->netif->dev);
348 }
// connect_rings这个函数的分析主要是关注与event-channel有关的方面，可能不够客观
/linux-2.6.18-xen.hg/drivers/xen/netback/xenbus.c
351 static int connect_rings(struct backend_info *be)
352 {
.................
355 unsigned int evtchn, rx_copy;
.................
361 err = xenbus_gather(XBT_NIL, dev->otherend,
362 "tx-ring-ref", "%lu", &tx_ring_ref,
363 "rx-ring-ref", "%lu", &rx_ring_ref,
364 "event-channel", "%u", &evtchn, NULL);
..................
419 /* Map the shared frame, irq etc. */
420 err = netif_map(be->netif, tx_ring_ref, rx_ring_ref, evtchn);
...................
427 return 0;
428 }
tx_ring_ref - - the grant table reference for the transmission ring queue
rx_ring_ref - - the grant table reference for the receiving ring queue
/linux-2.6.18-xen.hg/drivers/xen/netback/interface.c
306 int netif_map(netif_t *netif, unsigned long tx_ring_ref,
307 unsigned long rx_ring_ref, unsigned int evtchn)
308 {
......................
328 err = bind_interdomain_evtchn_to_irqhandler(
329 netif->domid, evtchn, netif_be_int, 0,
330 netif->dev->name, netif);
.......................
361 }
/linux-2.6.18-xen.hg/drivers/xen/core/evtchn.c
563 int bind_interdomain_evtchn_to_irqhandler(
564 unsigned int remote_domain,
565 unsigned int remote_port,
566 irqreturn_t (*handler)(int, void *, struct pt_regs *),
567 unsigned long irqflags,
568 const char *devname,
569 void *dev_id)
570 {
....................
573 irq = bind_interdomain_evtchn_to_irq(remote_domain, remote_port);
....................
577 retval = request_irq(irq, handler, irqflags, devname, dev_id);
....................
584 }
/linux-2.6.18-xen.hg/drivers/xen/core/evtchn.c
396 static int bind_interdomain_evtchn_to_irq(unsigned int remote_domain,
397 unsigned int remote_port)
398 {
399 struct evtchn_bind_interdomain bind_interdomain;
..............
405 err = HYPERVISOR_event_channel_op(EVTCHNOP_bind_interdomain,
406 &bind_interdomain);
407
408 return err ? : bind_local_port_to_irq(bind_interdomain.local_port); //如果成功，则返回local port
409 }
/linux-2.6.18-xen.hg/include/xen/interface/event_channel.h
68 #define EVTCHNOP_bind_interdomain 0
69 struct evtchn_bind_interdomain {
70 /* IN parameters. */
71 domid_t remote_dom;
72 evtchn_port_t remote_port;
73 /* OUT parameters. */
74 evtchn_port_t local_port;
75 };
（2）网络设备前端代码分析
/linux-2.6.18-xen.hg/drivers/xen/netfront/netfront.c
2200 static int __init netif_init(void)
2201 {
...............
2225 err = xenbus_register_frontend(&netfront_driver); //注册设备
...............
2232 }
2233 module_init(netif_init);
2187 static struct xenbus_driver netfront_driver = {
2188 .name = "vif",
2189 .owner = THIS_MODULE,
2190 .ids = netfront_ids,
2191 .probe = netfront_probe, // 前端回调函数
2192 .remove = __devexit_p(netfront_remove),
2193 .suspend = netfront_suspend,
2194 .suspend_cancel = netfront_suspend_cancel,
2195 .resume = netfront_resume,
2196 .otherend_changed = backend_changed, // 后端状态改变时的回调函数
2197 };
/linux-2.6.18-xen.hg/drivers/xen/netfront/netfront.c
240 /**
241 * Entry point to this code when a new device is created. Allocate the basic
242 * structures and the ring buffers for communication with the backend, and
243 * inform the backend of the appropriate details for those.
244 */
245 static int __devinit netfront_probe(struct xenbus_device *dev,
246 const struct xenbus_device_id *id)
247 {
.................
252 netdev = create_netdev(dev); // 创建网络设备
.................
262 err = register_netdev(info->netdev); // 注册网络设备
.................
269 err = xennet_sysfs_addif(info->netdev); // 将该设备加入文件系统
.................
283 }
/linux-2.6.18-xen.hg/drivers/xen/netfront/netfront.c
2037 static struct net_device * __devinit create_netdev(struct xenbus_device *dev)
2038 {
................
2043 netdev = alloc_etherdev(sizeof(struct netfront_info)); //创建以太网设备
................
2093 netdev->open = network_open;
2094 netdev->hard_start_xmit = network_start_xmit; // 网络设备前端发送函数
2095 netdev->stop = network_close;
2096 netdev->get_stats = network_get_stats;
2097 netdev->poll = netif_poll; // 网络设备前端接收函数
.................
2120 }
/linux-2.6.18-xen.hg/drivers/xen/netfront/netfront.c
528 /**
529 * Callback received when the backend's state changes.
530 */
531 static void backend_changed(struct xenbus_device *dev,
532 enum xenbus_state backend_state)
533 {
...................
539 switch (backend_state) {
...................
549 case XenbusStateInitWait:
550 if (dev->state != XenbusStateInitialising)
551 break;
552 if (network_connect(netdev) != 0)
553 break;
554 xenbus_switch_state(dev, XenbusStateConnected);
555 send_fake_arp(netdev);
556 break;
...................
561 }
562 }
/linux-2.6.18-xen.hg/drivers/xen/netfront/netfront.c
1775 static int network_connect(struct net_device *dev)
1776 {
...................
1801 err = talk_to_backend(np->xbdev, np); // 与后端交互
...................
1867 }
361 /* Common code used when first setting up, and when resuming. */
362 static int talk_to_backend(struct xenbus_device *dev,
363 struct netfront_info *info)
364 {
...................
379 /* Create shared ring, alloc event channel. */
380 err = setup_device(dev, info);
...................
466 }
468 static int setup_device(struct xenbus_device *dev, struct netfront_info *info)
469 {
470 struct netif_tx_sring *txs; //发送环指针
471 struct netif_rx_sring *rxs; // 接收环指针
...................
// 为发送环分配页面
481 txs = (struct netif_tx_sring *)get_zeroed_page(GFP_NOIO | __GFP_HIGH);
...................
487 SHARED_RING_INIT(txs); // 发送环始化
488 FRONT_RING_INIT(&info->tx, txs, PAGE_SIZE); //发送环前端初始化
489
490 err = xenbus_grant_ring(dev, virt_to_mfn(txs)); // 运行设备访问该页
...................
// 接收环分配页面
497 rxs = (struct netif_rx_sring *)get_zeroed_page(GFP_NOIO | __GFP_HIGH);
...................
503 SHARED_RING_INIT(rxs); // 接收环初始化
504 FRONT_RING_INIT(&info->rx, rxs, PAGE_SIZE); // 接收环前端页面初始化
505
506 err = xenbus_grant_ring(dev, virt_to_mfn(rxs)); // 运行设备访问接收环页面
..................
515 err = bind_listening_port_to_irqhandler( // 绑定事件通道端口
516 dev->otherend_id, netif_int, SA_SAMPLE_RANDOM, netdev->name,
517 netdev);
...................
526 }
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