[Qemu-devel] qemu virtfs 9p not working on arm?

[Rich Felker]

Hi,

I'm not sure whether this is a kernel problem or a qemu problem (or
even a user problem). The folks on OFTC #qemu suggested I email the
list and relevant section maintainers so that's what I'm doing -- hope
it's okay.

I'm trying to boot qemu-system-arm with rootfs on 9p, and experiencing
the following error:

| 9pnet: Installing 9P2000 support
| 9pnet_virtio: probe of virtio0 failed with error -2
| VFP support v0.3: implementor 41 architecture 1 part 20 variant b rev 4
| rtc-pl031 dev:e8: setting system clock to 2013-07-31 22:56:25 UTC (1375311385)
| 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)

That looks like ENOENT during the probe to me, but I can't find where
in the kernel source it's coming from. My configuration is:

-append "root=root rw rootflags=rw,trans=virtio,version=9p2000.L -rootfstype=9p"
-fsdev local,id=root,path=$(pwd)/root,security_model=none
-device virtio-9p-pci,fsdev=root,mount_tag=root

and this same configuration seems to work on x86. The kernels I'm
using are from the latest Aboriginal Linux images (3.10) and
/proc/config.gz seems to show that all the 9p/virtfs options are
enabled.

Attempting to mount the filesystem after booting also fails with:

| 9pnet_virtio: no channels available
| mount: mounting root on /mnt/ failed: No such file or directory

I have not tested other targets.

Finally, my version of qemu is 1.5.1 from the Debian packages.

Rich