I just reviewed our mmap(2) flags to compare them against Linux,
FreeBSD, Solaris, and Darwin's flags. Of the flags listed below, none
of them are specified by POSIX, and none of them do anything
interesting on OpenBSD: MAP_COPY just gets rewritten to MAP_PRIVATE,
and the rest are silently ignored by UVM.
Linux FreeBSD Solaris Darwin
MAP_COPY no YES* no YES*
MAP_RENAME no YES* YES* YES*
MAP_NORESERVE YES YES* YES YES*
MAP_INHERIT no YES** no no
MAP_NOEXTEND no no no YES*
MAP_HASSEMAPHORE no YES*** no YES***
MAP_TRYFIXED no no no no
* These are defined in the OS's <sys/mman.h>, but are undocumented in
their mmap(2) manual, and behave the same as on OpenBSD (i.e.,
MAP_COPY is an alias for MAP_PRIVATE; the others have no effect).
** MAP_INHERIT is documented in FreeBSD's mmap(2) manual (as "This
flag never operated as advertised", which is true on OpenBSD too), but
not defined in their <sys/mman.h>.
*** MAP_HASSEMAPHORE is documented in FreeBSD and Darwin's mmap(2)
manuals and defined in their <sys/mman.h>, but has no effects on
either's VM behavior.
So MAP_NORESERVE is perhaps necessary/worth keeping around, but the
others seem like candidates for removal if nothing in ports needs
them.
MAP_HASSEMAPHORE is used in rthread_sem.c, but it doesn't do anything,
so I suspect it's just cargo culting based on man page misinformation?
Are there architectures that actually have restrictions on semaphore
memory?
