random pwrite test

/* A pwrite() loop, for testing NFS random writes.
 * Run it under strace -tt -T, giving as argument a path located on a NFS server
 * It will try to write at random locations inside that file (4 GB by default,
 *  see filesize variable)
 * Bare with me for the possible coding errors ;)
 */

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <time.h>

#define BUFSIZE 32*1024
#define _FILE_OFFSET_BITS 64

int main (int argc, char **argv)
{
   unsigned char buf[BUFSIZE];
   ssize_t filesize = 4000000000;
   ssize_t res;
   size_t  blocksize = 1024;
   off_t off = 0;
   unsigned long val;
   int fd;
   int i;
   int seq = 0;

   if (!argv[1]) {
      fprintf(stderr, "Usage: %s <tmpfile> [blocksize] [seq|rnd]\n", argv[0]);
      exit(5);
   }

   if (argc >= 3 && sscanf(argv[2], "%lu", &val) > 0) {
      if (val > BUFSIZE)
         val = BUFSIZE;
      blocksize = (size_t)val;
   }

   if (argc >= 4 && !strcmp(argv[3], "seq"))
      seq = 1;

   memset(buf, 'a', BUFSIZE);

   if ((fd = open(argv[1], O_RDWR|O_CREAT|O_TRUNC)) == -1) {
      perror("open");
      exit(5);
   }

   fchmod(fd, S_IWUSR|S_IRUSR);
   srand(time(NULL));
   /* for (i = 0; ; i++) */
   for (i = 0; i < 100000; i++)
   {
      if (seq) {
         off += BUFSIZE;
         if (off > filesize)
            off = 0;
      } else {
         off = (off_t) (filesize * (rand() / (RAND_MAX + 1.0)));
         off = off % filesize;
      }
      res = pwrite(fd, buf, blocksize, off);
      if (res != blocksize) {
         perror("pwrite");
         break;
      }

      /* usleep(50); */
   }

   close(fd);
   exit(0);
}