[SOLVED] qemu - shared folder without networking ?

[sdauth]

Hi,
I have a win10 vm and would like to share a folder (/mnt/data/winshare) without having to enable any networking on the vm.
My vm is started with '-nic none' option, so basically I would like to replicate what virtualbox can easily do but with qemu. What are my options ?

Thanks!

[blu3bird]

virtiofs works okayish though permission can be a pain in the butt.

Personally, I'd go for a host-only network and just use samba.

[szatox]

There is 9P in kernel.
Qemu is said to be capable of exposing a host's directory to the guest as a 9p device. I've never used it though, for one-time stuff I'd just use a file as a block device because I already know how to use it.

[sdauth]

Hi,
So I tried virtfiofsd, not straightforward to setup, arch wiki was helpful.

On my qemu command line, I added the following :

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-object memory-backend-memfd,id=mem,size=16G,share=on \
-numa node,memdev=mem \
-chardev socket,id=char0,path=/mnt/vm/win10/win10-virtfs.sock \
-device vhost-user-fs-pci,chardev=char0,tag=winshare \

Before starting the vm, you need to start virtiofsd with the vm socket and dir to share :

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/usr/libexec/virtiofsd --socket-path=/mnt/vm/win10/win10-virtfs.sock --shared-dir /mnt/data/winshare --cache always

Some warning, error, I don't know yet how to solve this. (I start virtiofsd as user)

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2023-12-18T23:46:53Z WARN  virtiofsd::limits Failure when trying to set the limit to 1000000, the hard limit (4096) of open file descriptors is used instead.
2023-12-18T23:46:53Z WARN  virtiofsd::sandbox Couldn't set the process uid as root: -1
2023-12-18T23:46:53Z WARN  virtiofsd::sandbox Couldn't set the process gid as root: -1
2023-12-18T23:46:53Z INFO  virtiofsd Waiting for vhost-user socket connection...
2023-12-18T23:46:54Z INFO  virtiofsd Client connected, servicing requests
Warning: Cannot announce submounts, client does not support it
2023-12-18T23:57:51Z ERROR virtiofsd::passthrough::credentials failed to change uid back to root: Invalid argument (os error 22)
2023-12-18T23:57:51Z ERROR virtiofsd::passthrough::credentials failed to change gid back to root: Invalid argument (os error 22)
2023-12-19T00:03:12Z INFO  virtiofsd Client disconnected, shutting down

Nonetheless, the share works fine. I copied, deleted files without issue.

On the windows side, you need to install latest WinFsp & virtio-win (See: https://virtio-fs.gitlab.io/howto-windows.html )
After reboot, go in "Services" and make sure that virtiofs service is set to start automatically.

Also, I tried with a win7 vm but unfortunately it doesn't work.

Thanks for the suggestion blu3bird!

@szatox, isn't 9p only Linux though ? I'll give a try to file as block device later, this could be even better than virtiofsd for my use case...