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

[Daniel Walsh]

On 2/18/20 8:38 AM, Stefan Hajnoczi wrote:
> 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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Great, other then the potential for duplicate inodes, that is perfect.

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