table of contents
|MINHERIT(2)||System Calls Manual||MINHERIT(2)|
minherit — control
the inheritance of pages
Standard C Library (libc, -lc)
*addr, size_t len,
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
It has no effect on
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superseded by the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
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.
- 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.
- This option prevents the address space in question from being inherited at all. The address space will be unmapped in the child.
- 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.
- This option causes the address space in question to be mapped as new anonymous pages, which would be initialized to all zero bytes, in the child process.
minherit() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable errno is set to indicate the
minherit() system call will fail
fork(2), madvise(2), mincore(2), mprotect(2), msync(2), munmap(2), rfork(2)
minherit() system call first appeared
in OpenBSD and then in FreeBSD
INHERIT_ZERO support first appeared in
OpenBSD 5.6 and then in FreeBSD
Once you set inheritance to
MAP_SHARED, there is no way to recover the original
copy-on-write semantics short of unmapping and remapping the area.
|March 15, 2017||Debian|