How to allow guest to write on 9p/virtfs shared folder?

Hello,

today, I upgraded my kernel and I seem to have gotten a new kvm backend with this.

Now my guest systems are no longer able to write to the host filesystem.

I share the filesystem using the following command to qemu:

-virtfs local,id=fsdev0,path=$SHARED,security_model=passthrough,mount_tag=vmshared

and on guest side (fstab):

vmshared /mnt/vmshared 9p rw,comment=systemd.automount,trans=virtio,access=any 0 0

Versions:

$ uname -a
Linux manuelspc 3.11.1-1-ARCH #1 SMP PREEMPT Sat Sep 14 19:30:21 CEST 2013 x86_64 GNU/Linux
$ qemu-system-x86_64 --version
QEMU emulator version 1.5.2, Copyright (c) 2003-2008 Fabrice Bellard

Can someone please help me to get back my writing permissions?

Thank you in advance

Yours

Manuel

Hello,

I have to add another problem:

I changed "security_model=passthrough" to "security_model=mapped". This seems to give me back write permissions. I would prefer "passthrough", just as I did before, but this works as a workaround.

Now, If I try to execute a script from the mounted virtfs, then I get the following:

-bash: ./test.pl: /usr/bin/perl: bad interpreter: Numerical result out of range

If I call the same with "perl ./test.pl", then anything works. If I copy the script to somewhere outside of the mounted virtfs, then I can also call the script with "./test.pl". What's going on here?

Thanks in advance

Yours

Manuel

I downgraded the kernel on my system to 3.10.9. This fixed this issue.

So it seems like the "9p" kernel module is broken on Linux 3.11.1.

Can someone point me to the commit, where this was fixed, please?

Thanks in advance.

Greetings,

Manuel

Hello,

just to be sure I didn't miss important information:

My host system is still running with 3.11.1. I only downgraded the guest system to 3.10.9. So only the "guest part" is affected.

I'm running ArchLinux on both systems (host and guest).

Yours

Manuel