Add a manpage for the kenv(2) syscall that Chad David kindly

wrote for me.

Submitted by:	davidc

1 files changed, 172 insertions, 0 deletions

diff --git a/lib/libc/sys/kenv.2 b/lib/libc/sys/kenv.2
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+.\"
+.\" Copyright (C) 2001 Chad David <davidc@FreeBSD.org>. All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer as
+.\"    the first lines of this file unmodified other than the possible
+.\"    addition of one or more copyright notices.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+.\" DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
+.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+.\" DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd April 17, 2002
+.Dt KENV 2
+.Os
+.Sh NAME
+.Nm kenv
+.Nd kernel environment
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In kenv.h
+.Ft int
+.Fn kenv "int action" "const char *name" "char *value" "int len"
+.Sh DESCRIPTION
+The
+.Fn kenv
+function manipulates kernel environment variables.
+It supports the well known userland actions of getting, setting and unsetting
+environment variables, as well as the ability to dump all of the entries in
+the kernel environment.
+.Pp
+The
+.Fa action
+parameter can be one of the following:
+.Bl -tag -width ".Dv KENV_DUMP"
+.It Dv KENV_GET
+Returns the value associated with the named kernel environment variable.
+If the variable is not found -1 is returned and
+.Va errno
+is set to
+.Er ENOENT .
+Only the number of bytes available in
+.Fa value
+are copied out.
+.It Dv KENV_SET
+Sets or adds a new kernel environment variable.
+This option is only avaiable to the superuser.
+.It Dv KENV_UNSET
+Unsets the kernel environment variable
+.Fa name .
+If the variable does not exists -1 is returned and
+.Va errno
+is set to
+.Er EINVAL .
+This option is only available to the superuser.
+.It Dv KENV_DUMP
+Dumps as much of the kernel environment as will fit in
+.Fa value .
+If
+.Fa value
+is
+.Dv NULL ,
+.Fn kenv
+will return the number of bytes required to copy out the entire environment.
+.El
+.Pp
+The
+.Fa name
+parameter is the name of the environment variable to be affected.
+In the case of
+.Dv KENV_DUMP
+it is ignored.
+.Pp
+The
+.Fa value
+parameter contains either the value to set the environment variable
+.Fa name
+to in the case of
+.Dv KENV_SET ,
+or it points to the location where
+.Fn kenv
+should copy return data to in the case of
+.Dv KENV_DUMP
+and
+.Dv KENV_GET .
+If 
+.Fa value
+is
+.Dv NULL
+in the case of
+.Dv KENV_DUMP ,
+.Fn kenv
+will return the number of bytes required to copy out the entire environment.
+.Pp
+The
+.Fa len
+parameter indicates how many bytes of storage
+.Fa value
+points to.
+.Sh RETURN VALUES
+The
+.Fn kenv
+function returns 0 if successful in the case of
+.Dv KENV_SET
+and
+.Dv KENV_UNSET,
+and the number of bytes copied into
+.Fa value
+in the case of
+.Dv KENV_DUMP
+and
+.Dv KENV_GET .
+If an error occurs, a value of -1 is returned and
+.Va errno
+is set to indicate the error.
+.Sh ERRORS
+.Fn kenv
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+.Fa action
+is not a valid option, or the length of the
+.Fa value
+is less than 1 for a
+.Dv KENV_SET .
+.It Bq Er ENOENT
+no value could be found for
+.Fa name
+for a
+.Dv KENV_SET
+or
+.Dv KENV_UNSET .
+.It Bq Er EPERM
+a user other than the superuser attempted to set or unset an kernel
+environment variable.
+.It Bq Er EFAULT
+a bad address was encountered while attempting to copy in user arguments,
+or copy out value(s).
+.It Bq Er ENAMETOOLONG
+the name of a variable supplied by the user is longer than
+.Dv KENV_MNAMELEN
+or the value of a variable is longer than
+.Dv KENV_MVALLEN .
+.El
+.Sh SEE ALSO
+.Xr kenv 1
+.Sh AUTHORS
+.An -nosplit
+This man page was written by
+.An Chad David Aq davidc@FreeBSD.org .
+.Pp
+The 
+.Fn kenv
+system call was written by
+.An Maxime Henrion Aq mux@FreeBSD.org .