Expose a domain's capabilities - control, hardware or xenstore - through
stable get domain state hypercall.

The xenstore domain can use this information to assign appropriate
permissions on connections.

Repurpose the 16bit pad field for this purpose.

Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@amd.com>
---
v3:
Add Stefano's R-b

v2:
Init info->caps = 0
Remove stale comment on caps field
Add Juergen's R-b
---
 xen/common/domain.c         | 10 +++++++++-
 xen/include/public/domctl.h |  7 +++++--
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 303c338ef2..3c65cca5b0 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -195,6 +195,14 @@ static void set_domain_state_info(struct xen_domctl_get_domain_state *info,
         info->state |= XEN_DOMCTL_GETDOMSTATE_STATE_DYING;
     if ( d->is_dying == DOMDYING_dead )
         info->state |= XEN_DOMCTL_GETDOMSTATE_STATE_DEAD;
+
+    info->caps = 0;
+    if ( is_control_domain(d) )
+        info->caps |= XEN_DOMCTL_GETDOMSTATE_CAP_CONTROL;
+    if ( is_hardware_domain(d) )
+        info->caps |= XEN_DOMCTL_GETDOMSTATE_CAP_HARDWARE;
+    if ( is_xenstore_domain(d) )
+        info->caps |= XEN_DOMCTL_GETDOMSTATE_CAP_XENSTORE;
     info->unique_id = d->unique_id;
 }
 
@@ -205,7 +213,7 @@ int get_domain_state(struct xen_domctl_get_domain_state *info, struct domain *d,
     int rc = -ENOENT;
     struct domain *hdl;
 
-    if ( info->pad0 || info->pad1 )
+    if ( info->pad0 )
         return -EINVAL;
 
     if ( d )
diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index a69dd96084..0c75d9d27f 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -1265,8 +1265,11 @@ struct xen_domctl_get_domain_state {
 #define XEN_DOMCTL_GETDOMSTATE_STATE_SHUTDOWN  0x0002  /* Shutdown finished. */
 #define XEN_DOMCTL_GETDOMSTATE_STATE_DYING     0x0004  /* Domain dying. */
 #define XEN_DOMCTL_GETDOMSTATE_STATE_DEAD      0x0008  /* Domain dead. */
-    uint16_t pad0;           /* Must be 0 on input, returned as 0. */
-    uint32_t pad1;           /* Must be 0 on input, returned as 0. */
+    uint16_t caps;
+#define XEN_DOMCTL_GETDOMSTATE_CAP_CONTROL     0x0001  /* Control domain. */
+#define XEN_DOMCTL_GETDOMSTATE_CAP_HARDWARE    0x0002  /* Hardware domain. */
+#define XEN_DOMCTL_GETDOMSTATE_CAP_XENSTORE    0x0004  /* Xenstore domain. */
+    uint32_t pad0;           /* Must be 0 on input, returned as 0. */
     uint64_t unique_id;      /* Unique domain identifier. */
 };
 
-- 
2.50.1