[PATCH v2] libxl: Add suppress-vmdesc to QEMU machine

[Jason Andryuk <jandryuk@gmail.com>]

The device model state saved by QMP xen-save-devices-state doesn't
include the vmdesc json.  When restoring an HVM, xen-load-devices-state
always triggers "Expected vmdescription section, but got 0".  This is
not a problem when restore comes from a file.  However, when QEMU runs
in a linux stubdom and comes over a console, EOF is not received.  This
causes a delay restoring - though it does restore.

Setting suppress-vmdesc skips looking for the vmdesc during restore and
avoids the wait.

QEMU 5.2 enables suppress-vmdesc by default for xenfv, but this change
sets it manually for xenfv and xen_platform_pci=0 when -machine pc is
use.

QEMU commit 9850c6047b8b "migration: Allow to suppress vmdesc
submission" added suppress-vmdesc in QEMU 2.3.

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>

---
QEMU 2.3 came out in 2015, so setting suppress-vmdesc unilaterally
should be okay...  Is this okay?
---
 tools/libs/light/libxl_dm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/libs/light/libxl_dm.c b/tools/libs/light/libxl_dm.c
index d1ff35dda3..3da83259c0 100644
--- a/tools/libs/light/libxl_dm.c
+++ b/tools/libs/light/libxl_dm.c
@@ -1778,9 +1778,9 @@ static int libxl__build_device_model_args_new(libxl__gc *gc,
             /* Switching here to the machine "pc" which does not add
              * the xen-platform device instead of the default "xenfv" machine.
              */
-            machinearg = libxl__strdup(gc, "pc,accel=xen");
+            machinearg = libxl__strdup(gc, "pc,accel=xen,suppress-vmdesc=on");
         } else {
-            machinearg = libxl__strdup(gc, "xenfv");
+            machinearg = libxl__strdup(gc, "xenfv,suppress-vmdesc=on");
         }
         if (b_info->u.hvm.mmio_hole_memkb) {
             uint64_t max_ram_below_4g = (1ULL << 32) -
-- 
2.25.1