[Libguestfs] host Linux - guest Win7 fast file sharing [was: getting guestfs_rsync_out to work]

[Richard W.M. Jones]

On Tue, Feb 10, 2015 at 02:09:33PM -0600, Jeff Brower wrote:
> Using mount (read-only) and unmount commands in a script that loops
> continuously, we are able to see near instantaneous file
> modifications (less than 0.5 sec) performed on a Win7 live guest.
> We have to use the sync.exe utility
> (technet.microsoft.com/en-us/sysinternals/bb897438.aspx), otherwise
> changes are not visible for 10-20 sec.
>
> We tested sync.exe with our libguestfs test program (using various
> methods, including rsync_out, and w/wo sync on Linux side), but
> we're still not able to see live guest file changes until we
> relaunch the image.  Any advice on how to get around the relaunch
> requirement (which takes 3-5 sec due to loading the appliance Linux
> kernel), would be greatly appreciated.  There are many reasons why
> using libguestfs is a better solution for us in the long run.

It's not too surprising that sync doesn't work on the libguestfs
appliance side.

BTW you probably should also change the caching mode in qemu to `none'
or maybe `directsync' (default is now `writeback').

Unfortunately about 18 months ago we changed the caching modes and
removed the possibility of using `none':

https://rwmj.wordpress.com/2013/09/02/new-in-libguestfs-allow-cache-mode-to-be-selected/

So you'd have to patch libguestfs to add it back -- it's a fairly
straightforward patch.

I still think what you're trying to do is going to go wrong in
unexpected ways.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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