xenconsole: try to attach to PV console if HVM fails

HVM guests have always used the emulated serial console by default, but if
the emulated serial pty cannot be fetched from xenstore try to use the PV
console instead.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>

tools/console/client/main.c

@@ -333,7 +333,7 @@ int main(int argc, char **argv)
 		{ 0 },
 
 	};
-	char *dom_path = NULL, *path = NULL;
+	char *dom_path = NULL, *path = NULL, *test = NULL;
 	int spty, xsfd;
 	struct xs_handle *xs;
 	char *end;
@@ -415,9 +415,15 @@ int main(int argc, char **argv)
 	path = malloc(strlen(dom_path) + strlen("/device/console/0/tty") + 5);
 	if (path == NULL)
 		err(ENOMEM, "malloc");
-	if (type == CONSOLE_SERIAL)
+	if (type == CONSOLE_SERIAL) {
 		snprintf(path, strlen(dom_path) + strlen("/serial/0/tty") + 5, "%s/serial/%d/tty", dom_path, num);
-	else {
+		test = xs_read(xs, XBT_NULL, path, NULL);
+		free(test);
+		if (test == NULL)
+			type = CONSOLE_PV;
+	}
+	if (type == CONSOLE_PV) {
+
 		if (num == 0)
 			snprintf(path, strlen(dom_path) + strlen("/console/tty") + 1, "%s/console/tty", dom_path);
 		else