Блокировка файла на запись/чтение - C (СИ)

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
 
int i,j,fd;
char buf;
 
int main(int argc, char *argv)
{
  if (argc == 1)
  {
    printf("Please input filename\n");
    exit(-1);
  }
  
  if (fork())
  {
    if ((fd = open(argv[1], O_WRONLY | O_CREAT, 0755)) < 0)
    {
      printf("Can't open file for writing\n");
      exit(-1);
    }
    for (j = 0; j < 4; ++j)
    {
      for (i = 0; i < 62; ++i)
      {
         buf = 'A' + i;
         if (write(fd, &buf, 1)<=0)
         {
           printf("Can't write in the file\n");
         }
      }
    }
    close(fd);
  }
  else
  {
    if ((fd = open(argv[1], O_RDONLY | O_CREAT, 0755))<0)
    {
      printf("Can't open file for reading\n");
      exit(-1);
    }
    
    while(read(fd, &buf, 1))
    {
      printf("Symbol %s was successfully read\n", buf);
    }
    close(fd);
  }
  return 0;
}

...
struct flock lck;
...
// В пишущем процессе
lck.l_type = F_WRLCK;
lck.l_whence = SEEK_SET;
lck.l_len = 0;
 
while(fcntl(fd, F_SETLK, &lck)<0)
{
  printf("Blocking error\n");
}
...