open_excl - open a file for exclusive writing

       open_excl opens the file filename for writing and returns the file handle.  The file may not exist before
       the call to open_excl.  The file will be created with mode 0600.

       If there was an error creating the file, open_excl returns -1 and sets errno accordingly.

       Since  open_excl  relies on the O_EXCL flag to open, it does not work reliably over NFS (the NFS protocol
       is broken) and must be emulated using a lock file (create a file with a unique file name and  link(2)  it
       to the lock file.  Then stat the lock file and see if the link count is 2).

       open_excl - open a file for exclusive writing

open(2)

                                                                                                    open_excl(3)

#include<libowfat/open.h>

       int open_excl(const char *filename);