I use kqueue(2) on macOS, FreeBSD, NetBSD, OpenBSD, DragonflyBSD.

The kevent structure is defined as follow. Specifically, the field udata is a pointer for some user-specific data structure.

struct kevent {
        uintptr_t       ident;          /* identifier for this event */
        short           filter;         /* filter for event */
        u_short         flags;
        u_int           fflags;
        intptr_t        data;
        void            *udata;         /* opaque user data identifier */
};

This is true on all the above-mentioned systems, except for NetBSD where the documentation and the system headers are inconsistent.

$ uname -a
NetBSD vminetbsd 10.1 NetBSD 10.1 (GENERIC) #0: Mon Dec 16 13:08:11 UTC 2024  mkrepro@mkrepro.NetBSD.org:/usr/src/sys/arch/amd64/compile/GENERIC amd64
$ grep udata /usr/include/sys/event.h
        intptr_t        udata;          /* opaque user data identifier */

Here, the udata field is an integer and the compilation of the application fails when passing the address of a user data structure. Of course, it is possible to use some type cast in some #ifdef structure to make the application portable, although much less readable.

However, this is not so simple.

On the very same NetBSD system, man kqueue also displays intptr_t udata. However, the NetBSD web site documents the opposite.

On https://man.netbsd.org/kqueue.2, the title is "kqueue(2) - NetBSD Manual Pages" and the content says "void *udata", not integer.

The NetBSD web site also contains a nice kqueue tutorial in https://wiki.netbsd.org/tutorials/kqueue_tutorial/ which also says "void *udata", not integer.

So, it seems that NetBSD is somewhat inconsistent. The website and official documentation pretend to be "standard", or at least like all other BSD. But a real system with the latest version (10.1) contains something different, both in the header and the man page.

Can we say that this is a bug in NetBSD? And where should we report those bugs?

Using a type cast in the application code with #ifdef on NetBSD will then become incorrect later if they fix the issue.