[Virtio-fs] Adding notifications vq to the virtio-fs device

[Virtio-fs] Adding notifications vq to the virtio-fs device

[Stefan Hajnoczi]

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Hi Vivek,
There is discussion of adding the notifications vq to the virtio-fs
device so that FUSE Notification messages are possible.  This was
previously discussed on the VIRTIO mailing lists here:
https://lists.oasis-open.org/archives/virtio-dev/201902/msg00074.html

The main issue is how to handle the case where the device wishes to
raise notifications but the driver has not supplied enough buffers.

FUSE requires reliable notification delivery.  We cannot drop
notifications.

The mechanism will have to support reliable delivery.  For example, the
device may need to pause further operation until the driver makes
buffers available again.  But this could lead to DoS or deadlocks, so
care is needed!

I hope this link is useful in restarting the discussion about the
notifications vq.

Stefan

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Re: [Virtio-fs] Adding notifications vq to the virtio-fs device

[Dr. David Alan Gilbert]

* Stefan Hajnoczi (stefanha@redhat.com) wrote:
> Hi Vivek,
> There is discussion of adding the notifications vq to the virtio-fs
> device so that FUSE Notification messages are possible.  This was
> previously discussed on the VIRTIO mailing lists here:
> https://lists.oasis-open.org/archives/virtio-dev/201902/msg00074.html
> 
> The main issue is how to handle the case where the device wishes to
> raise notifications but the driver has not supplied enough buffers.
> 
> FUSE requires reliable notification delivery.  We cannot drop
> notifications.
> 
> The mechanism will have to support reliable delivery.  For example, the
> device may need to pause further operation until the driver makes
> buffers available again.  But this could lead to DoS or deadlocks, so
> care is needed!
> 
> I hope this link is useful in restarting the discussion about the
> notifications vq.

In the case we were recently discussing, notification of lock
availability, that's not necessarily a problem; if there's no
space on the notification queue then we stop notifying about
locks until there is some space.

Dave

> Stefan


--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK