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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 March 15, 2017 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to potentially 62share the address space with its children). 63.Pp 64Inheritance is a rather esoteric feature largely superseded by the 65.Dv MAP_SHARED 66feature of 67.Fn mmap . 68However, it is possible to use 69.Fn minherit 70to share a block of memory between parent and child that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.It Dv INHERIT_ZERO 95This option causes the address space in question to be mapped as new 96anonymous pages, 97which would be initialized to all zero bytes, 98in the child process. 99.El 100.Sh RETURN VALUES 101.Rv -std minherit 102.Sh ERRORS 103The 104.Fn minherit 105system call will fail if: 106.Bl -tag -width Er 107.It Bq Er EINVAL 108The virtual address range specified by the 109.Fa addr 110and 111.Fa len 112arguments is not valid. 113.It Bq Er EACCES 114The flags specified by the 115.Fa inherit 116argument were not valid for the pages specified 117by the 118.Fa addr 119and 120.Fa len 121arguments. 122.El 123.Sh SEE ALSO 124.Xr fork 2 , 125.Xr madvise 2 , 126.Xr mincore 2 , 127.Xr mprotect 2 , 128.Xr msync 2 , 129.Xr munmap 2 , 130.Xr rfork 2 131.Sh HISTORY 132The 133.Fn minherit 134system call first appeared in 135.Ox 136and then in 137.Fx 2.2 . 138.Pp 139The 140.Dv INHERIT_ZERO 141support first appeared in 142.Ox 5.6 143and then in 144.Fx 12.0 . 145.Sh BUGS 146Once you set inheritance to 147.Dv MAP_PRIVATE 148or 149.Dv MAP_SHARED , 150there is no way to recover the original copy-on-write semantics 151short of unmapping and remapping the area. 152