minherit(2) [linux man page]

MINHERIT(2)						      BSD 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 inheritance characteristic inherit.  Not all implementations will guaran-
     tee 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     Inheritance is a rather esoteric feature largely superseded by the MAP_SHARED feature of mmap().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 indi-
     cate 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.

BSD
								 October 30, 2007							       BSD

MADVISE(2)						      BSD System Calls Manual							MADVISE(2)

NAME

     madvise, posix_madvise -- give advice about use of memory

SYNOPSIS

     #include <sys/mman.h>

     int
     madvise(void *addr, size_t len, int advice);

     int
     posix_madvise(void *addr, size_t len, int advice);

DESCRIPTION

     The madvise() system call allows a process that has knowledge of its memory behavior to describe it to the system.  The advice passed in may
     be used by the system to alter its virtual memory paging strategy.  This advice may improve application and system performance.  The behavior
     specified in advice can only be one of the following values:

     MADV_NORMAL      Indicates that the application has no advice to give on its behavior in the specified address range.  This is the system
		      default behavior.  This is used with madvise() system call.

     POSIX_MADV_NORMAL
		      Same as MADV_NORMAL but used with posix_madvise() system call.

     MADV_SEQUENTIAL  Indicates that the application expects to access this address range in a sequential manner.  This is used with madvise()
		      system call.

     POSIX_MADV_SEQUENTIAL
		      Same as MADV_SEQUENTIAL but used with posix_madvise() system call.

     MADV_RANDOM      Indicates that the application expects to access this address range in a random manner.  This is used with madvise() system
		      call.

     POSIX_MADV_RANDOM
		      Same as MADV_RANDOM but used with posix_madvise() system call.

     MADV_WILLNEED    Indicates that the application expects to access this address range soon.  This is used with madvise() system call.

     POSIX_MADV_WILLNEED
		      Same as MADV_WILLNEED but used with posix_madvise() system call.

     MADV_DONTNEED    Indicates that the application is not expecting to access this address range soon.  This is used with madvise() system call.

     POSIX_MADV_DONTNEED
		      Same as MADV_DONTNEED but used with posix_madvise() system call.

     MADV_FREE	      Indicates that the application will not need the information contained in this address range, so the pages may be reused
		      right away.  The address range will remain valid.  This is used with madvise() system call.

     MADV_ZERO_WIRED_PAGES
		      Indicates that the application would like the wired pages in this address range to be zeroed out if the address range is
		      deallocated without first unwiring the pages (i.e. a munmap(2) without a preceding munlock(2) or the application quits).
		      This is used with madvise() system call.

     The posix_madvise() behaves same as madvise() except that it uses values with POSIX_ prefix for the advice system call argument.

RETURN VALUES

     Upon successful completion, a value of 0 is returned.  Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS

     madvise() fails if one or more of the following are true:

     [EINVAL]		The value of advice is incorrect.

     [EINVAL]		The address range includes unallocated regions.

     [ENOMEM]		The virtual address range specified by the addr and len are outside the range allowed for the address space.

LEGACY SYNOPSIS

     #include <sys/types.h>
     #include <sys/mman.h>

     int
     madvise(caddr_t addr, size_t len, int advice);

     int
     posix_madvise(caddr_t addr, size_t len, int advice);

     The include file <sys/types.h> is necessary.  The type of addr has changed.

SEE ALSO

     mincore(2), minherit(2), mprotect(2), msync(2), munmap(2), compat(5)

HISTORY

     The madvise function first appeared in 4.4BSD.  The posix_madvise function is part of IEEE 1003.1-2001 and was first implemented in Mac OS X
     10.2.

BSD
								   June 9, 1993 							       BSD