Switch to drive snapshots

README.md

@@ -2,8 +2,8 @@
 
 Dockerized QEMU image for reproducibly testing stuff on Windows.
 Prepare OS image as described below.
-If OS image is mounted to the Docker container as read-only
-it is first copied during Docker container launch.
+Disk image is used as read-only using the QEMU disk snapshot option,
+all local changes are lost after Docker container restart.
 Specify MAC address via environment variable `MAC`.
 For more example see `docker-compose.yml`
 You probably need the machines to come up with

docker-compose.yml

@@ -15,4 +15,4 @@ services:
     tmpfs:
       - /tmp
     environment:
-      - MAC=52:54:00:5e:00:05
+      - MAC=52:54:00:12:34:56

entrypoint.sh

@@ -2,16 +2,6 @@
 set -x
 set -e
 
-# Source image path
-IMAGE=/data/image.bin
-
-# TODO: With QEMU snapshots instead
-if [ ! -w $IMAGE ]; then
-    echo "Data volume is not writable, assuming discardable VM and copying to tmpfs"
-    cp $IMAGE /tmp/image.bin
-    IMAGE=/tmp/image.bin
-fi
-
 # Create macvlan interface on Docker's eth0
 ip link add link eth0 name macvtap0 type macvtap mode bridge
 ip link set dev macvtap0 address ${MAC:?}
@@ -26,11 +16,10 @@ mknod "/dev/tap$(cat /sys/class/net/macvtap0/ifindex)" c $major $minor
   -machine pc-i440fx-4.2,accel=kvm \
   -m 8192 \
   -device virtio-scsi-pci,id=scsi0,bus=pci.0,addr=0x6 \
-  -blockdev "{\"driver\":\"file\",\"filename\":\"$IMAGE\",\"node-name\":\"libvirt-1-storage\",\"auto-read-only\":true,\"discard\":\"unmap\"}" \
-  -blockdev "{\"node-name\":\"libvirt-1-format\",\"read-only\":false,\"driver\":\"raw\",\"file\":\"libvirt-1-storage\"}" \
-  -device scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,device_id=drive-scsi0-0-0-0,drive=libvirt-1-format,id=scsi0-0-0-0,bootindex=2 \
   -device virtio-net-pci,netdev=hostnet0,id=net0,mac=$(cat /sys/class/net/macvtap0/address) \
   -device virtio-balloon-pci \
+  -drive if=none,id=hd,file=/data/image.bin,snapshot=on,format=raw \
+  -device scsi-hd,drive=hd \
   -usb \
   -device usb-ehci,id=ehci                         \
   -device usb-tablet,bus=usb-bus.0 \