1 /*
2 * Copyright (C) 2011 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 #include "scoped_flock.h"
18
19 #include <sys/file.h>
20 #include <sys/stat.h>
21
22 #include "base/logging.h"
23 #include "base/stringprintf.h"
24 #include "base/unix_file/fd_file.h"
25
26 namespace art {
27
Init(const char * filename,std::string * error_msg)28 bool ScopedFlock::Init(const char* filename, std::string* error_msg) {
29 return Init(filename, O_CREAT | O_RDWR, true, error_msg);
30 }
31
Init(const char * filename,int flags,bool block,std::string * error_msg)32 bool ScopedFlock::Init(const char* filename, int flags, bool block, std::string* error_msg) {
33 while (true) {
34 if (file_.get() != nullptr) {
35 UNUSED(file_->FlushCloseOrErase()); // Ignore result.
36 }
37 file_.reset(OS::OpenFileWithFlags(filename, flags));
38 if (file_.get() == nullptr) {
39 *error_msg = StringPrintf("Failed to open file '%s': %s", filename, strerror(errno));
40 return false;
41 }
42 int operation = block ? LOCK_EX : (LOCK_EX | LOCK_NB);
43 int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), operation));
44 if (flock_result == EWOULDBLOCK) {
45 // File is locked by someone else and we are required not to block;
46 return false;
47 }
48 if (flock_result != 0) {
49 *error_msg = StringPrintf("Failed to lock file '%s': %s", filename, strerror(errno));
50 return false;
51 }
52 struct stat fstat_stat;
53 int fstat_result = TEMP_FAILURE_RETRY(fstat(file_->Fd(), &fstat_stat));
54 if (fstat_result != 0) {
55 *error_msg = StringPrintf("Failed to fstat file '%s': %s", filename, strerror(errno));
56 return false;
57 }
58 struct stat stat_stat;
59 int stat_result = TEMP_FAILURE_RETRY(stat(filename, &stat_stat));
60 if (stat_result != 0) {
61 PLOG(WARNING) << "Failed to stat, will retry: " << filename;
62 // ENOENT can happen if someone racing with us unlinks the file we created so just retry.
63 if (block) {
64 continue;
65 } else {
66 // Note that in theory we could race with someone here for a long time and end up retrying
67 // over and over again. This potential behavior does not fit well in the non-blocking
68 // semantics. Thus, if we are not require to block return failure when racing.
69 return false;
70 }
71 }
72 if (fstat_stat.st_dev != stat_stat.st_dev || fstat_stat.st_ino != stat_stat.st_ino) {
73 LOG(WARNING) << "File changed while locking, will retry: " << filename;
74 if (block) {
75 continue;
76 } else {
77 // See comment above.
78 return false;
79 }
80 }
81 return true;
82 }
83 }
84
Init(File * file,std::string * error_msg)85 bool ScopedFlock::Init(File* file, std::string* error_msg) {
86 file_.reset(new File(dup(file->Fd()), file->GetPath(), file->CheckUsage(), file->ReadOnlyMode()));
87 if (file_->Fd() == -1) {
88 file_.reset();
89 *error_msg = StringPrintf("Failed to duplicate open file '%s': %s",
90 file->GetPath().c_str(), strerror(errno));
91 return false;
92 }
93 if (0 != TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_EX))) {
94 file_.reset();
95 *error_msg = StringPrintf(
96 "Failed to lock file '%s': %s", file->GetPath().c_str(), strerror(errno));
97 return false;
98 }
99 return true;
100 }
101
GetFile() const102 File* ScopedFlock::GetFile() const {
103 CHECK(file_.get() != nullptr);
104 return file_.get();
105 }
106
HasFile()107 bool ScopedFlock::HasFile() {
108 return file_.get() != nullptr;
109 }
110
ScopedFlock()111 ScopedFlock::ScopedFlock() { }
112
~ScopedFlock()113 ScopedFlock::~ScopedFlock() {
114 if (file_.get() != nullptr) {
115 int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_UN));
116 CHECK_EQ(0, flock_result);
117 int close_result = -1;
118 if (file_->ReadOnlyMode()) {
119 close_result = file_->Close();
120 } else {
121 close_result = file_->FlushCloseOrErase();
122 }
123 if (close_result != 0) {
124 PLOG(WARNING) << "Could not close scoped file lock file.";
125 }
126 }
127 }
128
129 } // namespace art
130