device_tree: qemu_fdt_getprop converted to use the error API

Current qemu_fdt_getprop exits if the property is not found. It is
sometimes needed to read an optional property, in which case we do
not wish to exit but simply returns a null value.

This patch converts qemu_fdt_getprop to accept an Error **, and existing
users are converted to pass &error_fatal. This preserves the existing
behaviour. Then to use the API with your optional semantic a null
parameter can be conveyed.
Signed-off-by: NEric Auger <eric.auger@linaro.org>
Reviewed-by: NPeter Crosthwaite <crosthwaite.peter@gmail.com>
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>

device_tree.c

@@ -333,18 +333,18 @@ int qemu_fdt_setprop_string(void *fdt, const char *node_path,
 }
 
 const void *qemu_fdt_getprop(void *fdt, const char *node_path,
-                             const char *property, int *lenp)
+                             const char *property, int *lenp, Error **errp)
 {
     int len;
     const void *r;
+
     if (!lenp) {
         lenp = &len;
     }
     r = fdt_getprop(fdt, findnode_nofail(fdt, node_path), property, lenp);
     if (!r) {
-        error_report("%s: Couldn't get %s/%s: %s", __func__,
-                     node_path, property, fdt_strerror(*lenp));
-        exit(1);
+        error_setg(errp, "%s: Couldn't get %s/%s: %s", __func__,
+                  node_path, property, fdt_strerror(*lenp));
     }
     return r;
 }
@@ -353,7 +353,8 @@ uint32_t qemu_fdt_getprop_cell(void *fdt, const char *node_path,
                                const char *property)
 {
     int len;
-    const uint32_t *p = qemu_fdt_getprop(fdt, node_path, property, &len);
+    const uint32_t *p = qemu_fdt_getprop(fdt, node_path, property, &len,
+                                         &error_fatal);
     if (len != 4) {
         error_report("%s: %s/%s not 4 bytes long (not a cell?)",
                      __func__, node_path, property);

include/sysemu/device_tree.h

@@ -54,8 +54,19 @@ int qemu_fdt_setprop_string(void *fdt, const char *node_path,
 int qemu_fdt_setprop_phandle(void *fdt, const char *node_path,
                              const char *property,
                              const char *target_node_path);
+/**
+ * qemu_fdt_getprop: retrieve the value of a given property
+ * @fdt: pointer to the device tree blob
+ * @node_path: node path
+ * @property: name of the property to find
+ * @lenp: fdt error if any or length of the property on success
+ * @errp: handle to an error object
+ *
+ * returns a pointer to the property on success and NULL on failure
+ */
 const void *qemu_fdt_getprop(void *fdt, const char *node_path,
-                             const char *property, int *lenp);
+                             const char *property, int *lenp,
+                             Error **errp);
 uint32_t qemu_fdt_getprop_cell(void *fdt, const char *node_path,
                                const char *property);
 uint32_t qemu_fdt_get_phandle(void *fdt, const char *path);