commit 24a95d27c7c07fa219a044b5ffe2f87231a01df9
author Tom Cherry <tomcherry@google.com> Wed Oct 18 10:25:39 2017 -0700
committer Tom Cherry <tomcherry@google.com> Wed Oct 18 10:25:39 2017 -0700
tree 56a99831dca92c1fa7667fb82c71e21ba5c12230
parent ab9dc08bdd60d3709e1bce555625d923b32812be

Update CachedProperty to support long ro. properties

We store a pointer to the long ro. property within the shared property
area, as we know that this pointer will never change locations or be
invalidated and it saves us from needing to allocate arbitrarily sized
storage for the property.

Bug: 23102347
Bug: 34954705
Test: bionic-unit-tests
Change-Id: I9f9147a2f951f20f51e4664c6faf9ff7f6a9502a

libc/private/CachedProperty.h

diff --git a/libc/private/CachedProperty.h b/libc/private/CachedProperty.h
index 417a855..84ead01 100644
--- a/libc/private/CachedProperty.h
+++ b/libc/private/CachedProperty.h
@@ -42,7 +42,9 @@
     : property_name_(property_name),
       prop_info_(nullptr),
       cached_area_serial_(0),
-      cached_property_serial_(0) {
+      cached_property_serial_(0),
+      is_read_only_(strncmp(property_name, "ro.", 3) == 0),
+      read_only_property_(nullptr) {
     cached_value_[0] = '\0';
   }
 
@@ -76,7 +78,9 @@
         __system_property_read_callback(prop_info_, &CachedProperty::Callback, this);
       }
     }
-
+    if (is_read_only_ && read_only_property_ != nullptr) {
+      return read_only_property_;
+    }
     return cached_value_;
   }
 
@@ -86,10 +90,18 @@
   uint32_t cached_area_serial_;
   uint32_t cached_property_serial_;
   char cached_value_[PROP_VALUE_MAX];
+  bool is_read_only_;
+  const char* read_only_property_;
 
   static void Callback(void* data, const char*, const char* value, uint32_t serial) {
     CachedProperty* instance = reinterpret_cast<CachedProperty*>(data);
     instance->cached_property_serial_ = serial;
-    strcpy(instance->cached_value_, value);
+    // Read only properties can be larger than PROP_VALUE_MAX, but also never change value or
+    // location, thus we return the pointer from the shared memory directly.
+    if (instance->is_read_only_) {
+      instance->read_only_property_ = value;
+    } else {
+      strlcpy(instance->cached_value_, value, PROP_VALUE_MAX);
+    }
   }
 };