cmd-buildextend-metal: use serial= to mark target disk

Instead of using SCSI, use virtio-blk's `serial=` option so allow us to
identify the disk inside `create_disk.sh`. And since we already have
udev running there now, we don't have to walk sysfs anymore looking for
our block device.

src/cmd-buildextend-metal

@@ -234,13 +234,13 @@ if [ -n "${ref_is_temp}" ]; then
     ref_arg=${commit}
 fi
 
-target_device_opt="scsi-disk,drive=target,wwn=0x2a"
+extra_target_device_opts=""
 # we need 4096 block size for ECKD DASD and (obviously) metal4k
 if [[ $image_type == dasd || $image_type == metal4k ]]; then
-  target_device_opt="${target_device_opt},physical_block_size=4096,logical_block_size=4096"
+  extra_target_device_opts="physical_block_size=4096,logical_block_size=4096"
 fi
 target_drive=("-drive" "if=none,id=target,format=${image_format},file=${path}.tmp,cache=unsafe" \
-              "-device" "virtio-scsi-${devtype},id=scsitarget" "-device" "${target_device_opt}")
+              "-device" "virtio-blk,serial=target,drive=target${extra_target_device_opts}")
 
 runvm "${target_drive[@]}" -- \
         /usr/lib/coreos-assembler/create_disk.sh \

src/cmdlib.sh

@@ -36,16 +36,15 @@ export basearch
 # Get target architecture
 arch=$(uname -m)
 export arch
-devtype=pci
 
 case $arch in
-    "x86_64")  DEFAULT_TERMINAL="ttyS0"    ;;
-    "ppc64le") DEFAULT_TERMINAL="hvc0"     ;;
-    "aarch64") DEFAULT_TERMINAL="ttyAMA0"  ;;
-    "s390x")   DEFAULT_TERMINAL="ttysclp0"; devtype=ccw ;;
+    "x86_64")  DEFAULT_TERMINAL="ttyS0"   ;;
+    "ppc64le") DEFAULT_TERMINAL="hvc0"    ;;
+    "aarch64") DEFAULT_TERMINAL="ttyAMA0" ;;
+    "s390x")   DEFAULT_TERMINAL="ttysclp0";;
     *)         fatal "Architecture $(arch) not supported"
 esac
-export DEFAULT_TERMINAL devtype
+export DEFAULT_TERMINAL
 
 _privileged=
 has_privileges() {

src/create_disk.sh

@@ -80,23 +80,7 @@ udevtrig() {
 export PATH=$PATH:/sbin:/usr/sbin
 arch="$(uname -m)"
 
-if [ -z "${disk:-}" ]; then
-    # hex 0x2a = 42 in decimal; this is set in cmd-buildextend-metal.
-    # We use the WWN as an unambiguous way to identify our target disk,
-    # independent of other devices attached to the VM (caches, etc.)
-    wwn=000000000000002a
-    for dev in /sys/block/*; do
-        if grep -F -e "${wwn}" "${dev}/device/wwid" 2>/dev/null; then
-            disk="/dev/$(basename ${dev})"
-            break
-        fi
-    done
-    if [ -z "${disk:-}" ]; then
-        echo "failed to find disk with wwn ${wwn}" 1>&2
-        bash
-        exit 1
-    fi
-fi
+disk=$(realpath /dev/disk/by-id/virtio-target)
 
 buildid="${buildid:?--buildid must be defined}"
 imgid="${imgid:?--imgid must be defined}"