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

base/file_util_posix.cc

Index: base/file_util_posix.cc
diff --git a/base/file_util_posix.cc b/base/file_util_posix.cc
index e3bab95dd8e32554c81d8b41466909e5406e0027..893c2f126beb2cc6c686a83f85ec65d4c0b4d575 100644
--- a/base/file_util_posix.cc
+++ b/base/file_util_posix.cc
@@ -457,6 +457,38 @@ bool ReadSymbolicLink(const FilePath& symlink_path,
   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.