On Thu, Jan 29, 2015 at 04:47:23PM +0000, Richard W.M. Jones wrote: > On Thu, Jan 29, 2015 at 05:25:09PM +0100, Kashyap Chamarthy wrote: > > A simple reproducer below. > > > > Export a disk image over NBD (I realize port 10809 is default, thought > > I'd explicitly mention anyhow): > > > > $ qemu-nbd --f qcow2 -p10809 \ > > /var/lib/libvirt/images/cirros-0.3.3-x86_64-disk.img -t > > > > > > Create an overlay with backing file exported via NBD: > > > > $ qemu-img create -f qcow2 -F \ > > nbd -o backing_file=nbd://localhost overlay1.qcow2 > > Formatting 'overlay1.qcow2', fmt=qcow2 size=41126400 > > backing_file='nbd://localhost' backing_fmt='nbd' encryption=off > > cluster_size=65536 lazy_refcounts=off > > > > > > Let's attempt to boot the overlay with a minimal QEMU: > > > > $ qemu-system-x86_64 \ > > -nographic \ > > -nodefconfig \ > > -nodefaults \ > > -m 2048 \ > > -device virtio-scsi-pci,id=scsi \ > > -device virtio-serial-pci \ > > -serial stdio \ > > -drive file=./overlay1.qcow2,format=qcow2,if=virtio,cache=writeback > > Segmentation fault (core dumped) > > > > > > On the shell where `qemu-nbd` is running, I notice this > > > > nbd.c:nbd_receive_request():L756: read failed > > This is a "normal error" -- it just means the client dropped the > connection.
Yeah, deduced so. > You really need to get the stack trace from that core dump to > debug this further. I don't see the core dump locally (ABRT or some such not configured), will re-test this with `gdb` in a little while to get the traces. -- /kashyap
