在驅動模塊初始化函數中實現設備節點的自動創建 zz

我們在剛開始寫Linux設備驅動程序的時候，很多時候都是利用mknod命令手動創建設備節點，實際上Linux 內核爲我們提供了一組函數，可以用來在模塊加載的時候自動在/dev目錄下創建相應設備節點，並在卸載模塊時刪除該節點，當然前提條件是用戶空間移植了 udev。 內核中定義了struct class結構體，顧名思義，一個struct class結構體類型變量對應一個類，內核同時提供了class_create(…)函數，可以用它來創建一個類，這個類存放於sysfs下面，一旦創建好了這個類，再調用device_create(…)函數來在/dev目錄下創建相應的設備節點。這樣，加載模塊的時候，用戶空間中的udev會自動響應 device_create(…)函數，去/sysfs下尋找對應的類從而創建設備節點。 注意，在2.6較早的內核版本中，device_create(…)函數名稱不同，是 class_device_create(…)，所以在新的內核中編譯以前的模塊程序有時會報錯，就是因爲函數名稱不同，而且裏面的參數設置也有一些變化。 struct class和device_create(…) 以及device_create(…)都定義在/include/linux/device.h中，使用的時候一定要包含這個頭文件，否則編譯器會報錯。 在2.6.26.6內核版本中，struct class定義在頭文件include/linux/device.h中： /* * device classes */ struct class { const char *name; struct module *owner; nbsp;struct kset subsys; struct list_head devices; struct list_head interfaces; struct kset class_dirs; struct semaphore sem; /* locks children, devices, interfaces */ struct class_attribute *class_attrs; struct device_attribute *dev_attrs; int (*dev_uevent)(struct device *dev, struct kobj_uevent_env *env); void (*class_release)(struct class *class); void (*dev_release)(struct device *dev); int (*suspend)(struct device *dev, pm_message_t state); int (*resume)(struct device *dev); }; class_create(…)在/drivers/base/class.c中實現： /** * class_create - create a struct class structure * @owner: pointer to the module that is to "own" this struct class * @name: pointer to a string for the name of this class. * * This is used to create a struct class pointer that can then be used * in calls to device_create(). * * Note, the pointer created here is to be destroyed when finished by * making a call to class_destroy(). */ struct class *class_create(struct module *owner, const char *name) { struct class *cls; int retval; cls = kzalloc(sizeof(*cls), GFP_KERNEL); if (!cls) { retval = -ENOMEM; goto error; } cls->name = name; cls->owner = owner; cls->class_release = class_create_release; retval = class_register(cls); if (retval) goto error; return cls; error: kfree(cls); return ERR_PTR(retval); } 第一個參數指定類的所有者是哪個模塊，第二個參數指定類名。 在class.c中，還定義了class_destroy(…)函數，用於在模塊卸載時刪除類。 device_create(…)函數在/drivers/base/core.c中實現： /** * device_create - creates a device and registers it with sysfs * @class: pointer to the struct class that this device should be registered to * @parent: pointer to the parent struct device of this new device, if any * @devt: the dev_t for the char device to be added * @fmt: string for the device's name * * This function can be used by char device classes. A struct device * will be created in sysfs, registered to the specified class. * * A "dev" file will be created, showing the dev_t for the device, if * the dev_t is not 0,0. * If a pointer to a parent struct device is passed in, the newly created * struct device will be a child of that device in sysfs. * The pointer to the struct device will be returned from the call. * Any further sysfs files that might be required can be created using this * pointer. * * Note: the struct class passed to this function must have previously * been created with a call to class_create(). */ struct device *device_create(struct class *class, struct device *parent, dev_t devt, const char *fmt, ...) { va_list vargs; struct device *dev; va_start(vargs, fmt); dev = device_create_vargs(class, parent, devt, NULL, fmt, vargs); va_end(vargs); return dev; } 第一個參數指定所要創建的設備所從屬的類，第二個參數是這個設備的父設備，如果沒有就指定爲 NULL，第三個參數是設備號，第四個參數是設備名稱，第五個參數是從設備號。 下面以一個簡單字符設備驅動來展示如何使用這幾個函數 #include #include #include #include #include #include MODULE_LICENSE ("GPL"); int hello_major = 555; int hello_minor = 0; int number_of_devices = 1; struct cdev cdev; dev_t dev = 0; struct file_operations hello_fops = { .owner = THIS_MODULE }; static void char_reg_setup_cdev (void) { int error, devno = MKDEV (hello_major, hello_minor); cdev_init (&cdev, &hello_fops); cdev.owner = THIS_MODULE; cdev.ops = &hello_fops; error = cdev_add (&cdev, devno , 1); if (error) printk (KERN_NOTICE "Error %d adding char_reg_setup_cdev", error); } struct class *my_class; static int __init hello_2_init (void) { int result; dev = MKDEV (hello_major, hello_minor); result = register_chrdev_region (dev, number_of_devices, "hello"); if (result<0) { printk (KERN_WARNING "hello: can't get major number %d/n", hello_major); return result; } char_reg_setup_cdev (); /* create your own class under /sysfs */ my_class = class_create(THIS_MODULE, "my_class"); if(IS_ERR(my_class)) { printk("Err: failed in creating class./n"); return -1; } /* register your own device in sysfs, and this will cause udev to create corresponding device node */ device_create( my_class, NULL, MKDEV(hello_major, 0), "hello" "%d", 0 ); printk (KERN_INFO "Registered character driver/n"); return 0; } static void __exit hello_2_exit (void) { dev_t devno = MKDEV (hello_major, hello_minor); cdev_del (&cdev); device_destroy(my_class, MKDEV(adc_major, 0)); //delete device node under /dev class_destroy(my_class); //delete class created by us unregister_chrdev_region (devno, number_of_devices); printk (KERN_INFO "char driver cleaned up/n"); } module_init (hello_2_init); module_exit (hello_2_exit); 這樣，模塊加載後，就能在/dev目錄下找到hello0這個設備節點了。