Test direct IO in stap

diotest.c

/* I can be compiled with gcc -o diotest diotest.c -O0 */
#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <err.h>
#include <sysexits.h>
#include <string.h>

#include <sys/stat.h>
#include <fcntl.h>

#define FILENAME "./test_dio.dat"
#define SIZE 1048576

int main() {
  int fd = -1;
  void *buf = NULL;

  /* Open file and allocate some memory */
  if ((fd = open(FILENAME, O_RDWR|O_DIRECT|O_CREAT, S_IRUSR|S_IWUSR)) < 0)
    err(EX_OSERR, "Cannot open file %s", FILENAME);

  if (posix_memalign(&buf, 512, SIZE))
    err(EX_OSERR, "Cannot allocate memory");

  /* Unlink the file */
  if (unlink(FILENAME))
    err(EX_OSERR, "Cannot unlink file %s", FILENAME);

  memset(buf, 'A', SIZE);

  /* Do some work */
  while(1) {
    printf("Doing some work\n");
    if (write(fd, buf, SIZE) != SIZE)
      err(EX_OSERR, "Cannot write to file %s", FILENAME);
    if (lseek(fd, 0, SEEK_SET))
      err(EX_OSERR, "Cannot seek in file %s", FILENAME);

    if (read(fd, buf, SIZE) != SIZE)
      err(EX_OSERR, "Cannot read file %s", FILENAME);
    if (lseek(fd, 0, SEEK_SET))
      err(EX_OSERR, "Cannot seek in file %s", FILENAME);

    usleep(500000);
  }

  exit(0);
}