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

[Supriya Kher]

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


Option 2:
I next tried to append "root=  as indicated in the above error

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 \
 -append "root=/dev/sda1" \
  $interfaces

It appears that append option has to be accompanied with a
corresponding "-kernel " option. VM Failed with error :

-append only allowed with -kernel option

Can someone help me in bringing up the VM using virtio the right way ?

Thanks.
S. K