[Bug 1847793] Re: qemu 4.1.0 - Corrupt guest filesystem after new vm install

[Simon John]

i've seen guest data corruption and qcow2 corruption on ext4.

i've seen one case where the guest (win10) reports corruption but qemu-
img check does not, but that's the outlier, usually both guest and qemu-
img report corruption.

for me the issue seems to only be win10 guests using virtio-scsi, i've
not seen it on any of 25+ linux/solaris/macos/win2019 guests no matter
what device driver/cache/trim i use.

current workaround is convert from qcow2 to raw, everything else stays
the same and i have no issues.

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https://bugs.launchpad.net/bugs/1847793

Title:
  qemu 4.1.0 - Corrupt guest filesystem after new vm install

Status in QEMU:
  New

Bug description:
  When I install a new vm with qemu 4.1.0 all the guest filesystems are
  corrupt. The first boot from the install dvd iso is ok and the
  installer work fine. But the guest system hangs after the installer
  finishes and I reboot the guest. I can see the grub boot menue but the
  system cannot load the initramfs.

  Testet with:
  - RedHat Enterprise Linux 7.5, 7.6 and 7.7 (RedHat uses xfs for the /boot and 
/ partition)
  Guided install with the graphical installer, no lvm selected.
  - Debian Stable/Buster (Debian uses ext4 for / and /home partition)
  Guidet install with the graphical installer and default options.

  Used commandline to create the vm disk image:
  qemu-img create -f qcow2 /volumes/disk2-part2/vmdisks/vmtest10-1.qcow2 20G

  Used qemu commandline for vm installation:
  #!/bin/sh
  # vmtest10 Installation
  #
  /usr/bin/qemu-system-x86_64  -cpu SandyBridge-IBRS \
      -soundhw hda \
      -M q35 \
      -k de \
      -vga qxl \
      -machine accel=kvm \
      -m 4096 \
      -display gtk \
      -drive 
file=/volumes/disk2-part2/images/debian-10.0.0-amd64-DVD-1.iso,if=ide,media=cdrom
 \
      -drive 
file=/volumes/disk2-part2/images/vmtest10-1.qcow2,if=virtio,media=disk,cache=writeback
 \
      -boot once=d,menu=off \
      -device virtio-net-pci,mac=52:54:00:2c:02:6c,netdev=vlan0 \
      -netdev bridge,br=br0,id=vlan0 \
      -rtc base=localtime \
      -name "vmtest10" \
      -usb -device usb-tablet \
      -spice disable-ticketing \
      -device virtio-serial-pci \
      -device virtserialport,chardev=spicechannel0,name=com.redhat.spice.0 \
      -chardev spicevmc,id=spicechannel0,name=vdagent $*

  Host OS:
  Archlinux (last updated at 10.10.2019)
  Linux testing 5.3.5-arch1-1-ARCH #1 SMP PREEMPT Mon Oct 7 19:03:08 UTC 2019 
x86_64 GNU/Linux
  No libvirt in use.

  
  With qemu 4.0.0 it works fine without any errors.

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