xen: do not use '%ms' scanf specifier

The 'm' parameter used to request auto-allocation of the destination variable
is not supported on FreeBSD, and as such leads to failures to parse.

What's more, the current usage of '%ms' with xs_node_scanf() is pointless, as
it just leads to a double allocation of the same string.  Instead use
xs_node_read() to read the whole xenstore node.

Fixes: a783f8ad4ec9 ('xen: add a mechanism to automatically create XenDevice-s...')
Fixes: 9b7737469080 ('hw/xen: update Xen console to XenDevice model')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

hw/block/xen-block.c

@@ -239,7 +239,8 @@ static void xen_block_connect(XenDevice *xendev, Error **errp)
         return;
     }
 
-    if (xen_device_frontend_scanf(xendev, "protocol", "%ms", &str) != 1) {
+    str = xen_device_frontend_read(xendev, "protocol");
+    if (!str) {
         /* x86 defaults to the 32-bit protocol even for 64-bit guests. */
         if (object_dynamic_cast(OBJECT(qdev_get_machine()), "x86-machine")) {
             protocol = BLKIF_PROTOCOL_X86_32;

hw/char/xen_console.c

@@ -550,7 +550,8 @@ static void xen_console_device_create(XenBackendInstance *backend,
         goto fail;
     }
 
-    if (xs_node_scanf(xsh, XBT_NULL, fe, "type", errp, "%ms", &type) != 1) {
+    type = xs_node_read(xsh, XBT_NULL, NULL, errp, "%s/%s", fe, "type");
+    if (!type) {
         error_prepend(errp, "failed to read console device type: ");
         goto fail;
     }
@@ -568,7 +569,8 @@ static void xen_console_device_create(XenBackendInstance *backend,
 
     snprintf(label, sizeof(label), "xencons%ld", number);
 
-    if (xs_node_scanf(xsh, XBT_NULL, fe, "output", NULL, "%ms", &output) == 1) {
+    output = xs_node_read(xsh, XBT_NULL, NULL, NULL, "%s/%s", fe, "output");
+    if (output) {
         /*
          * FIXME: sure we want to support implicit
          * muxed monitors here?

hw/xen/xen-bus.c

@@ -156,8 +156,8 @@ again:
             !strcmp(key[i], "hotplug-status"))
             continue;
 
-        if (xs_node_scanf(xenbus->xsh, tid, path, key[i], NULL, "%ms",
-                          &val) == 1) {
+        val = xs_node_read(xenbus->xsh, tid, NULL, NULL, "%s/%s", path, key[i]);
+        if (val) {
             qdict_put_str(opts, key[i], val);
             free(val);
         }
@@ -650,6 +650,16 @@ int xen_device_frontend_scanf(XenDevice *xendev, const char *key,
     return rc;
 }
 
+char *xen_device_frontend_read(XenDevice *xendev, const char *key)
+{
+    XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
+
+    g_assert(xenbus->xsh);
+
+    return xs_node_read(xenbus->xsh, XBT_NULL, NULL, NULL, "%s/%s",
+                        xendev->frontend_path, key);
+}
+
 static void xen_device_frontend_set_state(XenDevice *xendev,
                                           enum xenbus_state state,
                                           bool publish)

include/hw/xen/xen-bus.h

@@ -91,6 +91,7 @@ void xen_device_frontend_printf(XenDevice *xendev, const char *key,
 int xen_device_frontend_scanf(XenDevice *xendev, const char *key,
                               const char *fmt, ...)
     G_GNUC_SCANF(3, 4);
+char *xen_device_frontend_read(XenDevice *xendev, const char *key);
 
 void xen_device_set_max_grant_refs(XenDevice *xendev, unsigned int nr_refs,
                                    Error **errp);