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Inheritance is a rather esoteric feature largely superseded by the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.