Add Locking calls to file_io.h plus implementations and test

util/file/file_io_posix.cc

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 #include "util/file/file_io.h"
 
 #include <fcntl.h>
+#include <sys/file.h>
 #include <unistd.h>
 
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/posix/eintr_wrapper.h"
 
 namespace {
 
 struct ReadTraits {
@@ skipping 65 matching lines @@
     flags |= O_EXCL;
 
   int fd = HANDLE_EINTR(
       open(path.value().c_str(),
            flags,
            permissions == FilePermissions::kWorldReadable ? 0644 : 0600));
   PLOG_IF(ERROR, fd < 0) << "open " << path.value();
   return fd;
 }
 
+bool LoggingLockFile(FileHandle file, FileLocking locking) {
+  int operation = locking == FileLocking::kShared ? LOCK_SH : LOCK_EX;
+  int rv = HANDLE_EINTR(flock(file, operation));
+  PLOG_IF(ERROR, rv != 0) << "flock";
+  return rv == 0;
+}
+
+bool LoggingUnlockFile(FileHandle file) {
+  int rv = flock(file, LOCK_UN);
+  PLOG_IF(ERROR, rv != 0) << "flock";
+  return rv == 0;
+}
+
 FileOffset LoggingSeekFile(FileHandle file, FileOffset offset, int whence) {
   off_t rv = lseek(file, offset, whence);
   PLOG_IF(ERROR, rv < 0) << "lseek";
   return rv;
 }
 
 bool LoggingCloseFile(FileHandle file) {
   int rv = IGNORE_EINTR(close(file));
   PLOG_IF(ERROR, rv != 0) << "close";
   return rv == 0;
 }
 
 }  // namespace crashpad