[Virtio-fs] One virtiofs daemon per exported dir requirement

[Stefan Hajnoczi]

On Fri, Feb 14, 2020 at 07:41:30PM +0000, Dr. David Alan Gilbert wrote:
> * Vivek Goyal (vgoyal at redhat.com) wrote:
> > Hi,
> > 
> > Dan Walsh and Mrunal mentioned that one virtiofsd daemon per exported
> > directory requirement sounds excessive. For container use case, they have
> > atleast 2-3 more directories they need to export (secrets and /etc/host). And
> > that means 3-4 virtiofsd running for each kata container. 
> > 
> > One option seems that bind mount all exports in one directory and export
> > that directory using one virtiofsd. I am aware of atleast one problem
> > with that configuraiton and that is possibility of inode number collision
> > if bind mounts are coming from different devices. Not sure how many
> > applications care though. Sergio is looking into solving this issue. It
> > might take a while though.
> 
> I thought the bind mount setup was the normal setup seen under both Kata
> and k8s?

Kata Containers works as follows:

kata-runtime manages a bind mount directory for each sandbox VM (k8s
pod) in /run/kata-containers/shared/sandboxes/$VM_ID.

That directory contains the bind-mounted rootfs as well as resolv.conf
and other per-container files.

When volumes (podman run --volume) are present they are also
bind-mounted alongside the rootfs.

So kata-runtime ends up with something like this:

  /run/kata-containers/shared/sandboxes/
  ... 61c192ae0e7154b6c8ffce6b13c4c5108d6dfe419a508f99ed381d9310268385/
      ... 61c192ae0e7154b6c8ffce6b13c4c5108d6dfe419a508f99ed381d9310268385/
          ... rootfs/
      ... 61c192ae0e7154b6c8ffce6b13c4c5108d6dfe419a508f99ed381d9310268385-04b134d40c6255cf-hostname
      ... 61c192ae0e7154b6c8ffce6b13c4c5108d6dfe419a508f99ed381d9310268385-62cff51b641310e5-resolv.conf
      ... 61c192ae0e7154b6c8ffce6b13c4c5108d6dfe419a508f99ed381d9310268385-b8dedcdf0c623c40-hosts
      ... 61c192ae0e7154b6c8ffce6b13c4c5108d6dfe419a508f99ed381d9310268385-d181eeeb4171c3c5-myvolume/

Only one virtio-fs device is used per sandbox VM.

Stefan
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