tools/libs/store: add get- and set-feature related functions

Add functions for getting and setting Xenstore features to libxenstore:

xs_get_features_supported(): return the features supported by the
running Xenstore implementation as defined in xs_wire.h via the
XENSTORE_SERVER_FEATURE_* macros.

xs_get_features_domain(): return the features offered for a specific
domain.

xs_set_features_domain(): set the features available for a specific
domain.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>

tools/include/xenstore.h

@@ -264,6 +264,19 @@ bool xs_path_is_subpath(const char *parent, const char *child);
  */
 bool xs_is_domain_introduced(struct xs_handle *h, unsigned int domid);
 
+/* Get the features supported by Xenstore.
+ * Returned as a bitmap of XENSTORE_SERVER_FEATURE_* values.
+ */
+bool xs_get_features_supported(struct xs_handle *h, unsigned int *features);
+
+/* Get the features available for a given domain. */
+bool xs_get_features_domain(struct xs_handle *h, unsigned int domid,
+			    unsigned int *features);
+
+/* Set the features available for a given domain. */
+bool xs_set_features_domain(struct xs_handle *h, unsigned int domid,
+			    unsigned int features);
+
 char *xs_control_command(struct xs_handle *h, const char *cmd,
 			 void *data, unsigned int len);
 /* Deprecated: use xs_control_command() instead. */