/*This program is used to allocate memory in kernel
and pass the physical address to userspace through proc file.*/

#include <linux/version.h>
#include <linux/module.h>
#include <linux/proc_fs.h>
#include <linux/mm.h>

#define PROC_MEMSHARE_DIR "memshare"
#define PROC_MEMSHARE_PHYADDR "phymem_addr"
#define PROC_MEMSHARE_SIZE "phymem_size"

/*alloc one page. 4096 bytes*/
#define PAGE_ORDER 0
/*this value can get from PAGE_ORDER*/
#define PAGES_NUMBER 1

struct proc_dir_entry *proc_memshare_dir ;
unsigned long kernel_memaddr = 0;
unsigned long kernel_memsize= 0;

static int proc_read_phymem_addr(char *page, char **start, off_t off, int count)
{
        return sprintf(page, "%08lx\n", __pa(kernel_memaddr));
}
static int proc_read_phymem_size(char *page, char **start, off_t off, int count)
{
        return sprintf(page, "%lu\n", kernel_memsize);
}

static int __init init(void)
{
        /*build proc dir "memshare"and two proc files: phymem_addr, phymem_size in the dir*/
        proc_memshare_dir = proc_mkdir(PROC_MEMSHARE_DIR, NULL);
        create_proc_info_entry(PROC_MEMSHARE_PHYADDR, 0, proc_memshare_dir, proc_read_phymem_addr);
        create_proc_info_entry(PROC_MEMSHARE_SIZE, 0, proc_memshare_dir, proc_read_phymem_size);

        /*alloc one page*/
        kernel_memaddr =__get_free_pages(GFP_KERNEL, PAGE_ORDER);
        if(!kernel_memaddr)
        {
                printk("Allocate memory failure!\n");
        }
        else
        {
                SetPageReserved(virt_to_page(kernel_memaddr));
                kernel_memsize = PAGES_NUMBER * PAGE_SIZE;
                printk("Allocate memory success!. The phy mem addr=%08lx, size=%lu\n", __pa(kernel_memaddr), kernel_memsize);
        }
        return 0;
}

static void __exit fini(void)
{
        printk("The content written by user is: %s\n", (unsigned char *) kernel_memaddr);
        ClearPageReserved(virt_to_page(kernel_memaddr));
        free_pages(kernel_memaddr, PAGE_ORDER);
        remove_proc_entry(PROC_MEMSHARE_PHYADDR, proc_memshare_dir);
        remove_proc_entry(PROC_MEMSHARE_SIZE, proc_memshare_dir);
        remove_proc_entry(PROC_MEMSHARE_DIR, NULL);

        return;
}
module_init(init);
module_exit(fini);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Godbach ([email]nylzhaowei@163.com[/email])");
MODULE_DESCRIPTION("Kernel memory share module.");

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/mman.h>

int main(int argc, char* argv[])
{
        if(argc != 2)
        {
                printf("Usage: %s string\n", argv[0]);
                return 0;
        }
        
        unsigned long phymem_addr, phymem_size;
        char *map_addr;
        char s[256];
        int fd;
        
        /*get the physical address of allocated memory in kernel*/
        fd = open("/proc/memshare/phymem_addr", O_RDONLY);
        if(fd < 0)
        {
                printf("cannot open file /proc/memshare/phymem_addr\n");
                return 0;
        }
        read(fd, s, sizeof(s));
        sscanf(s, "%lx", &phymem_addr);
        close(fd);

        /*get the size of allocated memory in kernel*/
        fd = open("/proc/memshare/phymem_size", O_RDONLY);
        if(fd < 0)
        {
                printf("cannot open file /proc/memshare/phymem_size\n");
                return 0;
        }
        read(fd, s, sizeof(s));
        sscanf(s, "%lu", &phymem_size);
        close(fd);
        
        printf("phymem_addr=%lx, phymem_size=%lu\n", phymem_addr, phymem_size);
        /*memory map*/
        int map_fd = open("/dev/mem", O_RDWR);
        if(map_fd < 0)
        {
                printf("cannot open file /dev/mem\n");
                return 0;
        }
        
        map_addr = mmap(0, phymem_size, PROT_READ|PROT_WRITE, MAP_SHARED, map_fd, phymem_addr);
        strcpy(map_addr, argv[1]);
        munmap(map_addr, phymem_size);
        close(map_fd);
        return 0;
        
}

debian:/home/km/memshare# insmod memshare_kernel.ko
debian:/home/km/memshare# ./memshare_user 'hello,world!'
phymem_addr=e64e000, phymem_size=4096
debian:/home/km/memshare# cat /proc/memshare/phymem_addr
0e64e000
debian:/home/km/memshare# cat /proc/memshare/phymem_size
4096
debian:/home/km/memshare# rmmod memshare_kernel
debian:/home/km/memshare# tail /var/log/messages
Sep 27 18:14:24 debian kernel: [50527.567931] Allocate memory success!. The phy mem addr=0e64e000, size=4096
Sep 27 18:15:31 debian kernel: [50592.570986] The content written by user is: hello,world!