129 lines
4.5 KiB
Java
129 lines
4.5 KiB
Java
/*
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* Copyright (C) 2021 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.android.internal.os;
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import android.util.IntArray;
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import com.android.internal.util.ProcFileReader;
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import java.io.FileInputStream;
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import java.io.IOException;
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/**
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* Reads and parses {@code locks} files in the {@code proc} filesystem.
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* A typical example of /proc/locks
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*
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* 1: POSIX ADVISORY READ 18403 fd:09:9070 1073741826 1073742335
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* 2: POSIX ADVISORY WRITE 18292 fd:09:34062 0 EOF
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* 2: -> POSIX ADVISORY WRITE 18291 fd:09:34062 0 EOF
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* 2: -> POSIX ADVISORY WRITE 18293 fd:09:34062 0 EOF
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* 3: POSIX ADVISORY READ 3888 fd:09:13992 128 128
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* 4: POSIX ADVISORY READ 3888 fd:09:14230 1073741826 1073742335
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*/
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@android.ravenwood.annotation.RavenwoodKeepWholeClass
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public class ProcLocksReader {
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private final String mPath;
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private ProcFileReader mReader = null;
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private IntArray mPids = new IntArray();
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public ProcLocksReader() {
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mPath = "/proc/locks";
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}
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public ProcLocksReader(String path) {
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mPath = path;
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}
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/**
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* This interface is for AMS to run callback function on every processes one by one
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* that hold file locks blocking other processes.
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*/
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public interface ProcLocksReaderCallback {
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/**
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* Call the callback function of handleBlockingFileLocks().
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* @param pids Each process that hold file locks blocking other processes.
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* pids[0] is the process blocking others
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* pids[1..n-1] are the processes being blocked
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* NOTE: pids are cleared immediately after onBlockingFileLock() returns. If the caller
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* needs to cache it, please make a copy, e.g. by calling pids.toArray().
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*/
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void onBlockingFileLock(IntArray pids);
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}
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/**
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* Checks if a process corresponding to a specific pid owns any file locks.
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* @param callback Callback function, accepting pid as the input parameter.
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* @throws IOException if /proc/locks can't be accessed or correctly parsed.
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*/
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public void handleBlockingFileLocks(ProcLocksReaderCallback callback) throws IOException {
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long last = -1;
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long id; // ordinal position of the lock in the list
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int pid = -1; // the PID of the process being blocked
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if (mReader == null) {
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mReader = new ProcFileReader(new FileInputStream(mPath));
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} else {
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mReader.rewind();
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}
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mPids.clear();
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while (mReader.hasMoreData()) {
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id = mReader.nextLong(true); // lock id
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if (id == last) {
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// blocked lock found
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mReader.nextIgnored(); // ->
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mReader.nextIgnored(); // lock type: POSIX?
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mReader.nextIgnored(); // lock type: MANDATORY?
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mReader.nextIgnored(); // lock type: RW?
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pid = mReader.nextInt(); // pid
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if (pid > 0) {
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mPids.add(pid);
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}
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mReader.finishLine();
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} else {
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// process blocking lock and move on to a new lock
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if (mPids.size() > 1) {
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callback.onBlockingFileLock(mPids);
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mPids.clear();
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}
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// new lock found
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mReader.nextIgnored(); // lock type: POSIX?
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mReader.nextIgnored(); // lock type: MANDATORY?
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mReader.nextIgnored(); // lock type: RW?
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pid = mReader.nextInt(); // pid
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if (pid > 0) {
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if (mPids.size() == 0) {
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mPids.add(pid);
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} else {
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mPids.set(0, pid);
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}
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}
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mReader.finishLine();
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last = id;
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}
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}
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// The last unprocessed blocking lock immediately before EOF
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if (mPids.size() > 1) {
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callback.onBlockingFileLock(mPids);
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}
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}
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}
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