hw/xen: Add gnttab operations to allow redirection to internal emulation

Move the existing code using libxengnttab to xen-operations.c and allow
the operations to be redirected so that we can add emulation of grant
table mapping for backend drivers.

In emulation, mapping more than one grant ref to be virtually contiguous
would be fairly difficult. The best way to do it might be to make the
ram_block mappings actually backed by a file (shmem or a deleted file,
perhaps) so that we can have multiple *shared* mappings of it. But that
would be fairly intrusive.

Making the backend drivers cope with page *lists* instead of expecting
the mapping to be contiguous is also non-trivial, since some structures
would actually *cross* page boundaries (e.g. the 32-bit blkif responses
which are 12 bytes).

So for now, we'll support only single-page mappings in emulation. Add a
XEN_GNTTAB_OP_FEATURE_MAP_MULTIPLE flag to indicate that the native Xen
implementation *does* support multi-page maps, and a helper function to
query it.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/softmmu/globals.c b/softmmu/globals.c
index eb62739..23bb27f 100644
--- a/softmmu/globals.c
+++ b/softmmu/globals.c
@@ -66,3 +66,4 @@ uint32_t xen_domid;
 enum xen_mode xen_mode = XEN_DISABLED;
 bool xen_domid_restrict;
 struct evtchn_backend_ops *xen_evtchn_ops;
+struct gnttab_backend_ops *xen_gnttab_ops;