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Shorten chardev

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This commit is contained in:
Jim Huang 2021-08-07 18:29:39 +08:00
parent 2303d5c851
commit 1ac7bacfb8
1 changed files with 44 additions and 73 deletions
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109
examples/chardev.c
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@ -1,6 +1,6 @@
/*
* chardev.c: Creates a read-only char device that says how many times
* you've read from the dev file
* you have read from the dev file
*/
#include <linux/cdev.h>
@ -13,11 +13,7 @@
#include <linux/module.h>
#include <linux/poll.h>
/*
* Prototypes - this would normally go in a .h file
*/
int init_module(void);
void cleanup_module(void);
/* Prototypes - this would normally go in a .h file */
static int device_open(struct inode *, struct file *);
static int device_release(struct inode *, struct file *);
static ssize_t device_read(struct file *, char *, size_t, loff_t *);
@ -27,91 +23,79 @@ static ssize_t device_write(struct file *, const char *, size_t, loff_t *);
#define DEVICE_NAME "chardev" /* Dev name as it appears in /proc/devices */
#define BUF_LEN 80 /* Max length of the message from the device */
/*
* Global variables are declared as static, so are global within the file.
*/
/* Global variables are declared as static, so are global within the file. */
static int Major; /* Major number assigned to our device driver */
static int Device_Open = 0; /* Is device open?
static int major; /* major number assigned to our device driver */
static int open_device_cnt = 0; /* Is device open?
* Used to prevent multiple access to device */
static char msg[BUF_LEN]; /* The msg the device will give when asked */
static char *msg_Ptr;
static char *msg_ptr;
static struct class *cls;
static struct file_operations chardev_fops = {.read = device_read,
static struct file_operations chardev_fops = {
.read = device_read,
.write = device_write,
.open = device_open,
.release = device_release};
.release = device_release,
};
/*
* This function is called when the module is loaded
*/
/* This function is called when the module is loaded. */
int init_module(void)
{
Major = register_chrdev(0, DEVICE_NAME, &chardev_fops);
major = register_chrdev(0, DEVICE_NAME, &chardev_fops);
if (Major < 0) {
pr_alert("Registering char device failed with %d\n", Major);
return Major;
if (major < 0) {
pr_alert("Registering char device failed with %d\n", major);
return major;
}
pr_info("I was assigned major number %d.\n", Major);
pr_info("I was assigned major number %d.\n", major);
cls = class_create(THIS_MODULE, DEVICE_NAME);
device_create(cls, NULL, MKDEV(Major, 0), NULL, DEVICE_NAME);
device_create(cls, NULL, MKDEV(major, 0), NULL, DEVICE_NAME);
pr_info("Device created on /dev/%s\n", DEVICE_NAME);
return SUCCESS;
}
/*
* This function is called when the module is unloaded
*/
/* This function is called when the module is unloaded. */
void cleanup_module(void)
{
device_destroy(cls, MKDEV(Major, 0));
device_destroy(cls, MKDEV(major, 0));
class_destroy(cls);
/*
* Unregister the device
*/
unregister_chrdev(Major, DEVICE_NAME);
/* Unregister the device */
unregister_chrdev(major, DEVICE_NAME);
}
/*
* Methods
*/
/* Methods */
/*
* Called when a process tries to open the device file, like
/* Called when a process tries to open the device file, like
* "sudo cat /dev/chardev"
*/
static int device_open(struct inode *inode, struct file *file)
{
static int counter = 0;
if (Device_Open)
if (open_device_cnt)
return -EBUSY;
Device_Open++;
open_device_cnt++;
sprintf(msg, "I already told you %d times Hello world!\n", counter++);
msg_Ptr = msg;
msg_ptr = msg;
try_module_get(THIS_MODULE);
return SUCCESS;
}
/*
* Called when a process closes the device file.
*/
/* Called when a process closes the device file. */
static int device_release(struct inode *inode, struct file *file)
{
Device_Open--; /* We're now ready for our next caller */
open_device_cnt--; /* We're now ready for our next caller */
/*
* Decrement the usage count, or else once you opened the file, you'll
/* Decrement the usage count, or else once you opened the file, you will
* never get get rid of the module.
*/
module_put(THIS_MODULE);
@ -119,8 +103,7 @@ static int device_release(struct inode *inode, struct file *file)
return SUCCESS;
}
/*
* Called when a process, which already opened the dev file, attempts to
/* Called when a process, which already opened the dev file, attempts to
* read from it.
*/
static ssize_t device_read(struct file *filp, /* see include/linux/fs.h */
@ -128,49 +111,37 @@ static ssize_t device_read(struct file *filp, /* see include/linux/fs.h */
size_t length, /* length of the buffer */
loff_t *offset)
{
/*
* Number of bytes actually written to the buffer
*/
/* Number of bytes actually written to the buffer */
int bytes_read = 0;
/*
* If we're at the end of the message,
* return 0 signifying end of file
*/
if (*msg_Ptr == 0)
/* If we are at the end of message, return 0 signifying end of file. */
if (*msg_ptr == 0)
return 0;
/*
* Actually put the data into the buffer
*/
while (length && *msg_Ptr) {
/*
* The buffer is in the user data segment, not the kernel
/* Actually put the data into the buffer */
while (length && *msg_ptr) {
/* The buffer is in the user data segment, not the kernel
* segment so "*" assignment won't work. We have to use
* put_user which copies data from the kernel data segment to
* the user data segment.
*/
put_user(*(msg_Ptr++), buffer++);
put_user(*(msg_ptr++), buffer++);
length--;
bytes_read++;
}
/*
* Most read functions return the number of bytes put into the buffer
*/
/* Most read functions return the number of bytes put into the buffer. */
return bytes_read;
}
/*
* Called when a process writes to dev file: echo "hi" > /dev/hello
*/
/* Called when a process writes to dev file: echo "hi" > /dev/hello */
static ssize_t device_write(struct file *filp,
const char *buff,
size_t len,
loff_t *off)
{
pr_alert("Sorry, this operation isn't supported.\n");
pr_alert("Sorry, this operation is not supported.\n");
return -EINVAL;
}