Split system_properties.cpp into its component pieces
system_properties.cpp is a little bit unmanageable in its current
form, and is overdue for a refactoring into more clearly defined
components.
Of particular interest, is creating of a Contexts interface that
handles mapping of system property name -> SEContext and its
associated prop_area, and creating two classes that implement the
current and legacy functionality. This is needed as there will likely
be a third even newer way to do this mapping.
Bug: 36001741
Test: boot bullhead, system property unit tests
Change-Id: Ie75ec6fea1a95f90813918f54669d533e51327c6
diff --git a/libc/system_properties/prop_info.h b/libc/system_properties/prop_info.h
new file mode 100644
index 0000000..99bcaaf
--- /dev/null
+++ b/libc/system_properties/prop_info.h
@@ -0,0 +1,92 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdatomic.h>
+#include <stdint.h>
+#include <sys/system_properties.h>
+
+#include "private/bionic_macros.h"
+
+#ifndef SYSTEM_PROPERTIES_PROP_INFO_H
+#define SYSTEM_PROPERTIES_PROP_INFO_H
+
+// The C11 standard doesn't allow atomic loads from const fields,
+// though C++11 does. Fudge it until standards get straightened out.
+static inline uint_least32_t load_const_atomic(const atomic_uint_least32_t* s, memory_order mo) {
+ atomic_uint_least32_t* non_const_s = const_cast<atomic_uint_least32_t*>(s);
+ return atomic_load_explicit(non_const_s, mo);
+}
+
+struct prop_info {
+ // Read only properties will not set anything but the bottom most bit of serial and the top byte.
+ // We borrow the 2nd from the top byte for extra flags, and use the bottom most bit of that for
+ // our first user, kLongFlag.
+ constexpr static uint32_t kLongFlag = 1 << 16;
+
+ // The error message fits in part of a union with the previous 92 char property value so there
+ // must be room left over after the error message for the offset to the new longer property value
+ // and future expansion fields if needed. Note that this value cannot ever increase. The offset
+ // to the new longer property value appears immediately after it, so an increase of this size will
+ // break compatibility.
+ constexpr static size_t kLongLegacyErrorBufferSize = 56;
+
+ public:
+ atomic_uint_least32_t serial;
+ // we need to keep this buffer around because the property
+ // value can be modified whereas name is constant.
+ union {
+ char value[PROP_VALUE_MAX];
+ struct {
+ char error_message[kLongLegacyErrorBufferSize];
+ uint32_t offset;
+ } long_property;
+ };
+ char name[0];
+
+ bool is_long() const {
+ return (load_const_atomic(&serial, memory_order_relaxed) & kLongFlag) != 0;
+ }
+
+ const char* long_value() const {
+ // We can't store pointers here since this is shared memory that will have different absolute
+ // pointers in different processes. We don't have data_ from prop_area, but since we know
+ // `this` is data_ + some offset and long_value is data_ + some other offset, we calculate the
+ // offset from `this` to long_value and store it as long_property.offset.
+ return reinterpret_cast<const char*>(this) + long_property.offset;
+ }
+
+ prop_info(const char* name, uint32_t namelen, const char* value, uint32_t valuelen);
+ prop_info(const char* name, uint32_t namelen, uint32_t long_offset);
+
+ private:
+ DISALLOW_IMPLICIT_CONSTRUCTORS(prop_info);
+};
+
+static_assert(sizeof(prop_info) == 96, "sizeof struct prop_info must be 96 bytes");
+
+#endif