Rewrite syslog(3) to use Android logging.

Since we don't have syslogd on Android and you can't run one on a non-rooted
device, it's more useful if syslog output just goes to the regular Android
logging system.

Bug: 14292866

(cherry picked from commit 3ad8ecb64e)

Change-Id: I3038855ca4f22532bf6d2c45d3f8028b866975f9

libc/bionic/syslog.cpp

@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <syslog.h>
+
+#include <stdlib.h>
+
+#include "private/libc_logging.h"
+
+static const char* syslog_log_tag = NULL;
+static int syslog_priority_mask = 0xff;
+
+void closelog() {
+}
+
+void openlog(const char* log_tag, int /*options*/, int /*facility*/) {
+  syslog_log_tag = log_tag;
+}
+
+int setlogmask(int new_mask) {
+  int old_mask = syslog_priority_mask;
+  // 0 is used to query the current mask.
+  if (new_mask != 0) {
+    syslog_priority_mask = new_mask;
+  }
+  return old_mask;
+}
+
+void syslog(int priority, const char* fmt, ...) {
+  va_list args;
+  va_start(args, fmt);
+  vsyslog(priority, fmt, args);
+  va_end(args);
+}
+
+void vsyslog(int priority, const char* fmt, va_list args) {
+  // Check whether we're supposed to be logging messages of this priority.
+  if ((syslog_priority_mask & LOG_MASK(LOG_PRI(priority))) == 0) {
+    return;
+  }
+
+  // What's our log tag?
+  const char* log_tag = syslog_log_tag;
+  if (log_tag == NULL) {
+    log_tag = getprogname();
+  }
+
+  // What's our Android log priority?
+  priority &= LOG_PRIMASK;
+  int android_log_priority;
+  if (priority < LOG_ERR) {
+    android_log_priority = ANDROID_LOG_ERROR;
+  } else if (priority == LOG_WARNING) {
+    android_log_priority = ANDROID_LOG_WARN;
+  } else if (priority <= LOG_INFO) {
+    android_log_priority = ANDROID_LOG_INFO;
+  } else {
+    android_log_priority = ANDROID_LOG_DEBUG;
+  }
+
+  __libc_format_log_va_list(android_log_priority, log_tag, fmt, args);
+}