nextboot(8): add a -a option for appending to a configuration.

By default, a nextboot invocation will clobber any existing nextboot
configuration.

MFC after:	2 weeks
Relnotes:	yes

sbin/reboot/nextboot.8

@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 17, 2015
+.Dd April 9, 2016
 .Dt NEXTBOOT 8
 .Os
 .Sh NAME
@@ -32,6 +32,7 @@
 .Nd "specify an alternate kernel and boot flags for the next reboot"
 .Sh SYNOPSIS
 .Nm
+.Op Fl a
 .Op Fl e Ar variable=value
 .Op Fl f
 .Op Fl k Ar kernel
@@ -53,6 +54,12 @@ configuration.
 .Pp
 The options are as follows:
 .Bl -tag -width ".Fl o Ar options"
+.It Fl a
+This option causes
+.Nm
+to append to an existing configuration in
+.Pa /boot/nextboot.conf .
+By default any existing configuration is overwritten.
 .It Fl D
 Invoking
 .Nm

sbin/reboot/nextboot.sh

@@ -26,6 +26,7 @@
 #
 # $FreeBSD$
 
+append="NO"
 delete="NO"
 kenv=
 force="NO"
@@ -48,12 +49,17 @@ add_kenv()
 }
 
 display_usage() {
-	echo "Usage: nextboot [-e variable=value] [-f] [-k kernel] [-o options]"
-	echo "       nextboot -D"
+	cat <<-EOF
+	Usage: nextboot [-e variable=value] [-f] [-k kernel] [-o options]
+	       nextboot -D
+	EOF
 }
 
-while getopts "De:fk:o:" argument ; do
+while getopts "aDe:fk:o:" argument ; do
 	case "${argument}" in
+	a)
+		append="YES"
+		;;
 	D)
 		delete="YES"
 		;;
@@ -106,7 +112,19 @@ df -Tn "/boot/" 2>/dev/null | while read _fs _type _other ; do
 	EOF
 done
 
-cat > ${nextboot_file} << EOF
+set -e
+
+nextboot_tmp=$(mktemp $(dirname ${nextboot_file})/nextboot.XXXXXX)
+
+if [ ${append} = "YES" -a -f ${nextboot_file} ]; then
+	cp -f ${nextboot_file} ${nextboot_tmp}
+fi
+
+cat >> ${nextboot_tmp} << EOF
 nextboot_enable="YES"
 $kenv
 EOF
+
+fsync ${nextboot_tmp}
+
+mv ${nextboot_tmp} ${nextboot_file}