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/*
* Exercises functions in fremap.c
*
* Takes a file as argument along with its size and creates a non linear mapping in memory
*
* then reverses the page order in memory using remap_file_pages system call
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
int main (int argc, char *argv[])
{
int fd;
unsigned long pagesize = getpagesize();
int i;
unsigned long size;
unsigned long no_of_pages;
/* initialize to NULL */
unsigned char *start = NULL;
unsigned char *end;
if (argc != 3) {
fprintf(stdout, "Usage : %s FILE SIZE\n", argv[0]);
exit(1);
}
size = atol(argv[2]);
no_of_pages = (size + pagesize - 1) / pagesize;
if ((fd = open(argv[1], O_RDWR | O_CREAT, 0666)) == -1) {
fprintf(stderr, "error opening file\n");
exit(1);
}
/* create a contiguous mapping */
if ((start = (unsigned char *) mmap(NULL, size, PROT_READ|PROT_WRITE,
MAP_SHARED|MAP_POPULATE, fd, 0)) == MAP_FAILED) {
fprintf(stderr, "%s: mmap failed: %s\n",
argv[1], strerror(errno));
exit(1);
}
end = (unsigned char *) (start + (no_of_pages - 1) * pagesize);
/* make mapping non-contiguous (reverse the page mapping order) */
for (i = 0; i < no_of_pages; i++) {
if (remap_file_pages(end - (i * pagesize),
pagesize, 0, i, MAP_SHARED|MAP_POPULATE) == -1) {
fprintf(stderr, "remap failed with error %s\n", strerror(errno));
exit(1);
}
}
close(fd);
return 0;
}
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