KVM Passthrough Filesystem

I'm trying the same to mount the passthrough filesystem, but I'm failing.

I guess I did it right on the host

<filesystem type='mount' accessmode='mapped'>
      <source dir='/srv/dev-disk-xxxx/DLNA'/>
      <target dir='/DLNA'/>
      <alias name='fs0'/>
      <address type='pci' domain='0x0000' bus='0x08' slot='0x00' function='0x0'/>
    </filesystem>

But what do I have to do on the guest?

Guestsystem is Home Assistant, I do not know if this matters.

I tried it with this on the guest

mount -t 9p -o trans=virtio /DLNA /media/Music

but without success. ("no such device")

Any idea how to mount the host folder?

hmmm

nothing?

on both (host and guest) the command is valid but no response

Okay I will try

Thanks for the support.

I will report.

seems it is not working or installed

modprobe: can't change directory to '/lib/modules': no such file or directory

tried to created the missing folder, but this does not help, too

modprobe: can't change directory to '5.15.72': no such file or directory

Any idea where I find the passthough filesystem on a generic Ubuntu?

Ah I see. What I do not get is, how to edit the XML config file over the OMV userinterface. I can edit it, but when I saved it and re-open all modifications are gone.

I tried to edit it, because I have this entry

    <filesystem type='mount' accessmode='mapped'>
      <source dir='/srv/dev-disk-by-uuid-xxx/DLNA'/>
      <target dir='DLNA'/>
      <alias name='fs0'/>
      <address type='pci' domain='0x0000' bus='0x06' slot='0x00' function='0x0'/>
    </filesystem>

But I would like to try this one

<filesystem type='mount' accessmode='passthrough'>
      <driver type='virtiofs'/>
      <source dir='/path'/>
      <target dir='mount_tag'/>
    </filesystem>

Anyway your command returns an error (worng filesystem, wrong options, Superblock corrupted).

Thanks again.

I tried it, with "shutoff"-state. But the XML won't save my changes.

But anyway, I guess this gets to complicated here for to less of use. I will try another way to get my Music Directory to the Home Assistant

Okay I figured it out. I solved it with an isolated network between host and guest and mounted the folder

I did manage to passthrough a folder using the method described in ryecoaaron 's link, with editing the xml and inserting the Memorybacking and Filesystem entries.

Only thing that threw me for a loop for a second is that when you use the UI to create a passthrough link, in the xml the accesmode is set as "mapped" instead as "passthrough", and I don't need mapped.

So my fix was to not use the UI and just do it all in the xml while the VM is down:

     <filesystem type='mount' accessmode='passthrough'>
      <driver type='virtiofs' queue='1024'/>
      <binary path='/usr/lib/qemu/virtiofsd'/>
      <source dir='/srv/dev-disk/shared_folder'/>
      <target dir='shared_folder_tag'/>
      <alias name='fs0'/>
      <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
    </filesystem>

After that in the VM create a mountpoint mount_here (with correct permissions, read section mapped, passthrough, squash in link) and mount the tag :

mount -t virtiofs shared_folder_tag /mnt/mount_here

EDIT : see my post below concerning unique hardware addressing.

And something to add : How to add unique passthrough hardware/folders

I only found this out afterwards, so only editing the xml would be more difficult. You need to use UI and edit xml.

The tricky bit is that in the xml the virtual addressing for the passthrough "hardware"" needs to be unique. This is in every device-entry handeled by this line :

<address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>

I tried changing for instance slot or bus to a random number but if you get it wrong (not unique or not conforming to general linux rules) the entire device-entry gets removed.

So what you can do is first use the UI to add a "mapped" folder in the xml. This way you get an entry with a unique address. And then you change accessmode "mapped" to "passthrough" and add two lines like in my post above.

      <driver type='virtiofs' queue='1024'/>
      <binary path='/usr/lib/qemu/virtiofsd'/>

Also, to mount automatically use this in /etc/fstab :

shared_folder_tag            /mnt/mount_here       virtiofs     defaults 0 0