Re: [Qemu-devel] QEMU dies on any attempt to load a Linux kernel module when using a 9P rootfs

Hi Richard,

On 11/25/2013 10:49 AM, Richard Yao wrote:

I booted a Gentoo Linux installation in QEMU with a 9P rootfs as follows:

sudo qemu-kvm -cpu host -m 1024 -kernel
/mnt/test/usr/src/linux-3.13-rc1/arch/x86/boot/bzImage -append
'root=/dev/root rootfstype=9p rootflags=trans=virtio,version=9p2000.L ro
console=ttyS0' -serial stdio -fsdev
local,id=root,path=/mnt/test,security_model=none -device
virtio-9p-pci,fsdev=root,mount_tag=/dev/root

The system boots fine, but attempting to load any module will fail:

localhost ~ # modprobe crc32
qemu-system-x86_64: virtio: trying to map MMIO memory

The behavior is consistent no matter what combination of things that I
try. So far, I have tried Linux 3.10.7-gentoo (Gentoo patchset) and
Linux 3.13-rc1. I have tried QEMU 1.4.2, QEMU 1.6.1 and QEMU HEAD. I
have also tried booting without KVM, but the behavior is the same:

sudo qemu-kvm --no-kvm -m 1024 -kernel
/mnt/test/usr/src/linux-3.13-rc1/arch/x86/boot/bzImage -append
'root=/dev/root rootfstype=9p rootflags=trans=virtio,version=9p2000.L ro
console=ttyS0' -serial stdio -fsdev
local,id=root,path=/mnt/test,security_model=none -device
virtio-9p-pci,fsdev=root,mount_tag=/dev/root

Have you used this setup recently?

With my 3.15.0+ kernel, qemu-system-x86_64 substituted for qemu-kvm, and the
path changed from your arguments I get:

9pnet_virtio: no channels available
VFS: Cannot open root device "root" or unknown-block(0,0): error -2
Please append a correct "root=" boot option; here are the available partitions:
0b00         1048575 sr0  driver: sr
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014

Thanks,
Christopher

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