1, globalmem virtual device instance
globalmem as "global memory" means, in globalmem apparatus allocates a character size GLOBALMEM_SIZE (4KB) memory space, and this provides read and write memory in the drive plate, the positioning and control functions for the user space processes Linux system calls can get and set this piece of memory.
(1) header, and macro-structure device
#include <linux/module.h> #include <linux/init.h> #include <linux/fs.h> #include <linux/cdev.h> #include <linux/slab.h> #include <linux/uaccess.h> #define GLOBALMEM_SIZE 0x1000 #define MEM_CLEAR 0x1 #define GLOBALMEM_MAJOR 230 static int globalmem_major = GLOBALMEM_MAJOR; module_param(globalmem_major, int, S_IRUGO); struct globalmem_dev { struct cdev cdev; unsigned char mem[GLOBALMEM_SIZE]; }; struct globalmem_dev *globalmem_devp;
globalmem_dev defined structure, including the character corresponding to globalmem the cdev device, memory used mem [GLOBALMEM_SIZE].
(2) globalmem device driver module load and unload functions
static void globalmem_setup_cdev(struct globalmem_dev *dev, int index) { int err, devno = MKDEV(globalmem_major, index); cdev_init(&dev->cdev, &globalmem_fops); dev->cdev.owner = THIS_MODULE; err = cdev_add(&dev->cdev, devno, 1); if (err) { printk(KERN_NOTICE "Error %d adding globalmem %d", err, index); } } static int __init globalmem_init(void) { int ret; dev_t devno = MKDEV(globalmem_major, 0); if (globalmem_major) { ret = register_chrdev_region(devno, 1, "globalmem"); } else { ret = alloc_chrdev_region(&devno, 0, 1, "globalmem"); globalmem_major = MAJOR(devno); } if (ret < 0) return ret; globalmem_devp = kzalloc(sizeof(struct globalmem_dev), GFP_KERNEL); if (!globalmem_devp) { ret = -ENOMEM; goto fail_malloc; } globalmem_setup_cdev(globalmem_devp, 0); return 0; fail_malloc: unregister_chrdev_region(devno, 1); return ret; } static void __exit globalmem_exit(void) { cdev_del(&globalmem_devp->cdev); kfree(globalmem_devp); unregister_chrdev_region(MKDEV(globalmem_major, 0), 1); }
globalmem_setup_cdev () function to complete the initialization and added cdev, kzalloc () application globalmem_dev a memory structure, which is clear and 0, in cdev_init () function, the file_operations structure associated with the cdev follows globalmem :
static const struct file_operations globalmem_fops = { .owner = THIS_MODULE, .open = globalmem_open, .release = globalmem_release, .read = globalmem_read, .write = globalmem_write, .llseek = globalmem_llseek, .unlocked_ioctl = globalmem_ioctl, };
Implementation (3) of the read and write functions
First read function, to achieve the following functions:
static ssize_t globalmem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos) { unsigned long p = *ppos; unsigned int count = size; int ret = 0; struct globalmem_dev *dev = filp->private_data; if (p > GLOBALMEM_SIZE) return 0; if (count > GLOBALMEM_SIZE - p) count = GLOBALMEM_SIZE - p; if (copy_to_user(buf, dev->mem + p, count)) { ret = -EFAULT; } else { *ppos += count; ret = count; printk(KERN_INFO "read %u bytes(s) from %lu\n", count, p); } return ret; }
Wherein * ppos read position with respect to the beginning of the file drift, if the drift is greater than or equal to GLOBALMEM_SIZE, it indicates that the file has come to the end, returns 0 (EOF).
