On 10.10.19 17:17, Max Reitz wrote:
> Hi everyone,
> 
> (CCs just based on tags in the commit in question)
> 
> I have two bug reports which claim problems of qcow2 on XFS on ppc64le
> machines since qemu 4.1.0.  One of those is about bad performance
> (sorry, is isn’t public :-/), the other about data corruption
> (https://bugzilla.redhat.com/show_bug.cgi?id=1751934).
> 
> It looks like in both cases reverting c8bb23cbdbe3 solves the problem
> (which optimized COW of unallocated areas).
> 
> I think I’ve looked at every angle but can‘t find what could be wrong
> with it.  Do any of you have any idea? :-/

I now have a reproducer with CentOS, so it’s actually useful outside of
Red Hat:

$ cd $TEST_DIR

(Download CentOS-8-x86_64-1905-dvd1.iso here, e.g. from
http://mirror1.hs-esslingen.de/pub/Mirrors/centos/8.0.1905/isos/x86_64/CentOS-8-x86_64-1905-dvd1.torrent
)

$ wget
http://mirror1.hs-esslingen.de/pub/Mirrors/centos/8.0.1905/BaseOS/x86_64/os/isolinux/vmlinuz
$ wget
http://mirror1.hs-esslingen.de/pub/Mirrors/centos/8.0.1905/BaseOS/x86_64/os/isolinux/initrd.img

$ mkdir ks
$ cat > ks/ks.cfg <<EOF
rootpw 123456
install
keyboard us
lang en_US.UTF-8
rootpw 123456
zerombr
autopart
clearpart --all --initlabel

%packages --default
@core
%end
EOF

$ $QEMU_BUILD_DIR/qemu-img create -f qcow2 disk.qcow2 30G
$ $QEMU_BUILD_DIR/x86_64-softmmu/qemu-system-x86_64 \
    -name 'centos' \
    -machine pc \
    -nodefaults \
    -vga std \
    -display gtk \
    -serial stdio \
    -device virtio-scsi-pci,id=virtio_scsi_pci0,bus=pci.0 \
    -blockdev "{'node-name': 'target-disk',
                'driver': 'qcow2',
                'file': {
                    'driver': 'file',
                    'filename': 'disk.qcow2',
                    'cache': {
                        'direct': true
                    },
                    'aio': 'native'
                } }" \
    -device scsi-hd,id=image1,drive=target-disk \
    -blockdev \
     file,node-name=install-cd,filename=CentOS-8-x86_64-1905-dvd1.iso \
    -device scsi-cd,drive=install-cd \
    -blockdev vvfat,node-name=kscfg,dir=ks,label=OEMDRV,read-only=on \
    -device scsi-hd,drive=kscfg \
    -kernel vmlinuz \
    -append 'ks=hd:LABEL=OEMDRV:/ks.cfg delay=60 console=ttyS0' \
    -initrd initrd.img \
    -boot order=cd,menu=off,strict=off \
    -m 2048 \
    -enable-kvm

This installation fails about 50/50 for me.  To retry, just run the last
two steps (qemu-img create and the installation itself).

Max