fine in core(fincore) in c

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Noticed it when I was looking into postgreSQL buffering
https://sites.google.com/site/itmyshare/database-tips-and-examples/postgresql-buffering.

Fincore is David Plonka's work, available at

http://net.doit.wisc.edu/~plonka/fincore/

It's a utility tells you how much a file cached in the kernel's buffer. It is a C code, but implemented in perl INLINE module.

Here is a pure c code, will do more later

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

int main(int argc, char *argv[]) {
    int fd,cnt;
    struct stat file_stat;
    void *file_mmap;
    unsigned char *mincore_vec;
    size_t page_size = getpagesize();
    size_t page_index;

    fd = open(argv[1],0);
    if (0 > fd) {
      perror("open file error");
      return 1;
    }
    if ( 0 != fstat(fd, &file_stat)) {
      perror("fstat error ");
      close(fd);
      return 1;
    }
    file_mmap = mmap((void *)0, file_stat.st_size, PROT_NONE, MAP_SHARED, fd, 0);
    if (MAP_FAILED == file_mmap) {
      perror("mmap error ");
      close(fd);
      return 1;
    }
    mincore_vec = calloc(1, (file_stat.st_size+page_size-1)/page_size);
    if ((void *)0 == mincore_vec) {
      perror("mincore calloc error");
      close(fd);
      return 1;
    }
    if(0 == mincore(file_mmap, file_stat.st_size, mincore_vec)) {
      printf("Cached Blocks of %s: ",argv[1]);
      for (page_index = 0; page_index <= file_stat.st_size/page_size; page_index++) {
        if (mincore_vec[page_index]&1) {
           /** printf("%lu ", (unsigned long)page_index);**/
            cnt++;
        }
      }
      printf("\n total pages in core: %d\n",cnt);
      free(mincore_vec);
      munmap(file_mmap, file_stat.st_size);
      close(fd);
      return 0;
    }
    else{
      fprintf(stderr, "mincore(%p, %lu, %p): %s\n", file_mmap, (unsigned long)file_stat.st_size, mincore_vec, strerror(errno));
      free(mincore_vec);
      munmap(file_mmap, file_stat.st_size);
      close(fd);
      return 1;
    }
}

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