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1 /*
2  * Copyright (C) 2021 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.android.internal.os;
18 
19 import com.android.internal.util.ProcFileReader;
20 
21 import java.io.FileInputStream;
22 import java.io.IOException;
23 
24 /**
25  * Reads and parses {@code locks} files in the {@code proc} filesystem.
26  * A typical example of /proc/locks
27  *
28  * 1: POSIX  ADVISORY  READ  18403 fd:09:9070 1073741826 1073742335
29  * 2: POSIX  ADVISORY  WRITE 18292 fd:09:34062 0 EOF
30  * 2: -> POSIX  ADVISORY  WRITE 18291 fd:09:34062 0 EOF
31  * 2: -> POSIX  ADVISORY  WRITE 18293 fd:09:34062 0 EOF
32  * 3: POSIX  ADVISORY  READ  3888 fd:09:13992 128 128
33  * 4: POSIX  ADVISORY  READ  3888 fd:09:14230 1073741826 1073742335
34  */
35 public class ProcLocksReader {
36     private final String mPath;
37     private ProcFileReader mReader = null;
38 
ProcLocksReader()39     public ProcLocksReader() {
40         mPath = "/proc/locks";
41     }
42 
ProcLocksReader(String path)43     public ProcLocksReader(String path) {
44         mPath = path;
45     }
46 
47     /**
48      * This interface is for AMS to run callback function on every processes one by one
49      * that hold file locks blocking other processes.
50      */
51     public interface ProcLocksReaderCallback {
52         /**
53          * Call the callback function of handleBlockingFileLocks().
54          * @param pid Each process that hold file locks blocking other processes.
55          */
onBlockingFileLock(int pid)56         void onBlockingFileLock(int pid);
57     }
58 
59     /**
60      * Checks if a process corresponding to a specific pid owns any file locks.
61      * @param callback Callback function, accepting pid as the input parameter.
62      * @throws IOException if /proc/locks can't be accessed or correctly parsed.
63      */
handleBlockingFileLocks(ProcLocksReaderCallback callback)64     public void handleBlockingFileLocks(ProcLocksReaderCallback callback) throws IOException {
65         long last = -1;
66         long id; // ordinal position of the lock in the list
67         int owner = -1; // the PID of the process that owns the lock
68         int pid = -1; // the PID of the process blocking others
69 
70         if (mReader == null) {
71             mReader = new ProcFileReader(new FileInputStream(mPath));
72         } else {
73             mReader.rewind();
74         }
75 
76         while (mReader.hasMoreData()) {
77             id = mReader.nextLong(true); // lock id
78             if (id == last) {
79                 mReader.finishLine(); // blocked lock
80                 if (pid < 0) {
81                     pid = owner; // get pid from the previous line
82                     callback.onBlockingFileLock(pid);
83                 }
84                 continue;
85             } else {
86                 pid = -1; // a new lock
87             }
88 
89             mReader.nextIgnored(); // lock type: POSIX?
90             mReader.nextIgnored(); // lock type: MANDATORY?
91             mReader.nextIgnored(); // lock type: RW?
92 
93             owner = mReader.nextInt(); // pid
94             mReader.finishLine();
95             last = id;
96         }
97     }
98 }
99