[PATCH] fix "Error flushing ioemu cache" message in xenpaging

[Han-Lin Li <astercase@gmail.com>]

While using xenpaging, "Error flushing ioemu cache" message will be shown
on screen even if the "flush-cache" command is sent to xenstore correctly.
That is because xenpaging assume xc_mem_paging_flush_ioemu_cache()
return non-zero value when operation fail.  But
xc_mem_paging_flush_ioemu_cache() return the return value from xs_write()
which is zero when operation fail. So,  we should invert the return value from
xs_write() before use it as return value to prevent printing those
incorrect error messages.

---
Another problem is that the "flush-cache"  command isn't supported by
xenstore until you apply the patch below
http://thread.gmane.org/gmane.comp.emulators.xen.devel/91768/focus=91770
This patch isn't merged to unstable version yet.
Users need to merge this patch manually to make this function work correctly.
Anyone knows why this patch isn't merged to the unstable version?

---
Signed-off-by: Han-Lin Li <Han-Lin.Li@itri.org.tw>

diff -r 89116f28083f tools/xenpaging/xc.c
--- a/tools/xenpaging/xc.c      Wed Dec 08 10:46:31 2010 +0000
+++ b/tools/xenpaging/xc.c      Wed Dec 15 19:23:53 2010 +0800
@@ -62,7 +62,7 @@
     xs_daemon_close(xsh);
-    return rc;
+    return !rc;
 }
 int xc_wait_for_event_or_timeout(xc_interface *xch, int xce_handle,
unsigned long ms)