.

t/qemu-runlinux

 #!/bin/sh -e
 # qemu-runlinux [options] <kernel> <program> ...
-# run kernel in QEMU with root fs taken from host
+# run kernel/program in QEMU with root fs taken from host
 #
-# Useful to test/debug just compiled kernel via running programs
-# edited/compiled on host.
+# Copyright (C) 2014-2019  Nexedi SA and Contributors.
+#                          Kirill Smelkov <kirr@nexedi.com>
+#
+# This program is free software: you can Use, Study, Modify and Redistribute
+# it under the terms of the GNU General Public License version 3, or (at your
+# option) any later version, as published by the Free Software Foundation.
+#
+# You can also Link and Combine this program with other software covered by
+# the terms of any of the Free Software licenses or any of the Open Source
+# Initiative approved licenses and Convey the resulting work. Corresponding
+# source of such a combination shall include the source code for all other
+# software used.
+#
+# This program is distributed WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+#
+# See COPYING file for full licensing terms.
+# See https://www.nexedi.com/licensing for rationale and options.
+
+# qemu-runlinux spawns linux kernel under qemu, setups rootfs to be taken from
+# / of host, and runs specified program inside.
+#
+# It might be useful, for example, to test/debug just compiled kernel via
+# running programs edited/compiled on host.
+
+# ---- init under spawned kernel ----
 
 # pid=1: we are running inside booted kernel as init.
 # mount /sys /proc etc and tail to the program.
-qshutdown() {
-	echo 1 >/proc/sys/kernel/sysrq
-	echo o >/proc/sysrq-trigger	# shutdown
+if [ $$ == 1 ]; then
+	echo "qinit ..."
 
-}
+	qshutdown() {
+		echo 1 >/proc/sys/kernel/sysrq
+		echo o >/proc/sysrq-trigger	# shutdown
 
-qdie() {
-	echo "E: $*" 1>&2
-	qshutdown
-	sleep 1d # give time for shutdown to happen
-	exit 1	 # just in case
-}
+	}
+
+	qdie() {
+		echo "E: $*" 1>&2
+		qshutdown
+		sleep 1d # give time for shutdown to happen
+		exit 1	 # just in case
+	}
 
-if [ $$ == 1 ]; then
-	echo "qinit ..."
 	mount -t sysfs      none /sys
 	mount -t debugfs    none /sys/kernel/debug
 	#mount -t bpf        none /sys/fs/bpf
@@ -48,8 +73,9 @@ if [ $$ == 1 ]; then
 	test $# != 0 || qdie "no program to run"
 	#cat /proc/cmdline
 	#env
-	#set +e -x
-	setsid "$@" <>/dev/ttyS0 >&0 2>&1	# run argv[1:] passes to init
+	#set -x
+	set +e
+	setsid "$@" <>/dev/ttyS0 >&0 2>&1	# run argv[1:] passed to init
 	echo "exit code: $?"
 
 	qshutdown
@@ -58,20 +84,40 @@ if [ $$ == 1 ]; then
 fi
 
 
-# ----------------------------------------
+# ---- qemu setup ----
 
 die() {
 	echo "$*" 1>&2
 	exit 1
 }
 
+usage() {
+	cat <<EOF
+Usage: qemu-runlinux [options] <kernel> <program> ...
+Run linux/program under QEMU with rootfs taken from host.
+
+<kernel>	is path vmlinuz-like kernel image
+<program> ...	is program to run and arguments to it.
+
+Options:
+
+	-g	run with graphics
+EOF
+}
+
+# by default output goes to stdout with both /dev/console and /dev/ttyS0 (where
+# program is run) attached there.
 nographic=y
 
 while test $# != 0
 do
 	case "$1" in
-	-g)
+	-g)	# with graphics UI, /dev/console goes to VGA; program to /dev/ttyS0
 		nographic=;;
+	-h)
+		usage
+		exit 0
+		;;
 	*)
 		break;;
 	esac
@@ -121,7 +167,3 @@ ${nographic:+console=ttyS0} init="$(realpath $0)" \
 CWD="$dir" HOME="$HOME" LANG="$LANG" TERM="$TERM" PATH="$PATH" \
 -- $prog \
 "
-
-
-# \
-#    -nographic  \