VirtFS: Cannot mount 9p during boot

[deleted]

I use as client Debian squeeze i386 with a custom kernel:
Linux (none) 2.6.35.5 #3 Thu Sep 23 18:36:02 UTC 2010 i686 GNU/Linux

And as host Debian squeeze amd64
Linux asd 2.6.32-5-amd64 #1 SMP Fri Sep 17 21:50:19 UTC 2010 x86_64 GNU/Linux

kvm version is:
kvm-88-5908-gdd67374

Started the client using:
sudo /usr/local/kvm/bin/qemu-system-x86_64 -m 1024 -kernel linux-2.6.35.5.qemu -drive file=root.img,if=virtio -net nic,macaddr=02:ca:ff:ee:ba:be,model=virtio,vlan=1 -net tap,ifname=tap1,vlan=1,script=no -virtfs local,path=/host,security_model=passthrough,mount_tag=host -nographic

I noticed that I cannot mount it (mapped or passthrough) using /etc/rc.local or /etc/fstab, but after login as root using

mount /mnt

or

mount -t 9p -o trans=virtio host /mnt

(the same stuff i tried inside /etc/rc.local)

The only output on a failed mount in rc.local/fstab I get is

[ 15.035920] device: '9p-1': device_add
[ 15.038180] 9p: no channels available
[ 15.038937] device: '9p-1': device_unregister
[ 15.049123] device: '9p-1': device_create_release

The stuff in /etc/fstab is:
host /mnt 9p trans=virtio 0 0

I intercepted the boot by adding `set -v; set +e; mount -t 9p -o trans=virtio host_share /mnt; /bin/sh` on top of my /etc/rc.local:
... but than it works quite well... well that is not what I expected. So I changed it to `set -v; mount /mnt || true; /bin/sh`.. and then it doesn't work anymore... mysterios but hey, did you notice that the share is actually called host and not host_share as I wrote inside the rc.local. So why does it work at all? Let me change it to `set -v; set +e; mount -t 9p -o trans=virtio host /mnt; /bin/sh` and reboot again.

What should i say: it says:
[ 8.004754] device: '9p-1': device_add
[ 8.006446] 9p: no channels available
[ 8.007156] device: '9p-1': device_unregister
[ 8.008650] device: '9p-1': device_create_release
mount: No such file or directory

But i have a shell now and can type the mount stuff inside it:
$ mount -v -t 9p -o trans=virtio host /mnt
mount -v -t 9p -o trans=virtio host /mnt
[ 70.982688] device: '9p-2': device_add
[ 70.986508] 9p: no channels available
[ 70.987969] device: '9p-2': device_unregister
[ 70.992937] device: '9p-2': device_create_release
mount: No such file or directory
$ ls -l /sys/bus/virtio/drivers/9pnet_virtio
total 0
--w------- 1 root root 4096 Sep 26 12:58 bind
--w------- 1 root root 4096 Sep 26 12:58 uevent
--w------- 1 root root 4096 Sep 26 12:58 unbind
lrwxrwxrwx 1 root root 0 Sep 26 12:58 virtio1 -> ../../../../devices/virtio-pci/virtio1
$ ls -l /sys/devices/virtio-pci/virtio1
total 0
lrwxrwxrwx 1 root root 0 Sep 26 13:00 bus -> ../../../bus/virtio
-r--r--r-- 1 root root 4096 Sep 26 13:00 device
lrwxrwxrwx 1 root root 0 Sep 26 13:00 driver -> ../../../bus/virtio/drivers/9pnet_virtio
-r--r--r-- 1 root root 4096 Sep 26 13:00 features
-r--r--r-- 1 root root 4096 Sep 26 13:00 modalias
-r--r--r-- 1 root root 4096 Sep 26 13:00 mount_tag
drwxr-xr-x 2 root root 0 Sep 26 12:58 power
-r--r--r-- 1 root root 4096 Sep 26 13:00 status
lrwxrwxrwx 1 root root 0 Sep 26 13:00 subsystem -> ../../../bus/virtio
-rw-r--r-- 1 root root 4096 Sep 26 13:00 uevent
-r--r--r-- 1 root root 4096 Sep 26 13:00 vendor
$ cat /sys/devices/virtio-pci/virtio1/mount_tag
host$ mount -v -t 9p -o trans=virtio host /mnt
[ 340.559853] device: '9p-3': device_add
[ 340.563699] 9p: no channels available
[ 340.565602] device: '9p-3': device_unregister
[ 340.569201] device: '9p-3': device_create_release
mount: No such file or director
$ mount -v -t 9p -o trans=virtio hostA /mnt
[ 406.218462] device: '9p-4': device_add
hostA on /mnt type 9p (rw,trans=virtio)
$ env
CONSOLE=/dev/console
HOME=/
runlevel=2
INIT_VERSION=sysvinit-2.88
COLUMNS=80
TERM=linux
PATH=/sbin:/usr/sbin:/bin:/usr/bin
RUNLEVEL=2
PREVLEVEL=N
SHELL=/bin/sh
PWD=/
previous=N
LINES=24
VERBOSE=no
$ id
uid=0(root) gid=0(root) groups=0(root)
$ hexdump asd
0000000 6f68 7473 0000 0000 0000 0000 0000 0000
0000010 0000 0000
0000014

