Hi, I don’t know much about libvirt, but I would have thought that any manual modification of the qemu command line isn’t supported and might always break.
Anyway, from a QEMU POV, -snapshot only works with -drive (this includes -hda, etc.). It doesn’t work with -blockdev. I can see that this isn’t documented for -snapshot, but basically whenever -blockdev is used, the user assumes full responsibility for the block graph (or at least that particular subgraph). We cannot enable snapshot functionality then. So this can’t be fixed in qemu, as -snapshot doesn’t make sense for -blockdev. This behavior should be documented, though. As for libvirt, I don’t know. I would be surprised if it had a guarantee for keeping manual qemu command line additions working, and I can’t imagine that it would scan the XML for “legacy” qemu parameters and interpret them itself (which it would need to do to keep -snapshot working for -blockdev). Max -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1860759 Title: [REGRESSION] option `-snapshot` ignored with blockdev Status in QEMU: New Bug description: After upgrade of qemu 3.1.0 → 4.2.0 I found that running with libvirt doesn't honor `-snapshot` option anymore. I.e. disk images get modified. Using `-hda` option honors `-snapshot` So I made a test case without libvirt. Testcase using 4.2.0: > qemu -hda tmp-16G.img -cdrom regular-rescue-latest-x86_64.iso -m 2G This works fine and tmp-16G.img stays unmodified. But: > /usr/bin/qemu-system-x86_64 -name guest=test-linux,debug-threads=on -S -machine pc-i440fx-3.1,accel=kvm,usb=off,vmport=off,dump-guest-core=off -cpu Broadwell-noTSX,vme=on,ss=on,f16c=on,rdrand=on,hypervisor=on,arat=on,tsc-adjust=on,xsaveopt=on,pdpe1gb=on,abm=on -m 2048 -overcommit mem-lock=off -smp 3,sockets=3,cores=1,threads=1 -uuid d32a9191-f51d-4fae-a419-b73d85b49198 -no-user-config -nodefaults -rtc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=delay -no-hpet -no-shutdown -global PIIX4_PM.disable_s3=1 -global PIIX4_PM.disable_s4=1 -boot strict=on -device ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x5.0x7 -device ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x5 -device ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pci.0,addr=0x5.0x1 -device ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pci.0,addr=0x5.0x2 -blockdev \{\"driver\":\"file\",\"filename\":\"/tmp/regular-rescue-latest-x86_64.iso\",\"node-name\":\"libvirt-2-storage\",\"auto-read-only\":true,\"discard\":\"unmap\"} -blockdev \{\"node-name\":\"libvirt-2-format\",\"read-only\":true,\"driver\":\"raw\",\"file\":\"libvirt-2-storage\"} -device ide-cd,bus=ide.0,unit=0,drive=libvirt-2-format,id=ide0-0-0,bootindex=1 -blockdev \{\"driver\":\"file\",\"filename\":\"/tmp/tmp-2G.img\",\"node-name\":\"libvirt-1-storage\",\"auto-read-only\":true,\"discard\":\"unmap\"} -blockdev \{\"node-name\":\"libvirt-1-format\",\"read-only\":false,\"driver\":\"qcow2\",\"file\":\"libvirt-1-storage\",\"backing\":null} -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x7,drive=libvirt-1-format,id=virtio-disk0 -netdev user,id=hostnet0 -device e1000,netdev=hostnet0,id=net0,mac=52:54:00:ab:d8:29,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -device qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pci.0,addr=0x2 -device intel-hda,id=sound0,bus=pci.0,addr=0x4 -device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6 -snapshot -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny -msg timestamp=on This modifies tmp-16G.img. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1860759/+subscriptions
