The acl_get_qualifier function is a POSIX.1e call that retrieves the qualifier of the tag for the ACL entry indicated by the argument entry_d into working storage and returns a pointer to that storage.
If the value of the tag type in the ACL entry referred to by entry_d is ACL_USER, then the value returned by acl_get_qualifier will be a pointer to type
.Vt uid_t .
If the value of the tag type in the ACL entry referred to by entry_d is ACL_GROUP, then the value returned by acl_get_qualifier will be a pointer to type
.Vt gid_t .
If the value of the tag type in the ACL entry referred to by entry_d is ACL_UNDEFINED_TAG, ACL_USER_OBJ, ACL_GROUP_OBJ, ACL_OTHER, ACL_MASK, or an implementation-defined value for which a qualifier is not supported, then acl_get_qualifier will return a value of
.Vt ( void * ) Ns Dv NULL and the function will fail.
This function may cause memory to be allocated. The caller should free any releasable memory, when the new qualifier is no longer required, by calling acl_free with
.Vt void * as the argument.
The acl_get_qualifier function returns a pointer to the allocated storage if successful; otherwise a NULL pointer is returned and the global variable errno is set to indicate the error.
The acl_get_qualifier fails if: