bionic: add __system_property_foreach

find_nth() will be inefficient on a trie.  Since find_nth() is only used
internally and only for enumerating properties, we can add a foreach()
function to do this directly.

Change-Id: I66bde9926c193073d74b244cce9fffd52108fff8
Signed-off-by: Greg Hackmann <ghackmann@google.com>

libc/bionic/system_properties.c

@@ -159,6 +159,22 @@ cleanup:
     return result;
 }
 
+int __system_property_foreach(
+        void (*propfn)(const prop_info *pi, void *cookie),
+        void *cookie)
+{
+    prop_area *pa = __system_property_area__;
+    unsigned i;
+
+    for (i = 0; i < pa->count; i++) {
+        unsigned entry = pa->toc[i];
+        prop_info *pi = TOC_TO_INFO(pa, entry);
+        propfn(pi, cookie);
+    }
+
+    return 0;
+}
+
 const prop_info *__system_property_find_nth(unsigned n)
 {
     prop_area *pa = __system_property_area__;

libc/include/sys/system_properties.h

@@ -76,13 +76,26 @@ int __system_property_read(const prop_info *pi, char *name, char *value);
 ** there is no nth property.  Use __system_property_read() to
 ** read the value of this property.
 **
-** This method is for inspecting and debugging the property 
+** Please do not call this method.  It only exists to provide
+** backwards compatibility to NDK apps.  Its implementation
+** is inefficient and order of results may change from call
+** to call.
+*/ 
+const prop_info *__system_property_find_nth(unsigned n);
+
+/* Pass a prop_info for each system property to the provided
+** callback.  Use __system_property_read() to read the value
+** of this property.
+**
+** This method is for inspecting and debugging the property
 ** system.  Please use __system_property_find() instead.
 **
 ** Order of results may change from call to call.  This is
 ** not a bug.
-*/ 
-const prop_info *__system_property_find_nth(unsigned n);
+*/
+int __system_property_foreach(
+        void (*propfn)(const prop_info *pi, void *cookie),
+        void *cookie);
 
 __END_DECLS
 

tests/system_properties_test.cpp

@@ -125,6 +125,25 @@ TEST(properties, fill_247) {
     }
 }
 
+static void foreach_test_callback(const prop_info *pi, void* cookie) {
+    size_t *count = static_cast<size_t *>(cookie);
+
+    ASSERT_NE((prop_info *)NULL, pi);
+    (*count)++;
+}
+
+TEST(properties, foreach) {
+    LocalPropertyTestState pa;
+    size_t count = 0;
+
+    ASSERT_EQ(0, __system_property_add("property", 8, "value1", 6));
+    ASSERT_EQ(0, __system_property_add("other_property", 14, "value2", 6));
+    ASSERT_EQ(0, __system_property_add("property_other", 14, "value3", 6));
+
+    ASSERT_EQ(0, __system_property_foreach(foreach_test_callback, &count));
+    ASSERT_EQ(3U, count);
+}
+
 TEST(properties, find_nth) {
     LocalPropertyTestState pa;