src/com/android/mtp/AppFuse.java

/*
 * Copyright (C) 2015 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.
 */

package com.android.mtp;

import android.annotation.WorkerThread;
import android.os.ParcelFileDescriptor;
import android.os.Process;
import android.os.storage.StorageManager;
import android.system.OsConstants;
import android.util.Log;
import com.android.internal.annotations.VisibleForTesting;
import com.android.internal.util.Preconditions;
import com.android.mtp.annotations.UsedByNative;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;

public class AppFuse {
    static {
        System.loadLibrary("appfuse_jni");
    }

    /**
     * Max read amount specified at the FUSE kernel implementation.
     * The value is copied from sdcard.c.
     */
    static final int MAX_READ = 128 * 1024;

    private final String mName;
    private final Callback mCallback;

    /**
     * Buffer for read bytes request.
     * Don't use the buffer from the out of AppFuseMessageThread.
     */
    private byte[] mBuffer = new byte[MAX_READ];

    private Thread mMessageThread;
    private ParcelFileDescriptor mDeviceFd;

    AppFuse(String name, Callback callback) {
        mName = name;
        mCallback = callback;
    }

    void mount(StorageManager storageManager) throws IOException {
        Preconditions.checkState(mDeviceFd == null);
        mDeviceFd = storageManager.mountAppFuse(mName);
        mMessageThread = new AppFuseMessageThread(mDeviceFd.dup().detachFd());
        mMessageThread.start();
    }

    @VisibleForTesting
    void close() {
        try {
            // Remote side of ParcelFileDescriptor is tracking the close of mDeviceFd, and unmount
            // the corresponding fuse file system. The mMessageThread will receive FUSE_FORGET, and
            // then terminate itself.
            mDeviceFd.close();
            mMessageThread.join();
        } catch (IOException exp) {
            Log.e(MtpDocumentsProvider.TAG, "Failed to close device FD.", exp);
        } catch (InterruptedException exp) {
            Log.e(MtpDocumentsProvider.TAG, "Failed to terminate message thread.", exp);
        }
    }

    public ParcelFileDescriptor openFile(int i) throws FileNotFoundException {
        return ParcelFileDescriptor.open(new File(
                getMountPoint(),
                Integer.toString(i)),
                ParcelFileDescriptor.MODE_READ_ONLY);
    }

    File getMountPoint() {
        return new File("/mnt/appfuse/" + Process.myUid() + "_" + mName);
    }

    static interface Callback {
        /**
         * Returns file size for the given inode.
         * @param inode
         * @return File size. Must not be negative.
         * @throws FileNotFoundException
         */
        long getFileSize(int inode) throws FileNotFoundException;

        /**
         * Returns flie bytes for the give inode.
         * @param inode
         * @param offset Offset for file bytes.
         * @param size Size for file bytes.
         * @param bytes Buffer to store file bytes.
         * @return Number of read bytes. Must not be negative.
         * @throws IOException
         */
        long readObjectBytes(int inode, long offset, long size, byte[] bytes) throws IOException;
    }

    @UsedByNative("com_android_mtp_AppFuse.cpp")
    @WorkerThread
    private long getFileSize(int inode) {
        try {
            return mCallback.getFileSize(inode);
        } catch (FileNotFoundException e) {
            return -OsConstants.ENOENT;
        }
    }

    @UsedByNative("com_android_mtp_AppFuse.cpp")
    @WorkerThread
    private long readObjectBytes(int inode, long offset, long size) {
        if (offset < 0 || size < 0 || size > MAX_READ) {
            return -OsConstants.EINVAL;
        }
        try {
            // It's OK to share the same mBuffer among requests because the requests are processed
            // by AppFuseMessageThread sequentially.
            return mCallback.readObjectBytes(inode, offset, size, mBuffer);
        } catch (IOException e) {
            return -OsConstants.EIO;
        } catch (UnsupportedOperationException e) {
            return -OsConstants.ENOTSUP;
        }
    }

    private native boolean native_start_app_fuse_loop(int fd);

    private class AppFuseMessageThread extends Thread {
        /**
         * File descriptor used by native loop.
         * It's owned by native loop and does not need to close here.
         */
        private final int mRawFd;

        AppFuseMessageThread(int fd) {
            super("AppFuseMessageThread");
            mRawFd = fd;
        }

        @Override
        public void run() {
            native_start_app_fuse_loop(mRawFd);
        }
    }
}