linux中的杂项设备所使用的misc_register()和 misc_deregister() 原理分析
相关的宏，定义在 kernel/include/linux/miscdevice.h
#ifndef _LINUX_MISCDEVICE_H #define _LINUX_MISCDEVICE_H #include <linux/module.h> #include <linux/major.h> /* * These allocations are managed by [email protected]. If you use an * entry that is not in assigned your entry may well be moved and * reassigned, or set dynamic if a fixed value is not justified. */ #define PSMOUSE_MINOR 1 #define MS_BUSMOUSE_MINOR 2 #define ATIXL_BUSMOUSE_MINOR 3 /*#define AMIGAMOUSE_MINOR 4 FIXME OBSOLETE */ #define ATARIMOUSE_MINOR 5 #define SUN_MOUSE_MINOR 6 #define APOLLO_MOUSE_MINOR 7 #define PC110PAD_MINOR 9 /*#define ADB_MOUSE_MINOR 10 FIXME OBSOLETE */ #define WATCHDOG_MINOR 130 /* Watchdog timer */ #define TEMP_MINOR 131 /* Temperature Sensor */ #define RTC_MINOR 135 #define EFI_RTC_MINOR 136 /* EFI Time services */ #define SUN_OPENPROM_MINOR 139 #define DMAPI_MINOR 140 /* DMAPI */ #define NVRAM_MINOR 144 #define SGI_MMTIMER 153 #define STORE_QUEUE_MINOR 155 #define I2O_MINOR 166 #define MICROCODE_MINOR 184 #define TUN_MINOR 200 #define MWAVE_MINOR 219 /* ACP/Mwave Modem */ #define MPT_MINOR 220 #define MPT2SAS_MINOR 221 #define HPET_MINOR 228 #define FUSE_MINOR 229 #define KVM_MINOR 232 #define BTRFS_MINOR 234 #define AUTOFS_MINOR 235 #define MISC_DYNAMIC_MINOR 255 struct device; struct miscdevice { int minor; const char *name; const struct file_operations *fops; struct list_head list; struct device *parent; struct device *this_device; const char *nodename; mode_t mode; }; extern int misc_register(struct miscdevice * misc); extern int misc_deregister(struct miscdevice *misc); #define MODULE_ALIAS_MISCDEV(minor) \ MODULE_ALIAS("char-major-" __stringify(MISC_MAJOR) \ "-" __stringify(minor)) #endif
杂项设备的核心函数的定义位于：kernel/drivers/char/misc.c
/**
* misc_register - register a miscellaneous device
* @misc: device structure
*
* Register a miscellaneous device with the kernel. If the minor
* number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
* and placed in the minor field of the structure. For other cases
* the minor number requested is used.
*
* The structure passed is linked into the kernel and may not be
* destroyed until it has been unregistered.
*
* A zero is returned on success and a negative errno code for
* failure.
*/
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;
}
}
if (misc->minor == MISC_DYNAMIC_MINOR) { //#define MISC_DYNAMIC_MINOR 255
int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS); //#define DYNAMIC_MINORS 64 /* like dynamic majors */
if (i >= DYNAMIC_MINORS) {
mutex_unlock(&misc_mtx);
return -EBUSY;
}
misc->minor = DYNAMIC_MINORS - i - 1;
set_bit(i, misc_minors);
}
dev = MKDEV(MISC_MAJOR, misc->minor); //#define MISC_MAJOR 10 // 在 kernel/include/linux/major.h 中定义。
misc->this_device = device_create(misc_class, misc->parent, dev, misc, "%s", misc->name);
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;
}
/*
* Add it to the front, so that later devices can "override"
* earlier defaults
*/
list_add(&misc->list, &misc_list);
out:
mutex_unlock(&misc_mtx);
return err;
}
/**
* misc_deregister - unregister a miscellaneous device
* @misc: device to unregister
*
* Unregister a miscellaneous device that was previously
* successfully registered with misc_register(). Success
* is indicated by a zero return, a negative errno code
* indicates an error.
*/
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);
"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;
}
/**
* device_destroy - removes a device that was created with device_create()
* @class: pointer to the struct class that this device was registered with
* @devt: the dev_t of the device that was previously registered
*
* This call unregisters and cleans up a device that was created with a
* call to device_create().
*/
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);