FreeBSD and OpenBSD support

[anuragsoni]

So far this library has been just tested on macOS. We should test this on the various BSD systems (starting with FreeBSD, OpenBSD), and add tests to ensure the library works on them.

Some differences across the various systems is the type definition for kevent.

macOS:

     struct kevent {
             uintptr_t       ident;          /* identifier for this event */
             int16_t         filter;         /* filter for event */
             uint16_t        flags;          /* general flags */
             uint32_t        fflags;         /* filter-specific flags */
             intptr_t        data;           /* filter-specific data */
             void            *udata;         /* opaque user data identifier */
     };

NetBSD

     struct kevent {
             uintptr_t ident;        /* identifier for this event */
             uint32_t  filter;       /* filter for event */
             uint32_t  flags;        /* action flags for kqueue */
             uint32_t  fflags;       /* filter flag value */
             int64_t   data;         /* filter data value */
             void     *udata;        /* opaque user data identifier */
     };

openBSD:

struct kevent {
	uintptr_t   ident;	/* identifier for this event */
	short	    filter;	/* filter for event */
	u_short	    flags;	/* action flags for kqueue */
	u_int	    fflags;	/* filter flag value */
	int64_t	    data;	/* filter data value */
	void	   *udata;	/* opaque user data identifier */
};

FreeBSD:

     struct kevent {
	     uintptr_t	ident;	     /*	identifier for this event */
	     short     filter;	     /*	filter for event */
	     u_short   flags;	     /*	action flags for kqueue	*/
	     u_int     fflags;	     /*	filter flag value */
	     int64_t   data;	     /*	filter data value */
	     void      *udata;	     /*	opaque user data identifier */
	     uint64_t  ext[4];	     /*	extensions */
     };

Another area that will take some work is to go over the various filters and filter flags (NOTE_*), to add os specific support for each platform. We already use ppx_optcomp for some conditional compilation, we could leverage it further to work with filters and flags that aren't defined on all platforms. The list of variables generated by our dune setup that can be consumed via ppx_optcomp is available at

kqueue-ml/lib/config/config.ml

Lines 32 to 38 in 521dca9

	let vars =
	[ "KQUEUE_AVAILABLE", C.C_define.Value.Switch (kqueue_available operating_systems)
	; "FREEBSD", List.assoc "__FreeBSD__" operating_systems
	; "OPENBSD", List.assoc "__OpenBSD__" operating_systems
	; "DRAGONFLY", List.assoc "__DragonFly__" operating_systems
	; "NETBSD", List.assoc "__NetBSD__" operating_systems
	; "KQUEUE_ML_ARCH_SIXTYFOUR", List.assoc "ARCH_SIXTYFOUR" system