Re: [Qemu-devel] core dump with drive-mirror

[Eric Blake]

On 06/30/2014 05:16 PM, Eric Blake wrote:
> I'm trying to track down a core dump with the QMP drive-mirror command.

Oh, and a followup question:

I discovered that if I try to use drive-mirror to a file that is not
already large enough, the job starts successfully but fails at the point
where it exceeds the block size.  It would be much nicer if the job
auto-resized the destination to be large enough to hold the copy, but if
that is not possible, then if the drive-mirror would fail up front
rather than succeeding at starting a job that is doomed to failure,
where the failure is only reported by an event and lacks useful
information at why it failed.  To trigger this scenario, alter my setup...

> 
> # in one terminal:
> cd /tmp
> rm -f base.img snap1.img snap2.img copy.img
> 
> # base.img <- snap1.img <- snap2.img; intentionally populating base.img
> # with a qcow2 header, but treating it as raw data
> qemu-img create -f qcow2 base.img 10M

...by creating the base.img file with '-f raw'...

> qemu-img create -f qcow2 -b base.img -o backing_fmt=raw snap1.img
> qemu-img create -f qcow2 -b snap1.img -o backing_fmt=qcow2 snap2.img
> cp base.img copy.img

...and using 'touch copy.img' instead of 'cp base.img copy.img'.

> # Yes, this command line is derived from libvirt...
> LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin \
>  QEMU_AUDIO_DRV=none gdb --args  /usr/bin/qemu-system-x86_64 \
>  -machine accel=kvm -name testvm1 -S \
>  -machine pc-i440fx-2.0,accel=kvm,usb=off -m 256 \
>  -realtime mlock=off -smp 1,sockets=1,cores=1,threads=1 \
>  -uuid 5a74eeb4-09c5-4fc2-869d-0e04c13f9db0 -no-user-config \
>  -nodefaults -chardev socket,id=charmonitor,\
> path=/var/lib/libvirt/qemu/testvm1.monitor,server,nowait \
>  -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc \
>  -no-shutdown -no-acpi -boot strict=on \
>  -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 \
>  -drive file=/tmp/snap2.img,if=none,id=drive-virtio-disk0,format=qcow2 \
>  -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x3,\
> drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 \
>  -vnc 127.0.0.1:0 -device cirrus-vga,id=video0,bus=pci.0,addr=0x2 \
>  -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4 \
>  -msg timestamp=on
> 
> # in next terminal:
> mkdir -p /var/lib/libvirt/qemu
> nc -u /var/lib/libvirt/qemu/testvm1.monitor
> {"execute":"qmp_capabilities"}
> {"execute":"cont"}
> {"execute":"drive-mirror","arguments":{"device":"drive-virtio-disk0",
> "target":"/tmp/copy.img","format":"raw", "mode":"existing","sync":"full"}}

everything else being the same, the drive-mirror starts but I get an
early event that the job fails, and query-blockjobs no longer knows
about it.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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