Arch Linux

neilzium

Member

Registered: 2011-12-17

Posts: 41

[SOLVED] QEMU: virtio block device as root partition

I'm currently trying to set up a Debian VM with QEMU, using the following script which has been modified from the wiki. This causes 100% cpu on one core, and QEMU simply hangs.

#!/bin/bash
USERID=`whoami`
IFACE=$(sudo tunctl -b -u $USERID)
printf -v macaddr "52:54:0E:8E:CC:7E"

qemu-kvm -netdev tap,id=vnet0,vhost=on,ifname=$IFACE -device virtio-net-pci,netdev=vnet0,id=net0,mac=$macaddr \
-kernel /boot/vmlinuz-debian -initrd /boot/initrd-debian -append root=/dev/vda -m 512 -vga none -display none -cpu host -daemonize -smp cores=2 -enable-kvm -nographic \
-drive file=/dev/sda8,if=none,id=virtio-disk0,format=raw,cache=none,aio=native -device virtio-blk-pci,scsi=off,drive=virtio-disk0,id=disk0 \
-device virtio-balloon-pci,id=balloon0

sudo tunctl -d $IFACE &> /dev/null

I've confirmed that I can load a virtio block device with the VM by modifying the qemu-kvm line as follows:

qemu-kvm -netdev tap,id=vnet0,vhost=on,ifname=$IFACE -device virtio-net-pci,netdev=vnet0,id=net0,mac=$macaddr \
-kernel /boot/vmlinuz-debian -initrd /boot/initrd-debian -append root=/dev/sda -m 512 -vga none -display none -cpu host -daemonize -smp cores=2 -enable-kvm -nographic \
-drive file=/dev/sda9,if=none,id=virtio-disk0,format=raw,cache=none,aio=native -device virtio-blk-pci,scsi=off,drive=virtio-disk0,id=disk0 \
-device virtio-balloon-pci,id=balloon0 /dev/sda8

this produces a device /dev/vda on the VM.

lspci -v

00:03.0 SCSI storage controller: Red Hat, Inc Virtio block device
        Subsystem: Red Hat, Inc Device 0002
        Flags: bus master, fast devsel, latency 0, IRQ 11
        I/O ports at c000 [size=64]
        Memory at febf1000 (32-bit, non-prefetchable) [size=4K]
        Capabilities: [40] MSI-X: Enable+ Count=2 Masked-
        Kernel driver in use: virtio-pci

lsmod|grep virtio

virtio_rng              1928  0
rng_core                3006  1 virtio_rng
virtio_blk              4209  0
virtio_balloon          2961  0
virtio_net             10573  0
virtio_pci              5511  0
virtio_ring             3258  1 virtio_pci
virtio                  3309  5 virtio_rng,virtio_blk,virtio_balloon,virtio_net,virtio_pci

I haven't found any information as to whether or not this is supported on a physical partition, however there are many examples where an image as the root partition with virtio. I'm not sure if this is a Debian issue or a QEMU issue.

EDIT:
I should mention that the VM's fstab is mounting root by the fs label. I've confirmed that e2label /dev/vda does report the correct label so this shouldn't be the issue

Last edited by neilzium (2012-08-19 07:37:18)

neilzium

Member

Registered: 2011-12-17

Posts: 41

Re: [SOLVED] QEMU: virtio block device as root partition

Finally solved this thanks to the bug report linked in this post. adding -global virtio-blk-pci.ioeventfd=off fixed the problem. Don't know if this has been fixed in QEMU already. If so, it's probably because of older virtio drivers in debian squeeze.