1 /*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * * Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * * Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in
12 * the documentation and/or other materials provided with the
13 * distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29 #include "system_properties/context_node.h"
30
31 #include <limits.h>
32 #include <unistd.h>
33
34 #include <async_safe/log.h>
35
36 #include "system_properties/system_properties.h"
37
38 // pthread_mutex_lock() calls into system_properties in the case of contention.
39 // This creates a risk of dead lock if any system_properties functions
40 // use pthread locks after system_property initialization.
41 //
42 // For this reason, the below three functions use a bionic Lock and static
43 // allocation of memory for each filename.
44
Open(bool access_rw,bool * fsetxattr_failed)45 bool ContextNode::Open(bool access_rw, bool* fsetxattr_failed) {
46 lock_.lock();
47 if (pa_) {
48 lock_.unlock();
49 return true;
50 }
51
52 PropertiesFilename filename(filename_, context_);
53 if (access_rw) {
54 pa_ = prop_area::map_prop_area_rw(filename.c_str(), context_, fsetxattr_failed);
55 } else {
56 pa_ = prop_area::map_prop_area(filename.c_str());
57 }
58 lock_.unlock();
59 return pa_;
60 }
61
CheckAccessAndOpen()62 bool ContextNode::CheckAccessAndOpen() {
63 if (!pa_ && !no_access_) {
64 if (!CheckAccess() || !Open(false, nullptr)) {
65 no_access_ = true;
66 }
67 }
68 return pa_;
69 }
70
ResetAccess()71 void ContextNode::ResetAccess() {
72 if (!CheckAccess()) {
73 Unmap();
74 no_access_ = true;
75 } else {
76 no_access_ = false;
77 }
78 }
79
CheckAccess()80 bool ContextNode::CheckAccess() {
81 PropertiesFilename filename(filename_, context_);
82 return access(filename.c_str(), R_OK) == 0;
83 }
84
Unmap()85 void ContextNode::Unmap() {
86 prop_area::unmap_prop_area(&pa_);
87 }
88