[Qemu-devel] virtfs fails after migration

[Qemu-devel] virtfs fails after migration

[Malte Starostik]

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Hello,

trying to get migration work on a setup with several libvirt based hosts, I'm 
struggling with those VMs that use virtfs shares.
I remember that in previous versions of qemu, the attempt to migrate 
those lead to chaos and mayhem, while now a *mounted* virtfs simply 
blocks migration.  Fine so far, none of the virtfs shares we use need to be 
mounted all the time.  However, when I unmount and then migrate 
(whether to a different host or just save/restore), the virtfs can't be 
mounted anymore.
mount fails with "no such device", and in dmesg I get:

9pnet_virtio: no channels available

The same thing applies to several combinations, the most up to date one 
is with host and guest both running a 3.8.13 kernel and qemu 1.4.0.

qemu command line:

/usr/bin/qemu-system-x86_64 -machine accel=kvm -name 
test01,process=qemu:test01 -S -M pc-1.2 -m 4096 -smp 
1,sockets=1,cores=1,threads=1 -uuid 9d7f74e7-4a90-fbd1-796d-
e23357931e80 -no-user-config -nodefaults -chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/test01.monitor,server,no
wait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -
no-shutdown -kernel /var/lib/libvirt/images/boot/vmlinuz-3.8.13-gentoo -
initrd /var/lib/libvirt/images/boot/initramfs-3.8.13-gentoo.img -append 
root=UUID=0ccbddca-dc76-4965-95cc-c16956d2670d quiet -device piix3-
usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -device virtio-serial-pci,id=virtio-
serial0,bus=pci.0,addr=0x4 -drive file=/dev/vg-
vms/test01,if=none,id=drive-virtio-disk0,format=raw -device virtio-blk-
pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-
disk0,bootindex=1 -fsdev local,security_model=passthrough,id=fsdev-
fs0,path=/mnt/portage,readonly -device virtio-9p-pci,id=fs0,fsdev=fsdev-
fs0,mount_tag=portage,bus=pci.0,addr=0x7 -netdev 
tap,fd=20,id=hostnet0,vhost=on,vhostfd=21 -device virtio-net-
pci,netdev=hostnet0,id=net0,mac=52:54:00:2b:26:e1,bus=pci.0,addr=0x
3 -chardev pty,id=charserial0 -device isa-
serial,chardev=charserial0,id=serial0 -chardev 
spicevmc,id=charchannel0,name=vdagent -device virtserialport,bus=virtio-
serial0.0,nr=1,chardev=charchannel0,id=channel0,name=com.redhat.spic
e.0 -spice port=5900,addr=127.0.0.1,disable-ticketing,seamless-
migration=on -vga qxl -global qxl-vga.ram_size=67108864 -global qxl-
vga.vram_size=67108864 -incoming fd:18 -device virtio-balloon-
pci,id=balloon0,bus=pci.0,addr=0x6

Need to reboot the guest for it to work again.  Removing the 9p and 
9pnet-virtio modules won't do.  Is there any known fix or workaround?

Kind regards,
Malte

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