Re: [Qemu-devel] bidirectional data exchange between guest and host without network

[Paul Brook]

>Yes, the thing is, I can not use the network, as it is used for another
>purpose, so I think I have to content myself with the basic linux
>filesystems.

That's just not going to work. Block devices don't provide the features 
necessary to implement a shared filesystem, you need some other mechanism 
(i.e. network) for handling locking and coherence. You can't take a regular 
filesystem and expect it to work. You have to use a proper network/clustered 
filesystem.

In theory SCSI has locking facilities, however this is not implemented by qemu 
(and probably not by your underlying storage), and AFAIK aren't used by any of 
the current cluster filesystems.

> I tried using a fat partition with the "sync" mount option, to avoid
> caching on both sides (still using virtio on /dev/sda8 on the host and
> /dev/vda on the guest).
>...
> Is there anything related to virtio that prevents this from working, as I
> think the mount option provides me with a filesystem that fulfils the
> conditions you just told me ?

I believe "sync" only disables the write cache.

Paul