From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MOXEo-00020J-W0 for qemu-devel@nongnu.org; Wed, 08 Jul 2009 09:31:07 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MOXEk-0001wQ-36 for qemu-devel@nongnu.org; Wed, 08 Jul 2009 09:31:06 -0400 Received: from [199.232.76.173] (port=36744 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MOXEj-0001wK-Sg for qemu-devel@nongnu.org; Wed, 08 Jul 2009 09:31:01 -0400 Received: from caffeine.csclub.uwaterloo.ca ([129.97.134.17]:40736) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MOXEj-0000Se-4l for qemu-devel@nongnu.org; Wed, 08 Jul 2009 09:31:01 -0400 Date: Wed, 8 Jul 2009 09:31:00 -0400 Subject: Re: [Qemu-devel] bidirectional data exchange between guest and host without network Message-ID: <20090708133059.GQ15751@csclub.uwaterloo.ca> References: <59673.89.3.148.243.1246956346.squirrel@webmail.aql.fr> <20090707090213.GB5690@shareable.org> <53352.89.3.148.243.1246972290.squirrel@webmail.aql.fr> <20090707141204.GL15751@csclub.uwaterloo.ca> <20090707143925.GA14392@shareable.org> <42816.89.3.148.243.1247047400.squirrel@webmail.aql.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <42816.89.3.148.243.1247047400.squirrel@webmail.aql.fr> From: lsorense@csclub.uwaterloo.ca (Lennart Sorensen) List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Lannuzel Cc: qemu-devel@nongnu.org On Wed, Jul 08, 2009 at 12:03:20PM +0200, Anthony Lannuzel wrote: > 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. > > 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. I remember many years ago in highschool we had a small set of machines that had a shared scsi drive between 5 machines (all daisy chained). You would shutdown all the machines, then start up the master machine, make the drive read/write, add new software and updates, then shutdown, switch the drive to read only, and boot all the systems. They could then all use the software on the drive, but anything you wanted to save had to be done to floppy disks on the individual machines. Writing a shared drive was simply not an option. -- Len Sorensen