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MINHERIT(2)		  FreeBSD System Calls Manual		   MINHERIT(2)

NAME
     minherit -- control the inheritance of pages

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <sys/mman.h>

     int
     minherit(void *addr, size_t len, int inherit);

DESCRIPTION
     The minherit() system call	changes	the specified pages to have the	inher-
     itance characteristic inherit.  Not all implementations will guarantee
     that the inheritance characteristic can be	set on a page basis; the gran-
     ularity of	changes	may be as large	as an entire region.  FreeBSD is capa-
     ble of adjusting inheritance characteristics on a page basis.  Inheri-
     tance only	effects	children created by fork().  It	has no effect on
     exec().  exec'd processes replace their address space entirely.  This
     system call also has no effect on the parent's address space (other than
     to	potentially share the address space with its children).

     Inheritance is a rather esoteric feature largely superseded by the
     MAP_SHARED	feature	of mmap().  However, it	is possible to use minherit()
     to	share a	block of memory	between	parent and child that has been mapped
     MAP_PRIVATE.  That	is, modifications made by parent or child are shared
     but the original underlying file is left untouched.

     INHERIT_SHARE  This option	causes the address space in question to	be
		    shared between parent and child.  It has no	effect on how
		    the	original underlying backing store was mapped.

     INHERIT_NONE   This option	prevents the address space in question from
		    being inherited at all.  The address space will be
		    unmapped in	the child.

     INHERIT_COPY   This option	causes the child to inherit the	address	space
		    as copy-on-write.  This option also	has an unfortunate
		    side effect	of causing the parent address space to become
		    copy-on-write when the parent forks.  If the original map-
		    ping was MAP_SHARED, it will no longer be shared in	the
		    parent after the parent forks and there is no way to get
		    the	previous shared-backing-store mapping without unmap-
		    ping and remapping the address space in the	parent.

RETURN VALUES
     The minherit() function returns the value 0 if successful;	otherwise the
     value -1 is returned and the global variable errno	is set to indicate the
     error.

ERRORS
     The minherit() system call	will fail if:

     [EINVAL]		The virtual address range specified by the addr	and
			len arguments is not valid.

     [EACCES]		The flags specified by the inherit argument were not
			valid for the pages specified by the addr and len
			arguments.

SEE ALSO
     fork(2), madvise(2), mincore(2), mprotect(2), msync(2), munmap(2),
     rfork(2)

HISTORY
     The minherit() system call	first appeared in OpenBSD and then in
     FreeBSD 2.2.

BUGS
     Once you set inheritance to MAP_PRIVATE or	MAP_SHARED, there is no	way to
     recover the original copy-on-write	semantics short	of unmapping and
     remapping the area.

FreeBSD	10.1		       October 30, 2007			  FreeBSD 10.1

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | HISTORY | BUGS

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