add mtrr entry in linux with C code

I am trying to add an entry to MTRR to mark a memory region as write combining, but the 开发者_开发知识库kernel does not accepts my call. It returns EINVAL errno. What could be the problem? I have tried everything but have no luck. Here is the code and the output after running it:

   #define NUM_ELTS        (1024*64)

    struct mtrr_sentry sentry;

    void register_wc(uint *addr);

    void register_wc(uint *addr) {
        int fd,ret;
        int aux1,aux2;
        int page_size;

        sentry.base=(ulong) addr;
        sentry.size=NUM_ELTS;
        sentry.type=MTRR_TYPE_WRCOMB;

        page_size=getpagesize();
        aux1=sentry.base & (page_size - 1);
        aux2=sentry.size & (page_size - 1);

        printf("aux1=%d, aux2=%d, base=%d, size=%d, type=%d\n",aux1,aux2,sentry.base,sentry.size,sentry.type);

        fd=open("/proc/mtrr",O_WRONLY); if (fd==-1) { perror("open()"); exit(2); }
        printf("fd=%d\n",fd);
        ret=ioctl(fd,MTRRIOC_ADD_ENTRY,&sentry); if (ret==-1) { perror("ioctl()"); exit(3); }
        sleep(10);
        close(fd);
    }
int main(int argc, char **argv) {
    ulong size;
    uint *data;

    size=sizeof(uint)*NUM_ELTS;

    data=(uint*) memalign(4096,size);   if (!data) { exit(1); }
    printf("data address is %d, PAGE_SIZE=%d\n",data,getpagesize());
    register_wc(data);
}

The output produced by the program is:

data address is -1420279808, PAGE_SIZE=4096
aux1=0, aux2=0, base=-1420279808, size=65536, type=1
fd=3
ioctl(): Invalid argument

The code is copied (almost) from /usr/src/linux/Documentation/x86/mtrr.txt

The base address you pass to MTRRIOC_ADD_ENTRY must be a physical address. It looks like you're passing in a logical address to a block of memory you just allocated, which doesn't make any sense. MTRRs are used to control access to memory-mapped hardware, not to RAM.

What @duskwulf said.

You haven't defined

struct mtrr_sentry sentry

and the members don't have addresses.

EDIT: I think you want to add the definition of mtrr_sentry.

#include <asm/mtrr.h>