133 lines
4.6 KiB
Groff
133 lines
4.6 KiB
Groff
.\" $FreeBSD$
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.\"
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.\" Copyright (c) 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)minherit.2 8.1 (Berkeley) 6/9/93
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.\"
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.Dd February 17, 1996
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.Dt MINHERIT 2
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.Os
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.Sh NAME
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.Nm minherit
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.Nd control the inheritance of pages
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/mman.h>
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.Ft int
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.Fn minherit "void *addr" "size_t len" "int inherit"
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.Sh DESCRIPTION
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The
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.Fn minherit
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system call
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changes the specified pages to have the inheritance characteristic
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.Fa inherit .
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Not all implementations will guarantee that the inheritance characteristic
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can be set on a page basis;
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the granularity of changes may be as large as an entire region.
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.Fx
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is capable of adjusting inheritance characteristics on a page basis.
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Inheritance only effects children created by
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.Fn fork .
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It has no effect on
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.Fn exec .
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exec'd processes replace their address space entirely. This function also
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has no effect on the parent's address space (other then to potentially
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share the address space with its children).
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.Pp
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Inheritance is a rather esoteric feature largely superceeded by the
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MAP_SHARED feature of
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.Fn mmap .
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However, it is possible to use
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.Fn minherit
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to share a block of memory between parent and child that has been mapped
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MAP_PRIVATE. That is, modifications made by parent or child are shared but
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the original underlying file is left untouched.
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.Bl -tag -width MAP_HASSEMAPHORE
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.It Dv INHERIT_SHARE
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This option causes the address space in question to be shared between
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parent and child. It has no effect on how the original underlying backing
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store was mapped.
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.It Dv INHERIT_NONE
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This option prevents the address space in question from being inherited
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at all. The address space will be unmapped in the child.
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.It Dv INHERIT_COPY
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This option causes the child to inherit the address space as copy-on-write.
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This option also has an unfortunate side effect of causing the parent
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address space to become copy-on-write when the parent forks. If the
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original mapping was MAP_SHARED, it will no longer be shared in the parent
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after the parent forks and there is no way to get the previous
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shared-backing-store mapping without unmapping and remapping the address
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space in the parent.
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.El
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.Sh RETURN VALUES
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.Rv -std minherit
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.Sh ERRORS
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The
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.Fn minherit
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The virtual address range specified by the
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.Fa addr
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and
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.Fa len
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arguments is not valid.
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.It Bq Er EACCES
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The flags specified by the
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.Fa inherit
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argument were not valid for the pages specified
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by the
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.Fa addr
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and
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.Fa len
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arguments.
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.El
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.Sh BUGS
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Once you set inheritance to MAP_PRIVATE or MAP_SHARED, there is no way to
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recover the originanl copy-on-write semantics short of unmapping and remapping
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the area.
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.Sh SEE ALSO
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.Xr fork 2 ,
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.Xr madvise 2 ,
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.Xr mincore 2 ,
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.Xr mprotect 2 ,
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.Xr msync 2 ,
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.Xr munmap 2 ,
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.Xr rfork 2
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.Sh HISTORY
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The
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.Fn minherit
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function first appeared in
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.Ox .
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