xen: add a global indicator for grant copy being available

The Xen qdisk backend needs to test whether grant copy operations is
available in the kernel. Unfortunately this collides with using
xengnttab_set_max_grants() on some kernels as this operation has to
be the first one after opening the gnttab device.

In order to solve this problem test for the availability of grant copy
in xen_be_init() opening the gnttab device just for that purpose and
closing it again afterwards. Advertise the availability via a global
flag and use that flag in the qdisk backend.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/hw/xen/xen_backend.c b/hw/xen/xen_backend.c
index c46cbb0759..0f849a26d2 100644
--- a/hw/xen/xen_backend.c
+++ b/hw/xen/xen_backend.c
@@ -44,6 +44,7 @@ BusState *xen_sysbus;
 /* public */
 struct xs_handle *xenstore = NULL;
 const char *xen_protocol;
+bool xen_feature_grant_copy;
 
 /* private */
 static int debug;
@@ -519,6 +520,8 @@ void xenstore_update_fe(char *watch, struct XenDevice *xendev)
 
 int xen_be_init(void)
 {
+    xengnttab_handle *gnttabdev;
+
     xenstore = xs_daemon_open();
     if (!xenstore) {
         xen_pv_printf(NULL, 0, "can't connect to xenstored\n");
@@ -532,6 +535,14 @@ int xen_be_init(void)
         goto err;
     }
 
+    gnttabdev = xengnttab_open(NULL, 0);
+    if (gnttabdev != NULL) {
+        if (xengnttab_grant_copy(gnttabdev, 0, NULL) == 0) {
+            xen_feature_grant_copy = true;
+        }
+        xengnttab_close(gnttabdev);
+    }
+
     xen_sysdev = qdev_create(NULL, TYPE_XENSYSDEV);
     qdev_init_nofail(xen_sysdev);
     xen_sysbus = qbus_create(TYPE_XENSYSBUS, DEVICE(xen_sysdev), "xen-sysbus");