get_user_pages example

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <asm/uaccess.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/mm.h>

static  struct  class *sample_class;

static int sample_open(struct inode *inode, struct file *file)
{
        printk(KERN_INFO "%s\n", __FUNCTION__);
        return (0);
}

static int sample_release(struct inode *inode, struct file *file)
{
        printk(KERN_INFO "%s\n", __FUNCTION__);
        return (0);

}

static ssize_t  sample_write(struct file *file, const char __user *buf, size_t count, loff_t *off)
{
        int     res;
        struct  page *page;
        char    *myaddr;
        printk(KERN_INFO "%s\n", __FUNCTION__);
        down_read(&current->mm->mmap_sem);
        res = get_user_pages(current, current->mm,
                (unsigned long)buf,
                1,
                1,              
                1,
                &page,
                NULL);
        if (res) {
                printk(KERN_INFO "Got mmaped.\n");
                myaddr = kmap(page);
                printk(KERN_INFO "%s\n", myaddr);
                strcpy(myaddr, "Mohan");
                page_cache_release(page);
        }
        up_read(&current->mm->mmap_sem);
        return (0);
}

static struct   file_operations sample_ops = {
        .owner  = THIS_MODULE,
        .open   = sample_open,
        .release = sample_release,
        .write  = sample_write
};

static int __init sample_init(void)
{
        int ret;
        ret = register_chrdev(42, "Sample", &sample_ops);
        sample_class = class_create(THIS_MODULE, "Sample");
        device_create(sample_class, NULL, MKDEV(42, 0), NULL, "Sample");
        return (ret);
}

static void __exit sample_exit(void)
{
        device_destroy(sample_class, MKDEV(42, 0));
        class_destroy(sample_class);
        unregister_chrdev(42, "Sample");
}

module_init(sample_init);
module_exit(sample_exit);

MODULE_LICENSE("GPL");





======

obj-m += sample.o
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)

all:
        $(MAKE) -C $(KDIR) M=$(PWD) modules

clean:
        $(MAKE) -C $(KDIR) M=$(PWD) clean


========


#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>

int
main()
{
        int fd;
        char *ptr;
        fd = open("/dev/Sample", O_RDWR);
        if (fd < 0) {
                perror("error");
        }
        posix_memalign((void **)&ptr, 4096, 4096);
        memcpy(ptr, "krishna", strlen("krishna"));  //Write String to Driver
        write(fd, ptr, 4096);
        printf("data is %s\n", ptr);   //Read Data from Driver
        close(fd);
}