SchedulingPolicyService.java revision 430c25428a351bbf3d02b152050c7403457875e2 
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 android.os;
18
19import android.content.Context;
20import android.content.pm.PackageManager;
21import android.os.Binder;
22import android.os.Process;
23import android.util.Log;
24
25/**
26 * The implementation of the scheduling policy service interface.
27 *
28 * @hide
29 */
30public class SchedulingPolicyService extends ISchedulingPolicyService.Stub {
31
32    private static final String TAG = "SchedulingPolicyService";
33
34    // Minimum and maximum values allowed for requestPriority parameter prio
35    private static final int PRIORITY_MIN = 1;
36    private static final int PRIORITY_MAX = 3;
37
38    public SchedulingPolicyService() {
39    }
40
41    public int requestPriority(int pid, int tid, int prio) {
42        //Log.i(TAG, "requestPriority(pid=" + pid + ", tid=" + tid + ", prio=" + prio + ")");
43
44        // Verify that caller is mediaserver, priority is in range, and that the
45        // callback thread specified by app belongs to the app that called mediaserver.
46        // Once we've verified that the caller is mediaserver, we can trust the pid but
47        // we can't trust the tid.  No need to explicitly check for pid == 0 || tid == 0,
48        // since if not the case then the getThreadGroupLeader() test will also fail.
49        if (Binder.getCallingUid() != Process.MEDIA_UID || prio < PRIORITY_MIN ||
50                prio > PRIORITY_MAX || Process.getThreadGroupLeader(tid) != pid) {
51            return PackageManager.PERMISSION_DENIED;
52        }
53        try {
54            // make good use of our CAP_SYS_NICE capability
55            Process.setThreadGroup(tid, Binder.getCallingPid() == pid ?
56                    Process.THREAD_GROUP_AUDIO_SYS : Process.THREAD_GROUP_AUDIO_APP);
57            // must be in this order or it fails the schedulability constraint
58            Process.setThreadScheduler(tid, Process.SCHED_FIFO, prio);
59        } catch (RuntimeException e) {
60            return PackageManager.PERMISSION_DENIED;
61        }
62        return PackageManager.PERMISSION_GRANTED;
63    }
64
65}
66