#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.