1.\" $FreeBSD$ 2.\" 3.\" Copyright (c) 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 4. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)minherit.2 8.1 (Berkeley) 6/9/93 31.\" 32.Dd October 30, 2007 33.Dt MINHERIT 2 34.Os 35.Sh NAME 36.Nm minherit 37.Nd control the inheritance of pages 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In sys/mman.h 42.Ft int 43.Fn minherit "void *addr" "size_t len" "int inherit" 44.Sh DESCRIPTION 45The 46.Fn minherit 47system call 48changes the specified pages to have the inheritance characteristic 49.Fa inherit . 50Not all implementations will guarantee that the inheritance characteristic 51can be set on a page basis; 52the granularity of changes may be as large as an entire region. 53.Fx 54is capable of adjusting inheritance characteristics on a page basis. 55Inheritance only effects children created by 56.Fn fork . 57It has no effect on 58.Fn exec . 59exec'd processes replace their address space entirely. 60This system call also 61has no effect on the parent's address space (other than to potentially 62share the address space with its children). 63.Pp 64Inheritance is a rather esoteric feature largely superseded by the 65.Dv MAP_SHARED 66feature of 67.Fn mmap . 68However, it is possible to use 69.Fn minherit 70to share a block of memory between parent and child that has been mapped 71.Dv MAP_PRIVATE . 72That is, modifications made by parent or child are shared but 73the original underlying file is left untouched. 74.Bl -tag -width ".Dv INHERIT_SHARE" 75.It Dv INHERIT_SHARE 76This option causes the address space in question to be shared between 77parent and child. 78It has no effect on how the original underlying backing 79store was mapped. 80.It Dv INHERIT_NONE 81This option prevents the address space in question from being inherited 82at all. 83The address space will be unmapped in the child. 84.It Dv INHERIT_COPY 85This option causes the child to inherit the address space as copy-on-write. 86This option also has an unfortunate side effect of causing the parent 87address space to become copy-on-write when the parent forks. 88If the original mapping was 89.Dv MAP_SHARED , 90it will no longer be shared in the parent 91after the parent forks and there is no way to get the previous 92shared-backing-store mapping without unmapping and remapping the address 93space in the parent. 94.El 95.Sh RETURN VALUES 96.Rv -std minherit 97.Sh ERRORS 98The 99.Fn minherit 100system call will fail if: 101.Bl -tag -width Er 102.It Bq Er EINVAL 103The virtual address range specified by the 104.Fa addr 105and 106.Fa len 107arguments is not valid. 108.It Bq Er EACCES 109The flags specified by the 110.Fa inherit 111argument were not valid for the pages specified 112by the 113.Fa addr 114and 115.Fa len 116arguments. 117.El 118.Sh SEE ALSO 119.Xr fork 2 , 120.Xr madvise 2 , 121.Xr mincore 2 , 122.Xr mprotect 2 , 123.Xr msync 2 , 124.Xr munmap 2 , 125.Xr rfork 2 126.Sh HISTORY 127The 128.Fn minherit 129system call first appeared in 130.Ox 131and then in 132.Fx 2.2 . 133.Sh BUGS 134Once you set inheritance to 135.Dv MAP_PRIVATE 136or 137.Dv MAP_SHARED , 138there is no way to recover the original copy-on-write semantics 139short of unmapping and remapping the area. 140