用户空间(userspace)引用jiffies

用户空间(userspace)引用jiffies

写在前面，该方法并非原创，乃是根据csdn中一网友回帖改编而来。此方法可以推广，用以引用任何内核中的资源。

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


int main ()
{
    unsigned long offset = 0xc06e1740; /* 0xc06e1740 is from

                                        * /boot/System.map-2.6.xx
                                        * c06e1740 D jiffies
                                        */

    offset -= 0xc0000000;

    int fd;
    fd = open("/dev/mem", O_RDONLY);

    void *p;
    p = mmap(0, 0x10000, PROT_READ, MAP_SHARED, fd, (off_t)(offset - offset%0x10000));

    volatile unsigned long *pJiffies;
    pJiffies = (volatile unsigned long *)((char *)p + offset%0x10000);
    
    int i;
    for (i = 0; i < 1000; i++)
    {
     printf ("jiffies = %ul\n",(unsigned long)(*pJiffies));
    }
}