DragonFly On-Line Manual Pages


MINHERIT(2)		 DragonFly System Calls Manual		   MINHERIT(2)

NAME

minherit -- control the inheritance of pages

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/types.h> #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. DragonFly is capable of adjusting inheritance characteristics on a page basis. Inher- itance only affects children created by fork(). It has no effect on exec(). exec'd processes replace their address space entirely. This function 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 Inheritance is a rather esoteric feature largely superseded by the MAP_SHARED feature of mmap().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() function 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() function first appeared in OpenBSD. DragonFly 4.1 February 17, 1996 DragonFly 4.1