python: Add XC binding for Xen build ID

Extend the list of xc() object methods with additional one to display
Xen's buildid. The implementation follows the libxl implementation
(e.g. max buildid size assumption being XC_PAGE_SIZE minus
sizeof(buildid->len)).

Signed-off-by: Pawel Wieczorkiewicz <wipawel@amazon.de>
Reviewed-by: Martin Mazein <amazein@amazon.de>
Reviewed-by: Andra-Irina Paraschiv <andraprs@amazon.com>
Reviewed-by: Norbert Manthey <nmanthey@amazon.de>
Acked-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

tools/python/xen/lowlevel/xc/xc.c

@@ -1214,6 +1214,26 @@ out:
     return ret_obj ? ret_obj : pyxc_error_to_exception(self->xc_handle);
 }
 
+static PyObject *pyxc_xenbuildid(XcObject *self)
+{
+    xen_build_id_t *buildid;
+    int i, r;
+    char *str;
+
+    buildid = alloca(XC_PAGE_SIZE);
+    buildid->len = XC_PAGE_SIZE - sizeof(*buildid);
+
+    r = xc_version(self->xc_handle, XENVER_build_id, buildid);
+    if ( r <= 0 )
+        return pyxc_error_to_exception(self->xc_handle);
+
+    str = alloca((r * 2) + 1);
+    for ( i = 0; i < r; i++ )
+        snprintf(&str[i * 2], 3, "%02hhx", buildid->buf[i]);
+
+    return Py_BuildValue("s", str);
+}
+
 static PyObject *pyxc_xeninfo(XcObject *self)
 {
     xen_extraversion_t xen_extra;
@@ -2297,6 +2317,13 @@ static PyMethodDef pyxc_methods[] = {
       "Returns [dict]: information about Xen"
       "        [None]: on failure.\n" },
 
+    { "buildid",
+      (PyCFunction)pyxc_xenbuildid,
+      METH_NOARGS, "\n"
+      "Get Xen buildid\n"
+      "Returns [str]: Xen buildid"
+      "        [None]: on failure.\n" },
+
     { "shadow_control", 
       (PyCFunction)pyxc_shadow_control, 
       METH_VARARGS | METH_KEYWORDS, "\n"