关于LINUX-2.6.11的USB驱动问题请教

ljf112621

我想请问一下 ,在LINUX-2.6.11的USB 驱动程序中, 当你插入一个U盘进行识别时,会调用usb/storage/usb.c中usb_stor_acquire_resource 函数,该函数定义如下:
/* Initialize all the dynamic resources we need */
static int usb_stor_acquire_resources(struct us_data *us)      
{                                                                                                               
        int p;

        us->current_urb = usb_alloc_urb(0, GFP_KERNEL);                                                //分配URB结构对象空间
        if (!us->current_urb) {
                US_DEBUGP("URB allocation failed\n");
                return -ENOMEM;
        }

        /* Lock the device while we carry out the next two operations */
        down(&us->dev_semaphore);

        /* For bulk-only devices, determine the max LUN value */
        if (us->protocol == US_PR_BULK) {
                p = usb_stor_Bulk_max_lun(us);
                if (p < 0) {
                        up(&us->dev_semaphore);
                        return p;
                }
                us->max_lun = p;
        }

        /* Just before we start our control thread, initialize
         * the device if it needs initialization */
        if (us->unusual_dev->initFunction)
                us->unusual_dev->initFunction(us);

        up(&us->dev_semaphore);

        /*
         * Since this is a new device, we need to register a SCSI
         * host definition with the higher SCSI layers.
         */
        us->host = scsi_host_alloc(&usb_stor_host_template, sizeof(us));
        if (!us->host) {
                printk(KERN_WARNING USB_STORAGE
                        "Unable to allocate the scsi host\n");
                return -EBUSY;
        }

        /* Set the hostdata to prepare for scanning */
        us->host->hostdata[0] = (unsigned long) us;

        /* Start up our control thread */
        p = kernel_thread(usb_stor_control_thread, us, CLONE_VM);
        if (p < 0) {
                printk(KERN_WARNING USB_STORAGE
                       "Unable to start control thread\n");
                return p;
        }
        us->pid = p;

        /* Wait for the thread to start */
        wait_for_completion(&(us->notify));

        return 0;
}

这个函数定义中有这么一步:
p = usb_stor_Bulk_max_lun(us);
注释说这主要是对批量的设备(U盘等)，得到最大逻辑单元值.我查了一下,好象在SCSI协议模型中，每个逻辑单元用来操作SCSI设备,但还是不是很懂.

哪位高人能够详细的解释一下什么是LUN吗?在USB识别过程中获取LUN值有什么用啊?
为什么我多数U盘获得的LUN值都是0呢?

usb_stor_Bulk_max_lun函数在usb/storage/transport.c中定义为
/*
* Bulk only transport
*/

/* Determine what the maximum LUN supported is */
int usb_stor_Bulk_max_lun(struct us_data *us)
{
        int result;

        /* issue the command */
        result = usb_stor_control_msg(us, us->recv_ctrl_pipe,
                                 US_BULK_GET_MAX_LUN,
                                 USB_DIR_IN | USB_TYPE_CLASS |
                                 USB_RECIP_INTERFACE,
                                 0, us->ifnum, us->iobuf, 1, HZ);

        US_DEBUGP("GetMaxLUN command result is %d, data is %d\n",
                  result, us->iobuf[0]);

        /* if we have a successful request, return the result */
        if (result > 0)
                return us->iobuf[0];

        /*
         * Some devices (i.e. Iomega Zip100) need this -- apparently
         * the bulk pipes get STALLed when the GetMaxLUN request is
         * processed.   This is, in theory, harmless to all other devices
         * (regardless of if they stall or not).
         */
        if (result == -EPIPE) {
                usb_stor_clear_halt(us, us->recv_bulk_pipe);
                usb_stor_clear_halt(us, us->send_bulk_pipe);
        }

        /*
         * Some devices don't like GetMaxLUN.  They may STALL the control
         * pipe, they may return a zero-length result, they may do nothing at
         * all and timeout, or they may fail in even more bizarrely creative
         * ways.  In these cases the best approach is to use the default
         * value: only one LUN.
         */
        return 0;
}

ljf112621

来个高手指点一下啊!给个资料链接也可以啊!