#include <stdio.h>  #include <stdlib.h>  #include <string.h>  #include <errno.h>  #include <unistd.h>  #include <fcntl.h>  #include <sys/types.h>     int main(int argc, char *argv[])  {      char *buf = NULL;      int fd_src = -1;      int fd_dest = -1;      int buf_size = 4096;      int cnt = 0;      struct flock lock;         if (argc < 3) {          printf("usage: %s <src_file> <dest_file> [buf_size]\n", argv[0]);          return 0;      }         if ((fd_src=open(argv[1], O_RDONLY)) == -1) {          perror("open src. file");          return 1;      }      if ((fd_dest=open(argv[2], O_WRONLY|O_CREAT|O_EXCL, 0664)) == -1) {          perror("open dest. file");          close(fd_src);          return 2;      }      if (argc == 4) {          buf_size = atoi(argv[3]);      }      buf = sbrk(buf_size);      if ((void*)-1 == buf) {          perror("malloc");          close(fd_src);          close(fd_dest);          return 3;      }         lock.l_type = F_RDLCK;      lock.l_whence = SEEK_SET;      lock.l_start = 0;      lock.l_len = 0;      lock.l_pid = -1;      if (fcntl(fd_src, F_SETLK, &lock) == -1) {          fprintf(stderr, "%s has been locked by other process\n", argv[1]);          close(fd_src);          close(fd_dest);          return 8;      }         errno = 0;      while ((cnt = read(fd_src, buf, buf_size)) > 0) {          if (write(fd_dest, buf, cnt) < cnt) {              perror("write");              close(fd_src);              close(fd_dest);              return 4;          }      }      if (0 != errno) {          perror("read");      }      close(fd_src);      fd_src = -1;      close(fd_dest);      fd_dest = -1;      brk(buf);         return 0;  }