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Re: [Qemu-devel] bidirectional data exchange between guest and host with
From: |
Jamie Lokier |
Subject: |
Re: [Qemu-devel] bidirectional data exchange between guest and host without network |
Date: |
Sat, 11 Jul 2009 01:01:16 +0100 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Lennart Sorensen wrote:
> On Wed, Jul 08, 2009 at 12:03:20PM +0200, Anthony Lannuzel wrote:
> > 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).
>
> sync only affects write caching, it does nothing for read caching,
> which is where your real problem is.
>
> > The host now reads data written by the guest but the guest does not see
> > the host data.
> >
> > 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 ?
>
> Just the fact any sane OS does read caching is what makes it not work.
> Filesystems are NOT going to do this for you. You can not share
> filesystems like that unless explicitly designed for it.
Many guest OSes have O_DIRECT or equivalent. That bypasses read and
write caching, and can be used for direct access to the underlying
block device.
You can share data over a block device that way, by _not_ using a
filesystem, only using your own protocol on the block filesystem.
-- Jamie
- [Qemu-devel] bidirectional data exchange between guest and host without network, Anthony Lannuzel, 2009/07/07
- Re: [Qemu-devel] bidirectional data exchange between guest and host without network, Jamie Lokier, 2009/07/07
- Re: [Qemu-devel] bidirectional data exchange between guest and host without network, Anthony Lannuzel, 2009/07/07
- Re: [Qemu-devel] bidirectional data exchange between guest and host without network, Paul Brook, 2009/07/08
- Re: [Qemu-devel] bidirectional data exchange between guest and host without network, Jamie Lokier, 2009/07/08
- Re: [Qemu-devel] bidirectional data exchange between guest and host without network, Anthony Lannuzel, 2009/07/09
- Re: [Qemu-devel] bidirectional data exchange between guest and host without network, Jamie Lokier, 2009/07/10
- Re: [Qemu-devel] bidirectional data exchange between guest and host without network, Richard W.M. Jones, 2009/07/12
- Re: [Qemu-devel] bidirectional data exchange between guest and host without network, Jamie Lokier, 2009/07/13
- Re: [Qemu-devel] bidirectional data exchange between guest and host without network, Richard W.M. Jones, 2009/07/14
- Re: [Qemu-devel] bidirectional data exchange between guest and host without network, Amit Shah, 2009/07/16