fcntl is as specified in the Single UNIX Specification, Version 3, but with differences as listed below.
According to the Single UNIX Specification, only an application sets fcntl flags, for example O_LARGEFILE. However, this specification also allows implementations to set O_LARGEFILE in a case in which the default behavior matches the O_LARGEFILE behavior. [1] Or in other words, calling fcntl with the F_GETFL command may return O_LARGEFILE as well as flags explicitly set by the application.
| [1] | For example, if off_t is 64 bits. |