linux 3.0.35下globalmem 字符设备驱动实现

1、Makefile

KDIR=/home/xxx/s-linux-3.0.35
PWD:=$(shell pwd)

# kernel modules
obj-m := globalmem.o

modules:
    make -C $(KDIR) M=$(PWD) modules

clean:
    rm -rf *.o *.ko *.mod.c *.markesr *.order *.symvers

.PHONY:modules clean

2、globalmem.c

#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <linux/slab.h>

#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>

#define GLOBALMEM_SIZE 0x1000 // 4KB

// create device node in the board side.
// mknod /dev/globalmem c 120 0
#define GLOBALMEM_MAJOR 120 // preset major number

// define ioctl cmd
#define GLOBALMEM_MAGIC 0x01
#define MEM_CLEAR _IO(GLOBALMEM_MAGIC, 0)

static int globalmem_major = GLOBALMEM_MAJOR;

// globalmem struct
struct globalmem_dev {
    struct cdev cdev; // cdev struct
    unsigned char mem[GLOBALMEM_SIZE]; // global memory
};

struct globalmem_dev *globalmem_devp; // device struct instance

int globalmem_open(struct inode *inode, struct file *filp)
{
        // set device struct pointer to file privatedata pointer
    filp->private_data = globalmem_devp;

    return 0;
}

int globalmem_release(struct inode *inode, struct file *filp)
{
    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; // get device struct pointer
        
        // analysis and get valid read length
    if (p >= GLOBALMEM_SIZE) // overflow
        return 0;

    if (count > GLOBALMEM_SIZE - p) // count is too large
        count = GLOBALMEM_SIZE - p;

        // kernel buf -> user buf
    if (copy_to_user(buf, (void *)(dev->mem + p), count))
        ret = -EFAULT;
    else {
        *ppos += count;
        ret = count;
        printk(KERN_INFO "read %d bytes from %ld
", 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; // get device stuct pointer

        // analysis and get valid write length
    if (p >= GLOBALMEM_SIZE) // write overflow
        return 0;

    if (count > GLOBALMEM_SIZE - p) // write count is too large
        count = GLOBALMEM_SIZE - p;

        // user buf -> kernel buf
    if (copy_from_user(dev->mem + p, buf, count))
        ret = -EFAULT;
    else {
        *ppos += count;
        ret = count;
        printk(KERN_INFO "written %d bytes from %ld
", 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: // from the file head
            if (offset < 0 || ((unsigned int) offset > GLOBALMEM_SIZE)) {
                ret = -EINVAL;
                break;
            }
            filp->f_pos = (unsigned int) offset;
            ret = filp->f_pos;
            break;

        case 1: // from current position
            if ((filp->f_pos + offset) > GLOBALMEM_SIZE || (filp->f_pos + offset) < 0) {
                ret = - EINVAL;
                break;
            }
            filp->f_pos += offset;
            ret = filp->f_pos;
            break;
    }

    return ret;
}


static long globalmem_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{

    struct globalmem_dev *dev = filp->private_data; // get device stuct pointer
    
    switch (cmd) {
        case MEM_CLEAR:
            memset(dev->mem, 0, GLOBALMEM_SIZE);
            printk(KERN_INFO "globalmem is set to zero
");
            break;

        default:
            return -EINVAL; // not supported
    }

    return 0;
}

// file operations struct
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,
};

// init and add cdev struct
static void globalmem_setup_cdev(struct globalmem_dev * dev, int index)
{
    int err;
    int devno = MKDEV(globalmem_major, 0);

    cdev_init(&dev->cdev, &globalmem_fops);
    err = cdev_add(&dev->cdev, devno, 1);
    if (err)
        printk(KERN_NOTICE "Error %d adding globalmem", err);
}

// globalmem device init function
int globalmem_init(void)
{
    int result;
    dev_t devno = MKDEV(globalmem_major, 0);

        // apply globalmem device kernel region
    if (globalmem_major)
        result = register_chrdev_region(devno, 1, "globalmem");
    else {
            // get major no dynamically
        result = alloc_chrdev_region(&devno, 0, 1, "globalmem");
        globalmem_major = MAJOR(devno);
    }

    if (result < 0)
        return result;

        // apply device struct memory
    globalmem_devp = kmalloc(sizeof(struct globalmem_dev), GFP_KERNEL);
    if (!globalmem_devp) {
        result = - ENOMEM;
        goto fail_malloc;
    }

    memset(globalmem_devp, 0, sizeof(struct globalmem_dev));
    globalmem_setup_cdev(globalmem_devp, 0);

    return 0;

  fail_malloc:
    unregister_chrdev_region(devno, 1);
    return result;
}

// globalmem device exit function
void globalmem_exit(void)
{
    // del cdev struct
    cdev_del(&globalmem_devp->cdev); 
    // free device struct memory
    kfree(globalmem_devp); 
    // unregister device region
    unregister_chrdev_region(MKDEV(globalmem_major, 0), 1); 
}

module_param(globalmem_major, int, S_IRUGO);
module_init(globalmem_init);
module_exit(globalmem_exit);

MODULE_AUTHOR("TT <TT@idle.com>");
MODULE_LICENSE("Dual BSD/GPL");