Re: [Qemu-devel] [PATCH v4 for-4.0 4/7] libvhost-user: Support tracking inflight I/O in shared memory

[Michael S. Tsirkin]

On Tue, Jan 15, 2019 at 03:52:21PM +0800, Jason Wang wrote:
> Well, this may work but here're my points:
> 
> 1) The code want to recover from backed crash by introducing extra space to
> store inflight data, but it still depends on the backend to set/get the
> inflight state
> 
> 2) Since the backend could be killed at any time, the backend must have the
> ability to recover from the partial inflight state
> 
> So it looks to me 1) tends to be self-contradictory and 2) tends to be
> recursive. The above lines show how tricky could the code looks like.

This is a well studied field. Basically you make sure you commit with an
atomic write.  Restartable sequences allow accelerating this even
further.

> Solving this at vhost-user level through at backend is probably wrong. It's
> time to consider the support from virtio itself.
> 
> Thanks

I think both approaches have their space.

-- 
MST