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Re: [Qemu-devel] QEMU segfault: Booting an overlay with backing_file ove
From: |
Kashyap Chamarthy |
Subject: |
Re: [Qemu-devel] QEMU segfault: Booting an overlay with backing_file over NBD: nbd.c:nbd_receive_request():L756: read failed |
Date: |
Thu, 29 Jan 2015 18:22:22 +0100 |
User-agent: |
Mutt/1.5.23.1-rc1 (2014-03-12) |
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