Given the behaviour of Solaris DOORS, the flags selected are very cleverly chosen. Sensible engineering :).

But now I am wondering... Which organization defines flags like S_IFSOCK or S_IFIFO?. Posix members?. I am worried about flag collision between OSs.

For instance, if DOORS were a real flag defined in Solaris, how other OSs would know to not reuse that flag for some other purpose? :).

Your comment is very valuable and solve my doubts about it. Implementation is truly trivial and could be supported everywhere.