Create the arm64/aarch64 VM disk image as MBR instead of

GPT scheme.  UEFI needs to know the unique partition GUID
with GPT, which changes each time.  Specifically, the QEMU
EFI BIOS file has this hard-coded.[1]

Since the GPT labels are now unavailable, unconditionally
label the root filesystem as 'rootfs' with newfs(8), since
it does not hurt anything anywhere else.  For the arm64 case,
'/' is mounted from /dev/ufs/rootfs; for all other VM images,
'/' is mounted from /dev/gpt/rootfs.

Unfortunately, since the /dev/gpt/swapfs label is also lost,
set NOSWAP=1 for the arm64/aarch64 images.  This is temporary,
until I figure out a scalable solution to this.  But, a certain
piece of softare was written "very fast", and ended up living
for 15 years.  We can deal with this for a week or so.

Information from:	andrew, emaste [1]
Sponsored by:	The FreeBSD Foundation

release/scripts/mk-vmimage.sh

@@ -93,6 +93,16 @@ main() {
 		. "${VMCONFIG}"
 	fi
 
+	case ${TARGET}:${TARGET_ARCH} in
+		arm64:aarch64)
+			ROOTLABEL="ufs"
+			NOSWAP=1
+			;;
+		*)
+			ROOTLABEL="gpt"
+			;;
+	esac
+
 	vm_create_base
 	vm_install_base
 	vm_extra_install_base

release/tools/vmimage.subr

@@ -30,10 +30,9 @@ write_partition_layout() {
 				-o ${VMIMAGE}
 			;;
 		arm64:aarch64)
-			mkimg -s gpt \
-				-p efi/efiboot:=${BOOTFILES}/efi/boot1/boot1.efifat \
-				${SWAPOPT} \
-				-p freebsd-ufs/rootfs:=${VMBASE} \
+			mkimg -s mbr \
+				-p efi:=${BOOTFILES}/efi/boot1/boot1.efifat \
+				-p freebsd:=${VMBASE} \
 				-o ${VMIMAGE}
 			;;
 		powerpc:powerpc*)
@@ -77,7 +76,7 @@ vm_create_base() {
 	mkdir -p ${DESTDIR}
 	truncate -s ${VMSIZE} ${VMBASE}
 	mddev=$(mdconfig -f ${VMBASE})
-	newfs /dev/${mddev}
+	newfs -L rootfs /dev/${mddev}
 	mount /dev/${mddev} ${DESTDIR}
 
 	return 0
@@ -97,7 +96,7 @@ vm_copy_base() {
 	truncate -s ${VMSIZE} ${VMBASE}.tmp
 	mkdir -p ${DESTDIR}/new
 	mdnew=$(mdconfig -f ${VMBASE}.tmp)
-	newfs /dev/${mdnew}
+	newfs -L rootfs /dev/${mdnew}
 	mount /dev/${mdnew} ${DESTDIR}/new
 
 	tar -cf- -C ${DESTDIR}/old . | tar -xUf- -C ${DESTDIR}/new
@@ -123,7 +122,7 @@ vm_install_base() {
 
 	echo '# Custom /etc/fstab for FreeBSD VM images' \
 		> ${DESTDIR}/etc/fstab
-	echo '/dev/gpt/rootfs   /       ufs     rw      1       1' \
+	echo "/dev/${ROOTLABEL}/rootfs   /       ufs     rw      1       1" \
 		>> ${DESTDIR}/etc/fstab
 	if [ -z "${NOSWAP}" ]; then
 		echo '/dev/gpt/swapfs  none    swap    sw      0       0' \