Re: [Qemu-discuss] Starting qemu with virtio and .raw image file

[Mike Lovell]

On 07/13/2012 01:10 AM, Supriya Kher wrote:
> Hi,
>
> I am using qemu-system_x86_64 to create a nested virtualization setup.
> The inner guest VM is seen to be very slow. In order to improve guest
> VM performance I have been attempting to start external/outer VM using
> virtio option. However I encounter kernel crashes/failures each time.
>
> I start the outer VM running on Ubuntu using the following command
> line ( The VM image resides as a disk file of .raw format)
>
> # start qemu-kvm
>     sudo $TOOLKIT_PATH/bin/qemu-system-x86_64 -nographic \
>     -echr 20 \
>     -cpu host \
>     -m $MEMORY_SIZE \
>     -smp $NUM_VCPUS \
>     -drive file=$IMAGE_DISK,if=ide \
>     $interfaces
>
> Option 1:
>
> Changed if=ide to if=virtio
>
> sudo $TOOLKIT_PATH/bin/qemu-system-x86_64 -nographic \
>   -echr 20 \
>   -cpu host \
>   -m $MEMORY_SIZE \
>   -smp $NUM_VCPUS \
>   -drive file=$IMAGE_DISK,media=disk,if=virtio \
>    $interfaces
>
> VM crashed with the following trace:
>
> md: ... autorun DONE.
> Root-NFS: No NFS server available, giving up.
> VFS: Unable to mount root fs via NFS, trying floppy.
> VFS: Cannot open root device "sda6" or unknown-block(2,0)
> Please append a correct "root=" boot option; here are the available partitions:
> VFS: Unable to mount root fs on unknown-block(2,0)
> User configuration error - no valid root filesystem found
> Kernel panic - not syncing: Invalid configuration from end user
> prevents continuing
> Pid: 1, comm: swapper Not tainted 2.6.34.10-grsec-WR4.3.0.0_cgl #1
> Call Trace:
> [<ffffffff817015d8>] ? gss_kerberos_ops+0xb9db8/0x1477e0
> [<ffffffff817015d8>] ? gss_kerberos_ops+0xb9db8/0x1477e0
> [<ffffffff815c1551>] panic+0xf5/0x16a
> [<ffffffff8161cde0>] ? vga_con+0x0/0xd0
> [<ffffffff818aa25b>] mount_block_root+0x1e3/0x1fa
> [<ffffffff818aa33c>] mount_root+0xca/0xf6
> [<ffffffff818aa4d8>] prepare_namespace+0x170/0x1a9
> [<ffffffff818a9796>] kernel_init+0x21f/0x23b
> [<ffffffff81003474>] kernel_thread_helper+0x4/0x10
> [<ffffffff815c4d55>] ? restore_args+0x0/0x30
> [<ffffffff818a9577>] ? kernel_init+0x0/0x23b
> [<ffffffff81003470>] ? kernel_thread_helper+0x0/0x10

this is expected. when using virtio for the disk interface, the disks 
appear to the guest as /dev/vd* instead of /dev/sd*. you need to change 
the boot loader in the guest to use 'root=/dev/vda6' instead of 
'root=/dev/sda6'. if you're using grub as the boot loader in the guest, 
you should be able to interrupt it during boot and change the options.

hope that helps.

mike