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 @android.ravenwood.annotation.RavenwoodKeepWholeClass
38 public class ProcLocksReader {
39     private final String mPath;
40     private ProcFileReader mReader = null;
41     private IntArray mPids = new IntArray();
42 
ProcLocksReader()43     public ProcLocksReader() {
44         mPath = "/proc/locks";
45     }
46 
ProcLocksReader(String path)47     public ProcLocksReader(String path) {
48         mPath = path;
49     }
50 
51     /**
52      * This interface is for AMS to run callback function on every processes one by one
53      * that hold file locks blocking other processes.
54      */
55     public interface ProcLocksReaderCallback {
56         /**
57          * Call the callback function of handleBlockingFileLocks().
58          * @param pids Each process that hold file locks blocking other processes.
59          *             pids[0] is the process blocking others
60          *             pids[1..n-1] are the processes being blocked
61          * NOTE: pids are cleared immediately after onBlockingFileLock() returns. If the caller
62          * needs to cache it, please make a copy, e.g. by calling pids.toArray().
63          */
onBlockingFileLock(IntArray pids)64         void onBlockingFileLock(IntArray pids);
65     }
66 
67     /**
68      * Checks if a process corresponding to a specific pid owns any file locks.
69      * @param callback Callback function, accepting pid as the input parameter.
70      * @throws IOException if /proc/locks can't be accessed or correctly parsed.
71      */
handleBlockingFileLocks(ProcLocksReaderCallback callback)72     public void handleBlockingFileLocks(ProcLocksReaderCallback callback) throws IOException {
73         long last = -1;
74         long id; // ordinal position of the lock in the list
75         int pid = -1; // the PID of the process being blocked
76 
77         if (mReader == null) {
78             mReader = new ProcFileReader(new FileInputStream(mPath));
79         } else {
80             mReader.rewind();
81         }
82 
83         mPids.clear();
84         while (mReader.hasMoreData()) {
85             id = mReader.nextLong(true); // lock id
86             if (id == last) {
87                 // blocked lock found
88                 mReader.nextIgnored(); // ->
89                 mReader.nextIgnored(); // lock type: POSIX?
90                 mReader.nextIgnored(); // lock type: MANDATORY?
91                 mReader.nextIgnored(); // lock type: RW?
92 
93                 pid = mReader.nextInt(); // pid
94                 if (pid > 0) {
95                     mPids.add(pid);
96                 }
97 
98                 mReader.finishLine();
99             } else {
100                 // process blocking lock and move on to a new lock
101                 if (mPids.size() > 1) {
102                     callback.onBlockingFileLock(mPids);
103                     mPids.clear();
104                 }
105 
106                 // new lock found
107                 mReader.nextIgnored(); // lock type: POSIX?
108                 mReader.nextIgnored(); // lock type: MANDATORY?
109                 mReader.nextIgnored(); // lock type: RW?
110 
111                 pid = mReader.nextInt(); // pid
112                 if (pid > 0) {
113                     if (mPids.size() == 0) {
114                         mPids.add(pid);
115                     } else {
116                         mPids.set(0, pid);
117                     }
118                 }
119                 mReader.finishLine();
120                 last = id;
121             }
122         }
123         // The last unprocessed blocking lock immediately before EOF
124         if (mPids.size() > 1) {
125             callback.onBlockingFileLock(mPids);
126         }
127     }
128 }
129