debvm-run: add a --skip option

As with debvm-create, this option allows skipping default configuration
to let a user override things in their way.

Link: https://bugs.debian.org/1036918

1 files changed, 54 insertions, 11 deletions

diff --git a/bin/debvm-run b/bin/debvm-run
index ddd6d1f..ead9942 100755
--- a/bin/debvm-run
+++ b/bin/debvm-run
@@ -35,6 +35,31 @@ Note that B<debvm-create> defaults to installing a cloud kernel if available, so
 This option specifies the location of the virtual machine image file.
 By default F<rootfs.ext4> in the working directory is used.
 
+=item B<--skip>=I<task>
+
+Skip a particular task or feature.
+The option may be specified multiple times or list multiple tasks to be skipped by separating them with a comma.
+By default, no tasks are skipped.
+The following tasks may be skipped.
+
+=over 4
+
+=item B<network>
+
+Do not pass configure network card.
+
+=item B<rngdev>
+
+Do not pass a random number generator device.
+
+=item B<rootdev>
+
+A block device for the root filesystem is no longer passed.
+This can be used to customize the block device.
+The label of the root filesystem will still be passed.
+
+=back
+
 =item B<-s> I<sshport>, B<--sshport>=I<sshport>
 
 If given, B<qemu> is configured to pass connections to I<127.0.0.1:sshport> to port 22 of the virtual machine.
@@ -96,6 +121,7 @@ set -u
 IMAGE=rootfs.ext4
 SSHPORT=
 GRAPHICAL=
+SKIP=,
 
 nth_arg() {
 	shift "$1"
@@ -128,6 +154,9 @@ opt_graphical() {
 opt_image() {
 	IMAGE=$1
 }
+opt_skip() {
+	SKIP="$SKIP$1,"
+}
 opt_sshport() {
 	SSHPORT=$1
 }
@@ -145,12 +174,12 @@ while getopts :gi:s:-: OPTCHAR; do
 				graphical)
 					"opt_$OPTARG"
 				;;
-				image|sshport)
+				image|skip|sshport)
 					test "$OPTIND" -gt "$#" && usage_error "missing argument for --$OPTARG"
 					"opt_$OPTARG" "$(nth_arg "$OPTIND" "$@")"
 					OPTIND=$((OPTIND+1))
 				;;
-				image=*|sshport=*)
+				image=*|skip=*|sshport=*)
 					"opt_${OPTARG%%=*}" "${OPTARG#*=}"
 				;;
 				*)
@@ -178,6 +207,13 @@ if ! printf '\123\357' | cmp --bytes=2 "$IMAGE" - 1080; then
 	die "image '$IMAGE' is not in ext4 format"
 fi
 
+check_skip() {
+	case "$SKIP" in
+		*",$1,"*)	return 0 ;;
+		*)		return 1 ;;
+	esac
+}
+
 cleanup() {
 	set +x
 	test -n "$KERNELTMP" && rm -f "$KERNELTMP"
@@ -266,10 +302,14 @@ set -- \
 	-m 1G \
 	-kernel "/proc/self/fd/$KERNELFD" \
 	-initrd "/proc/self/fd/$INITRDFD" \
-	-drive "media=disk,format=raw,discard=unmap,file=$IMAGE,if=virtio,cache=unsafe" \
-	-object rng-random,filename=/dev/urandom,id=rng0 \
 	"$@"
 
+if ! check_skip rootdev; then
+	set -- \
+		-drive "media=disk,format=raw,discard=unmap,file=$IMAGE,if=virtio,cache=unsafe" \
+		"$@"
+fi
+
 # Translate KERNELARCH (a Debian architecture) to a Debian CPU name.
 # This utilizes the QEMU Debian package symlink mapping that ensures that
 # calling qemu-system-${DEB_HOST_ARCH_CPU} will run the QEMU binary providing
@@ -358,8 +398,11 @@ if test -z "$MAX_SMP" || test "$MAX_SMP" -gt 1; then
 		set -- -smp "$NPROC" "$@"
 	fi
 fi
-if test -n "$RNG_DEV"; then
-	set -- -device "$RNG_DEV" "$@"
+if test -n "$RNG_DEV" && ! check_skip rngdev; then
+	set -- \
+		-device "$RNG_DEV" \
+		-object rng-random,filename=/dev/urandom,id=rng0 \
+		"$@"
 fi
 
 if test -z "$GRAPHICAL"; then
@@ -397,11 +440,11 @@ DNSSEARCH=$(dnsdomainname)
 if test -n "$DNSSEARCH"; then
 	NETDEV="$NETDEV,domainname=$DNSSEARCH"
 fi
-set -- \
-	-append "$KERNEL_CMDLINE" \
-	-netdev "$NETDEV" \
-	-device "$NIC_DEV" \
-	"$@"
+set -- -append "$KERNEL_CMDLINE" "$@"
+
+if ! check_skip network; then
+	set -- -netdev "$NETDEV" -device "$NIC_DEV" "$@"
+fi
 
 echo "+ $QEMU $*" 1>&2
 exec "$QEMU" "$@"