定义：字符设备的一种，它们共享一个主设备号(10),但次设备号不同，所有的混杂设备形成一个链表，对设备访问时内核根据次设备号查找到相应的miscdevice设备。
例如:触摸屏，LED,按键，串口。
即：为了节约主设备号，将某些设备用链表的形式连接在一起，最后通过查找次设备区分。这里用主设备无法匹配出设备驱动，只能找到链表，再通过次设备号，才能找到设备驱动。而之前所学的，一般字符设备，通过主设备号，就能找到设备驱动了。
混杂设备驱动内置有自动创建设备节点的代码，所以编译好之后，能自动创建设备节点。
相关的宏，定义在 kernel/include/linux/miscdevice.h
[cpp]
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1. #ifndef _LINUX_MISCDEVICE_H
2. #define _LINUX_MISCDEVICE_H
3. #include
4. #include
5.
6.
7.
8. #define PSMOUSE_MINOR 1
9. #define MS_BUSMOUSE_MINOR 2
10. #define ATIXL_BUSMOUSE_MINOR 3
11.
12. #define ATARIMOUSE_MINOR 5
13. #define SUN_MOUSE_MINOR 6
14. #define APOLLO_MOUSE_MINOR 7
15. #define PC110PAD_MINOR 9
16.
17. #define WATCHDOG_MINOR 130
18. #define TEMP_MINOR 131
19. #define RTC_MINOR 135
20. #define EFI_RTC_MINOR 136
21. #define SUN_OPENPROM_MINOR 139
22. #define DMAPI_MINOR 140
23. #define NVRAM_MINOR 144
24. #define SGI_MMTIMER 153
25. #define STORE_QUEUE_MINOR 155
26. #define I2O_MINOR 166
27. #define MICROCODE_MINOR 184
28. #define TUN_MINOR 200
29. #define MWAVE_MINOR 219
30. #define MPT_MINOR 220
31. #define MPT2SAS_MINOR 221
32. #define HPET_MINOR 228
33. #define FUSE_MINOR 229
34. #define KVM_MINOR 232
35. #define BTRFS_MINOR 234
36. #define AUTOFS_MINOR 235
37. #define MISC_DYNAMIC_MINOR 255
38.
39. struct device;
40.
41. struct miscdevice {
42. int minor; //次设备号
43. const char *name; //设备名
44. const struct file_operations *fops;//文件操作
45. struct list_head list; //形成链表
46. struct device *parent;
47. struct device *this_device;
48. const char *nodename;
49. mode_t mode;
50. };
51.
52. extern int misc_register(struct miscdevice * misc); //混杂设备注册
53. extern int misc_deregister(struct miscdevice *misc); //混杂设备注销
54.
55. #define MODULE_ALIAS_MISCDEV(minor) \
56. "char-major-" __stringify(MISC_MAJOR) \
57. "-" __stringify(minor))
58. #endif
杂项设备的核心函数的定义位于：kernel/drivers/char/misc.c
int misc_register(struct miscdevice * misc)
{
struct miscdevice *c;
dev_t dev;
int err = 0; INIT_LIST_HEAD(&misc->list);
mutex_lock(&misc_mtx);
list_for_each_entry(c, &misc_list, list) {
if (c->minor == misc->minor) {
mutex_unlock(&misc_mtx);
return -EBUSY;
}
} //#define MISC_DYNAMIC_MINOR 255
int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS); //#define DYNAMIC_MINORS 64
if (i >= DYNAMIC_MINORS) {
mutex_unlock(&misc_mtx);
return -EBUSY;
}
misc->minor = DYNAMIC_MINORS - i - 1;
set_bit(i, misc_minors);
} //获得设备号
//#define MISC_MAJOR 10
misc->this_device = device_create(misc_class, misc->parent, dev, misc, "%s", misc->name);//说明了混杂设备驱动内部有自动设备驱动，可自动
//创建设备节点 if (IS_ERR(misc->this_device)) {
int i = DYNAMIC_MINORS - misc->minor - 1;
if (i < DYNAMIC_MINORS && i >= 0)
clear_bit(i, misc_minors);
err = PTR_ERR(misc->this_device);
goto out;
}
list_add(&misc->list, &misc_list);
out:
mutex_unlock(&misc_mtx);
return err;
}
int misc_deregister(struct miscdevice *misc)
{
int i = DYNAMIC_MINORS - misc->minor - 1; if (list_empty(&misc->list))
return -EINVAL; mutex_lock(&misc_mtx);
list_del(&misc->list);
device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor)); if (i < DYNAMIC_MINORS && i >= 0)
clear_bit(i, misc_minors);
EXPORT_SYMBOL(misc_register);
EXPORT_SYMBOL(misc_deregister);
static char *misc_devnode(struct device *dev, mode_t *mode){
struct miscdevice *c = dev_get_drvdata(dev); if (mode && c->mode)
*mode = c->mode;
if (c->nodename)
return kstrdup(c->nodename, GFP_KERNEL);
return NULL;
}
static int __init misc_init(void)
{
int err; #ifdef CONFIG_PROC_FS
proc_create("misc", 0, NULL, &misc_proc_fops);
#endif
misc_class = class_create(THIS_MODULE, "misc"); err = PTR_ERR(misc_class);
if (IS_ERR(misc_class))
goto fail_remove; err = -EIO;
if (register_chrdev(MISC_MAJOR,"misc",&misc_fops))
goto fail_printk;
misc_class->devnode = misc_devnode;
return 0; fail_printk:
printk("unable to get major %d for misc devices\n", MISC_MAJOR);
class_destroy(misc_class);
fail_remove:
remove_proc_entry("misc", NULL);
return err; }
subsys_initcall(misc_init);
以下是创建自动设备节点相关代码
"kernel/drivers/base/core.c"
struct device *device_create(struct class *class, struct device *parent, dev_t devt, void *drvdata, const char *fmt, ...)
{
va_list vargs;
struct device *dev; va_start(vargs, fmt);
dev = device_create_vargs(class, parent, devt, drvdata, fmt, vargs); va_end(vargs);
return dev;
}
EXPORT_SYMBOL_GPL(device_create); static int __match_devt(struct device *dev, void *data)
{
dev_t *devt = data; return dev->devt == *devt;
}
void device_destroy(struct class *class, dev_t devt)
{
struct device *dev; dev = class_find_device(class, NULL, &devt, __match_devt);
if (dev) {
put_device(dev);
device_unregister(dev);
}
}
EXPORT_SYMBOL_GPL(device_destroy);
