cdev_init和register_chrdev区别

---

01：include/linux/fs.h

static inline int register_chrdev(unsigned int major, const char *name,                                                              const struct file_operations *fops)
{
return __register_chrdev(major, 0, 256, name, fops);
}

fs/char_dev.c

/**
* __register_chrdev() - create and register a cdev occupying a range of minors
* @major: major device number or 0 for dynamic allocation
* @baseminor: first of the requested range of minor numbers
* @count: the number of minor numbers required
* @name: name of this range of devices
* @fops: file operations associated with this devices
*
* If @major == 0 this functions will dynamically allocate a major and return
* its number.
*
* If @major > 0 this function will attempt to reserve a device with the given
* major number and will return zero on success.
*
* Returns a -ve errno on failure.
*
* The name of this device has nothing to do with the name of the device in
* /dev. It only helps to keep track of the different owners of devices. If
* your module name has only one type of devices it's ok to use e.g. the name
* of the module here.
*/
int __register_chrdev(unsigned int major, unsigned int baseminor,
¦   ¦ unsigned int count, const char *name,
¦   ¦ const struct file_operations *fops)
{
struct char_device_struct *cd;
struct cdev *cdev;
int err = -ENOMEM;

cd = __register_chrdev_region(major, baseminor, count, name);
if (IS_ERR(cd))
return PTR_ERR(cd);

cdev = cdev_alloc();
if (!cdev)
goto out2;

cdev->owner = fops->owner;
cdev->ops = fops;
kobject_set_name(&cdev->kobj, "%s", name);

err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
if (err)
goto out;

cd->cdev = cdev;

return major ? 0 : cd->major;
out:
kobject_put(&cdev->kobj);
out2:
kfree(__unregister_chrdev_region(cd->major, baseminor, count));
return err;
}

02：fs/char_dev.c

/**
* cdev_init() - initialize a cdev structure
* @cdev: the structure to initialize
* @fops: the file_operations for this device
*
* Initializes @cdev, remembering @fops, making it ready to add to the
* system with cdev_add().
*/
void cdev_init(struct cdev *cdev, const struct file_operations *fops)
{
memset(cdev, 0, sizeof *cdev);
INIT_LIST_HEAD(&cdev->list);
kobject_init(&cdev->kobj, &ktype_cdev_default);
cdev->ops = fops;
}

---------------------------------使用--------------------------

static int flashlight_probe(struct platform_device *dev)
{
int ret = 0, err = 0;

logI("[flashlight_probe] start ~");

#ifdef ALLOC_DEVNO
ret = alloc_chrdev_region(&flashlight_devno, 0, 1, FLASHLIGHT_DEVNAME);
if (ret) {
logI("[flashlight_probe] alloc_chrdev_region fail: %d ~", ret);
goto flashlight_probe_error;
} else {
logI("[flashlight_probe] major: %d, minor: %d ~", MAJOR(flashlight_devno),
¦   ¦MINOR(flashlight_devno));
}
cdev_init(&flashlight_cdev, &flashlight_fops);
flashlight_cdev.owner = THIS_MODULE;
err = cdev_add(&flashlight_cdev, flashlight_devno, 1);
if (err) {
logI("[flashlight_probe] cdev_add fail: %d ~", err);
goto flashlight_probe_error;
}
#else
#define FLASHLIGHT_MAJOR 242
ret = register_chrdev(FLASHLIGHT_MAJOR, FLASHLIGHT_DEVNAME, &flashlight_fops);
if (ret != 0) {
logI("[flashlight_probe] Unable to register chardev on major=%d (%d) ~",
¦   ¦FLASHLIGHT_MAJOR, ret);
return ret;
}
flashlight_devno = MKDEV(FLASHLIGHT_MAJOR, 0);
#endif

flashlight_class = class_create(THIS_MODULE, "flashlightdrv");
if (IS_ERR(flashlight_class)) {
logI("[flashlight_probe] Unable to create class, err = %d ~",
¦   ¦(int)PTR_ERR(flashlight_class));
goto flashlight_probe_error;
}
flashlight_device =
¦   device_create(flashlight_class, NULL, flashlight_devno, NULL, FLASHLIGHT_DEVNAME);
if (NULL == flashlight_device) {
logI("[flashlight_probe] device_create fail ~");
goto flashlight_probe_error;
}

/* initialize members */
spin_lock_init(&flashlight_private.lock);
init_waitqueue_head(&flashlight_private.read_wait);
/* init_MUTEX(&flashlight_private.sem); */
sema_init(&flashlight_private.sem, 1);

flashlight_gpio_init(dev);
logI("[flashlight_probe] Done ~");
return 0;

flashlight_probe_error:
#ifdef ALLOC_DEVNO
if (err == 0)
cdev_del(&flashlight_cdev);
if (ret == 0)
unregister_chrdev_region(flashlight_devno, 1);
#else
if (ret == 0)
unregister_chrdev(MAJOR(flashlight_devno), FLASHLIGHT_DEVNAME);
#endif
return -1;
}

---