allocate a Cdb struct rather than using a single static one, note that cdb_free does _not_ call alloc_free, just releases the map, in fact alloc_free is not called anywhere!

#include <sys/types.h>
#include <fcntl.h>
#include "open.h"

int open_read(char *fn)
{ return open(fn,O_RDONLY | O_NDELAY); }