Android—— 4.2 Vold挂载管理_Kernel_USB_Uevent (七)

在前文Android—— 4.2 Vold挂载管理_NetlinkManager (四)中有解析到Vold 是从kernel中获取uevent事件，来获取device信息，其中是通过一个Netlink的套接字，目前整个Vold机制也分析完了，

上篇 Android—— 4.2 Vold挂载管理_MountService (六)分析了机制中最上层的，这里分析一下最下层的kernel uevent事件的发送，以USB设备为例！

撰写不易,转载请注明出处：http://blog.csdn.net/jscese/article/details/39006999

一.USB_HUB_EVENT:

usb driver在/drivers/usb/目录下，这个目录下有多个文件夹，具体编译使用的是哪一个就要看kernel的.config了，可查看目录下的Makefile中的CONFIG*宏是否有定义.

我这边的kernel version 3.1.10,根据config我的kernel用的驱动在/drivers/usb/core目录下，usb.c 为入口.

static int __init usb_init(void){    int retval;    if (nousb) {        pr_info("%s: USB support disabled\n", usbcore_name);        return 0;    }    retval = usb_debugfs_init();//debug 文件的初始化    if (retval)        goto out;    retval = bus_register(&usb_bus_type);    if (retval)        goto bus_register_failed;    retval = bus_register_notifier(&usb_bus_type, &usb_bus_nb);    if (retval)        goto bus_notifier_failed;    retval = usb_major_init(); //    if (retval)        goto major_init_failed;    retval = usb_register(&usbfs_driver);    if (retval)        goto driver_register_failed;    retval = usb_devio_init();    if (retval)        goto usb_devio_init_failed;    retval = usbfs_init();    if (retval)        goto fs_init_failed;    retval = usb_hub_init(); //循环监测的初始化  ...}subsys_initcall(usb_init);

可以看到初始入口即为usb_init，在里面初始化了usb相关各种参数配置，这里着重分析与插拔usb设备的usb_hub_init().

调用到/drivers/usb/core/hub.c中的usb_hub_init：

int usb_hub_init(void){    if (usb_register(&hub_driver) < 0) {        printk(KERN_ERR "%s: can't register hub driver\n",            usbcore_name);        return -1;    }    khubd_task = kthread_run(hub_thread, NULL, "khubd");//创建一个线程，执行hub_thread函数，线程名为khubd    if (!IS_ERR(khubd_task))        return 0;    /* Fall through if kernel_thread failed */    usb_deregister(&hub_driver);    printk(KERN_ERR "%s: can't start khubd\n", usbcore_name);    return -1;}

看线程函数hub_thread：

static int hub_thread(void *__unused){    /* khubd needs to be freezable to avoid intefering with USB-PERSIST     * port handover.  Otherwise it might see that a full-speed device     * was gone before the EHCI controller had handed its port over to     * the companion full-speed controller.     */    set_freezable();    do {        hub_events(); //进入有条件的循环，持续监测        wait_event_freezable(khubd_wait,                !list_empty(&hub_event_list) ||                kthread_should_stop());    } while (!kthread_should_stop() || !list_empty(&hub_event_list));    pr_debug("%s: khubd exiting\n", usbcore_name);    return 0;}

再看hub_events:

static void hub_events(void){    struct list_head *tmp;    struct usb_device *hdev;    struct usb_interface *intf;    struct usb_hub *hub;    struct device *hub_dev;  ...    while (1) {        /* Grab the first entry at the beginning of the list */        spin_lock_irq(&hub_event_lock);        if (list_empty(&hub_event_list)) {            spin_unlock_irq(&hub_event_lock);            break;        }   ...           /* deal with port status changes */        for (i = 1; i <= hub->descriptor->bNbrPorts; i++) {  // 遍历usb的端口，检测端口状态            if (test_bit(i, hub->busy_bits))                continue;            connect_change = test_bit(i, hub->change_bits);            if (!test_and_clear_bit(i, hub->event_bits) &&                    !connect_change)                continue;            ret = hub_port_status(hub, i,                    &portstatus, &portchange); // 依次判断端口状态是否被改变            if (ret < 0)                continue;            if (portchange & USB_PORT_STAT_C_CONNECTION) { //判断端口状态改变情况                clear_port_feature(hdev, i,                    USB_PORT_FEAT_C_CONNECTION);                connect_change = 1;                #if defined(ENABLE_BATTERY_CHARGE) && (MP_USB_MSTAR==1)                if (hdev->parent == NULL) {                    usb_bc_enable(hcd, true);                                }                #endif                /* patch for DM always keep high issue */                #if (_USB_HS_CUR_DRIVE_DM_ALLWAYS_HIGH_PATCH) && (MP_USB_MSTAR==1)                /* turn on overwrite mode */                if (hdev->parent == NULL)                {                    writeb(readb((void*)(hcd->utmi_base+0x0*2)) | BIT1, (void*) (hcd->utmi_base+0x0*2)); //tern_ov = 1                }                #endif            }           ...                if (connect_change)                hub_port_connect_change(hub, i,                        portstatus, portchange); // 处理变化的端口           ...     }     ...  }}

