Add NIS automounter map, which supports rewriting of self-hosted locations

to make them nullfs.

PR:		221010
Submitted by:	G. Paul Ziemba
MFC after:	2 weeks

etc/autofs/Makefile

@@ -1,6 +1,6 @@
 # $FreeBSD$
 
-FILES=		include_ldap special_hosts special_media special_noauto special_null
+FILES=		include_ldap include_nis special_hosts special_media special_noauto special_null
 
 NO_OBJ=
 FILESDIR=	/etc/autofs

etc/autofs/include_nis

@@ -0,0 +1,180 @@
+#!/usr/bin/awk -f
+#-
+# Copyright (c) 2017 G. Paul Ziemba
+# 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, this list of conditions and the following disclaimer.
+#  2. Redistributions in binary form must reproduce the above copyright
+#     notice, 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 AUTHOR AND CONTRIBUTORS ``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 AUTHOR OR CONTRIBUTORS 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.
+#
+# $FreeBSD$
+#
+
+#
+# /etc/autofs/include_nis
+#
+# automountd Directory Services script for NIS
+#
+# SYNOPSIS
+#       include_nis <mapname>
+#
+#       include_nis <mapname> <key>
+#
+# DESCRIPTION
+#
+#       This script provides a Directory Services map for automountd
+#       based on NIS. Please see auto_master(5) for general information.
+#
+#       The first form, with one argument, emits the entire named NIS map.
+#       The second form, with two arguments, emits the map entry for the
+#       key given in the second argument. 
+#
+#       This script attempts to determine the names and IP addresses
+#       of the local host. Map entries matching the local host are
+#       rewritten to specify nullfs mounts (instead of the default
+#       NFS) to reduce access overhead in the kernel.
+#
+#	If a map entry contains multiple location fields, it is not changed.
+#
+
+
+# Populate list of names and IP addrs thet mean "this host"
+# into myhostnames array
+BEGIN {
+    #
+    # Set self hostnames
+    #
+
+    "hostname -s" | getline;
+    myhostnames[$0] = 1;
+
+    "hostname -f" | getline;
+    myhostnames[$0] = 1;
+
+    myhostnames["localhost"] = 1
+
+    "hostname -f" | getline;
+    localdomain=$0
+    myhostnames["localhost."localdomain] = 1
+
+    while ("ifconfig" | getline) {
+	if ($1 == "inet") {
+	    myhostnames[$2] = 1;
+	}
+    }
+
+    # debug
+#            print "--- hostname list start ----"
+#            for (i in myhostnames) {
+#                print i
+#            }
+#            print "--- hostname list end ----"
+
+    if (ARGC == 2) {
+	# mapname only
+	while ("ypcat -k " ARGV[1] | getline) {
+	    proc_mapline(1)
+	}
+    }
+    if (ARGC == 3) {
+	# mapname and keyname
+	while ("ypmatch " ARGV[2] " " ARGV[1] | getline) {
+	    proc_mapline(0)
+	}
+    }
+    exit 0
+}
+
+function is_self(hostname)
+{
+    if (myhostnames[hostname]) {
+	return 1
+    }
+    return 0
+}
+
+#
+# Lines are of the form [key] [-opts] location1 [... locationN]
+#
+# indicate index of key field with first positional parameter
+# 1 means keyfield is the first field
+# 0 means keyfield is not present
+#
+function proc_mapline(keyfield)
+{
+    optionsfield = 0
+    locationfield = 0
+    locationcount = 0
+
+    for (i=keyfield+1; i <= NF; ++i) {
+	if (!optionsfield) {
+	    if ($i ~ /^-/) {
+		# the first options field found on the line
+		optionsfield = i;
+		continue
+	    }
+	}
+	# Assumption: location contains colon (":")
+	if (optionsfield && ($i ~ /:/) && ($i !~ /^-/)) {
+	    ++locationcount
+	    if (!locationfield) {
+		# the first location field found on the line
+		locationfield = i
+	    }
+	}
+    }
+
+    #
+    # If location not found, do not modify.
+    #
+    # If there is more than one location, do not modify. Rationale:
+    # Options are applied to all locations. We ca not have "nullfs"
+    # for only some locations and "nfs" for others for a given
+    # map key (i.e., a line). The usual reason for multiple
+    # locations is for redundancy using replicated volumes on
+    # multiple hosts, so multiple hosts imply fstype=nfs (the
+    # FreeBSD default for automounter maps).
+    #
+    # Hypothetically there could be a map entry with multiple
+    # locations all with host parts matching "me". In that case,
+    # it would be safe to rewrite the locations and specify
+    # nullfs, but the code does not handle this case.
+    #
+    if (locationcount == 1) {
+	#
+	# We have a line with exactly one location field
+	#
+	# Assumption: location has no more than one colon (":")
+	#
+	n=split($locationfield,location,":")
+	if (is_self(location[1])) {
+	    $locationfield = ":" location[2]
+	    if (optionsfield) {
+		# append to existing options
+		$optionsfield = $optionsfield ",fstype=nullfs"
+	    } else {
+		# sneak in ahead of location
+		$locationfield = "-fstype=nullfs " $locationfield
+	    }
+	}
+    }
+
+    print
+}