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 inheritance characteristic
inherit. Not all
implementations will guarantee that the inheritance characteristic can be set
on a page basis; the granularity of changes may be as large as an entire
region.
FreeBSD is capable of adjusting inheritance
characteristics on a page basis. Inheritance 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Inheritance is a rather esoteric feature largely superseded by the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 mapping 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 unmapping
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.