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Rework minherit(2) man page into a table. 

XXX Do we not guarantee page-granularity inheritance?  Cursory glance
at uvm suggests we do -- can we nix the caveats about regions vs
pages?
This commit is contained in:
riastradh 2014-08-05 15:01:03 +00:00
parent 3d52f18626
commit 19aeab521f
1 changed files with 35 additions and 29 deletions
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64
lib/libc/sys/minherit.2
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@ -1,4 +1,4 @@
.\" $NetBSD: minherit.2,v 1.19 2014/07/18 12:39:17 christos Exp $
.\" $NetBSD: minherit.2,v 1.20 2014/08/05 15:01:03 riastradh Exp $
.\"
.\" Copyright (c) 1991, 1993
.\" The Regents of the University of California. All rights reserved.
@ -29,7 +29,7 @@
.\"
.\" @(#)minherit.2 8.1 (Berkeley) 6/9/93
.\"
.Dd July 18, 2014
.Dd August 5, 2014
.Dt MINHERIT 2
.Os
.Sh NAME
@ -44,38 +44,43 @@
.Sh DESCRIPTION
The
.Fn minherit
system call
changes the specified range of virtual addresses to have the specified
fork-time inheritance characteristic
system call changes the specified range of virtual addresses to have
the inheritance characteristic
.Fa inherit ,
which can be set to
.Dv MAP_INHERIT_NONE ,
which determines how
.Xr fork 2
will map the region in the child process.
The supported inheritance characteristics are:
.Bl -tag -offset abcd -width MAP_INHERIT_DEFAULT
.It MAP_INHERIT_COPY
The child is given a private copy of the region: writes from parent or
child are not seen by the other.
.It MAP_INHERIT_NONE
The region is unmapped in the child.
.It MAP_INHERIT_SHARE
The child is shares the region with the parent: writes from parent and
child are seen by both.
.It MAP_INHERIT_ZERO
The region is mapped in the child to anonymous pages filled with
zeros.
.El
.Pp
Normally, the parent's virtual address space is copied for the child
as if with
.Dv MAP_INHERIT_COPY ,
.Dv MAP_INHERIT_SHARE ,
or
.Dv MAP_INHERIT_ZERO .
Also possible is
.Dv MAP_INHERIT_DEFAULT ,
which defaults to
.Dv MAP_INHERIT_COPY .
for which the alias
.Dv MAP_INHERIT_DEFAULT
is provided.
Regions in the parent mapped using
.Xr mmap 2
with the
.Dv MAP_SHARED
flag are by default shared with the child as if with
.Dv MAP_INHERIT_SHARED .
.Pp
Not all implementations will guarantee that the inheritance characteristic
can be set on a page basis;
the granularity of changes may be as large as an entire region.
.Pp
Normally, the entire address space is marked
.Dv MAP_INHERIT_COPY ;
when the process calls
.Fn fork ,
the child receives a (virtual) copy of the entire address space.
Pages or regions marked
.Dv MAP_INHERIT_SHARE
are shared between the address spaces, while pages or regions marked
.Dv MAP_INHERIT_NONE
will be unmapped in the child.
Finally pages or regions marked
.Dv MAP_INHERIT_ZERO
will still be present at the child, but will be initialized to
.Dv 0 .
.Sh RETURN VALUES
.Rv -std minherit
.Sh ERRORS
@ -89,6 +94,7 @@ An invalid region or invalid parameters were specified.
.Xr fork 2 ,
.Xr madvise 2 ,
.Xr mincore 2 ,
.Xr mmap 2 ,
.Xr mprotect 2 ,
.Xr msync 2 ,
.Xr munmap 2