Implement write function as follows:
static ssize_t globalmem_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos) { unsigned long p = *ppos; unsigned int count = size; int ret = 0; struct globalmem_dev *dev = filp->private_data; if (p > GLOBALMEM_SIZE) return 0; if (count > GLOBALMEM_SIZE - p) count = GLOBALMEM_SIZE - p; if (copy_from_user(dev->mem + p, buf, count)) { return -EFAULT; } else { *ppos += count; ret = count; printk(KERN_INFO "written %u bytes(s) from %lu\n", count, p); } return ret; }
Implement (4) seek function
seek () function of the start address of the file may be located at the beginning of the file (SEEK_SET, 0), the current position (SEEK_CUR, 1) and the end of the file (SEEK_END, 2), when positioning, to check the validity of the user's request, If legitimate, the function returns the error number, if the current legal position, update the file, and returns the new position, achieved as follows:
static loff_t globalmem_llseek(struct file *filp, loff_t offset, int orig) { loff_t ret = 0; switch (orig) { case 0: if (offset < 0) { ret = -EINVAL; break; } if ((unsigned int)offset > GLOBALMEM_SIZE) { ret = -EINVAL; break; } filp->f_pos = (unsigned int)offset; ret = filp->f_pos; break; case 1: if ((filp->f_pos + offset) > GLOBALMEM_SIZE) { ret = -EINVAL; break; } if ((filp->f_pos + offset) < 0) { ret = -EINVAL; break; } filp->f_pos += offset; ret = filp->f_pos; break; default: ret = - chosen; break ; } Return ret; }
(5) ioctl function to achieve
static long globalmem_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) { struct globalmem_dev *dev = filp->private_data; switch (cmd) { case MEM_CLEAR: memset(dev->mem, 0, GLOBALMEM_SIZE); printk(KERN_INFO "globalmem is set to zero\n"); break; default: return -EINVAL; } return 0; }
Private data (6) use file
The private data file private_data pointing device structure, and then use the read (), write (), ioctl (), llseek () function and the like by private_data access device structure, as shown below:
static int globalmem_open(struct inode *inode, struct file *filp) { filp->private_data = globalmem_devp; return 0; } static int globalmem_release(struct inode *inode, struct file *filp) { return 0; }
(7) full driver code globalmem
#include <linux/module.h> #include <linux/init.h> #include <linux/fs.h> #include <linux/cdev.h> #include <linux/slab.h> #include <linux/uaccess.h> #define GLOBALMEM_SIZE 0x1000 #define MEM_CLEAR 0x1 #define GLOBALMEM_MAJOR 230 static int globalmem_major = GLOBALMEM_MAJOR; module_param(globalmem_major, int, S_IRUGO); struct globalmem_dev { struct cdev cdev; unsigned char mem[GLOBALMEM_SIZE]; }; struct globalmem_dev *globalmem_devp; static int globalmem_open(struct inode *inode, struct file *filp) { filp->private_data = globalmem_devp; return 0; } static int globalmem_release(struct inode *inode, struct file *filp) { return 0; } static long globalmem_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) { struct globalmem_dev *dev = filp->private_data; switch (cmd) { case MEM_CLEAR: memset(dev->mem, 0, GLOBALMEM_SIZE); printk(KERN_INFO "globalmem is set to zero\n"); break; default: return -EINVAL; } return 0; } static ssize_t globalmem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos) { unsigned long p = *ppos; unsigned int count = size; int ret = 0; struct globalmem_dev *dev = filp->private_data; if (p > GLOBALMEM_SIZE) return 0; if (count > GLOBALMEM_SIZE - p) count = GLOBALMEM_SIZE - p; if (copy_to_user(buf, dev->mem + p, count)) { ret = -EFAULT; } else { *ppos += count; ret = count; printk(KERN_INFO "read %u bytes(s) from %lu\n", count, p); } return ret; } static ssize_t globalmem_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos) { unsigned long p = *ppos; unsigned int count = size; int ret = 0; struct globalmem_dev *dev = filp->private_data; if (p > GLOBALMEM_SIZE) return 