VirtFS mapped symlinks resolved wrong

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I tried to map a folder with qemu-kvm qemu-kvm-0.13.0-rc1-3-gc9c2179 (this is v0.13.0-rc1-16667-gc9c2179). I mounted it first in passthrough mode and saw all symlinks as expected. Then I used mapped and noticed that the target of a symlink changed to the actual data inside the linked folder as target instead of the target filename.

So for example if you have a file abc with the content "omg, this is important stuff" and a symlink lnkme -> abc then it wiill look inside the kvm with mounted 9p virtio (mapped) like that:

lnkme -> omg, this is important stuff

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Why not using simple symlinks on the host with xattr like on normal files instead of those hacks which either don't work on client or don't work on the host?

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And maybe you should use lsetxattr and lgetxattr instead of the symlink resolving versions setxattr and getxattr

[Venkateswararao Jujjuri (JV) (jvrao)]

Responding to multiple issues raised above.

- Let us track this bug for the security/symlink issue and open a different defect for the mount issue.
- I tried to reproduce this defect with the QEMU mainline. I don't see the problem. More description on
  the environment (Host OS/Guest OS/ QEMU command line etc) and how to reproduce the problem will
  be helpful.
  [root@localhost mmnt]# cat file1
  omg it is important
  [root@localhost mmnt]# ln -sf file1 sym1
  [root@localhost mmnt]# ls -l
  total 16
  -rw-r--r-- 1 root root 20 2010-09-24 01:24 file1
  lrwxrwxrwx 1 root root 6 2010-09-24 01:24 sym1 -> file1
  [root@localhost mmnt]# logout
- Moshroom:
  - There are multiple security models here, if you use 'passthrough' same type of files are created on the
     host/guest. But if you use 'mapped' security model this is how we do it.
     This security model is for cloud use case scenarios. Please read more in this post
     http://<email address hidden>/msg31452.html
  - No need to use lsetattr/lgetattr here because we always create regular files in this model.

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Host OS is Debian sid/experimental amd64 with 2.6.32-5-amd64 (2.6.32-23). qemu-kvm version can be found above. As said before the symlink were created outside the vm and then tried to access inside the vm.

So I have to use passthrough in host/client shared folders... which means I have to run kvm as root. :(

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But mapped is also really confusing. Everything inside the vm:

$ id
uid=0(root) gid=0(root) groups=0(root)
$ touch newfile
$ -rw-r--r-- 1 root 1000 0 Sep 24 20:39 newfile

So the gid is not set correctly. On thhe host:

% xattr newfile
user.virtfs.uid
user.virtfs.mode

I started it using:
% /usr/local/kvm/bin/qemu-system-x86_64 -m 1024 -kernel linux-2.6.35.5.qemu -drive file=root.cow1,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=/shared,security_model=mapped,mount_tag=host -nographic

[Venkateswararao Jujjuri (JV) (jvrao)]

Passthrough model needs to be used if you want the compatibility on/off the virtfs mount.
The mapped model virtfs-izes the filesystem. For mapped model, one need to start a fresh share and continue
to use it only from the guest.

Regarding gid is not being correct, please use 9P2000.L protocol, on the mount specify -o version=9p2000.L.
The default is 9P2000.U which doesn't support gid.

Ex mount command:

mount -t 9p -o trans=virtio -o version=9p2000.L -o debug=0xFFFF v_map_virtfs /mmnt

We recently added some info the the external wiki. (http://wiki.qemu.org/Documentation/9psetup)

- JV

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Fixed by the mentioned documentation