inode获取设备号

当我们打开一个设备文件时，我们如何从该设备文件获取到设备文件的设备号呢？

当然是从代表一个设备文件的struct inode中找到代表设备文件的dev_t啦！

struct inode

struct inode {
...
<span style="font-size:18px;color:#ff0000;">dev_ti_rdev;  /*设备号*/</span>
...
const struct inode_operations*i_op;
const struct file_operations*i_fop;/* former ->i_op->default_file_ops */
...
struct list_headi_devices;
union {
struct pipe_inode_info*i_pipe;
struct block_device*i_bdev;
struct cdev*i_cdev;  /*此处指向的内容的次设备号是0*/
};
....
}

struct file_operations {
struct module *owner;
l ...
<span style="font-size:18px;color:#ff0000;">int (*open) (struct inode *, struct file *);</span>
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *);
...
};

struct cdev *i_cdev

struct cdev is the kernel’s internal structure that represents char devices; this

field contains a pointer to that structure when the inode refers to a char device

file.

struct cdev 是内核内部的结构，其作用是用来表示一字符设备（即c前缀的原因），该域包含了一个指针，当该节点指向一个设备文件时，该指针指向那个设备文件的节点。

<pre name="code" class="plain">static int chery_drv_open(struct inode *inode, struct file *file)
{
dev_t cdev = inode->i_cdev->dev;
printk("minor %d\n",MINOR(inode->i_rdev<span style="font-family: Arial, Helvetica, sans-serif;">));</span>

return 0;
}

static struct file_operations chery_drv_fops = { .owner = THIS_MODULE, /* 这是一个宏，指向编译模块时自动创建的__this_module变量 */ .open = chery_drv_open, };