On successful completion, pthread_mutexattr_getprotocol() returns 0. Any other return value indicates that an error occurred.
If either of the following conditions occurs, pthread_mutexattr_getprotocol() might fail and return the corresponding value.
EINVAL
Description:The value specified by attr is NULL, or the value specified by attr or protocol is invalid.
EPERM
Description:The caller does not have the privilege to perform the operation.