god@god-virtual-machine:/proc/bus/input$ cat /proc/devices Character devices: 1 mem 4 /dev/vc/0 4 tty 4 ttyS 5 /dev/tty 5 /dev/console 5 /dev/ptmx 5 ttyprintk 6 lp 7 vcs 10 misc 13 input ...... 252 ndctl 253 tpm 254 gpiochip Block devices: 7 loop 8 sd ...... 135 sd 253 device-mapper 254 mdp 259 blkext
由上可知，设备分为字符设备和块设备，数字表示主设备号
以下介绍的，无论是设备号，还是设备注册，都是指字符设备。
以下函数功能，包含了设备号的申请、字符设备的申请、字符设备添加到内核
static inline int register_chrdev(unsigned int major, const char *name,
const struct file_operations *fops)
{
return __register_chrdev(major, 0, 256, name, fops);
}
以下函数，只包含设备号的申请，from是起始设备号，由12位主设备号 + 20子设备号组成32bit值，count是申请设备号的数量
int register_chrdev_region(dev_t from, unsigned count, const char *name)
以下函数，只包含设备号的申请，register_chrdev() 和 register_chrdev_region() 最终都是调用此函数进行设备号的申请
static struct char_device_struct *__register_chrdev_region(unsigned int major, unsigned int baseminor, int minorct, const char *name)
register_chrdev |
设备号的申请，字符设备的申请、字符设备添加到内核 |
register_chrdev_region |
设备号的申请（函数名具有迷惑性，没有字符设备添加到内核功能） |
__register_chrdev_region |
设备号的申请（函数名具有迷惑性，没有字符设备添加到内核功能） |
static struct char_device_struct *
__register_chrdev_region(unsigned int major, unsigned int baseminor,
int minorct, const char *name)
{
struct char_device_struct *cd, *curr, *prev = NULL;
int ret;
int i;
if (major >= CHRDEV_MAJOR_MAX) {
pr_err("CHRDEV \"%s\" major requested (%u) is greater than the maximum (%u)\n",
name, major, CHRDEV_MAJOR_MAX-1);
return ERR_PTR(-EINVAL);
}
if (minorct > MINORMASK + 1 - baseminor) {
pr_err("CHRDEV \"%s\" minor range requested (%u-%u) is out of range of maximum range (%u-%u) for a single major\n",
name, baseminor, baseminor + minorct - 1, 0, MINORMASK);
return ERR_PTR(-EINVAL);
}
cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
if (cd == NULL)
return ERR_PTR(-ENOMEM);
mutex_lock(&chrdevs_lock);
if (major == 0) {
ret = find_dynamic_major();
if (ret < 0) {
pr_err("CHRDEV \"%s\" dynamic allocation region is full\n",
name);
goto out;
}
major = ret;
}
ret = -EBUSY;
i = major_to_index(major);
for (curr = chrdevs[i]; curr; prev = curr, curr = curr->next) {
if (curr->major < major)
continue;
if (curr->major > major)
break;
if (curr->baseminor + curr->minorct <= baseminor)
continue;
if (curr->baseminor >= baseminor + minorct)
break;
goto out;
}
cd->major = major;
cd->baseminor = baseminor;
cd->minorct = minorct;
strlcpy(cd->name, name, sizeof(cd->name));
if (!prev) {
cd->next = curr;
chrdevs[i] = cd;
} else {
cd->next = prev->next;
prev->next = cd;
}
mutex_unlock(&chrdevs_lock);
return cd;
out:
mutex_unlock(&chrdevs_lock);
kfree(cd);
return ERR_PTR(ret);
}
由此函数可知，主设备号虽然由12位，但是主设备号的范围只支持 0~511，子设备号则占满20bit
标签：字符,major,curr,name,int,申请,cd,注册,设备 From： https://www.cnblogs.com/god-of-death/p/17228557.html