I rebooted again and now just ctrl+d in my rc.local shell to get to my real root login with zsh:
$ cat /sys/devices/virtio-pci/virtio1/mount_tag > asd
$ hexdump asd
0000000 6f68 7473 0000 0000 0000 0000 0000 0000
0000010 0000 0000
0000014
$ id
uid=0(root) gid=0(root) groups=0(root)
$ env
TERM=linux
HOME=/root
SHELL=/bin/zsh
USER=root
LOGNAME=root
PATH=/host/usr/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
MAIL=/var/mail/root
HUSHLOGIN=FALSE
SHLVL=1
PWD=/root
OLDPWD=/root
COLORTERM=yes
LINKS_XTERM=screen
EDITOR=vim
PAGER=less -r
BROWSER=iceweasel
LESS=-RIM
LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arj=01;31:*.taz=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.dz=01;31:*.gz=01;31:*.lz=01;31:*.xz=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.rar=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.jpg=01;35:*.jpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.axv=01;35:*.anx=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.axa=00;36:*.oga=00;36:*.spx=00;36:*.xspf=00;36:
HISTFILE=/root/.zsh_history
HISTSIZE=10000
SAVEHIST=10000
_=/usr/bin/env
$ mount -v -t 9p -o trans=virtio host /mnt
[ 224.087952] device: '9p-2': device_add
host on /mnt type 9p (rw,trans=virtio)

So the next step was to change my login shell to /bin/sh (dash) and reboot:
$ id
uid=0(root) gid=0(root) groups=0(root)
$ env
USER=root
MAIL=/var/mail/root
OLDPWD=/root
HOME=/root
HUSHLOGIN=FALSE
PS1=\h:\w\$
LOGNAME=root
TERM=linux
PATH=/host/usr/bin:/host/usr/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
SHELL=/bin/sh
PWD=/host
$ mount -v -t 9p -o trans=virtio host /mnt
[ 15.330643] device: '9p-2': device_add
host on /mnt type 9p (rw,trans=virtio)

Next step was to boot up, change my env and then use the correct mount:
$ for i in USER MAIL OLDPWD HOME HUSHLOGIN PS1 LOGNAME TERM PATH SHELL PWD; do unset $i; done
$ env
$ /bin/mount -v -t 9p -o trans=virtio host /mnt
[ 431.742839] device: '9p-2': device_add
host on /mnt type 9p (rw,trans=virtio)

[deleted (to-delete)]

Next steps were to use the old envs:

$ for i in USER MAIL OLDPWD HOME HUSHLOGIN PS1 LOGNAME TERM PATH SHELL PWD; do unset $i; done
$ export CONSOLE=/dev/console
$ export HOME=/
$ export runlevel=2
$ export INIT_VERSION=sysvinit-2.88
$ export COLUMNS=80
$ export TERM=linux
$ export PATH=/sbin:/usr/sbin:/bin:/usr/bin
$ export RUNLEVEL=2
$ export PREVLEVEL=N
$ export SHELL=/bin/sh
$ export PWD=/
$ export previous=N
$ export LINES=24
$ export VERBOSE=no
$ /bin/sh
$ env
CONSOLE=/dev/console
HOME=/
runlevel=2
INIT_VERSION=sysvinit-2.88
COLUMNS=80
TERM=linux
PATH=/sbin:/usr/sbin:/bin:/usr/bin
RUNLEVEL=2
PREVLEVEL=N
SHELL=/bin/sh
PWD=/host
previous=N
LINES=24
VERBOSE=no
$ mount -v -t 9p -o trans=virtio host /mnt
[ 44.554805] device: '9p-2': device_add
host on /mnt type 9p (rw,trans=virtio)

Next step was to strace on rc.local sh:
/bin/sh: can't access tty; job control turned off
$ strace -o /mount1 mount -v -t 9p -o trans=virtio host /mnt
[ 131.002908] device: '9p-2': device_add
[ 131.006914] 9p: no channels available
[ 131.009720] device: '9p-2': device_unregister
[ 131.013135] device: '9p-2': device_create_release
mount: No such file or directory

And then inside the normal root shell
$ strace -o /mount2 mount -v -t 9p -o trans=virtio host /mnt

[deleted (to-delete)]

Important information: There exists a folder /host in the guest filesystem

[deleted (to-delete)]

So it is a problem that pwd inside the root shell is / and thus it finds /host and informs the kernel that it should mount /host using 9p to /mnt (which is of course bogus). I am quite unsure how to work around that problem without a stupid hack in rc.local instead of /etc/fstab

So there is still the problem that it mounts host_share even if that does not exists

[deleted (to-delete)]

Fixed for me by http://article.gmane.org/gmane.linux.utilities.util-linux-ng/3500/raw and http://article.gmane.org/gmane.linux.kernel/1041020/raw

[Thomas Huth (th-huth)]

If I've got the previous comments right, this was not a QEMU bug, but a bug in "mount" and the guest kernel ... so closing this QEMU ticket here now.