Use virt-manager to share files between Linux host and Windows guest

file-sharingkvmvirt-manager

Is it possible to use "Filesystem Passthrough" virtual hardware option inside virt-manager to share a folder on my Linux host with my Windows guest? I found some tutorials for how to do this with a Linux guest, but when I try this with my Windows guest I receive the following error message when attempting to start the VM:

Error starting domain: Unable to read from monitor: Connection reset by peer

Traceback (most recent call last):   File "/usr/share/virt-manager/virtManager/asyncjob.py", line 100, in cb_wrapper
    callback(asyncjob, *args, **kwargs)   File "/usr/share/virt-manager/virtManager/asyncjob.py", line 122, in tmpcb
    callback(*args, **kwargs)   File "/usr/share/virt-manager/virtManager/domain.py", line 1210, in startup
    self._backend.create()   File "/usr/lib64/python2.7/site-packages/libvirt.py", line 698, in create
    if ret == -1: raise libvirtError ('virDomainCreate() failed', dom=self)
libvirtError: Unable to read from monitor: Connection reset by peer

I tried sourcing some documentation but all I could find was the official page linking to a FAQ and "some screenshots".

Best Answer

I don't believe this is possible using Windows guests. I usually setup a Samba server on the Linux KVM host and then share a folder out using that to my KVM guests.

Filesystem Passthrough

The documentation on sharing a KVM host's directory with the KVM guests (Linux) is available here on the virt-manager website. The page is titled: Example Sharing Host files with the Guest.

Setting up Samba

The linux-kvm website also contains directions for setting up Samba. That documentation is available here, titled: Tip: How you can share files on your Linux Host with a Windows Guest using Samba.

Samba

If you want to share files stored on Linux Linux, install a Samba server on the Linux machine. Follow the documentation (Red Hat 6, CentOS 5, Ubuntu).

If you want to share files from Windows, your file manager on Linux can probably connect to a Windows share with no extra effort on your part. Try browsing smb:///. If you want access from the command line, run

mkdir /media/somedir
sudo mount -t cifs //servername/sharename /media/somedir

(If you need help on the Windows side, ask on a Windows site.)

QEMU File Sharing – Shared Folder Between Windows Guest and Linux Host

QEMU's built-in Samba service

The not-functioning -net user,smb option was caused by an incompatibility with newer Samba versions (>= 4). This is fixed in QEMU v2.2.0 and newer with these changes:

b87b8a8 slirp/smb: Move ncalrpc directory to tmp (since v2.1.0)
44d8d2b net/slirp: specify logbase for smbd (since v2.2.0)
7912d04 slirp/smbd: modify/set several parameters in generated smbd.conf (since v2.2.0, disables printer too)

(Debian has backported the latter two patches to 2.1+dfsg-6 which is present in Jessie.)

Usage

You can export one folder as \\10.0.2.4\qemu when using User networking:

qemu-system-x86_64 \
    -net user,smb=/absolute/path/to/folder \
    -net nic,model=virtio \
    ...

When QEMU is successfully started with these options, a new /tmp/qemu-smb.*-*/ directory will be created containing a smb.conf. If you are fast enough, then this file could be modified to make paths read-only or export more folders.

Mode of operation

The samba daemon is executed whenever ports 139 or 445 get accessed over a "user" network. Communication happens via standard input/output/error of the smbd process. This is the reason why newer daemons failed, it would write its error message to the pipe instead of protocol messages.

Due to this method of operation, the daemon will not listen on host ports, and therefore will only be accessible to the guest. So other clients in the network and even local users cannot gain access to folders using this daemon.

Since QEMU v2.2.0 printer sharing is completely disabled through the samba configuration, so another worry is gone here.

The speed depends on the network adapter, so it is recommended to use the virtio netkvm driver under Windows.

Also note that the daemon is executed by its absolute path (typically /usr/sbin/smbd) as specified at compile time (using the --smbd option). Whenever you need to try a new binary or interpose smbd, you will need to modify the file at that path.

Other caveats

Executables (*.exe) must be executable on the host (chmod +x FILE) for the guest to have execute permissions. To allow execution of any file, add the acl allow execute always = True option to a share.

Example read-only smb.conf configuration which allows execution of any file (based on QEMU v2.2.0):

...
[qemu]
path=/home/peter/windows
read only=yes
guest ok=true
force user=peter
acl allow execute always = True