#include <db.h>
int
db_env_set_func_read(ssize_t (*func_read)(int fd, void *buf, 
    size_t nbytes));  
      Replace Berkeley DB calls to the IEEE/ANSI Std 1003.1 (POSIX) read function with func_read, which must conform to the standard interface specification.
         The db_env_set_func_read() function configures all operations performed by
         a process and all of its threads of control, not operations confined
         to a single database environment.
    
         Although the db_env_set_func_read() function may be called at any time
         during the life of the application, it should normally be called
         before making calls to the db_env_create or
         db_create methods.
    
         The db_env_set_func_read() 
                  function returns a non-zero error value on failure and 0 on success.