Trying to start a domain with a qdisk backend on an old dom0 kernel
(non-pvops xen kernel) will fail as xengnttab_set_max_grants() will
succeed only if called directly after opening the gnttab device.

These two patches address the issue by:

- moving the test for availability of xengnttab_grant_copy() from
  the qdisk backend to generic backend handling in order to not have
  to issue the grant copy ioctl with the qdisk specific file handle
- opening the gnttab device in blk_connect() only in order to
  guarantee xengnttab_set_max_grants() is called just after opening
  the gnttab device


Juergen Gross (2):
  xen: add a global indicator for grant copy being available
  xen: dont try setting max grants multiple times

 hw/block/xen_disk.c          | 30 +++++++++++++++++-------------
 hw/xen/xen_backend.c         | 11 +++++++++++
 include/hw/xen/xen_backend.h |  1 +
 3 files changed, 29 insertions(+), 13 deletions(-)

-- 
2.12.3