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 android.util.IntArray;
20 
21 import com.android.internal.util.ProcFileReader;
22 
23 import java.io.FileInputStream;
24 import java.io.IOException;
25 
26 /**
27  * Reads and parses {@code locks} files in the {@code proc} filesystem.
28  * A typical example of /proc/locks
29  *
30  * 1: POSIX  ADVISORY  READ  18403 fd:09:9070 1073741826 1073742335
31  * 2: POSIX  ADVISORY  WRITE 18292 fd:09:34062 0 EOF
32  * 2: -> POSIX  ADVISORY  WRITE 18291 fd:09:34062 0 EOF
33  * 2: -> POSIX  ADVISORY  WRITE 18293 fd:09:34062 0 EOF
34  * 3: POSIX  ADVISORY  READ  3888 fd:09:13992 128 128
35  * 4: POSIX  ADVISORY  READ  3888 fd:09:14230 1073741826 1073742335
36  */
37 public class ProcLocksReader {
38     private final String mPath;
39     private ProcFileReader mReader = null;
40     private IntArray mPids = new IntArray();
41 
ProcLocksReader()42     public ProcLocksReader() {
43         mPath = "/proc/locks";
44     }
45 
ProcLocksReader(String path)46     public ProcLocksReader(String path) {
47         mPath = path;
48     }
49 
50     /**
51      * This interface is for AMS to run callback function on every processes one by one
52      * that hold file locks blocking other processes.
53      */
54     public interface ProcLocksReaderCallback {
55         /**
56          * Call the callback function of handleBlockingFileLocks().
57          * @param pids Each process that hold file locks blocking other processes.
58          *             pids[0] is the process blocking others
59          *             pids[1..n-1] are the processes being blocked
60          * NOTE: pids are cleared immediately after onBlockingFileLock() returns. If the caller
61          * needs to cache it, please make a copy, e.g. by calling pids.toArray().
62          */
onBlockingFileLock(IntArray pids)63         void onBlockingFileLock(IntArray pids);
64     }
65 
66     /**
67      * Checks if a process corresponding to a specific pid owns any file locks.
68      * @param callback Callback function, accepting pid as the input parameter.
69      * @throws IOException if /proc/locks can't be accessed or correctly parsed.
70      */
handleBlockingFileLocks(ProcLocksReaderCallback callback)71     public void handleBlockingFileLocks(ProcLocksReaderCallback callback) throws IOException {
72         long last = -1;
73         long id; // ordinal position of the lock in the list
74         int pid = -1; // the PID of the process being blocked
75 
76         if (mReader == null) {
77             mReader = new ProcFileReader(new FileInputStream(mPath));
78         } else {
79             mReader.rewind();
80         }
81 
82         mPids.clear();
83         while (mReader.hasMoreData()) {
84             id = mReader.nextLong(true); // lock id
85             if (id == last) {
86                 // blocked lock found
87                 mReader.nextIgnored(); // ->
88                 mReader.nextIgnored(); // lock type: POSIX?
89                 mReader.nextIgnored(); // lock type: MANDATORY?
90                 mReader.nextIgnored(); // lock type: RW?
91 
92                 pid = mReader.nextInt(); // pid
93                 if (pid > 0) {
94                     mPids.add(pid);
95                 }
96 
97                 mReader.finishLine();
98             } else {
99                 // process blocking lock and move on to a new lock
100                 if (mPids.size() > 1) {
101                     callback.onBlockingFileLock(mPids);
102                     mPids.clear();
103                 }
104 
105                 // new lock found
106                 mReader.nextIgnored(); // lock type: POSIX?
107                 mReader.nextIgnored(); // lock type: MANDATORY?
108                 mReader.nextIgnored(); // lock type: RW?
109 
110                 pid = mReader.nextInt(); // pid
111                 if (pid > 0) {
112                     if (mPids.size() == 0) {
113                         mPids.add(pid);
114                     } else {
115                         mPids.set(0, pid);
116                     }
117                 }
118                 mReader.finishLine();
119                 last = id;
120             }
121         }
122         // The last unprocessed blocking lock immediately before EOF
123         if (mPids.size() > 1) {
124             callback.onBlockingFileLock(mPids);
125         }
126     }
127 }
128