#define _LARGEFILE64_SOURC

#include <iostream>
#include <stdio.h>
#include <string>
#include <stddef.h>
#include <sys/time.h>

#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <libaio.h>
#include <time.h>
#include <stdio.h>
#include <errno.h>
#include <sys/uio.h>
#include <unistd.h>
#include <sys/types.h>
#include <linux/unistd.h>
#include <errno.h>

using namespace std;

int main (int argc, char *argv[])
{
  if (argc<6){
	cout << "usage  <device name>  <size to write in kb> <offset in kb > <diskSizeGB> <loops>" << endl;
	return 0;
  }

  char* dev_name = argv[1];

  int fd = open(dev_name, O_LARGEFILE | O_DIRECT | O_WRONLY , 777 );
  if (fd<0){
	perror("open ");
	return (-1);
  }

  long long write_sz_bytes    = ( (long long)atoi(argv[2]))<<10;
  long long offset_sz_bytes   = ( (long long) atoi(argv[3]) )<<10;
  long long diskSizeBytes        = ( (long long)atoi(argv[4]))<<30;
  int loops = atoi(argv[5]);
 
  struct iovec vec[10];
  int blocks = (write_sz_bytes >>20);

  for( int i = 0 ; i < blocks; i++){
  
    char* buffer = (char*)valloc((1<<20));
    if (!buffer) {
	    perror("alloc : ");
        return -1;
    }
    vec[i].iov_base = buffer;
    vec[i].iov_len = 1048576;
    memset(buffer,0x00,1048576);
  }

  int ret=0;
 
  while( (--loops)>0 ){

    if ( lseek64(fd,offset_sz_bytes,SEEK_SET) < 0  ){
      printf("%s: failed on lseek offset=%lld\n",offset_sz_bytes);
      return (0);
    }
    
    ret = writev(fd,(struct iovec*)&vec,blocks);
    if ( ret != write_sz_bytes ) {
      perror("failed to write: ");
      printf("write size=%lld offset=%lld\n",write_sz_bytes,offset_sz_bytes);
      return -1;
    }

    offset_sz_bytes =  write_sz_bytes *(  random() % diskSizeBytes );

    long long rnd = (long long)random();
    offset_sz_bytes =  write_sz_bytes * (long long)( rnd %  diskSizeBytes );

    if(offset_sz_bytes>diskSizeBytes){
            offset_sz_bytes =  (offset_sz_bytes - diskSizeBytes ) % diskSizeBytes;
            offset_sz_bytes =  (offset_sz_bytes/write_sz_bytes)*write_sz_bytes;
    }

    printf("writing %d bytes at offset %lld\n",ret,offset_sz_bytes);
  }
  
  return(0);
}