通过对usb端口状态的循环监测，来处理usb设备的插拔！

端口处理就从检测到变化开始：

static void hub_port_connect_change(struct usb_hub *hub, int port1,                    u16 portstatus, u16 portchange){    struct usb_device *hdev = hub->hdev;    struct device *hub_dev = hub->intfdev;    struct usb_hcd *hcd = bus_to_hcd(hdev->bus);    unsigned wHubCharacteristics =            le16_to_cpu(hub->descriptor->wHubCharacteristics);    struct usb_device *udev;   ...    for (i = 0; i < SET_CONFIG_TRIES; i++) {         /* reallocate for each attempt, since references         * to the previous one can escape in various ways         */        udev = usb_alloc_dev(hdev, hdev->bus, port1);   ...//一些初始赋值电流 速度什么的        /* reset (non-USB 3.0 devices) and get descriptor */        status = hub_port_init(hub, udev, port1, i); //对端口的初始操作        if (status < 0)            goto loop;  ...        status = usb_new_device(udev); //定义一个新的usb设备} ...}

usb driver的检测部分大体就是这样，主要是通过对port的监测！

二.kobject_uevent_env:

在上面的hub_event中分析了kernel对插入设备的检测与识别，到usb_new_device：

int usb_new_device(struct usb_device *udev){    int err; ...    /* Tell the world! */    announce_device(udev); //打印出识别到的usb设备相关信息，包括 name idVendor idProduct 等...    err = device_add(&udev->dev); //添加识别到的这个设备...}

再看device_add:

int device_add(struct device *dev){    struct device *parent = NULL;...    /* first, register with generic layer. */    /* we require the name to be set before, and pass NULL */    error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);...    kobject_uevent(&dev->kobj, KOBJ_ADD); //发送这个设备事件，事件类型为添加...}

最后调用到真正发送uevent事件的是/lib/kobject_uevent.c下的 kobject_uevent_env

int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,               char *envp_ext[]){    struct kobj_uevent_env *env;    const char *action_string = kobject_actions[action]; //根据定义数组    const char *devpath = NULL;    const char *subsystem;...    /* originating subsystem */    if (uevent_ops && uevent_ops->name)        subsystem = uevent_ops->name(kset, kobj);    else        subsystem = kobject_name(&kset->kobj);...    /* environment buffer */    env = kzalloc(sizeof(struct kobj_uevent_env), GFP_KERNEL);    retval = add_uevent_var(env, "ACTION=%s", action_string);//按照格式添加到env中    if (retval)        goto exit;    retval = add_uevent_var(env, "DEVPATH=%s", devpath);    if (retval)        goto exit;    retval = add_uevent_var(env, "SUBSYSTEM=%s", subsystem);    if (retval)        goto exit;...    /* send netlink message */ //从这里开始才是真正的发送操作，使用的是netlink的套接字    mutex_lock(&uevent_sock_mutex);    list_for_each_entry(ue_sk, &uevent_sock_list, list) {        struct sock *uevent_sock = ue_sk->sk;        struct sk_buff *skb;        size_t len;        /* allocate message with the maximum possible size */        len = strlen(action_string) + strlen(devpath) + 2;        skb = alloc_skb(len + env->buflen, GFP_KERNEL);        if (skb) {            char *scratch;            /* add header */            scratch = skb_put(skb, len);            sprintf(scratch, "%s@%s", action_string, devpath);            /* copy keys to our continuous event payload buffer */            for (i = 0; i < env->envp_idx; i++) {                len = strlen(env->envp[i]) + 1;                scratch = skb_put(skb, len);                strcpy(scratch, env->envp[i]);            }  //抽取上面准备的数据            NETLINK_CB(skb).dst_group = 1;            retval = netlink_broadcast_filtered(uevent_sock, skb,  //发送函数                                0, 1, GFP_KERNEL,                                kobj_bcast_filter,                                kobj);            /* ENOBUFS should be handled in userspace */            if (retval == -ENOBUFS || retval == -ESRCH)                retval = 0;        } else            retval = -ENOMEM;    }    mutex_unlock(&uevent_sock_mutex);...}

最后通过netlink_broadcast_filtered发送设备uevent的信息，对于kernel中的usb driver 我接触的不多，这里只是简单解析了一下往Vold 发送uevent的流程，

其中很多复杂的流程我都没写，以后有机会学习usb driver时再研究！

一.USB_HUB_EVENT:

二.kobject_uevent_env:

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