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From: Mark Williamson <mark.williamson@cl.cam.ac.uk>
Subject: Re: [Qemu-devel] file system sharing
Date: Sun, 31 Jul 2005 02:58:12 +0100
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To: qemu-devel@nongnu.org
Cc: "Eric S. Johansson" <esj@harvee.org>

> can I write a file based file system and read it from the host?  I can
> guarantee I have stopped writing before I read on the host side.  I can
> even unmount before reading.

If only one machine (host or guest) has mounted the device then it should 
always be safe to do this.  You may get away with read only mounting in one 
and writing in the other but it's not a reliable solution.  Never allow more 
than one writer to the filesystem - this does bad things to your filesystem!

If you're using a file-based disk and it's partitioned you'll need to use 
lomount http://www.dad-answers.com/qemu/utilities/QEMU-HD-Mounter/lomount/ to 
mount the right partition in the host.

> ideally, I would like to "import" my flash memory device into the guest
> OS side (USB based) but if I can create a "virtual" flash disk and when
> I'm done modifying it, physically copy the file based image to the
> physical flash, I would be happy.

I imagine just giving the guest access to the device file would work.

HTH,
Mark