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
26namespace art {
27
28bool ScopedFlock::Init(const char* filename, std::string* error_msg) {
29  return Init(filename, O_CREAT | O_RDWR, true, error_msg);
30}
31
32bool 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
85bool 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
102File* ScopedFlock::GetFile() const {
103  CHECK(file_.get() != nullptr);
104  return file_.get();
105}
106
107bool ScopedFlock::HasFile() {
108  return file_.get() != nullptr;
109}
110
111ScopedFlock::ScopedFlock() { }
112
113ScopedFlock::~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