[PATCH v2 1/2] hw/xen: detect when running inside stubdomain

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

Introduce global xen_is_stubdomain variable when qemu is running inside
a stubdomain instead of dom0. This will be relevant for subsequent
patches, as few things like accessing PCI config space need to be done
differently.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
---
Changes in v2:
- use sigend int for domid to match xenstore_read_int() types, domid is
  in a signed range anyway
- fix code style
---
 hw/xen/xen-legacy-backend.c | 16 ++++++++++++++++
 include/hw/xen/xen.h        |  1 +
 system/globals.c            |  1 +
 3 files changed, 18 insertions(+)

diff --git a/hw/xen/xen-legacy-backend.c b/hw/xen/xen-legacy-backend.c
index 124dd5f3d6..6bd4e6eb2f 100644
--- a/hw/xen/xen-legacy-backend.c
+++ b/hw/xen/xen-legacy-backend.c
@@ -603,6 +603,20 @@ static void xen_set_dynamic_sysbus(void)
     machine_class_allow_dynamic_sysbus_dev(mc, TYPE_XENSYSDEV);
 }
 
+static bool xen_check_stubdomain(void)
+{
+    char *dm_path = g_strdup_printf("/local/domain/%d/image", xen_domid);
+    int32_t dm_domid;
+    bool is_stubdom = false;
+
+    if (!xenstore_read_int(dm_path, "device-model-domid", &dm_domid)) {
+        is_stubdom = dm_domid != 0;
+    }
+
+    g_free(dm_path);
+    return is_stubdom;
+}
+
 void xen_be_init(void)
 {
     xenstore = qemu_xen_xs_open();
@@ -616,6 +630,8 @@ void xen_be_init(void)
         exit(1);
     }
 
+    xen_is_stubdomain = xen_check_stubdomain();
+
     xen_sysdev = qdev_new(TYPE_XENSYSDEV);
     sysbus_realize_and_unref(SYS_BUS_DEVICE(xen_sysdev), &error_fatal);
     xen_sysbus = qbus_new(TYPE_XENSYSBUS, xen_sysdev, "xen-sysbus");
diff --git a/include/hw/xen/xen.h b/include/hw/xen/xen.h
index 37ecc91fc3..ecb89ecfc1 100644
--- a/include/hw/xen/xen.h
+++ b/include/hw/xen/xen.h
@@ -36,6 +36,7 @@ enum xen_mode {
 extern uint32_t xen_domid;
 extern enum xen_mode xen_mode;
 extern bool xen_domid_restrict;
+extern bool xen_is_stubdomain;
 
 int xen_pci_slot_get_pirq(PCIDevice *pci_dev, int irq_num);
 int xen_set_pci_link_route(uint8_t link, uint8_t irq);
diff --git a/system/globals.c b/system/globals.c
index b6d4e72530..ac27d88bd4 100644
--- a/system/globals.c
+++ b/system/globals.c
@@ -62,6 +62,7 @@ bool qemu_uuid_set;
 uint32_t xen_domid;
 enum xen_mode xen_mode = XEN_DISABLED;
 bool xen_domid_restrict;
+bool xen_is_stubdomain;
 struct evtchn_backend_ops *xen_evtchn_ops;
 struct gnttab_backend_ops *xen_gnttab_ops;
 struct foreignmem_backend_ops *xen_foreignmem_ops;
-- 
2.43.0