Re: [Xen-devel] [PATCH] Rlibxl: refuse to try and migrate an HVM guest using qemu-xen

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2012-06-29 at 17:03 +0100, Ian Jackson wrote:
> Ian Campbell writes ("[PATCH] Rlibxl: refuse to try and migrate an HVM guest 
> using qemu-xen"):
> > > I think we should add an appropriate error message as a blocker. We
> > > should also try to fix this on the QEMU side, but given that the QEMU
> > > 1.0 stable tree is pretty much unmaintaned, we won't be able to backport
> > > the fix there, so we cannot be sure that a distro will end up with a
> > > QEMU with or without the fix.
> > 
> > How about this for the time being, we can always revert or enhance as
> > necessary before 4.2.
> ...
> > +    libxl_device_model_version dm =
> > +        libxl__device_model_version_running(gc, domid);
> 
> libxl__device_model_version_running can return -1.  (Its error
> handling is pretty bad but that's no excuse for making matters worse.)
> I suggest we retcon it as returning a libxl error code.

the current callers all do something like
        switch (libxl__device_model_version_running(gc, domid)) {
        case LIBXL_DEVICE_MODEL...
                ...
        default: return ERROR_INVAL;
        }

and would need some rejigging to support a switch to ERROR_*, and
associated chance of triggering gcc's switch(enum) warnings.

I think fixing this properly can be left to 4.3 and for now I'll just
follow this same pattern.

Ian.

# HG changeset patch
# User Ian Campbell <ian.campbell@xxxxxxxxxx>
# Date 1341227605 -3600
# Node ID c6a2abdee84d5ae0692728dc169327314991090a
# Parent  d29a88850da26424b52520a617ca449d49124143
libxl: refuse to try and migrate an HVM guest using qemu-xen

libxl/qemu-upstream currently do not collude together to enable log-dirty mode
and therefore migrations are unsafe. Refuse to even try for now.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

diff -r d29a88850da2 -r c6a2abdee84d tools/libxl/libxl.c
--- a/tools/libxl/libxl.c       Mon Jul 02 12:06:22 2012 +0100
+++ b/tools/libxl/libxl.c       Mon Jul 02 12:13:25 2012 +0100
@@ -746,6 +746,22 @@ int libxl_domain_suspend(libxl_ctx *ctx,
         goto out_err;
     }
 
+    if (type == LIBXL_DOMAIN_TYPE_HVM && flags & LIBXL_SUSPEND_LIVE) {
+        switch (libxl__device_model_version_running(gc, domid)) {
+        case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN:
+            LOG(ERROR,
+                "cannot live migrate HVM domains with qemu-xen device-model");
+            rc = ERROR_FAIL;
+            goto out_err;
+        case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL:
+            /* No problem */
+            break;
+        default:
+            rc = ERROR_FAIL;
+            goto out_err;
+        }
+    }
+
     libxl__domain_suspend_state *dss;
     GCNEW(dss);
 



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