0; if (count > GLOBALMEM_SIZE - p) count = GLOBALMEM_SIZE - p; if (copy_from_user(dev->mem + p, buf, count)) { return -EFAULT; } else { *ppos += count; ret = count; printk(KERN_INFO "written %u bytes(s) from %lu\n", count, p); } return ret; } static loff_t globalmem_llseek(struct file *filp, loff_t offset, int orig) { loff_t ret = 0; switch (orig) { case 0: if (offset < 0) { ret = -EINVAL; break; } if ((unsigned int)offset > GLOBALMEM_SIZE) { ret = -EINVAL; break; } filp->f_pos = (unsigned int)offset; ret = filp->f_pos; break; case 1: if ((filp->f_pos + offset) > GLOBALMEM_SIZE) { ret = -EINVAL; break; } if ((filp->f_pos + offset) < 0) { ret = -EINVAL; break; } filp->f_pos += offset; ret = filp->f_pos; break; default: ret = -EINVAL; break; } return ret; } static const struct file_operations globalmem_fops = { .owner = THIS_MODULE, .llseek = globalmem_llseek, .read = globalmem_read, .write = globalmem_write, .unlocked_ioctl = globalmem_ioctl, .open = globalmem_open, .release = globalmem_release, }; static void globalmem_setup_cdev(struct globalmem_dev *dev, int index) { int err, devno = MKDEV(globalmem_major, index); cdev_init(&dev->cdev, &globalmem_fops); dev->cdev.owner = THIS_MODULE; err = cdev_add(&dev->cdev, devno, 1); if (err) { printk(KERN_NOTICE "Error %d adding globalmem %d", err, index); } } static int __init globalmem_init(void) { int ret; dev_t devno = MKDEV(globalmem_major, 0); if (globalmem_major) { ret = register_chrdev_region(devno, 1, "globalmem"); } else { ret = alloc_chrdev_region(&devno, 0, 1, "globalmem"); globalmem_major = MAJOR(devno); } if (ret < 0) return ret; globalmem_devp = kzalloc(sizeof(struct globalmem_dev), GFP_KERNEL); if (!globalmem_devp) { ret = -ENOMEM; goto fail_malloc; } globalmem_setup_cdev(globalmem_devp, 0); return 0; fail_malloc: unregister_chrdev_region(devno, 1); return ret; } static void __exit globalmem_exit(void) { cdev_del(&globalmem_devp->cdev); kfree(globalmem_devp); unregister_chrdev_region(MKDEV(globalmem_major, 0), 1); } module_init(globalmem_init); module_exit(globalmem_exit); MODULE_AUTHOR("HLY"); MODULE_LICENSE("GPL");
(8) globalmem driver verification
Using the compiled command to make the drive module globalmem.ko source file, the compiler need Makefile as follows:
# Makefile for globalmem driver obj-m += globalmem.o all: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules clean: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
Then using the drive command module load module, as follows:
$ sudo insmod globalmem.ko $ lsmod
Then use the following command to view the device number globalmem virtual devices:
$ cat /proc/devices
Then, use mknod to create a device node:
# Mknod / dev / globalmem c 230 0 # the ls al / dev / globalmem
Next, use the command to test the read and write to the file:
# echo “Hello World” > /dev/globalmem # cat /dev/globalmem
You can also use the system call function open, write and read test of the virtual device, app.c file test is as follows:
#include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <unistd.h> #include <stdio.h> #include <string.h> #define LENGTH 100 int main(int argc, char *argv[]) { int fd,len; char str[LENGTH]; fd = open("/dev/globalmem", O_RDWR); if (fd) { write(fd, "Hello World", strlen("Hello World")); close(fd); } fd = open("/dev/globalmem", O_RDWR); len = read(fd, str, LENGTH); str[len] = '\0'; printf("str:%s\n", str); close(fd); return 0; }
App.c the preparation of the Makefile file, as follows:
# Makefile by HLY all: myapp # Which compiler CC = gcc # Where are include files INCLUDE = . # Options for development CFLAGS = -g -Wall -ansi myapp: app.o $(CC) -o myapp app.o clean: rm -rf *.o myapp
Use the make command to app.c compiled into an executable file myapp, then the implementation of the program, to complete the reading and writing files.