4 files changed, 43 insertions, 16 deletions

diff --git a/hw/xen/trace-events b/hw/xen/trace-events
index a07fe41c6d..b67942d07b 100644
--- a/hw/xen/trace-events
+++ b/hw/xen/trace-events
@@ -38,7 +38,7 @@ xen_device_remove_watch(const char *type, char *name, const char *node, const ch
 xs_node_create(const char *node) "%s"
 xs_node_destroy(const char *node) "%s"
 xs_node_vprintf(char *path, char *value) "%s %s"
-xs_node_vscanf(char *path, char *value) "%s %s"
+xs_node_read(const char *path, const char *value) "%s %s"
 xs_node_watch(char *path) "%s"
 xs_node_unwatch(char *path) "%s"
 
diff --git a/hw/xen/xen-bus-helper.c b/hw/xen/xen-bus-helper.c
index b2b2cc9c5d..288fad422b 100644
--- a/hw/xen/xen-bus-helper.c
+++ b/hw/xen/xen-bus-helper.c
@@ -105,25 +105,22 @@ int xs_node_vscanf(struct qemu_xs_handle *h,  xs_transaction_t tid,
                    const char *node, const char *key, Error **errp,
                    const char *fmt, va_list ap)
 {
-    char *path, *value;
+    char *value;
     int rc;
 
-    path = (strlen(node) != 0) ? g_strdup_printf("%s/%s", node, key) :
-        g_strdup(key);
-    value = qemu_xen_xs_read(h, tid, path, NULL);
-
-    trace_xs_node_vscanf(path, value);
+    if (node && strlen(node) != 0) {
+        value = xs_node_read(h, tid, NULL, errp, "%s/%s", node, key);
+    } else {
+        value = xs_node_read(h, tid, NULL, errp, "%s", key);
+    }
 
     if (value) {
         rc = vsscanf(value, fmt, ap);
     } else {
-        error_setg_errno(errp, errno, "failed to read from '%s'",
-                         path);
         rc = EOF;
     }
 
     free(value);
-    g_free(path);
 
     return rc;
 }
@@ -142,6 +139,28 @@ int xs_node_scanf(struct qemu_xs_handle *h,  xs_transaction_t tid,
     return rc;
 }
 
+char *xs_node_read(struct qemu_xs_handle *h, xs_transaction_t tid,
+                   unsigned int *len, Error **errp,
+                   const char *path_fmt, ...)
+{
+    char *path, *value;
+    va_list ap;
+
+    va_start(ap, path_fmt);
+    path = g_strdup_vprintf(path_fmt, ap);
+    va_end(ap);
+
+    value = qemu_xen_xs_read(h, tid, path, len);
+    trace_xs_node_read(path, value);
+    if (!value) {
+        error_setg_errno(errp, errno, "failed to read from '%s'", path);
+    }
+
+    g_free(path);
+
+    return value;
+}
+
 struct qemu_xs_watch *xs_node_watch(struct qemu_xs_handle *h, const char *node,
                                     const char *key, xs_watch_fn fn,
                                     void *opaque, Error **errp)
diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index adfc4efad0..feeb612681 100644
--- a/hw/xen/xen-bus.c
+++ b/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)
diff --git a/hw/xen/xen_pvdev.c b/hw/xen/xen_pvdev.c
index c5ad71e8dc..c9143ba259 100644
--- a/hw/xen/xen_pvdev.c
+++ b/hw/xen/xen_pvdev.c
@@ -22,6 +22,7 @@
 #include "qemu/main-loop.h"
 #include "hw/qdev-core.h"
 #include "hw/xen/xen-legacy-backend.h"
+#include "hw/xen/xen-bus-helper.h"
 #include "hw/xen/xen_pvdev.h"
 
 /* private */
@@ -81,12 +82,9 @@ int xenstore_write_str(const char *base, const char *node, const char *val)
 
 char *xenstore_read_str(const char *base, const char *node)
 {
-    char abspath[XEN_BUFSIZE];
-    unsigned int len;
     char *str, *ret = NULL;
 
-    snprintf(abspath, sizeof(abspath), "%s/%s", base, node);
-    str = qemu_xen_xs_read(xenstore, 0, abspath, &len);
+    str = xs_node_read(xenstore, 0, NULL, NULL, "%s/%s", base, node);
     if (str != NULL) {
         /* move to qemu-allocated memory to make sure
          * callers can safely g_free() stuff. */