Check property for sdcardfs use

Sdcardfs is only used if present in the kernel, and
external_storage.sdcardfs.enabled=0. For compatibility, this property
defaults to 1.

Bug: 155222498
Test: mount|grep "type sdcardfs" should find nothing after boot complete
      if external_storage.sdcardfs.enabled=0
Change-Id: Ide648405c260ac46d07877c3a7b78a8bee48e09a

1 files changed, 43 insertions, 0 deletions

diff --git a/core/jni/filesystem_utils.h b/core/jni/filesystem_utils.h
new file mode 100644
index 000000000000..c4728a09883b
--- /dev/null
+++ b/core/jni/filesystem_utils.h
@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2020 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.
+ */
+
+#ifndef FRAMEWORKS_BASE_CORE_JNI_MISC_UTILS_H_
+#define FRAMEWORKS_BASE_CORE_JNI_MISC_UTILS_H_
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <android-base/properties.h>
+#include <fcntl.h>
+#include <linux/fs.h>
+
+namespace {
+static constexpr const char* kExternalStorageSdcardfs = "external_storage.sdcardfs.enabled";
+
+static bool IsFilesystemSupported(const std::string& fsType) {
+    std::string supported;
+    if (!android::base::ReadFileToString("/proc/filesystems", &supported)) {
+        ALOGE("Failed to read supported filesystems");
+        return false;
+    }
+    return supported.find(fsType + "\n") != std::string::npos;
+}
+
+static inline bool IsSdcardfsUsed() {
+    return IsFilesystemSupported("sdcardfs") &&
+            android::base::GetBoolProperty(kExternalStorageSdcardfs, true);
+}
+} // namespace
+#endif // FRAMEWORKS_BASE_CORE_JNI_MISC_UTILS_H_