Add the methods to change and get a posix file permission to file_util.

base/file_util_posix.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/file_util.h"
 
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <fnmatch.h>
@@ skipping 439 matching lines @@
 
   if (count <= 0) {
     target_path->clear();
     return false;
   }
 
   *target_path = FilePath(FilePath::StringType(buf, count));
   return true;
 }
 
+bool GetPosixFilePermissions(const FilePath& path, int* mode) {
+  base::ThreadRestrictions::AssertIOAllowed();
+  DCHECK(mode);
+
+  stat_wrapper_t file_info;
+  // Uses stat(), because on symbolic link, lstat() may not return valid

[satorux1, 2012/07/10 00:06:54]

may not -> does not 

[yoshiki, 2012/07/10 01:31:17]

Done.

+  // information in the permission bits st_mode.

[satorux1, 2012/07/10 00:06:54]

information in the permission bits st_mode. ->
permission bits in st_mode

[yoshiki, 2012/07/10 01:31:17]

Done.

+  if (CallStat(path.value().c_str(), &file_info) != 0)
+    return false;
+
+  *mode = file_info.st_mode & FILE_PERMISSION_MASK;
+  return true;
+}
+
+bool SetPosixFilePermissions(const FilePath& path,
+                             int mode) {
+  base::ThreadRestrictions::AssertIOAllowed();
+  DCHECK((mode & ~FILE_PERMISSION_MASK) == 0);
+
+  stat_wrapper_t stat_buf;
+  if (CallStat(path.value().c_str(), &stat_buf) != 0)
+    return false;

[satorux1, 2012/07/10 00:06:54]

Why should we get the current permission? This looks unnecessary. 

Cannot we just call chmod()? chmod() will fail if the file is not present
anyway.

[yoshiki, 2012/07/10 01:31:17]

This obtains the higher bits (S_ISUID, S_ISGID and S_ISVTX).
SetPosixFilePermissions() accept only lower bits (user, group and others
permission bits), so we have to perserve the other bits.

On 2012/07/10 00:06:54, satorux1 wrote:

[satorux1, 2012/07/10 06:57:17]

Oh i see. Then please leave some comment like:

// Call stat() so that we can preserve the higher bits like S_ISGID.

+
+  mode_t updated_mode_bits = stat_buf.st_mode & ~FILE_PERMISSION_MASK;
+  updated_mode_bits |= mode & FILE_PERMISSION_MASK;
+
+  if (HANDLE_EINTR(chmod(path.value().c_str(), updated_mode_bits)) != 0)
+    return false;
+
+  return true;
+}
+
 // Creates and opens a temporary file in |directory|, returning the
 // file descriptor. |path| is set to the temporary file path.
 // This function does NOT unlink() the file.
 int CreateAndOpenFdForTemporaryFile(FilePath directory, FilePath* path) {
   base::ThreadRestrictions::AssertIOAllowed();  // For call to mkstemp().
   *path = directory.Append(TempFileName());
   const std::string& tmpdir_string = path->value();
   // this should be OK since mkstemp just replaces characters in place
   char* buffer = const_cast<char*>(tmpdir_string.c_str());
 
@@ skipping 645 matching lines @@
 
     allowed_group_ids.insert(group_record->gr_gid);
   }
 
   return VerifyPathControlledByUser(
       kFileSystemRoot, path, kRootUid, allowed_group_ids);
 }
 #endif  // defined(OS_MACOSX)
 
 }  // namespace file_util