SchedulingPolicyService.java revision 9158825f9c41869689d6b1786d7c7aa8bdd524ce 
1/*
2 * Copyright (C) 2012 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
17package com.android.server.os;
18
19import android.content.pm.PackageManager;
20import android.os.Binder;
21import android.os.ISchedulingPolicyService;
22import android.os.Process;
23
24/**
25 * The implementation of the scheduling policy service interface.
26 *
27 * @hide
28 */
29public class SchedulingPolicyService extends ISchedulingPolicyService.Stub {
30
31    private static final String TAG = "SchedulingPolicyService";
32
33    // Minimum and maximum values allowed for requestPriority parameter prio
34    private static final int PRIORITY_MIN = 1;
35    private static final int PRIORITY_MAX = 3;
36
37    public SchedulingPolicyService() {
38    }
39
40    public int requestPriority(int pid, int tid, int prio) {
41        //Log.i(TAG, "requestPriority(pid=" + pid + ", tid=" + tid + ", prio=" + prio + ")");
42
43        // Verify that caller is mediaserver, priority is in range, and that the
44        // callback thread specified by app belongs to the app that called mediaserver.
45        // Once we've verified that the caller is mediaserver, we can trust the pid but
46        // we can't trust the tid.  No need to explicitly check for pid == 0 || tid == 0,
47        // since if not the case then the getThreadGroupLeader() test will also fail.
48        if (Binder.getCallingUid() != Process.MEDIA_UID || prio < PRIORITY_MIN ||
49                prio > PRIORITY_MAX || Process.getThreadGroupLeader(tid) != pid) {
50            return PackageManager.PERMISSION_DENIED;
51        }
52        try {
53            // make good use of our CAP_SYS_NICE capability
54            Process.setThreadGroup(tid, Binder.getCallingPid() == pid ?
55                    Process.THREAD_GROUP_AUDIO_SYS : Process.THREAD_GROUP_AUDIO_APP);
56            // must be in this order or it fails the schedulability constraint
57            Process.setThreadScheduler(tid, Process.SCHED_FIFO, prio);
58        } catch (RuntimeException e) {
59            return PackageManager.PERMISSION_DENIED;
60        }
61        return PackageManager.PERMISSION_GRANTED;
62    }
63
64}
65