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

1 files changed, 105 insertions, 0 deletions

diff --git a/libc/system_properties/context_node.cpp b/libc/system_properties/context_node.cpp
new file mode 100644
index 000000000..440b865a9
--- /dev/null
+++ b/libc/system_properties/context_node.cpp
@@ -0,0 +1,105 @@
+/*
+ * 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 "context_node.h"
+
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include <async_safe/log.h>
+
+#include "system_property_globals.h"
+
+// pthread_mutex_lock() calls into system_properties in the case of contention.
+// This creates a risk of dead lock if any system_properties functions
+// use pthread locks after system_property initialization.
+//
+// For this reason, the below three functions use a bionic Lock and static
+// allocation of memory for each filename.
+
+bool ContextNode::Open(bool access_rw, bool* fsetxattr_failed) {
+  lock_.lock();
+  if (pa_) {
+    lock_.unlock();
+    return true;
+  }
+
+  char filename[PROP_FILENAME_MAX];
+  int len =
+      async_safe_format_buffer(filename, sizeof(filename), "%s/%s", property_filename, context_);
+  if (len < 0 || len > PROP_FILENAME_MAX) {
+    lock_.unlock();
+    return false;
+  }
+
+  if (access_rw) {
+    pa_ = prop_area::map_prop_area_rw(filename, context_, fsetxattr_failed);
+  } else {
+    pa_ = prop_area::map_prop_area(filename);
+  }
+  lock_.unlock();
+  return pa_;
+}
+
+bool ContextNode::CheckAccessAndOpen() {
+  if (!pa_ && !no_access_) {
+    if (!CheckAccess() || !Open(false, nullptr)) {
+      no_access_ = true;
+    }
+  }
+  return pa_;
+}
+
+void ContextNode::ResetAccess() {
+  if (!CheckAccess()) {
+    Unmap();
+    no_access_ = true;
+  } else {
+    no_access_ = false;
+  }
+}
+
+bool ContextNode::CheckAccess() {
+  char filename[PROP_FILENAME_MAX];
+  int len =
+      async_safe_format_buffer(filename, sizeof(filename), "%s/%s", property_filename, context_);
+  if (len < 0 || len > PROP_FILENAME_MAX) {
+    return false;
+  }
+
+  return access(filename, R_OK) == 0;
+}
+
+void ContextNode::Unmap() {
+  if (!pa_) {
+    return;
+  }
+
+  munmap(pa_, pa_size);
+  pa_ = nullptr;
+}